GSM RNO Subject-Troubleshooting of Problems in Stages of Call Setup_R1.0_20130311

Troubleshooting of Problems in Stages of Call Setup

R1.0

Troubleshooting of Problems in Stages of Call Setup Internal Use Only▲

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Revision History

Product Version Document Version Serial Number Reason for Revision

R1.0 First published

Author

Date Document Version Prepared

by Reviewed by Approved by

2012-11-18 R1.0 Yang Tao Zheng Hao Zheng Hao


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Intended audience: GSM Network Optimization Engineers

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About This Document

Summary

Chapter Description

1 Signaling Flow and Relevant Counters and KPIs at the Random Access Stage

Describes the Signaling Flow and Relevant Counters and KPIs at the Random Access Stage

2 SDCCH Signaling Flow and Relevant Counters and KPIs

Describes the SDCCH Signaling Flow and Relevant Counters and KPIs

3 Signaling Flow and Relevant Counters and KPIs During the Voice Channel Allocation

Describes the Signaling Flow and Relevant Counters and KPIs During the Voice Channel Allocation.

4 Call Connection Process Describes the Call Connection Process.

5 Signaling Flow and Relevant Counters and KPIs During the Terminating Paging Stage

Describes the Signaling Flow and Relevant Counters and KPIs During the Terminating Paging Stage.

6 Signaling Flow of the Terminating Connection Stage

Describes the Signaling Flow of the Terminating Connection Stage.

7 Features of the V4 Allocation Process Statistics

Describes the Features of the V4 Allocation Process Statistics.

8 Cases Describes some cases.


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TABLE OF CONTENTS

1 Signaling Flow and Relevant Counters and KPIs at the Random Access Stage 1 1.1 Signaling Flow at the Random Access Stage .................................................. 1 1.1.1 Channel Mode Changing Program ................................................................. 3 1.2 Counter List of the Random Access Stage...................................................... 4 1.3 SDCCH Congestion Description, Cause, and Handling Flow ........................... 5 1.3.1 SDCCH Congestion Description ..................................................................... 5 1.3.2 SDCCH Congestion Rate KPI Definition ......................................................... 6 1.3.3 SDCCH Congestion Counters ........................................................................ 6 1.3.4 Main Causes of the SDCCH Congestion ...................................................... 10 1.3.5 SDCCH Congestion Handling Flow .............................................................. 12 1.4 SDCCH Assignment Failure Description and Troubleshooting ....................... 13 1.4.1 Definitions of SDCCH Assignment Success Rate KPIs ................................. 13 1.4.2 Counters Relevant to the SDCCH Assignment Success Rate ........................ 14 1.4.3 Troubleshooting of High SDCCH Assignment Failure Rate ............................ 15

2 SDCCH Signaling Flow and Relevant Counters and KPIs ........................ 21 2.1 SDCCH Signaling Setup Flow ...................................................................... 21 2.2 SDCCH Counter List ................................................................................... 21 2.3 SDCCH Call Drop KPI Definition and Affecting Factors ................................. 22 2.3.1 SDCCH Call Drop Definition......................................................................... 22 2.3.2 Counters Relevant to the SDCCH Call Drop ................................................. 23 2.3.3 Factors Affecting the SDCCH Call Drop........................................................ 25

3 Signaling Flow and Relevant Counters and KPIs During the Voice Channel Allocation 27 3.1 Signaling Flow During the Voice Channel Allocation ..................................... 27 3.2 Relevant Counter List During the TCH Allocation .......................................... 28 3.3 TCH Allocation Success Rate Definition and Failure Cause Description......... 33 3.3.1 TCH Allocation Success Rate KPI Definition ................................................. 33 3.3.2 TCH Allocation Failure Description ............................................................... 34 3.3.3 Main Causes of TCH Allocation Failure ........................................................ 34 3.3.4 Problem Handling Process........................................................................... 36 3.4 TCH Congestion Description, Cause, and Handling Flow .............................. 37 3.4.1 TCH Congestion Description ........................................................................ 37 3.4.2 TCH Congestion Rate KPI Definition ............................................................ 37 3.4.3 Counters Relevant to the TCH Congestion ................................................... 38 3.4.4 Main Causes of the TCH Congestion ........................................................... 47 3.4.5 TCH Congestion Handling Process .............................................................. 48

4 Call Connection Process ........................................................................... 50 4.1 Signaling Flow of the Call Connection Process ............................................. 50 4.2 Counters in the Call Connection Process ...................................................... 51 4.3 Call Drop During the Call Connection Process .............................................. 53 4.3.1 Causes of Call Drops due to Radio Link Fault ............................................... 53


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4.3.2 Causes of Call Drops Due to LAPD Link Failure ........................................... 55

5 Signaling Flow and Relevant Counters and KPIs During the Terminating Paging Stage .............................................................................................................. 56 5.1 Paging Principle .......................................................................................... 56 5.2 Basic Signaling Flow of the Radio Paging ..................................................... 57 5.3 Paging Counters of ZTE BSS ....................................................................... 58 5.4 Paging Success Rate KPI Definition ............................................................. 60 5.5 Factors Affecting the Paging Success Rate .................................................. 61 5.6 Procedure and Method of Low Paging Success Rate Optimization ................ 62

6 Signaling Flow of the Terminating Connection Stage .............................. 66 6.1 Signaling Flow of the Terminating Connection Stage .................................... 66 6.2 Relevant KPIs of the Terminating Connection Stage ..................................... 67

7 Features of the V4 Allocation Process Statistics ...................................... 68 7.1 Change of the Allocation Flow ...................................................................... 68 7.2 Change of Allocation Statistics ..................................................................... 68 7.2.1 Counter Adding ........................................................................................... 68 7.2.2 Counter Deleting ......................................................................................... 68 7.2.3 Modification and KPI Change ....................................................................... 68

8 Cases ......................................................................................................... 70 8.1 Cases of SDCCH Assignment Failure .......................................................... 70 8.1.1 SDCCH Assignment Failure Due to the LAPD Time Delay ............................ 70 8.1.2 High SDCCH Assignment Failure Rate Due to Co-BCCH and Co-BSIC ......... 73 8.1.3 Noise Signal Access .................................................................................... 74 8.1.4 SDCCH Assignment Failure Due to Co-BCCH and Co-BSIC Handover ......... 75 8.1.5 SDCCH Assignment Failure Due to Poor Network Coverage......................... 76 8.1.6 SDCCH Assignment Failure Due to Continuous Location Update Requests ... 77 8.1.7 Improper Setting of the Tx-Integer Parameter ............................................... 79 8.2 SD\TCH Channel Congestion Cases ............................................................ 80 8.2.1 SD congestion due to LAPD Delay Caused by Transmission Fault ................ 80 8.2.2 SD Congestion due to Strong Interference.................................................... 81 8.3 Paging Cases .............................................................................................. 83 8.3.1 No Paging Response due to the SDCCH Congestion.................................... 83 8.3.2 Call Failure due to the MSC Flow Control ..................................................... 83 8.3.3 No Paging Response due to Wrong T3212 Setting ....................................... 84 8.3.4 Low Paging Success Rate due to Location Area Division .............................. 84 8.3.5 GSM Paging Success Rate Optimization of a China Unicom Branch ............. 85 8.4 V4 Cases .................................................................................................... 88


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FIGURES

Figure 1-1 Signaling Flow at the Random Access Flow ......................................................1

Figure 1-2 Channel Mode Changing Program ....................................................................3

Figure 1-3 SDCCH Allocation Flow ...................................................................................5

Figure 1-4 Immediate Assignment Flow ............................................................................7

Figure 1-5 Immediate Assignment Occupation Failure Flow ...............................................8

Figure 1-6 Immediate Assignment Flow ............................................................................9

Figure 1-7 Immediate Assignment Flow .......................................................................... 15

Figure 1-8 LAPD Delay ................................................................................................... 17

Figure 2-1 SDCCH Signaling Flow .................................................................................. 21

Figure 2-2 Immediate Assignment Flow .......................................................................... 24

Figure 3-1 Signaling Flow of TCH Allocation .................................................................... 27

Figure 3-2 Voice Channel Allocation Flow ....................................................................... 34

Figure 3-3 Common Assignment Flow (Internal TC)......................................................... 39

Figure 3-4 Common Assignment Flow (External TC) ....................................................... 39

Figure 3-5 Common Assignment Failure Flow 1 (Internal TC) .......................................... 40

Figure 3-6 Intra-BSC Handover Occupation Failure Flow ................................................. 41

Figure 3-7 Inter-BSC Handover Occupation Failure Flow ................................................. 42

Figure 3-8 Flow of Handling TCH Congestion .................................................................. 49

Figure 4-1 Call Connection Process ................................................................................ 50

Figure 4-2 Call Drop Caused by the Radio Link Fault ....................................................... 52

Figure 5-1 Paging Message Delivery ............................................................................... 56

Figure 5-2 Basic Signaling Flow of the Radio Paging ....................................................... 57

Figure 5-3 Radio Access Process ................................................................................... 58

Figure 5-4 Measurement Point of the BSC Sending the Abis Message to the BTS ............ 60

Figure 6-1 Signaling Flow of the Terminating Connection Stage ....................................... 66

Figure 8-1 Time Stamp Checking .................................................................................... 71

Figure 8-2 Signaling Flow Checking 1 ............................................................................. 71



Figure 8-5 Signaling Tracing Data Observing 1................................................................ 74




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Figure 8-9 SD Channel Congestion Report Analysis (Case 1) .......................................... 80

Figure 8-10 No Response From the BTS (Case 1) ........................................................... 81

Figure 8-11 A Large Number of CHANNEL REQUEST Messages (Case 3) ...................... 82

Figure 8-12 Signaling Tracing Data Observing 5 .............................................................. 84

Figure 8-13 Number of Location Update Times................................................................ 85

Figure 8-14 Paging Success Rate ................................................................................... 88

Figure 8-15 TCH 2 Measurement .................................................................................... 92

TABLES

Table 1-1 Counter List of the Random Access Stage .........................................................4

Table 1-2 T3122 ...............................................................................................................5

Table 1-3 SDCCH Congestion Rate KPI Definition ............................................................6

Table 1-4 Definitions of SDCCH Assignment Success Rate KPIs ..................................... 13

Table 1-5 Corresponding Relationship Between the Tx-Integer Parameter and Interval Between Two Channel Request Messages ........................................................................ 16

Table 2-1 SDCCH Counter List ....................................................................................... 21

Table 2-2 SDCCH Call Drop KPI Definition...................................................................... 23

Table 3-1 List of Counters During the TCH Allocation (for V3) .......................................... 28

Table 3-2 TCH Allocation Success Rate (Handover Excluded) KPI Definition ................... 33

Table 3-3 TCH Congestion Rate Definition ...................................................................... 37

Table 4-1 Counters in the Call Connection Process ......................................................... 51

Table 5-1 Paging Success Rate KPI Definition ................................................................ 60

Table 8-1 Cell Basic Measurement Data 1....................................................................... 76

Table 8-2 Cell Basic Measurement Data 2....................................................................... 77

Table 8-3 Site Information .............................................................................................. 79

Table 8-4 SDCCH Congestion Information ...................................................................... 83

Table 8-5 TCH Congestion KPIs ..................................................................................... 89

Table 8-6 TCH Measurement Analysis ............................................................................ 90

Table 8-7 KPIs in the OMC Statistics .............................................................................. 91


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1 Signaling Flow and Relevant Counters and KPIs at the Random Access Stage

1.1 Signaling Flow at the Random Access Stage

Figure 1-1 Signaling Flow at the Random Access Flow

MS BTS BSC MSC

1 Channel Request(RACH)

2 Channel Required

3 Channel Activationg

4 Channel Activationg ACK

5 Immediate Assigment

Command6 Immediate Assigment (AGCH)

7 CM Service Requst(SDCCH)

8 CM Service Requst

Establish Indicationg9 CM Service Requst

10 UA(SDCCH)

The signaling flow of the random access stage is described as follows.

1. Channel requiring

The MS applies for one channel from one BTS through sending one random access

burst on the RACH dynamically.

In the CHANNEL REQUEST message, the setup reason is included. The reason

may be “response paging”, “emergency call”, “mobile originating call”, “short

message service”, or “others”, such as “location update”. What is more, this

message also includes the random parameters. The MS selects five bits as the

random parameters randomly. With these parameters, when two MSs access the

network at the same time, the network can distinguish the MSs.

2. Channel applying

The BTS sends a CHANNEL REQUIRED message to the BSC. Through this

message, the BTS transfers the channel request initiated by the MS to the BSC.



Actually, the CHANNEL REQUIRED message includes some information of the

channel request and some information added through the BTS. The application

parameters can be acquired from the channel request information and the initial

time advance is added to this message by the BTS.

3. Channel activation

After receiving the CHANNEL REQUIRED message sent from the BTS, the BSC

starts to find and allocate the SDCCH for this call according to a certain condition. At

the same time, the BSC sends one channel activation message to the BTS. The

important point is which BTS should be allocated with this SDCCH and the SDCCH

combination. In this message, the parameters included are DTX control, channel ID

(distinguishment), channel description, maximum power levels of mobile allocation,

MS and BTS, and initial time advance of this access calculated by the BSC.

4. Channel activation confirmation

This is a response to the channel activation message. After the BTS receives the

channel activation message, it starts to send and receive messages on the SACCH.

5. Immediate assignment command

The BSC informs the BTS of the used SDCCH.

6. Immediate assignment

The BTS sub-system informs the MS of the used SDCCH condition through the

AGCH. In fact, this message is an indication about moving from the AGCH to

defined SDCCH sent from the network to the MS. In this message, the included

parameters are paging mode, SDCCH description, associated SACCH,

frequency-hopping, application parameters, initial time advance, and frequency

allocation (frequency-hopping application).

7. CM service request

The MS sends a CM service request to the network, so as to apply one service for

the connection management sub-layer entity, such as circuit switch connection

setup, subsidiary service activation, or SMS sending.

8. CM service request (setup indication)

The BTS confirms the immediate assignment command through returning the setup

indication message. The setup indication message has two functions. First, it points

out that the MS is on the SDCCH from the BTS aspect. Then the BTS sends one

message to the BSC to indicate that the CM service request of the MS is sent on the

described SDCCH. What is more, the BTS will distinguish this connection and add

the received L3 message to this message.

9. CM service request



This CM service request message is sent to the mobile switch center (MSC).

10. No ID confirmation

When the L2 link is built in the LAPDm protocol, no ID confirmation is L2

confirmation in the normal condition.

1.1.1 Channel Mode Changing Program

If the TCH should be used as the signaling mode due to no SDCCH during the immediate

assignment, or the system requires for the rate change during the data sending process,

it is necessary to send the channel mode changing program to the TCH, so as to meet

the rate requirement, as shown in the following figure.

Figure 1-2 Channel Mode Changing Program

MS BTS BSC MSCAssignment Request

Mode Modify

Mode Modify ACK

Channel Mode Modify

Channel Mode Modify

Channel Mode Modify ACK

Channel Mode Modify ACK

Assignment Complete

The channel mode changing is always initiated by the network. The network sends a

channel mode changing message to the MS. This message includes the channel

description and the new mode adopted by the channel.

After the MS receives the channel mode changing message, it changes the mode of

the indicated channel and sends a channel mode changing confirmation message to

indicate the new channel mode.

If the MS does not support the specified mode, it will keep the original mode and

send one channel mode confirmation message of the corresponding channel mode

information.



1.2 Counter List of the Random Access Stage

The counters of this stage mainly include the CS measurement, radio access

measurement, SDCCH measurement, and TCH F/H measurement counters.

The counters of the random access stage are shown in the following figure. The V4 and

V3 counters are the same.

Table 1-1 Counter List of the Random Access Stage

Counter ID Counter Name

C900060003 Number of SDCCH seizure attempts for assignment

C900060004 Number of SDCCH seizure success for assignment

C900060005 Number of SDCCH seizure failure for assignment

C900060008 Number of SDCCH allocation success for assignment

C900060009 Number of SDCCH allocation failure for assignment

C900060010 Number of signaling TCH/F seizure attempts for assignment

C900060011 Number of signaling TCH/F seizure failure for assignment

C900060014 Number of signaling TCH/F allocation success for assignment

C900060015 Number of signaling TCH/F allocation failure for assignment

C900060017 Number of signaling TCH/F assignment success for assignment

C900060018 Number of voice TCH/F assignment failure for assignment

C900060038 Number of signaling TCH/H seizure attempts for assignment

C900060039 Number of signaling TCH/H seizure failure for assignment

C900060174 Number of signaling TCH/H allocation failure for assignment

C900060235 Number of signaling TCH/H assignment success for assignment

C900060241 Number of SDCCH assignment attempts

C900060242 Number of SDCCH assignment success

C900060243 Number of SDCCH assignments failure

C900060136 Number of MOC access attempts

C900060236 Number of MOC access success

C901250007 Number of SDCCH seizure attempts for assignment

C901110001 Number of invalid access requests

C901110003 Number of MOC access success for processes

C901110017 Number of other causes access attempts

C901110018 Number of successful random access processes for other causes

C901110019 Number of other causes access success

C901110033 Number of wireless accesses due to other causes

C901260002 Number of signaling TCH/F seizure success for assignment

C901260007 Number of signaling TCH/F allocation attempts for assignment

C901260013 Number of signaling TCH/F assignment attempts

C901270002 Number of signaling TCH/H seizure success for assignment




C901270007 Number of signaling TCH/H allocation attempts for assignment

C901270008 Number of signaling TCH/H allocation success for assignment

C901270013 Number of signaling TCH/H assignment attempts

1.3 SDCCH Congestion Description, Cause, and

Handling Flow

1.3.1 SDCCH Congestion Description

Figure 1-3 SDCCH Allocation Flow

MS BTS BSC MSC

Channel Request(RACH)

Channel Required

Channel Activationg

Channel Activationg ACK

Immediate Assigment

Reject

Immediate Assigment

Reject/T3122

When the BSC receives the CHANNEL REQUIRED message sent by the MS through

the BTS, it acquires the SDCCH resources. If the BSC finds no available SDCCH, it will

send an IMMEDIATE ASSIGNMENT REJECT message to the MS to ask it to wait for a

while (T3122) before requiring for the access again and add 1 to the SDCCH congestion

counter.

T3122 defines the minimum time interval of forbidding the next call of the MS temporarily,

so as to avoid the network congestion.

Table 1-2 T3122

Protection Period of Access Attempt (T3122, s)

Value range 0 ~ 255

Unit s

Default value

10



Protection Period of Access Attempt (T3122, s)

Description

After the network receives the channel request message sent by the MS. If there is no proper channel for the MS, the network will send an IMMEDIATE ASSIGNMENT REJECT message to the MS. The T3122,

that is the waiting indication message unit, is included in the IMMEDIATE ASSIGNMENT REJECT message, so as to avoid the

channel congestion due to continuous channel requests of the MS.

After the MS receives IMMEDIATE ASSIGNMENT REJECT message,

MS cannot start a new call until T3122 expires. This timer is one of the system control parameters, which is sent to MS in the IMMEDIATE ASSIGNMENT REJECT message.

The recommended value for T3122 is 10~15 s, and 15~25s in areas with dense traffic.

1.3.2 SDCCH Congestion Rate KPI Definition

Table 1-3 SDCCH Congestion Rate KPI Definition

KPI SDCCH blocking rate

Definition Number of signaling channel blocking times × 100%/Number of signaling channel call attempts

Counter formula

V2 (C11625 - C11626 + C11697) × 100%/(C11625 + C11696)

V3

V6.0 (C100030005 + C100030011 + C100030039) × 100%/(C100030003 + C100030010 + C100030038)

V6.2

(C900060005 + C900060011 + C900060039) ×100%/(C900060003 +

C900060010 + C900060038)

V4 V6.50.10 (C901250003 + C901260003 + C901270003)/(C901250001 + C901260001 + C901270001)

For the V3 formula definition, the basic measurement counter is adopted; for the V4

formula definition, the common measurement counter is adopted. And the counter

meaning and formula definitions of the two versions are consistent.

1.3.3 SDCCH Congestion Counters

C900060005: number of SDCCH seizure failure for assignment

Description

The SDCCH allocation attempt is activated by the MS channel request

message CHL_REQ. After the BSC receives this message, it attempts to

allocate the channel for the request. If the allocate succeeds but occupation

fails, this counter accumulates; if the request returns that the transceiver is

faulty, this counter does not change. For failures in other cases, this counter

accumulates.



Measurement point

This counter counts when the BSC requests for channel (due to assignment)

but fails to occupy the channel. The measurement point is A1, as shown in the

following figure.

Figure 1-4 Immediate Assignment Flow

MS BSC

CHL_REQ

CHL_RQD

CHL_ACT

CHL_ACT_ACK

IMM _ASS _CMD

IMM_ASS

SABM

EST_IND

BTS

A1

A2

A3

C900060011: number of signaling TCH/F seizure failure for assignment

Description

This counter counts the number of TCH/F channel occupation failures during

assigning signaling channels.

After the BSC receives the channel request, it attempts to allocate channel for

the request. If occupation fails, this counter accumulates. If the request returns

that the transceiver is faulty, this counter does not change. For failures in other

cases, this counter accumulates.

Measurement point

The BSC requests for channel (due to assignment and the channel is used as

signaling channel) but fails to occupy the channel, or the BSC fails to wait for

internal resource. The measurement point is A1 in the following figure.



Figure 1-5 Immediate Assignment Occupation Failure Flow

MS

CHL_REQCHL_RQD

BSCBTS

A1IMM_ASS_REJ

C900060039: number of signaling TCH/H seizure failure for assignment

Description

This counter counts the number of TCH/H channel occupation failures during

assigning signaling channels.

After the BSC receives the channel request, it attempts to allocate channel for

the request. If occupation fails, this counter accumulates. If the request returns

that the transceiver is faulty, this counter does not change. For failures in other

cases, this counter accumulates.

Measurement point


signaling channel) but fails to occupy the channel, or the BSC fails to wait for

internal resource. The measurement point is A1 in Figure 1-5.

C900060003: number of SDCCH seizure attempts for assignment

Description

The SDCCH channel allocation attempt is activated by the MS channel request

message CHL_REQ. After BSC receives this message, it attempts to allocate

channel for the request. If allocation and occupation succeed, C900060003

and C900060004 accumulate simultaneously. If occupation fails and the failure

is due to transceiver fault, C900060003, C900060004, and C900060005 do not

change. For failures in other cases, C900060003 and C900060005

accumulate simultaneously.

Measurement point

This counter counts when the BSC completes requesting for channel (due to

assignment) (C900060004 + C900060005). The measurement point is A1 in

the following figure.




MS BSC

CHL_REQ

CHL_RQD

CHL_ACT

CHL_ACT_ACK

IMM _ASS _CMD

IMM_ASS

SABM

EST_IND

BTS

A1

A2

A3

C900060010: number of signaling TCH/F seizure attempts for assignment

Description

This counter counts the number of TCH/F channel occupation attempts during

assigning signaling channels, including the number of occupation success

(C901260002) and the number of occupation failure (C900060011).

After BSC receives the channel request, it attempts to allocate channel for the

request. If allocation and occupation succeed, C900060010 and C901260002

accumulate simultaneously. If the request returns that the transceiver is faulty,

C900060010, C901260002, and C900060011 do not change. For other cases,

C900060010 and C900060011 accumulate simultaneously.

Measurement point

This counter counts when BSC completes requesting for channel (due to

assignment and the channel is used as signaling channel) (C901260002 +

C900060011). The measurement point is A1 in Figure 1-6.

C900060038: number of signaling TCH/H seizure attempts for assignment

Description:

This counter counts the number of TCH/H channel being attempted to be

occupied during signaling channel assignment, including the number of



occupation success (C901270002) and the number of occupation failure

(C900060039).

After BSC receives the channel request massage, it attempts to allocate


and C901270002 accumulate simultaneously. If the request returns that the

transceiver is faulty, C900060038, C901270002, and C900060039 do not

change. For other cases, C900060038 and C900060039 accumulate

simultaneously.

Measurement point



C900060039). The measurement point is A1 in Figure 1-6.

1.3.4 Main Causes of the SDCCH Congestion

From the aspect of singling flow, there are two main types of causes of SD congestion.

Too many CHANNEL REQUIRED messages exceeds network capacity and all the

SDCCHs are occupied.

Too many CHANNEL REQUIRED messages means the cell is busy, while few

SDCCH are configured, which results in frequent occupancy of SDCCH and

overflow.

During the SD congestion troubleshooting, the engineers should check

whether the traffic increases firstly.

Note:

Some operations at the OMCR (such as HLR configuration or LAC re-planning) may lead

to traffic increase in network.

The occupancy period of SDCCH is too long, due to non-in-time ending of signaling

flow

If signaling flow doesn’t end in time, which means channel activation/release

period is too long due to some reason (say, transmission fault), it will lead to

long period of SDCCH occupancy and reduce SDCCH resource, and

eventually result in SDCCH overflow.

Too-long channel activation/release period causes the MS to repeat the

channel request again and again (the number of repetition is decided by



system parameter MaxRetrans), and to occupy SDCCH repeatedly, which

worsens SDCCH overflow.

The problem of the intelligent network with the USSD service or the CN with

the LOC leads to the suspension of the MS during the SMS or LOC. The MS

occupies the SDCCH for a long time, which leads to the SDCCH congestion.

From the aspect of fault categories, the main causes of SDCCH congestion are

described as follows.

Unreasonable LAC planning

If the LAC boundary is set at high traffic areas or main transportation ways, where

subscribers are in great number and in frequent movement, LAC renewal can be

very frequent, which will form unreasonable calling modes and lower system

capacity as well;

Unreasonable parameter settings

The relevant parameters of C1 and C2 algorithms are set unreasonably. T3101,

T3122, and T3212 are set unreasonably.

Hardware fault

If the LAPD and TRX become faulty or unstable, the BSC cannot activate the

ground resources of this channel during the immediate allocation. Then, the user

makes multiple SD attempts, which leads to the SD congestion.

Problems with adjacent cells

Because of the faulty adjacent cell, the serving cell absorbs some extra traffic and

the congestion happens.

Frequent registration of the illegal users

The engineers should check whether the congestion is caused by the frequent

registration of the users with roaming limit. If the new service is used in this area,

when the users with roaming limit stay in the limit area and the mobiles are powered

on, the MSs will attempt to register in this network but the authentification always

fails, which increases the signaling load.

Abrupt SMS

In some areas, a large number of abrupt SMSs about the mark-six lottery, soccer

gambling, or SMS fraud, exist, which leads to serious SD congestion.



1.3.5 SDCCH Congestion Handling Flow

1. Observe the performance report to check whether the congestion happens in all the

cells of the site or only in one cell. The SD congestion in all the cells in the site

seldom happens and it is always relevant to the land transmission or parameter

configuration.

2. Observe the performance report to check whether the channel allocation failure

(channel activation expiration or failure) happens during the SD congestion. If the

channel allocation fails, the transmission or the CMB and TRX of the site may be

faulty. It is suggested to check the transmission equipment or the site CMB or TRX

fault.

Note:

Too large LAPD flow will lead to LAPD transmission delay, which causes timer expiration

before channel activation is completed. This kind of timer expiration shall be differentiated

from that caused by transmission fault.

3. Check the radio access measurement, analyze the access reason of Channel

Request which causes SD congestion, count the number of Channel Request

attempts and success times due to different reasons, and compare indicators with

those in normal period.

The access cause of Channel Request falls into four categories.

MOC

MTC

LOC

Other reasons (call re-establishment)

Usually, the number of LOC attempts is the largest. The number of MOC attempts is

equivalent to that of the MTC attempts and they are relevant to the user’s call

behavior. The number of other reasons is basically 0.

Here are explanations for each category of cause.

If there are a big number of attempts due to other reasons, and all end in failure, the

cause can be confirmed to be interference.

When the number of MOC attempts is big, and even exceeds the number of LOC,

the reasons could be:

The first possible reason is that there is MS malicious pager in the network.



The second possible reason is interference.

Judge the reasons through analyzing number of MOC success.

Although the MS malicious pager leads to a large number of MOC attempts, the

corresponding success times also increase. The interference cannot lead to the

increase of number of success times.

4. If number of LOC increases abnormally, check if there are any changes on network

parameters, such as re-planning of LAC or amendments of the HLR and VLR.

5. Generally speaking, SD congestion caused by LOC won’t bring large number of

assignment failures. If SD congestion is accompanied with large number of

assignment failures, it’s very possible that the cell traffic volume is high or

co-channel interference exists.

Note:

For BSCV2 system, basic measurement includes the number of attempts/success of

MOC, MTC, LOC and other accesses. For the iBSC system, there is a special radio

access measurement, which needs to establish measurement task. In CS basic

measurement, number of MOC/MTC attempts and number of MOC/MTC success are

included, through which we can calculate the number of attempts/success of LOC

access.

6. Make enquiries and find out if there are newly-setup sites, adjustments on

LAC/HLR;

7. Check the performance report of the week when the problem appears, analyze if SD

congestion exists for a long time during busy hours.

If the SD congestion is a long standing issue, and there’s no big fluctuation in the

number of MOC, MTC, LOC attempt and success times, this means the cell is busy

and its traffic volume is high, and expansion is needed.

1.4 SDCCH Assignment Failure Description and

Troubleshooting

1.4.1 Definitions of SDCCH Assignment Success Rate KPIs

Table 1-4 Definitions of SDCCH Assignment Success Rate KPIs

KPI SDCCH Assignment Success Rate



Definition SDCCH assignment success rate × 100/(Number of SDCCH assignment success + number of SDCCH assignment failure)

Counter formula

V2 C11644 × 100%/( C11644 + C11645)

V3 V6.0 C100420014 ×100%/(C100420014 + C100420015)

V6.2 C900060242 × 100%/(C900060242 + C900060243)

V4 V6.50.10 C901250014 × 100%/(C901250014 + C901250015)




1.4.2 Counters Relevant to the SDCCH Assignment Success Rate

C900060242: number of SDCCH assignments success

Description

After BSC responds to the channel request to allocate and activate SDCCH

channel successfully, BSC sends the IMM_ASS message to notify MS to use

this channel. After MS receives this message, it sends SABM frame to BTS on

SDCCH. BTS then sends the EST_IND message to BSC after receiving the

SABM frame.

If BSC receives the correct EST_IND message within specified time, it

indicates that the SDCCH channel assignment succeeds, and then this counter

increments.

This counter counts the number of MS successfully accessing SDCCH channel

when BSC sends the IMM_ASS message, as shown in the following figure.

Measurement point

This counter counts when BSC receives the correct EST_IND message or the

assignment completion message. The measurement point is A3.




MS BSC

CHL_REQ

CHL_RQD

CHL_ACT

CHL_ACT_ACK

IMM _ASS _CMD

IMM_ASS

SABM

EST_IND

BTS

A1

A2

A3

C900060243: number of SDCCH assignments failure

Description

After BSC responds to the channel request to allocate and activate SDCCH

channel successfully, BSC sends the IMM_ASS message to notify MS to use

this channel. After MS receives this message, it sends SABM frame to BTS on

SDCCH. BTS then sends the EST_IND message to BSC after receiving the

SABM frame.

If BSC receives the incorrect EST_IND message or T3101 is timeout, it

indicates that the SDCCH channel assignment fails, and then this counter

increments.

Measurement point

This counter counts when BSC receives the incorrect EST_IND message or

when T3101 is timeout. The measurement point is A3, as shown in Figure 1-7.

1.4.3 Troubleshooting of High SDCCH Assignment Failure Rate

Improper setting of the Tx-Integer parameter

The corresponding relationship between the Tx-Integer parameter and interval

between two channel request messages is described as follows.



Table 1-5 Corresponding Relationship Between the Tx-Integer Parameter and Interval Between Two Channel Request Messages

TxInteger

Time interval (ms) Time interval (ms)

(CCCHs not Combined With SDCCHs)

(CCCHs Combined With SDCCHs)

12 501ms ~ 593 ms (109~129 slot)

267ms ~ 359 ms (58 ~ 78 slot)

13 750ms ~ 865 ms (163~188 slot)

396ms ~ 511 ms (86 ~ 111slot)

14 998ms ~ 1146 ms (217~249 slot)

529ms ~ 676 ms (115 ~ 147 slot)

15 253ms ~ 483 ms (55~105 slot) 189ms ~ 419 ms (41 ~ 91 frames)

Usually, the Tx-Integer parameter is set to 14 by default. When the transmission

link delay is long and the Tx-Integer parameter is set to be too small, the MS will

send the access request for many times.

Usually, the one-way time delay of the signaling transmission on the Abis interface

is about 60 ms ~ 100 ms. For example, with the time delay on the Um interface

being ignored, the time delay of one immediate assignment flow is shown as

follows.

The CHANNEL REQUIRED signaling: UL: 60 ms

The CHANNEL ACTIVATION signaling: DL: 60 ms

The CHANNEL ACTIVATION ACK signaling: UL: 60 ms

The IMMEDIATE ASSIGN signaling: DL: 60 ms

Total: The time delay from the MS sending a CHANNEL REQUEST message to it

receiving a CHANNEL REQUEST message is about 240 ms.

If the delay of the TX link is large and TxInteger is improperly set — for example, it

is set to 15, and the corresponding the CHANNEL REQUEST message expire time

is 300 ms — the CHANNEL REQUEST message expires before the MS receives

the IMM ASSIGN message and then the MS resends the CHANNEL REQUEST

message. Then the MS receives the IMM ASSIGN message corresponding to the

last CHANNEL REQUEST message and finishes the access flow. The IMM

ASSIGN message corresponding to the second CHANNEL REQUEST fails.

High SDCCH assignment failure rate due to LAPD time delay

The possible causes of LAPD time delay are described as follows.



If LAPD multiplexing 1:4 is used on site, multiple BCCH TRXs may be

multiplexed on one LAPD, and the traffic volume will be heavy and the delay is

large.

The delay is caused by large LAPD flow. For example, improper LAC dividing

will trigger LAPD flow control.

The transmission equipment fault leads to the message loss of the LAPD link

or too long time delay of the LAPD link. This condition and the SDCCH

allocation failure always happen at the same time. The SDCCH allocation

failure counter accumulates only at the time of activation failure or no response

to activation request. No response to the activation request has two specific

conditions. One is message loss on the LAPD link. Then the BTS cannot

receive the channel activation message or the BSC cannot receive the

activation responding message. Another condition is too long time delay on the

LAPD link, which leads to the expiration of the channel activation timer. Both of

the two conditions indicate that the LAPD link transmission is faulty.

The delay of the TX equipment is large, for example, satellite TX is used on the

Abis interface.

The affection of the PS service. Because the PS service is more sensitive to

the network time delay, the LAPD time delay can lead to the resending of the

PS service message. And the message resending increases the traffic, which

leads to longer LAPD time delay.

If the LAPD time delay achieves to a certain degree, the MS will resend the

CHANNEL REQUEST message, which leads to the SDCCH assignment

failure, even the SDCCH allocation failure.

Figure 1-8 LAPD Delay

MS BTS BSC MSC

1 Channel Request(RACH)

2 Channel Required




Command6 Immediate Assigment (OK)

1 Channel Request (Re-Send)

2 Channel Required




Command6 Immediate Assigment (Fail)

Lapd

Delay

TxInteger

MS change

to SDCCH



Co-frequency and co-BSIC interference

Co-BCCH and co-BSIC interference has two conditions:

Two co-BCCH and co-BSIC cells: The CHANNEL REQUEST message sent

by the MS is received by two cells at the same time and the SDCCH

assignment is made. Because the MS accesses only one SDCCH, the SDCCH

assignment of one cell will fail. During the RACH coding, 6-bit color codes are

added. The 6-bit color codes are acquired through Mod 2 of 6-bit BSIC and

6-bit odd and even verification codes. Therefore, co-BCCH and co-BSIC may

lead to wrong decoding of the initial accesses of MSs of other sites. As a result,

the SDCCH assignment failure happens.

The two cells are co-BSIC and the TCH ARFCN of one cell is the same with

the BCCH ARFCN of another cell. Then the handover access request on the

TCH of one cell is received by the other cell as the CHANNEL REQUEST

message and SDCCH assignment is performed, which will surely lead to large

number of SDCCH assignment failures. The engineers check the faulty

signaling and find the RAs are the same, the TAs are consistent, and the FNs

are continuous. The continuous CHANNEL REQUEST messages indicate the

false access caused by the handover access of the co-BCCH cells.

If the two cells are only co-BCCH and they are near to each other, the DL

interference will happen, which leads to the SDCCH assignment failure.

Overshooting

There are two conditions of overshooting.

If the coverage range of the cell is too large, the signals at the marginal area

will be weak and they will be interfered by other cells. Then, the signaling loss

may happen during the random access, which leads to the SD assignment

failure.

If the coverage range of the cell is too large, this cell and one cell far from it are

co-BCCH and co-BSIC.

For the overshooting problem, the most fundamental solution is to adjust the

engineering parameters of the antenna, so as to control the coverage range. What

is more, the TA_allowed parameter can reduce the number of SDCCH assignment

failures due to overshooting effectively. The side effect is that the MS far from the

site cannot access the network. Therefore, the threshold of the TA_allowed

parameter should be set to be a little bit higher than the actual coverage range. For

the cell coverage range calculation, the influence of the transmission distance of the

repeater should be considered.



For the TA_Allowed parameter adjustment, the risk is that the MS cannot make

reselection after being limited by the TA_Allowed parameter. The engineers make

a test for this problem.

If the MS selects a cell with the strongest power but the location update fails due to

the TA_Allowed parameter, the MS will select one cell with the second strongest

power in the reselection cells (If the CI of this cell is larger than 0, the MS can

access this cell) and it will not stay in the original cell. The time interval of the cell

reselection is decided by the random waiting time and maximum number of

resending times. And it always lasts for several seconds. The specific calculation

method is shown as follows.

Time interval of cell reselection = Random waiting time × Maximum retransmission

times + T3126

Judging from the reselection, during the cell reselection of the MS, there is penalty

strategy for the cells with reselection failure. Therefore, the MS can make

reselection even after it is limited by the TA_Allowed parameter.

Note:

For the TA_Allowed parameter, other vendors have the similar parameters. For

example, the corresponding parameter of Nortel is the RNDACCTIMADV parameter.

This parameter is relevant to the actual coverage range of the cell. If the threshold of the

parameter is setting properly, the pseudo-RACH request can be filtered. The

unnecessary SDCCH assignment should be avoided. Judging from the test, for the cell

with short coverage radius, if this parameter is set to 35, the RACH misjudgment (The

system decodes the noise as the RACH pulse wrongly) will be 30% of the total RACH

requests. If the threshold of the RNDACCTIMADV parameter is set to 2, there is no

RACH misjudgment.

UL noise interference

The BTS RX sensitivity is from –112 dBm to –125 dBm. If random access signals

lower than the BTS RX sensitivity is received, the signals are usually interference.

This type of interference will surely lead to SDCCH assignment failure.

The RACHMin parameter (network parameter) is set for the BTS filtering noise

signals, corresponding to the BTS receiving sensitivity. If the receiving level is lower

than that of the random access signal of the RACHMin parameter, the signal will be

abandoned as the noise signal. The SDCCH assignment success rate can be

enhanced effectively through the RACHMin parameter adjustment.

The interference signals usually have weak RxLev and large TA (larger than the

actual coverage scope). With parameters RACHAccMin and TA_allowed, the

engineers can greatly reduce the impact of interference.



Note:

The engineers must be cautious when setting the RachMin parameter. If it is too large,

the paging success rate will be impacted.

Frequent location update initiated by the MS due to poor DL quality

Because the receiving sensitivity of the MS is lower than that of the BTS, the BTS

can receive the CHANNEL REQUEST message sent by the MS but the MS cannot

receive the IMM ASSIGN message sent by the BTS, especially when the MS is put

in the drawer or under the pillow. If the MS needs to initiate the location update, it

will send the CHANNEL REQUEST message frequently, with the cause being

location update. But it cannot receive the IMM ASSIGN message, which leads to a

large number of SDCCH assignment failures.



2 SDCCH Signaling Flow and Relevant Counters and KPIs

After the random access, authentification, distinguishment, and encryption, the MS stays

on the SDCCH and starts to call and set up signaling.

2.1 SDCCH Signaling Setup Flow

Figure 2-1 SDCCH Signaling Flow

MS BTS BSC MSC Setup(SDCCH)

Setup

Call Proceeding

Call Proceeding(SDCCH)

Assignment Request

The call connection signaling flow is described as follows.

First, the MS sends one SETUP message to the network. This message includes

the specific service category required in this call and the bearing capability of the

MS.

After the MSC receives the SETUP message, it makes the call connection

according to the provided message. The MSC sends a CALL PROCEEDING

message to the MS.

After the call control entity of the MS receives the CALL PROCEEDING message, it

enters the mobile originating connection state.

2.2 SDCCH Counter List

This list mainly includes the CS measurement and call drop measurement counters. The

counters in the following table are applicable for V3 and V4.

Table 2-1 SDCCH Counter List


C900060053 Number of SDCCH drops

C901070001 Number of call drops due to disconnection with RANA (On




SDCCH)

C901070002 Number of radio link failures (On SDCCH)

C901070003 Number of LAPD link failures (On SDCCH)

C901070004 Number of OMC-R forced releases (On SDCCH)

C901070005 Number of forced releases due to other calls (On SDCCH)

C901070007 Number of other failures (On SDCCH)

C901070008 Number of call drops due to disconnection with RANA (On TCH/F signaling)

C901070009 Number of radio link failures (On TCH/F signaling)

C901070010 Number of LAPD link failures (On TCH/F signaling)

C901070011 Number of OMC-R forced releases (On TCH/F signaling)

C901070012 Number of forced releases due to other calls (On TCH/F signaling)

C901070014 Number of other failures (On TCH/F signaling)

C901070029 Number of call drops due to disconnection with RANA (On TCH/H signaling)

C901070030 Number of radio link failures (On TCH/H signaling)

C901070031 Number of LAPD link failures (OnTCH/H signaling)

C901070032 Number of OMCR forced releases (On TCH/H signaling)

C901070033 Number of forced releases due to other calls (On TCH/H signaling)

C901070035 Number of other failures (On TCH/H signaling)

C901070053 Number of SDCCH link failures

C901070054 Number of TCH/F link failures

C901070055 Number of TCH/H link failures

C901070056 Number of RANA link releases due to other cause on SDCCH

2.3 SDCCH Call Drop KPI Definition and Affecting Factors

2.3.1 SDCCH Call Drop Definition

The SDCCH call drops indicate the call drops that happen when the BSC has allocated

the SDCCH channel to the MS but has not allocated the TCH channel successfully during

the call.

Statistical point: after the BSC receives the correct EST_IND message or after the

assignment completion and before the TCH assignment completion.



Table 2-2 SDCCH Call Drop KPI Definition

KPI SDCCH Drop Rate

Definition Number of SDCCH call drop × 100%/(Random access call attempts + Number of voice channel call attempts (handover excluded) (signaling))

Counter formula

V2 C11605 × 100%/(C11625 + C11696)

V3

V6.0 C100030053 × 100%/(C100030003 + C100030010 + C100030038)

V6.2 C900060053 ×100%/(C900060003+C900060010 + C900060038)

V4 C901070050 × 100%/(C901250001+C901260001 + C901270001)




2.3.2 Counters Relevant to the SDCCH Call Drop

C900060053: number of SDCCH drops

Description

This counter counts the number of call drops on SDCCH channel due to radio

link failure, LAPD link break, or handover failure. Call drop occurs after MS

requests for TCH/H channel successfully. The counter increments if call drop is

due to the above causes.

Measurement point

This counter increments when call drop occurs on SDCCH channel due to

radio link failure, LAPD link failure, or handover failure.

C900060003: number of SDCCH seizure attempts for assignment

Description

The SDCCH channel allocation attempt is activated by the MS channel request

message CHL_REQ. After BSC receives this message, it attempts to allocate


and C900060004 accumulate simultaneously. If occupation fails and the failure

is due to transceiver fault, C900060003, C900060004, and C900060005 do not

change. For failures in other cases, C900060003 and C900060005

accumulate simultaneously.

Measurement point:



This counter counts when the BSC completes requesting for channel (due to

assignment) (C900060004 + C900060005). The measurement point is A1 in



MS BSC

CHL_REQ

CHL_RQD

CHL_ACT

CHL_ACT_ACK

IMM _ASS _CMD

IMM_ASS

SABM

EST_IND

BTS

A1

A2

A3

C900060010: number of signaling TCH/F seizure attempts for assignment

Description

This counter counts the number of TCH/F channel occupation attempts during

assigning signaling channels, including the number of occupation success

(C901260002) and the number of occupation failure (C900060011).After BSC

receives the channel request massage, it attempts to allocate channel for the

request. If allocation and occupation succeed, C901260002 and C900060010


C901260002, C900060010, and C900060011 do not change. For other cases,

C900060010 and C900060011 accumulate simultaneously.

Measurement point



C900060011). The measurement point is A1.

C900060038: number of signaling TCH/H seizure attempts for assignment

Description






(C900060039).



and C900060038 accumulate simultaneously. If the request returns that the

transceiver is faulty, C901270002, C900060038, and C900060039 do not

change. For other cases, C900060038 and C900060039 accumulate

simultaneously.

Measurement point



C900060039). The measurement point is A1 in Figure 2-2 .

2.3.3 Factors Affecting the SDCCH Call Drop

Radio environment

The SDCCH call drop happens frequently in the area with poor signal coverage.

Interference, such as the internal interference due to improper frequency planning

and other external interference

Configuration of radio parameters

If he minimum access level of the cell is set to be too low, the call drop may

happen in the weak coverage area.

If the radio link fault timer is set to be too low, the call drop may happen due to

expiration in the condition of sudden deterioration. If the timer is set to be too

high, the radio resource utilization rate will decrease.

The power control parameter is improperly set. For example, if the level or

quality power control threshold is improperly set, the power of the MS may

decrease at the time of poor signal and call quality.

The frequency hopping parameter is improperly set. For example, the MAIO is

set improperly, which leads to the co-frequency and neighbor-frequency

interference in the same site and then the call drop.

Hardware fault



For example, too weak power amplifier output power, large difference between the

transmission power of different carriers, and carrier transmitters, combiner, and

divider faults can lead to the SDCCH call drop.

Antenna and feeder system fault

For example, if the tilts and azimuths of two antennas in the cell are not consistent,

the SWR is large, the antenna is too high, or the downtilt is improper, the coverage

range will be too large, which leads to the overshooting. As a result, the remote

isolated-island effect exists and the call drop happens.

BTS transmission problem

For example, the transmission is interrupted or the transmission is unstable.

BTS hardware malfunction

For example, the E1 cable is unreliable and the CMM/CMB board and backplane

connections are faulty.

User factor

For example, the contact of the MS battery is poor.



3 Signaling Flow and Relevant Counters and KPIs During the Voice Channel Allocation

3.1 Signaling Flow During the Voice Channel

Allocation

Figure 3-1 Signaling Flow of TCH Allocation

MS BTS BSC MSCAssignment

RequestChannel Activation

Channel Activation ACK

Assignment Command(SDCCH)

SABM(FACCH)Establish Indicationg

UA(FACCH)

Assignment Complete(FACCH)

Assignment Complete

The signaling flow of the voice channel allocation is shown as follows.

After the MSC sends a CALL PROCEEDING message to the MS, it sends an

ASSIGNMENT REQUEST message to the BSC to require the BSC to allocate the

TCH voice channel for this call. This message includes the call priority, DL DTX,

radio channel distinguish, and available interface bandwidth.

After the BSC receives the ASSIGNMENT REQUEST message from the MSC, if

there is any needed resource, it will send a CHANNEL ACTIVATION message to

the BTS to activate the TCH. This message includes the channel, frequency, time

slot, and frequency-hopping.

If the BTS finishes the resource (such as circuit) preparation, it will send a

CHANNEL ACTIVATIONG ACK message to the BSC. If there is no corresponding

ground resource, the BSC will send a RESOURCE FAILURE message to the MSC.

If the system allows queuing, the BSC will send a QUEUING INDICATION message

to the MSC and put the ASSIGNMENT REQUEST message into the queue and

enable T11. If this timer expires, the BSC will send a CLEAR REQUEST message

to the MSC.



After the BSC receives the CHANNEL ACTIVATIONG ACK message, it will send

an ASSIGNMENT COMMAND message to the MS through the signaling channel.

This message includes channel description and channel mode (full rate/half rate).

After the MS receives the ASSIGNMENT COMMAND message from the network, it

hands over to the allocated channel.Then, the MS initiates the low layer connection

setup and arrange the sending and receiving configuration to this TCH and then

sends a SABM message to the BTS through the FACCH.

After the BTS receives the SABM message, it will send an ESTABLISH

INDICATION message to the BSC and send one UA confirmation frame to the MS

through the FACCH to make the preemptive judgment.

If the MS occupies the allocated channel successfully, it will send an ASSIGNMENT

COMPLETE message to the system through the FACCH.

The FACCH and TCH use the same channel. The only difference is that the ID of the

TCH burst pulse is changed from 0 to 1. This is called as frame stealing.

Note:

If the MS cannot occupy the specific channel because of radio interface failure, radio

interface message failure, or assignment message distinguish failure due to interference

and hardware problem, the MS will send an ASSIGNMENT FAILURE message to the

system on the original channel.

If the MS cannot receive the assignment command from the system or the system cannot

receive the response from the MS due to interference and then the T3107 expires, the

system will release the allocated channel.

3.2 Relevant Counter List During the TCH Allocation

This list mainly includes the CS measurement and TCH measurement counters.

In V4, the TCH2/F measurement counters and TCH2/H measurement counters are

added and the allocation flow is improved. The V4 allocation flow will be described in

Chapter 7.

Table 3-1 List of Counters During the TCH Allocation (for V3)


C900060019 Number of voice TCH/F seizure attempts for assignment

C900060020 Number of voice TCH/F seizure failure for assignment

C900060023 Number of TCH/F allocation success for assignment (speech version 1)

C900060024 Number of TCH/F allocation failure for assignment (speech version 1)






C900060027 Number of TCH/F allocation failure for assignment (speech version 3)

C900060028 Number of voice TCH/F assignment success

C900060029 Number of voice TCH/F assignment failure for assignment

C900060042 Number of voice TCH/H seizure attempts for assignment

C900060043 Number of voice TCH/H seizure failure for assignment

C900060125 Average number of available radio channel

C900060126 Average number of unavailable radio channel

C900060127 TCH/H busy time

C900060128 Maximum number of busy TCH/F

C900060129 TCH/F busy time

C900060138 Number of TCH/F allocation failure due to BTS connection failure for assignment (speech version 1)

C900060139 Number of TCH/F allocation failure due to BIU connection failure for assignment (speech version 1)

C900060140 Number of TCH/F allocation failure due to TCU connection failure for assignment (speech version 1)

C900060141 Number of TCH/F allocation failure due to channel activation failure for assignment (speech version 2)







C900060148 Number of data TCH/F allocation failure due to BTS connection failure for assignment

C900060149 Number of data TCH/F allocation failure due to BIU connection failure for assignment

C900060150 Number of data TCH/F allocation failure due to TCU connection failure for assignment

C900060175 Number of TCH/H allocation failure due to channel activation failure for assignment (speech version 1)

C900060176 Number of TCH/H allocation failure due to BTS connection failure for assignment (speech version 1)




C900060177 Number of TCH/H allocation failure due to BIU connection failure for assignment (speech version 1)

C900060178 Number of TCH/H allocation failure due to TCU connection failure for assignment (speech version 1)









C900060199 Number of voice TCH/H assignment success

C900060200 Number of voice TCH/H assignment failure

C900060201 Number of voice TCH/H handover success

C900060202 Number of data TCH/H allocation failure due to channel activation failure for assignment

C900060203 Number of data TCH/H allocation failure due to BTS connection failure for assignment

C900060204 Number of data TCH/H allocation failure due to BIU connection failure for assignment

C900060205 Number of data TCH/H allocation failure due to TCU connection failure for assignment

C900060217 Number of unavailable defined TCH/H

C900060218 Number of unavailable defined TCH/F

C900060244 Number of voice TCH/F drops due to radio link failure

C900060245 Number of voice TCH/H drops due to radio link failure

C901260021 Number of voice TCH/F seizure success for assignment

C901260026 Number of TCH/F allocation attempts for assignment (speech version 1)



C901260062 Number of voice TCH/F assignment attempts

C901260065 Number of voice TCH/F handover attempts




C901260067 Number of voice TCH/F handover failure

C901260068 Number of voice TCH/F handover failure messages do not received by BSC

C901260094 Number of data TCH/F allocation failure for assignment due to TIPB connection failure (speech version 1)

C901260095 Number of data TCH/F allocation failure for assignment due to resource request to iTC failure (speech version 1)





C901260106 Number of TCH/F allocation failure due to request AIPB resource failure for assignment (speech version 1)

C901260107 Number of TCH/F allocation failure due to request UDP port failure for assignment (speech version 1)

C901260108 Number of TCH/F allocation failure due to AIPB connection failure for assignment (speech version 1)







C901270021 Number of voice TCH/H seizure success for assignment

C901270026 Number of TCH/H allocation attempts for assignment by BSC (speech version 1)

C901270027 Number of TCH/H allocation success for assignment (speech version 1)

C901270038 Number of TCH/H allocation attempts by BSC for assignment (speech version 2)

C901270039 Number of TCH/H allocation success by BSC for assignment (speech version 2)

C901270050 Number of TCH/H allocation attempts for assignment (speech version 3)




C901270051 Number of TCH/H allocation success for assignment (speech version 3)

C901270062 Number of voice TCH/H assignment attempts by BSC

C901270065 Number of voice TCH/H handover attempts

C901270067 Number of voice TCH/H handover failure

C901270068 Number of voice TCH/H handover failure messages do not received by BSC

C901270094 Number of TCH/H allocation failure for assignment due to TIPB connection failure (speech version 1)

C901270095 Number of TCH/H allocation failure for assignment due to resource request to iTC failure (speech version 1)


C901270102 Number of TCH/F allocation failure for assignment due to TIPB connection failure (speech version 3)


C901270106 Number of TCH/H allocation failure due to request AIPB resource failure for assignment (speech version 1)

C901270107 Number of TCH/H allocation failure due to request UDP port failure for assignment (speech version 1)

C901270108 Number of TCH/H allocation failure due to AIPB connection failure for assignment (speech version 1)







C901270124 Number of TCH/H allocation failure due to request AIPB resource failure for assignment (data)

C901270125 Number of TCH/H allocation failure due to request UDP port failure for assignment (data)

C901270126 Number of TCH/H allocation failure due to AIPB connection failure for assignment (data)



3.3 TCH Allocation Success Rate Definition and

Failure Cause Description

3.3.1 TCH Allocation Success Rate KPI Definition

Table 3-2 TCH Allocation Success Rate (Handover Excluded) KPI Definition

KPI TCH Allocate Success Rate (%) (Exclude Handover)

Definition Number of TCH allocation success times (handover excluded)/Number of TCH allocation requests (handover excluded)

Counter formula

V2 (1-(C11654+C11610+C11658)/(C11609) × 100%

V3

V6.0

(C100030017 + C100030028 + C100030036 + C100030235 + C100030199 + C100030210) × 100%/(C100030010 + C100030019 + C100030030 + C100030038 + C100030042 + C100030046)

V6.2

(C900060017 + C900060028 + C900060036+C900060235 + C900060199 + C900060210) × 100%/(C900060010 + C900060019 + C900060030 + C900060038 + C900060042 + C900060046)

V4

(C900060017 + C900060028 + C900060036 + C900060235 + C900060199 + C900060210) × 100%/(C900060010 + C900060019 + C900060030 + C900060038 + C900060042 + C900060046)

In V4, for the allocation success rate, part of TCH 2 measurement statistics are not

considered, which is good for the allocation success rate.

ZTE defines three stages for the TCH allocation process: occupation (congestion),

allocation (channel activation), and assignment

TCH occupation (congestion): After receiving an ASSIGN REQUEST message, the

BSC checks the database to confirm whether there is any available channel. If there

is, the occupation is successful. If there is no available channel and the queuing,

directional retry, or force release function does not exist, the TCH congestion

happens. If the queuing, directional retry, or force release function exists, start the

corresponding timer and enable the function, so as to wait the available resources. If

available resources appear within the time range of the timer, the occupation is

successful. If the timer expires, the TCH congestion happens.

TCH allocation (activation): After the channel resources are applied successfully

from the data base, the BSC send a CHANNEL ACTIVATION message to the BTS,

that is the TCH allocation attempt. After the BSC receives a

CHANNELACTIVATIONACK message from the BTS, the allocation is successful. If

the BSC receives a CHANNELACTIVATIONNACK message from the BTS or it

does not receives the CHANNELACTIVATIONACK message within the time range

of the timer, the allocation fails.



TCH assignment: After the BSC receives the CHANNELACTIVATIONACK

message during the channel allocation, it will send an ASSIGN COMMAND

message on the DL SDCCH and one TCH assignment attempt is counted. After the

BSC receives an ASSIGN COMPLETE message from the BTS, this assignment is

successful. Otherwise, the assignment fails.

3.3.2 TCH Allocation Failure Description

The voice channel allocation flow is shown in the following figure.

Figure 3-2 Voice Channel Allocation Flow

The ASSIGNMENT FAILURE message corresponds to the ASSIGNMENT REQUEST

message, which reflects one TCH allocation failure.For assignment failure 1, in most

cases, the cause is no idle channel; for assignment failure 2, the cause is the channel

allocation failure due to BTS fault; for assignment failure 3, it mainly indicates the channel

assignment failure on the air interface and the causes include the coverage and

interference.

3.3.3 Main Causes of TCH Allocation Failure

The common TCH allocation failure may be caused by the following issues.



Cell traffic congestion

If the congestion rate of the cell is high, when the MS applies for the voice channel,

the system will find that there is no TCH resource for allocation, which will lead to

the allocation failure

Hardware fault

When the TRX is faulty, the allocation failure rate is always high and the

incoming handover failure rate is also high, for the BSC assigns the channel for

the MS at the time of incoming handover. If the cell allocation failure rate is

higher than 10%, possibility of TRX fault is high. For this kind of cells, in order

to locate the faulty TRX, the engineers can record the Abis-interface signaling

of these cells and find out the specific TRX leading to the allocation failure

through the signaling analysis.

Combiner fault, such as no forward power output

Clock board fault or internal cable fault

Co-frequency or neighbor-frequency interference

Because of the high code error rate caused by interference, MS is unable to set up

L2 link with BTS, which will result in handover failure;

Antenna and feeder system fault

The feeders are corroded or worn down, which leads to high VSWR and affects the

RX performance.

The main and diversity antennas are blocked or the coverage is uneven. When the

antenna with the TCH is blocked is not the same with another antenna with the

BCCH or SDCCH, the MS cannot occupy this TCH.

Improper parameters

If the frequency-hopping is adopted and the HSM or MAIO is set improperly, the

co-frequency or neighbor-frequency interference will be serious in the cell or

between the same cells in the frequency-hopping group, which will lead to the

allocation failure.

If T3107 is set to be too small, the network will release the channel due to T3107

expiration before it receives the assignment completion message.

Transmission fault on the A interface or Abis interface

If the transmission error code rate on the A interface or Abis interface is high, the

signaling exchange cannot be completed normally between the MS and network,

which leads to the allocation failure.



Influence from the repeater

When the outdoor repeater is adopted, the microwave transmission mode is usually

adopted. Therefore, when the repeater amplifies the UL and DL signals, the

interference signals will also be amplified, which leads to the poor quality

deterioration and call drop. As a result, the TCH allocation failure rate increases

obviously.

3.3.4 Problem Handling Process

It’s recommended to locate problem through checking radio parameters and hardware.

Procedure of handling TCH handover failure problem is described as follows.

1. Check the traffic to confirm whether there is any congestion. If there is, solve the

problem through the capacity expansion and traffic balancing.

2. Check whether the radio parameter setting is reasonable, such as the

frequency-hopping parameter and frequency data. For the improper parameters,

make optimization and adjustment.

3. Check KPIs, just like BER and idle interference band, so as to reduce or eliminate

radio interference.

4. Check the cell hardware, including CDU, RF connection lines between boards, and

change hardware with faults;

5. Check antenna system, including VSWR, direction of antennas in the same cell,

wrong installation or reversed installation of antenna feeders, make necessary

adjustment and changes.



3.4 TCH Congestion Description, Cause, and

Handling Flow

3.4.1 TCH Congestion Description

After receiving the ASSIGNMENT REQUEST message from the MSC, the BSC will

search for suitable TCHs. If there is no available TCH, the BSC will send an

ASSIGNMENT FAILURE message to the MSC with the cause of no radio resource

available.

3.4.2 TCH Congestion Rate KPI Definition

Table 3-3 TCH Congestion Rate Definition

KPI TCH Congestion Rate

Definition Number of TCH congestion times × 100%/Number of TCH call attempts

Counter formula

V2 (C11612 - C11699) × 100%/(C11611-C11698)

V3 V6.0

(C100030020 + C100030031 + C100030043 + C100030047 + C100030022 +

C100030033 + C100030045 + C100030049) ×

100%/(C100030019 + C100030030+ C100030042 + C100030046 + C100030021 + C100030032 + C100030044 + C100030048)



KPI TCH Congestion Rate

V6.2

(C900060020 + C900060031 + C900060043 + C900060047 + C900060022 + C900060033+ C900060045 + C900060049) × 100%/(C900060019 + C900060030 + C900060042 + C900060046 + C900060021 + C900060032 + C900060044 + C900060048)

V4

(C900060020 + C900060031 + C900060043+ C900060047 + C900060022 + C900060033 + C900060045 + C900060049) ×100%/(C900060019 + C900060030 + C900060042 + C900060046 + C900060021 + C900060032 + C900060044 + C900060048)

3.4.3 Counters Relevant to the TCH Congestion

C900060019: number of voice TCH/F seizure attempts

Description

This counter counts the number of TCH/F channel being attempted to be

occupied during voice channel assignment, including the number of occupation

success (C901260021) and the number of occupation failure (C900060020).



and C901260021 accumulate simultaneously. If occupation fails, C900060019

and C900060020 accumulate simultaneously. If the request returns no channel

available but queuing or forced release is possible, enter the state of waiting

for resource. If the waiting for resource succeeds, C900060019 and

C901260021 accumulate simultaneously. If the waiting for resource fails,

C900060019 and C900060020 accumulate simultaneously. If the request

returns that the transceiver is faulty, C900060019, C901260021, and

C900060020 do not change. For failures in other cases, C900060019 and

C900060020 accumulate simultaneously.

Measurement point

The BSC completes requesting for channel (due to assignment and the

channel is used as voice channel), or BSC receives the internal message of

waiting for resource successfully or waiting for resource failed (C901260021 +

C900060020). The measurement point is B1, as shown in Figure 3-2 and

Figure 3-3.



Figure 3-3 Common Assignment Flow (Internal TC)

MS

SABM

ASS_COM

ASS_CMD

BSCBTS

CHL_ACT

CHL_ACT_ACK

B1

B2

UA EST_IND

B3

MSC

ASS_REQ

ASS_CMD

Abis，TCU connect

B4ASS_COM

B5 ASS_COM

Figure 3-4 Common Assignment Flow (External TC)

MS BTS BSC

B1

CHL_ACT

ASS_REQ

B2

ASS_CMDASS_CMD

SABM

EST_IND

B3

iTC

CHL_ACT_ACK

UA

ASS_COMASS_COM

ASS_COM

B4

B5

MSC

TCRescr Req

TCRescr Ack

iTC Connect Req

iTC Connect Ack

C900060020: number of voice TCH/F seizure failure

Description

This counter counts the number of TCH/F channel occupation failure during

voice channel assignment.



After BSC receives the channel request message, it attempts to allocate

channel for the request. If occupation fails, this counter accumulates. If the

request returns no channel available but queuing or forced release is possible,

enter the state of waiting for resource. If the waiting for resource fails, this

counter accumulates. If the request returns that the transceiver is faulty, this

counter does not change. For failures in other cases, this counter

accumulates.Measurement point


voice channel) but fails to occupy the channel, or BSC fails to wait for internal

resource. The measurement point is B1, as shown in the following figure.

Figure 3-5 Common Assignment Failure Flow 1 (Internal TC)

C900060021: number of voice TCH/F seizure attempts for handover

Description


occupied during voice channel handover, including the number of occupation













Measurement point



The BSC completes requesting for channel (due to handover and the channel

is used as voice channel), or BSC receives the internal message of waiting for

resource successfully or waiting for resource failed (C901260024 +

C900060022).

C900060022: number of voice TCH/F seizure failure for handover

Description


voice channel handover.


channel for the request. If allocation or occupation fails, this counter

accumulates. If the request returns no channel available but queuing or forced

release is possible, enter the state of waiting for resource. If the waiting for

resource fails, this counter accumulates. If the request returns that the

transceiver is faulty, this counter does not change. For failures in other cases,

this counter accumulates.

Measurement point

The BSC requests for channel (due to handover and the channel is used as


resource. The measurement point is C1, as shown in Figure 3-5, and D1, as

shown in Figure 3-6.

Figure 3-6 Intra-BSC Handover Occupation Failure Flow



Figure 3-7 Inter-BSC Handover Occupation Failure Flow

C900060030: number of data TCH/F seizure attempts for assignment

Description


occupied during data channel handover, including the number of occupation













Measurement point


channel is used as data channel), or BSC receives the internal message of



Figure 3-3.

C900060031: number of data TCH/F seizure failure for assignment

Description


data channel assignment.








counter does not change. For failures in other cases, this counter accumulates.

Measurement point


data channel) but fails to occupy the channel, or BSC fails to wait for internal

resource. The measurement point is B1, as shown in Figure 3-4.

C900060032: number of data TCH/F seizure attempts for handover

Description




If allocation and occupation succeed, C900060032 and C901260073

accumulate simultaneously. If occupation fails, C900060032 and C900060033

accumulate simultaneously. If the request returns no channel available but

queuing or forced release is possible, enter the state of waiting for resource. If

the waiting for resource succeeds, C900060032 and C901260073 accumulate

simultaneously. If the waiting for resource fails, C900060032 and C900060033


C900060032, C901260073, and C900060033 do not change. For failures in

other cases, C900060032 and C900060033 accumulate simultaneously.

Measurement point


is used as data channel), or BSC receives the internal message of waiting for


C900060033).

C900060033: number of data TCH/F seizure failure for handover

Description


data channel handover.









Measurement point


data channel) but fails to occupy the channel, or BSC fails to wait for internal

resource. The measurement point is C1 in Figure 3-2 and D1 in Figure 3-3.

C900060042: number of voice TCH/H seizure attempts for assignment

Description



success (C901270021) and the number of occupation failure (C900060043)..

Measurement point


channel is used as voice channel), or BSC receives the internal message of


C900060043). The measurement point is C1 in Figure 3-2 and D1 in Figure

3-3.

C900060043: number of voice TCH/H seizure failure for assignment

Description

This counter counts the number of TCH/H channel occupation failure during

voice channel assignment.







Measurement point



resource. The measurement point is B1, as shown in Figure 3-4.

C900060044: number of voice TCH/H seizure attempts for handover

Description

















Measurement point: The BSC completes requesting for channel (due to

handover and the channel is used as voice channel), or BSC receives the

internal message of waiting for resource successfully or waiting for resource

failed (C901260024 + C900060045).

C900060045: number of voice TCH/H seizure failure for handover

Description


voice channel handover.


channel for the request. If allocation or occupation fails, this counter

accumulates. If the request returns no channel available but queuing or forced

release is possible, enter the state of waiting for resource. If the waiting for

resource fails, this counter accumulates. If the request returns that the

transceiver is faulty, this counter does not change. For failures in other cases,

this counter accumulates.

Measurement point

The BSC requests for channel (due to handover and the channel is used as


resource. The measurement point is C1, as shown in Figure 3-2, and D1, as

shown in Figure 3-3.

C900060046: number of data TCH/H seizure attempts for assignment

Description




(C900060047).














Measurement point


channel is used as data channel), or the BSC receives the internal message of



Figure 3-3.

C900060047: number of data TCH/H seizure failure for assignment

Description


data channel assignment.

After the BSC receives the channel request message, it attempts to allocate






Measurement point


data channel) but fails to occupy the channel, or the BSC fails to wait for

internal resource. The measurement point is B1, as shown in Figure 3-4.

C900060048: number of data TCH/H seizure attempts for handover

Description






Measurement point


is used as data channel), or BSC receives the internal message of waiting for


C900060049).

C900060049: number of data TCH/H seizure failure for handover

Description


data channel handover.

After the BSC receives the channel request message, it attempts to allocate






Measurement point


data channel) but fails to occupy the channel, or the BSC fails to wait for

internal resource. The measurement point is C1 in Figure 3-2 and D1 in Figure

3-3.

3.4.4 Main Causes of the TCH Congestion

Main causes for channel congestion are as follows:

High traffic density, which even exceeds the designed capacity of BTS

Transmission failure

When the transient or high error code happens for the transmission on the Abis

interface, because this fault has not been happened on the BSC, the congestion

happens due to unavailable ground circuit resource at the time of channel activation

of the BSC. After the queuing function is activated, this event is more obvious.

Unstable hardware

For example, the lack of usable resources or channel congestion caused by

unstable equipment performance

Problems with adjacent cells



Because of the faulty adjacent cell, the serving cell absorbs some extra traffic and

the congestion happens.

Unreasonable parameter setting

The T3107 and T3103 are set to be too large and the queuing parameters are set

unreasonably; the handover threshold and capacity are set improperly; the minimum

access level and BTS power are defined improperly.

Too large coverage, leading to the isolated-island effect

3.4.5 TCH Congestion Handling Process

The Handling steps for TCH congestion are as follows:

1. Check if the problem cell and its adjacent cells operate normally; check the TCH

usability to locate the unstable equipment. If adjacent cells work abnormally, the

problem cell will have to bear their traffic besides its own load.

2. Check the MS mobility to see if the TCH congestion is caused by excess incoming

handovers. It it’s true, optimize the handover parameters (increasing the HO_

Margin parameter) to reduce number of handovers from adjacent cells to the

congested cell, so as to ease the cell from congestion.

3. Check setting of radio parameters. The unreasonable setting of these parameters

(such as delay of cell reselection, handover tolerance limit, and level of outgoing

handover trigger) can result in pingpong location renewal and pingpong handover.

4. Through test of field strength, analyze if coverage is too large and if the

isolated-island effect exists. When the isolated-island effect happens to one cell in

an area, where predefined adjacent cells cannot be detected, the MS will constantly

stay with the serving cell; and normal handovers cannot be triggered, in spite of any

changes on signals, and finally call drops will be caused. To avoid this case, two

methods can be adopted. The first one is adjusting the antenna of the isolated cell to

eliminate the effect. However, due to the complexity in electric wave transmission, it

takes several tests to abate the effect, and it is really difficult to completely eliminate

the effect due to high buildings. The second method is defining new adjacent cells

for the isolated cell. The principle for defining related parameters is that

handovers/LAC renewal from the isolated cell to normal cells has priority over the

reversed ones.

5. Congestion due to high traffic density

Check if the BTS capacity configuration reaches the max. If not, expand it with

enough TRXs.

The general flow for handling TCH congestion is shown in the following figure.



Figure 3-8 Flow of Handling TCH Congestion

The TCH congestion of one

cell is too high.

Check the channel

availability rate of the

cell

Check whether the

coverage is too large

and the isolated-island

effect exists.

Reduce the coverage

and eliminate the

isolated-island effect.

Set the parameters

properly.

Optimize the

handover parameter

and reduce the

handovers.

Check whether the

neighbor cell is faulty.

Check whether the fault

is caused by excessive

handovers.

Check the radio

parameter setting.

Yes

Troubleshoot the

neighbor cell fault.

Troubleshoot the

hardware fault.

Low

Yes

Improper

Yes

The congestion is caused by

the high traffic density.

Check whether the BTS

has the maximum

configuration.

End

Plan enough TRXs for the

expansion.

Reduce the BTS

power and increase

the downtilt, so as to

reduce the

congestion.

Yes



4 Call Connection Process

4.1 Signaling Flow of the Call Connection Process

After the TCH allocation, the call connection process starts. The signaling process is

described as follows.

Figure 4-1 Call Connection Process

MS BTS BSC MSC GMSCRF Channel Release

RF Channel Release

ACKAlerting

ACM

Alerting （SDCCH)

ANSWER

Connect

Connect (SDCCH)

Connect ACK (FACCH)

Connect ACK

Measurement

Report (SACCH) Measurement Report

IAI

When the MS informs the network that it has occupied the TCH and it is

unnecessary to build the SDCCH for occupation for this call. The SDCCH is

released through the channel release program.

The MSC receives an ADDRESS COMPLETE message from the terminating end

and sends an ALERTING message to the MS. At this time, the originating user can

hear the alerting, which means that the terminating user is in alerting.

After the terminating user answers the call, the terminating end will send an

ANSWER message to the originating MSC. At this time, the link between the

originating end and terminating end is connected and the MS send a CONNECT

message to the MS. After the MS receives a CONNECT message, it sends one

connection confirmation message. All the local alerting indications are stopped and



the billing starts. At this time, the call is set up and the two ends enter the

conversation stage.

After the main signaling channel is built, the MS sends the measurement report

about the voice quality twice per second.

4.2 Counters in the Call Connection Process

Table 4-1 Counters in the Call Connection Process


C900060244 Number of voice TCH/F drops due to radio link failure

C900060245 Number of voice TCH/H drops due to radio link failure

C901070017 Number of voice TCH/F drops due to LAPD link failure

C901070038 Number of voice TCH/H drops due to LAPD link failure

C900060054 Number of TCH/F link failures

C900060055 Number of TCH/H link failures

C900060244 (C900060245)

Description

This counter counts the number of voice TCH/F drops due to radio link failure.

After MS applies for TCH/F voice channel, call drops. If this problem is caused

by radio link failure, then this counter increments.

Measurement point

On TCH/F voice channel, when BSC receives a CONNECTION FAILURE

INDICATION message at Abis interface, this counter counts. The

measurement point is A, as shown in the following figure.



Figure 4-2 Call Drop Caused by the Radio Link Fault

C901070017 (C901070018)

Description

This counter counts the number of call drop due to LAPD link failures (on

TCH/F voice channel). The counter increments if the phenomenon that the call

drop after MS has obtained TCH/F voice channel is caused by LAPD link

failures.

Measurement point

The counter increments when BSC receives a DLREL_IND message from

LAPD on TCH/F voice channel.

C900060054 (C900060055)

Description

This counter counts the number of call drops on TCH/F channel due to radio

link failure, LAPD link break, or handover failure. Call drop occurs after MS

requests for TCH/H channel successfully. The counter increments if call drop is

due to the above causes.

Measurement point

This counter increments when call drop occurs on TCH/F channel due to radio

link failure, LAPD link failure, or handover failure.



4.3 Call Drop During the Call Connection Process

In the mobile communication, the call drop indicates the call loss or interruption due to a

certain cause after the TCH allocation. The call drop causes a lot of inconveniences for

the user and it is a hot spot for user’s complaint.

The call drops fall into the following categories.

Call drops due to radio link fault (RF loss call drop)

Call drops due to handover failure

LAPD call drops

In this chapter, only the call drops due to radio link fault and LAPD call drops during the

call connection are described.

4.3.1 Causes of Call Drops due to Radio Link Fault

The radio link fault is divided into UL failure and DL failure.

The DL failure

According to the GSM protocol, one initial value is given to the timer S (T100) in the

MS, which is the value of the radio_link_timeout parameter. This value is

broadcasted on the BCCH. When the MS cannot decode one SACCH message

(four SACCH congestion times) correctly, the S will be reduced by 1.When the MS

decodes one SACCH message correctly, the S will be increased by 2.But the value

of S is no larger than the initial value of the radio_link_timeout parameter. When

the value of S is 0, the MS will give up the radio resource connection and enter the

idle mode. As a result, one call drop will happen.

The UL failure

The parameter for the system monitoring the UL link failure is the link_fail

parameter. When the BTS cannot decode one SACCH message correctly, the

counter in the HDPC (the maximum value is decided by the link_fail parameter.)

will be reduced by 1. When the BTS decodes one SACCH message correctly, the

counter will be increased by 2 (The value of the counter cannot exceed the value

decided by the Link_fail parameter.)When the value of the counter is 0, the BTS will

stop transmitting the DL SACCH and start the rr_t3109 (rr_t3109 > T100).When the

T100 of the MS expires, the MS will return to the idle mode and the call drop

happens. When the rr_t3109 expires, the BTS will release the radio channel. And

the BSC needs to send one CLEAR REQUEST message to the MSC.

Either the UL failure or the DL failure can stop the SACCH transmission. Then the radio

resource release is triggered. If one link failure (link_fail) happens on the TCH, one

RF_LOSSES_TCH will be counted.

The main causes of call drops due to radio link fault are listed as follows.



The weak coverage area exists and the radio signal is poor.

The interference exists, such as the internal interference due to improper frequency

planning and external interference.

Improper configuration of radio parameters

The minimum access level is set to be too low and the MS makes calls in the

weak coverage area and the call drop happens easily.

The NCC Permitted parameter is improperly set. In some network, the serving

cell and neighbor cells may use different NCCs. It is necessary to add the

NCCs used by the corresponding neighbor cells to the NCC Permitted

parameter. Once the setting is improper, the MS will not detect the neighbor

cells with a certain NCC, which leads to the handover failure. Then the RF loss

and call drop happen.

If the radio link fault timer is set to be too low, the call drop may happen due to

expiration in the condition of sudden deterioration. If the timer is set to be too

high, the radio resource utilization rate will decrease.

The setting of power control parameter is unreasonable, such as the level and

the quality power control threshold. As a result, the MS may have poor signal

and quality and the power may become weaker.

The setting of frequency-hopping parameter is unreasonable, such as the

MAIO configuration. Then the co-frequency and neighbor-frequency

interference exists in the same site.

The incomplete neighbor cell data definition or configuration error leads to the

signal improvement through the handover and then the call drop happens due

to the signal deterioration.

The handover parameter setting is improper and the MS cannot make the

handover in time in the condition of poor quality to improve the radio quality. As

a result, the call drop happens.

The handover parameter setting is improper and the MS cannot make the

handover in time in the condition of poor quality to improve the radio quality. As

a result, the call drop happens. The neighbor cell congestion problem should

be solved.

Hardware fault, such as the too low power amplifier output power, great difference

between the transmission power of different TRXs, and the fault of TRX transmitter,

combiner, and divider.

Antenna and feeder system fault, such as different tilts and azimuths of two

antennas in the cell, large SWR, too high antenna or improper downtilt, can lead to



too large coverage range and the overshooting. Then the remote isolated-island

effect and then the call drop happen.

User factor

For example, the contact of the battery of the MS is poor.

4.3.2 Causes of Call Drops Due to LAPD Link Failure

BTS transmission problem, such as unstable transmission or transmission

interruption

BTS hardware malfunction, such as unreliable E1 cable and CMM board or back

board connection fault.

BSC hardware problem, such as the LAPD handling board fault.



5 Signaling Flow and Relevant Counters and KPIs During the Terminating Paging Stage

5.1 Paging Principle

Radio paging is a communication process in which the MSC finds out the MS through

paging. Only when the mobile subscriber has been found out can the MSC carry out next

call connection.

Figure 5-1 Paging Message Delivery



5.2 Basic Signaling Flow of the Radio Paging

Figure 5-2 Basic Signaling Flow of the Radio Paging

MS BTS BSC MS

7 Channel Activation ACK


Command9 Immediate Assigment (AGCH)

1 Paging2 Paging Command

3 Paging Request

4 Channel

Request(RACH) 5 Channel Request

6 Channel Activation

10 SABM Paging

Response(SDCCH)

11 Paging Response(SDCCH)

Establish Indicationg12 Paging Response

13 UA(SDCCH)

As shown in the above figure, the basic paging signaling flow is described.

1. The MSC sends, after getting the current LAC information of the MS from the VLR,

paging messages to all BSCs in the LAC.

2. After receiving the paging message, the BSC will send out the paging command

messages to all the cells within this LAC.

3. After the BTS receives the paging command, it will send out, on the paging

sub-channel of the paging group where the IMSI stays, a PAGING REQUEST

message, which carries the IMSI or TMSI number of the paged subscriber.

4. After receiving the PAGING REQUEST message, the MS will request through the

RACH for the SDCCH allocation. And the BSC will assign this SDCCH to the MS

through an IMMEDIATE ASSIGNMENT message on the AGCH after it confirms the

activation of the needed SDCCHs made by the BTS.

5. And MS will use this SDCCH to send a PAGING RESPONSE message.BSC will

then forward this PAGING RESPONSE message to the MSC and one radio paging

will be completed successfully.

Now, the switch in GSM network usually adopts second paging with a paging interval of 5

seconds. After the MSC acquires the LAC of the MS from the VLR, it will send the paging

messages to all the BSCs in the LAC where the MS stays. If the MSC cannot receive the

PAGING RESPONSE message in five seconds after it sends the paging message, the

MSC will send the paging message again. For the second time, the MSC sends the



paging messages to all the BSCs in the LAC where the MS stays. If the MSC still cannot

receive the PAGING RESPONSE message in five seconds, this radio paging fails. At the

same time, the MSC will send the record notice of “The number you dialed cannot be

connected for the moment” to the originating user.ZTE switch usually adopts second

paging (It can be set as third paging.).

5.3 Paging Counters of ZTE BSS

C900060001: number of MTC random access attempts

Description

This counter counts the number of channel requests due to the MTC random

access. When the MS sends the CHL_REQ message to the BSC through the

BTS to request for radio channel, if the TA does not exceed the cell range and

the access reason is “MTC”, the counter increments.

Measurement point

The counter counts when the MS requests for channel from the BSC and the

TA does not exceed the cell range. The measurement point is A1, as shown in


Figure 5-3 Radio Access Process

MS BSC

CHL_REQ

CHL_RQD

CHL_ACT

CHL_ACT_ACK

IMM_ASS_CMD

IMM_ASS

SABM

EST_IND

BTS

A1

A2

A3

A4

C901110006: number of MTC access success for process

Description



This counter counts the number of MTC access success for processes. The

counter increments when the BSC allows the MS to be accessed into the

network due to the MTC attempts and accepts channel request sent by the MS

and allocates and activates channel successfully. Meanwhile, the BSC sends

an IMM_ASS message to MS.

Measurement point

The counter increments when channel is activated successfully. The

measurement point is A3 in Figure 5-3.

C900060002: number of MTC access success

Description

This counter counts the number of the MS successfully accessing the channel

assigned in the immediate assignment message (the access reason is due to

the MTC). The counter increments when the following two conditions are

satisfied: the MS receives the IMM_ASS message from BSC and successfully

accesses the channel. The BSC receives the EST_IND message from the MS.

Measurement point

The counter counts when the BSC receives the EST_IND message. The

measurement point is A4, as shown in Figure 5-3 Radio Access Process.

C900060137 number of wireless access due to paging responses

Description

This counter counts the number of accesses due to paging responses. After

BSC receives the EST_IND message, if the access cause in the layer-3

information in this message is "paging responses”, this counter increments.

Measurement point

The counter counts when the BSC receives the EST_IND message. The

measurement point is A4, as shown in Figure 5-3 Radio Access Process.

C900060152: number of ABIS interface paging command messages

Description

This counter counts the number of paging command messages from

A-interface. These messages are part of Abis interface messages sent from

BSC.

Measurement point



When the BSC sends an ABIS_INTER_PAGING_CMD message to the BTS,

this counter increments. The measurement point is A in the following figure.

Figure 5-4 Measurement Point of the BSC Sending the Abis Message to the BTS

Formulae of calculating the paging success rate at the BSS side are displayed as follows.

V2: Paging success rate (BSC)=∑C10022/C20064

V3: Paging success rate (BSC)= ∑C900060002 / C900060152

5.4 Paging Success Rate KPI Definition

Table 5-1 Paging Success Rate KPI Definition

KPI Paging Success Rate (%)

Definition Number of paging responses × 100%/Number of paging requests

Counter formula

V2 C10022/C20064 × 100%

V3 C900060002/C900060152

V4 C900060002/C900060152

Remarks

The BSC can provide this KPI indirectly. But the statistical point is different from that of the MSC statistics. The main difference is whether one BSC has only one LAC and whether one LAC belongs to only one BSC for the call on the A interface.

The number of paging requests is defined as the sum of PAGING messages sent out by

all the MSCs in the local area, not including the second paging messages. The

measurement point is the MSC.

The number of paging responses refers to the sum of PAGING RES messages received

by all the MSCs in local area, including the second response messages. The

measurement point is the MSC.

The paging success rate, one important network quality KPI of the GSM network, can

affect the call completion rate and radio system connection rate directly. The sound

paging performance is quite important for being the terminating party successfully of all

the users. Therefore, the paging success rate optimization analysis is quite necessary.



5.5 Factors Affecting the Paging Success Rate

The PAGING message fails to be sent on the radio channel.

The heavy link load leads to the loss of bottom layer SCCP message.

MSC/VLR and BSC flow control leads to the message discarding.

The heavy load results in longer queuing time of messages and delay in receiving

messages of the MS.

The poor transmission link quality leads to the loss of bottom LAPD message.

The T3212 parameter is set unreasonably.

Too many paging messages results in the loss of message on the radio interface

(group sending of short messages).

Abnormal number of sending paging message times in BSC is caused by the

redundant cell data in MSC.

The MS fails to receive the PAGING message.

Coverage issues, including the coverage blind area, poor general coverage rate, the

user not staying in the coverage area, network coverage loophole, and individual

coverage blind point.

Frequent MS reselections

Frequent location update

The MS cannot monitor the messages on the BCCH when it is in GPRS service.

The paging group is set unreasonably, which leads to long paging time or paging

lost. Sometimes, the paging groups of two adjacent cells are different.

The time of the seconding paging is set improperly, so the second paging does take

effect. Besides, the system load also is increased. When the large difference

between adjacent cells causes frequent reselections, the monitoring time will be

different, tending to cause paging lost.

The relevant messages fail to reach the MSC when the MS is responding to the

PAGING message.

SDCCH congestion

SDCCH assignment failure

UL and DL imbalance, with weak UL



Poor transmission link leading to the message loss

The special case: when two MSs call the same MS simultaneously, the MSC will

connect to only one caller and reply “no paging response” to another.

The time of sending the MSC paging message is improper. Before the MS ends the

call release, the MSC finishes the release and delivers the new paging, but it is

replied with “no paging response.”

5.6 Procedure and Method of Low Paging Success

Rate Optimization

Step 1: Exclude the abnormal phenomena caused by the system

Check the flow control alarm and see whether flow control alarms exist in the

MSC, VLR, or BSC. Keep the trunk link on the A interface or Abis interface in

good maintenance, pay close attention to signaling load on the A interface or

Abis interface, and add signaling link timely, so as to reduce paging failure

caused by too heavy signaling load.

Check whether there is transient transmission interruption alarm in the BTS.

The unstable link between systems (such as the LAPD link on the Abis

interface, and interface link between different entities at the network side) and

within a system (such as the MEM link between the MSC and VLR and links

between BSC or MSC modules) will cause the message loss, leading to the

low paging success rate. This kind of problems can be discovered by checking

alarms.

Check whether there is redundant data in MSC database. As a result of

continuous network expansion and cutover, the cell data in the MSC may differ

from that in the BSC. Therefore, it is necessary to check the cell data and

delete the redundant data timely. In some areas, network expansion adopts

the "dot-distributed network" (such as inserting some ZTE BTSs in the area

under the MOTO BTS coverage), leading to the possibility that there are many

LACs under one BSC. In this case, this BSC will receive paging messages

from many different LACs, resulting in heavier paging load of the BTS in this

BSC.

Step 2: Check the latest status of the MS.

At present, the VLR probe is the only tool for checking the latest status of the MS.

In test, the status of the MS can be judged through the recording signaling on the

SGSN, MSC, and Abis interfaces.

Step 3: Exclude the influence from the GPRS.



Check whether the GPRS routing area is set correctly. Set the same routing area for

the same site and the routing area of the cells with frequent reselection should be

the same.

Check whether the routing area update cycle is set reasonably.

Use a mobile phone without GPRS function to test.

Step 4: Analyze the KPIs.

Check the SDCCH congestion condition. The SDCCH congestion rate in the

traffic statistics should be 0 or nearly 0.The condition of “no paging response”

caused by the SDCCH congestion should be eliminated.

Analyze whether the MTC success rate is abnormal.

Analyze whether the number of cell location update times is abnormal.

Analyze the average TA and the maximum TA to judge whether there is

overshooting.

Step 5: Check and optimize the radio parameters.

Check the parameter setting relevant to the paging, access, and immediate

assignment. Check the traffic statistics and alarms to see whether there are

messages about RACH, PCH and SDCCH overload.

Improper configuration of the BS-AG-BLKS-RES parameter and

BS-PA-MFRMS parameter tends to cause the PCH congestion or low paging

speed. The large value of the BS_PA_MFRMS parameter is at the expense of

average time delay on radio channel, that is to say, the larger the value of the

BS_PA_MFRMS is, the longer time delay the paging messages will spend in

the air section. Thus, the average service performance of system will also

deteriorate and there will be a longer time for the MS to wait for being paged.

On the one hand, reducing the value of the BS-PA-MFRMS parameter helps to

shorten the user response time, increasing the overall service capability; on

the other hand, when the BS-PA-MFRMS parameter of ZTE BTS <=3, paging

messages can be sent twice, increasing the number of resending paging

messages, so as to increase the paging response rate of MS, which increases

the paging success rate.

If the parameters, such as the MAX retrans parameter and TX-integer

parameter, are set improperly, channel requests may collide or cannot be

detected.

Check whether T3212 (periodic location updating timer) and IDETTIM

(implicate detach time) are set properly. One of the paging failures may be

caused by the MS entering into coverage hole or MS power-down. If the



IDETTIM of the switch does not expires, (The MSC will check the ATTACH

users regularly and set the MS that has no contact with system to the implicate

detach status.), the MSC will still send the paging message to this user but the

MS cannot respond. At the BSC side, each BTS is set with a timer T3212 to

make MSs contact the system regularly; only in this way will there be the latest

user information in the VLR.T3212 in the BSC and IDETTIM in MSC should

meet the condition of T3212 < IDETTIM.

Check whether the LAC is divided properly and whether the overlapping area

between LACs is configured properly. Please pay attention to the following

points in the LAC configuration. A LAC should be within the same MSC and

MSC crossing is not permitted. Paging capacity and the number of location

update must be balanced. The most important principle for LAC configuration

is that the maximum paging capacity of BTS should not be exceeded. Once it

is exceeded, the LAC splitting should be taken into account.

Step 6: Analyze the MSC paging strategy.

Check whether the system capacity allows the multi-paging. If it does, analyze the

influence upon the system from multi-paging. The MSC forms paging messages and

can resend the paging message in the condition of receiving no response. The

interval between two paging is a vital parameter. From the radio aspect, the longer

the interval between two paging is, the less the MS is correlated with the radio

environment when it is responding paging message, and the more easily the MS will

respond to paging messages successfully. But too long the interval will make MOC

subscriber wait for a long time that he or she tends to hang up. In optimization,

paging interval needs to be adjusted gradually according to paging success rate and

subscriber hang-up ratio. Prolonging the paging interval properly can enhance the

paging success rate. The disadvantage is that the time of waiting for the record

notice of the originating user becomes longer if the terminating user is out of the

service. Some vendors may adopt global paging in the second paging, that is to say.

paging the MS within the whole MSC. However, devices of some vendors do not

support this function. It is recommended that this function should be enabled in the

switch that has the function. This function helps a lot for enhancing the paging

success rate of the MSC that has two or more LACs.

Step 7: Make the field test.

Field test is the most important step, through which the actual phenomenon can be

captured.

When the problem is easily to be reproduced by common mobile phones rather than

the testing handset, it is necessary to use two SIM cards belonging to the same

paging group to conduct the test. Thus, it can be possible to judge whether common

mobile phones respond correctly to paging messages that have been sent normally.



Check whether frequent reselections occur. If any, modify the reselection

parameters (such as the CRO parameter, TMO parameter, and PT

parameter).Check whether there is any coverage blind area.



6 Signaling Flow of the Terminating Connection Stage

After the paging, authentification, identity appraisal, and encryption, the terminating

connection stage starts.

6.1 Signaling Flow of the Terminating Connection

Stage

Figure 6-1 Signaling Flow of the Terminating Connection Stage

MS BTS BSC MSCSetup

Setup(SDCCH)

Call Confirm(SDCCH) Call Confirm

Assignment RequestChannel Activation

Assignment Command(SDCCH)

SABM(FACCH)

Establish Indication

UA(FACCH)

Assignment Complete(FACCH)

Assignment Complete

RF Channel Release

RF Channel Release ACK

Alerting (SDCCH)

Alerting

Connect (SDCCH)

Connect

Connect ACK

Connect ACK (FACCH)

Channel Activation ACK

The call connection signaling flow is described in the above figure.

The MSC sends a SETUP message to the MS and this message includes all the

necessary details of the call (such as the required service type and the originating

number.



The terminating MS receives the SETUP message. And it sends a CALL

CONFIRMED message to the MSC after the test of call capabilities of all the

compatible equipment is completed. This message indicates that all the necessary

information for the call connection setup has been received. No more information is

needed.

After the MSC receives the CALL CONFIRMED message, it will send a Assignment

Request to the BSC, so as to allocate the TCH for this call. The terminating TCH

assignment is similar to the originating TCH assignment.

After the assignment, the terminating MS sends an ALERTING message to the

network. After the terminating MSC receives this message, it sends an ACM

message to the originating end. The originating end sends the ALERTING message

to the originating user after receiving the ACM message.

After receiving the ALERTING message, the terminating user sends a CONNECT

message to the MSC. Then the MSC sends an ANSWER message to the

originating end and sends a CONNECT message to the terminating end.

Then all the transmission links are connected to the network and the end-to-end

transmission of the user is set up.

6.2 Relevant KPIs of the Terminating Connection Stage

The terminating connection stage is corresponding to the originating call setup stage and

TCH assignment stage. The relevant KPIs are displayed as follows.

SDCCH congestion rate

SDCCH assignment success rate

TCH congestion rate

TCH allocation success rate

KPIs described in the originating signaling flow



7 Features of the V4 Allocation Process Statistics

7.1 Change of the Allocation Flow

Pre-application: applying for the ITC resources (external TC) > selecting the board >

making pre-application

Allocation: acceptation on the A interface and Abis interface > channel activation >

connection

7.2 Change of Allocation Statistics

7.2.1 Counter Adding

TCH/F measurement 2

TCH/H measurement 2

The counters reflect the success or failure statistics of all the stages of resource

application.

7.2.2 Counter Deleting

The statistics of the allocation related to the service handling flow is adjusted and the

original counters relevant to the allocation are deleted.

7.2.3 Modification and KPI Change

The statistical counters are configured. First, the counter information is acquired from the

configuration table of the OMC. After the MO, the counter information can only be

acquired from the BSC. The content should be consistent to that of the V3 (non-MO).

The KPI formula adjustment principle is that the formula should be applicable for the V3

non-MO and V3 MO.

Suppose the original formula is KPI = A + B

After the MO, the formula is KPI = A + C

A means the counters existing in all the versions.



B means the counters existing in the non-MO version (not included in the statistics in the

MO version).

C means the newly-added counters in the MO version (not existing in the non-MO

version)

Finally, the KPI formula is KPI = A + B + C



8 Cases

8.1 Cases of SDCCH Assignment Failure

8.1.1 SDCCH Assignment Failure Due to the LAPD Time Delay

8.1.1.1 LAPD Time Delay Due to Large Paging Traffic

Fault description

On a certain field, the engineers found that the SD assignment success rate of ZTE

BSC3 was low, especially in the busy hours at night, through the performance KPI

analysis. The rate was only about 60%.

Fault analysis

The engineers checked the statistical data and found that the high SD

assignment failure existed in each cell. Therefore, the poor assignment due to

radio parameter of the cell was excluded.

Judging from the statistical data, the congestion rate of SD channel was only

0.02%.

The SD assignment success rates of ZTE BSC 1, BSC 2, and BSC 4 were

higher than 95%, which was normal. Only the BSC 3 was abnormal. Because

the BSC 3 was under the MSC 7, being isolated, the engineers contacted the

China Unicom personnel and found that the SD assignment success rates of

all the BSCs (including the BSC of Siemens) under the MSC 7 were about 60%.

And the paging success rate of MSC 7 was quite low. According to the China

Unicom personnel, there was only one LAC under the MSC 7. Because all the

cells under the LAC were included during the paging, the larger the traffic was,

the larger the paging traffic was.

Solution

The engineers communicated with the engineers from Siemens and asked them to

add one LAC for MSC 7 and change the LAC IDs to the new IDs for the cells of

some BSCs of Siemens. After the modification, the SD assignment success rate of

BSC 3 was normal, higher than 95%.



8.1.1.2 Satellite Transmission Time Delay

Fault description

All the four sites, TBT-G, TBT-D, GWD-G, and GJR-G, were under BSC 01 but they

belong to different peripheral modules. Judging from the performance KPIs, the SD

assignment failure rate of these sites were above 50%.

Fault analysis

The engineers recorded the signaling on the Abis interface of TBT 1, TBT 4, TBT 5,

TBT 6, GAR, and GWD. Take the TBT 5 signaling as an example to describe the

signaling analysis.

Judging from the time stamp, the average time of successful channel activation

was 0.58 s.

Figure 8-1 Time Stamp Checking

Judging from the signaling below, the engineers checked whether the two

pieces of signaling were the CHANNEL REQUIRED messages sent by the

same MS.

Figure 8-2 Signaling Flow Checking 1

The engineers can calculate the FNs of T1, T2, and T3. The formula is FN =

T1× 26 × 51 + ((T3 - T2)mod 26) × 51 + T3

The difference of FN between two messages is 32454 - 32227 = 227 (frames).



The engineers traced the whole process of the first channel request and found

it was a complete signaling process of power-off. And they traced the second

channel request and found the immediate assignment failure. The BSC cannot

receive the ESTABLISH INDICATION message and the channel was released

after the T3101 expiration.



The two pieces of signaling had the same access delay. The maximum number

of retransmission times was 4 and TxInteger was 14 (T = 32 and S =217). The

interval between two CHANNEL REQUIRED messages sent by a MS in one

call was a random time slot among 217 ~ 248. That is to say, the shortest time

of the MS sending two CHANNEL REQUIRED message was 1001 ms and the

longest time was 1144 ms.

The time interval of the BSC receiving the two CHANNEL REQUIRED

messages was 1.031 s (1.906 - 0.875). For the BTS and BSC signaling

transmission time delays, suppose the UL and DL signaling delays were

consistent, the time length of total immediate assignment signaling was 1.16 s

(0.58 × 2), similar to 1.031 s.

According to the frame ID calculation, the actual interval of the two messages

was 227 frames (1048). Therefore, the two messages were sent by one MS in

one service call attempt.



Conclusion

Because these sites were far away from the urban area, the satellite transmission

was adopted. The time delay of the one-way transmission of the satellite

transmission is about 260 ms. Therefore, the transmission time delay of four pieces

of signaling is 1040 ms, which is consistent with the above signaling analysis.

8.1.2 High SDCCH Assignment Failure Rate Due to Co-BCCH and Co-BSIC

8.1.2.1 Interference of the Co-BCCH and Co-BSIC Coverage Overlapping Area

Fault description

On a certain field, the high SDCCH assignment failure problem was not solved. The

SDCCH assignment failure rates of many cells in the whole network were over 25%.

Handling process

The engineers changed all the hardware and the problem was still not solved. Then

the engineers traced the signaling and found that the co-BCCH and co-BSIC signals

of another cell were received at the time of TA = 20, which led to the SDCCH

assignment failure. According to this point, the engineers planed the BSICs of more

than ten cells in the whole network again. After the replanning, the KPIs of all the

cells with BSIC modification became normal.

Fault analysis and conclusion

If one MS stays in the area covered by two co-BCCH and co-BSIC cells, the

SDCCH assignment failure may happen. The triggering condition of this possibility

is that the time slots of the SDCCHs of the two co-BCCH and co-BSIC cells are

synchronized. After the MS and BTS are synchronized, if the MS selects one cell for

access, another cell will be interfered.

Therefore, for the SDCCH assignment failure (the high SDCCH assignment failure

rate due to co-BCCH and co-BSIC cells within a certain multiplexing distance), there

are two solutions.

Reset the CMM of the cell with high failure rate, so as to reset the clock. Then

the SDCCH time slots were misaligned and the influence can be reduced. This

is a temporary solution. For the field, the engineers should modify the

parameter and restore them.

Avoid the co-BCCH and co-BSIC condition, which is the fundamental solution.



8.1.3 Noise Signal Access

8.1.3.1 The Rxlev Lower Than the BTS Rev Sensitivity

Fault description

The SDCCH assignment failure rate of a certain cell was high but the TCH

assignment success rate was normal.

Fault analysis

The EDGE TRX was adopted in this cell and the Rxlev of the random access can be

reported in the physical context in the CHANNEL REQUEST message. The

engineers observed the signaling tracing data of this cell and found a large number

of CHANNEL REQUEST message with Rxlev being –135 dBm (0 × 87). These

messages led to a lot of SDCCH assignment failures.

Figure 8-5 Signaling Tracing Data Observing 1

The engineers judged that most of these CHANNEL REQUEST messages were

noise interference signals. This problem can be solved through the RACHMin

parameter setting.



8.1.4 SDCCH Assignment Failure Due to Co-BCCH and Co-BSIC Handover

Note:

The co-BCCH and co-BSIC means that the ARFCN of the target channel of the handover

is the same with the BCCH of the faulty cell and the BSIC of the target cell is the same

with that of the faulty cell.

Fault description

The signaling of a certain faulty cell is shown in the following figure. Judging from

the signaling, the engineers found out continuous CHANNEL REQUEST messages,

with the same RA and TA and continuous frame IDs. The SDCCH assignments

corresponding to these CHANNEL REQUEST message all failed. What is more, in

the basic measurement, the number of other access request attempts was high.

Therefore, the continuous CHANNEL REQUEST messages indicated the false

access caused by the handover access of the co-BCCH cells.




8.1.5 SDCCH Assignment Failure Due to Poor Network Coverage

Fault description

In a certain cell, the SDCCH assignment failure rate and the TCH assignment failure

rate were high. The out-going handover attempts were frequent and the call drop

rate was high, with complaints. The reset TRX or site cannot be restored.

Fault analysis

Judging from the basic measurement of this cell, the access causes corresponding

to the SDCCH assignment failures were various, including the originating access

and terminating access. The number of samples with UL RQ larger than 3 was large.

The UL quality was poor. Therefore, the UL signals of this cell were affected by the

interference or poor coverage.

Table 8-1 Cell Basic Measurement Data 1

Time

11644 (Number of SDCCH

Assignment Success

Times)

11645 (Number of SDCCH

Assignment Failures

)

116114 (Number of Samples with

UL RQ = 0)

116115 (Number of Samples with

UL RQ = 1)

116116(Number

of Samp

les with UL

RQ = 2)

116117(Number

of Samp

les with UL

RQ = 3)

116118(Number

of Samp

les with UL

RQ = 4)

116119(Number

of Samp

les with UL

RQ = 5)

116120(Number

of Samp

les with UL

RQ = 6)

116121(Number

of Samp

les with UL

RQ = 7)

2007-9-28 16:15

68 11 1580

73 106 100 89 140 95 102

2007-9-28 16:30

65 12 2906

144

192 168 185 185 122 120

2007-9-28 16:45

50 12 2573

123

167 166 132 105 51 58

2007-9-28 17:00

67 9 2559

180

256 226 206 142 81 76



8.1.6 SDCCH Assignment Failure Due to Continuous Location Update

Requests

Fault description

In some boundary sites and suburban sites of City A, the SDCCH assignment failure

rate was increased abruptly and irregularly, but other KPIs of the cells were normal.

The recorded signaling and basic measurement at the time of high SDCCH

assignment failure rate are shown in the following figure. Judging from the signaling,

one MS initiated the channel request with the access cause being location update

continuously but all the requests failed.

Table 8-2 Cell Basic Measurement Data 2

SITE ID

CELL ID

Time

11636 (Number of

MOC

Access Succes

s Times)

11637 (Number of MTC

Access Succes

s Times)

11638(Number of LOC

Access

Success

Times)

11644

(Number of

SDCCH

Assignment

Success

Times)

11645 (Number

of SDCCHAssignme

nt Failures)

11684 (Number of MOC

Access Attempts)

11685(Number of MTC

Access

Attempts)

11686(Number of LOC

Access

Attempts)

32

3 2007-8-31 4:15

4 0 9 13 192 4 0 202

32

3 2007-8-31 4:30

0 0 10 10 155 0 0 165

32

3 2007-8-31 4:45

0 0 16 16 206 0 0 223

32

3 2007-8-31 5:00

2 0 15 17 172 2 0 188

32

3 2007-8-31 5:15

2 1 12 15 174 2 1 187

32

3 2007-8-31 5:30

7 2 13 22 188 7 1 187

32

3 2007-8-31

4 2 18 24 208 4 2 198



SITE ID

CELL ID

Time

11636 (Number of

MOC

Access Succes

s Times)

11637 (Number of MTC

Access Succes

s Times)

11638(Number of LOC

Access

Success

Times)

11644

(Number of

SDCCH

Assignment

Success

Times)

11645 (Number

of SDCCHAssignme

nt Failures)

11684 (Number of MOC

Access Attempts)

11685(Number of MTC

Access

Attempts)

11686(Number of LOC

Access

Attempts)

5:45

32

3 2007-8-31 6:00

1 2 17 20 170 1 2 187

32

3 2007-8-31 6:15

14 4 14 32 160 14 4 198

32

3 2007-8-31 6:45

7 6 10 23 196 7 6 209

32

3 2007-8-31 7:00

5 1 15 21 237 5 1 249




8.1.7 Improper Setting of the Tx-Integer Parameter

Fault description

In a certain cell, the common SDCCH assignment failure rate was about 20% and it

was 30% in the busy hours. But other KPIs (such as the TCH assignment failure

rate and in-coming success rate) were normal.

Table 8-3 Site Information

DATETIME

BSC_NAME BSCID

CELL_ID

SITE_NAME MYHO

UR SD_ASSN_FAI

L_RATE

13-Dec-07

JAYANAGAR-BSC

102 12282 THAYAGRAJNAGAR-2-s

21 30.21

Fault analysis

The engineers traced the signaling of the cell and found that the pair of CHANNEL

REQUEST messages (same TA and channel request cause) always appeared in

this cell. The IMM Assign corresponding to the first CHANNEL REQUEST message

was successful, but the one corresponding to the second CHANNEL REQUEST

message was a failure.


As shown in the above figure, the FN of the first CHANNEL REQUEST message

was 964 and the FN of the second CHANNEL REQUEST message was 1086, with



the difference being 124 frames, corresponding to the Tx-Integer parameter (12)

set by the OMC. Therefore, the two CHANNEL REQUEST messages are sent by

one MS. Because of the delay of the transmission link, the MS resent the

CHANNEL REQUEST message.

The engineers modified the TX-Integer parameter to 14 and the SDCCH

assignment failure rate of the cell was lower than 10%.

8.2 SD\TCH Channel Congestion Cases

8.2.1 SD congestion due to LAPD Delay Caused by Transmission Fault

The performance report shows that the number of SDCCH allocation failures was high

during SD congestion (SDCCH occupancy failure counter).

Figure 8-9 SD Channel Congestion Report Analysis (Case 1)

Number of

SDCCH

Occupation Attem

pts (for Assignment)

Number of

SDCCH

Occupation

Success

Times (for

Assignment)

Number of

SDCCH

Occupation

Failures (for

Assignment)

Number of

SDCCH

Occupation Attem

pts (for

Handover)

Number of

SDCCH

Occupation

Success

Times (for

Handover)

Number of

SDCCH

Occupation Failures (for Hando

ver)

Number of

SDCCH

Allocation

Attempts (for Assignment)

Number of

SDCCH

Allocation

Success

Times (for

Assignment)

Number of

SDCCH

Allocation

Failures (for

Assignment)

1782 1791 63 0 0 0 1720 1062 658

1455 1441 14 0 0 0 1441 908 533

1542 1524 18 0 0 0 1524 928 596

1759 1648 111 0 0 0 1645 1009 636

1606 1583 23 0 0 0 1588 957 631

1628 1582 46 0 0 0 1582 1004 578

2053 1905 148 0 0 0 1904 1068 863

2409 2215 194 0 0 0 2214 1111 1103

1563 1467 96 0 0 0 1469 758 711

1650 1628 22 0 0 0 1622 858 764

1784 1752 32 0 0 0 1754 856 898

1903 1878 25 0 0 0 1879 947 932

873 852 21 0 0 0 855 381 474



The signaling flow shows that BTS did not respond to the CHANNEL ACTIVATION

message sent by BSC.

Figure 8-10 No Response From the BTS (Case 1)

The engineers found the transmission alarm at the time of the fault.

After the BTS was reset, the problem disappeared.

After the transmission was adjusted, the problem was completely solved.

8.2.2 SD Congestion due to Strong Interference

Fault description

On one night, large amount of SD congestion occurred in one cell, which lasted for a

long time.

Normal condition didn’t return even after the reset of CMM and TRM.

The congestion disappeared after adjustment of the ARFCN and the BCC.

The congestion phenomenon appeared again after the ARFCN and BCC were

changed back.

The congestion finally disappeared 30 minutes after the adjustment of the TA

access threshold.

The engineers observed the signaling and found that the SD congestion was

caused by a large quantity of the abnormal CHANNEL REQUEST messages. All



the Imm Assign generated from these CHANNEL REQUEST messages ended in

failure.

The abnormal CHANNEL REQUEST messages appeared once every four frames;

all the RAs were 01; the TA diminished from 63 to 0 and then restarted from 63 after

815 frames; the level value remained 63, as shown in the following figure.

Figure 8-11 A Large Number of CHANNEL REQUEST Messages (Case 3)

The normal condition did not return even after the reset of the CMM and TRM, which

indicated that the problem was irrelevant to the BTS hardware and software.

The problem disappeared after the adjustment of the ARFCN and BCC, but

reoccurred when the ARFCN was changed back, which indicated that the problem

was relevant to the ARFCN.

Considering the rule of the CHANNEL REQUEST messages, the engineers

confirmed that there was a kind of interference signals were co-BCCH with the site

and the signals just contained all the training sequence of AB frame. The

interference signals were periodical and it created periodical deviation to the window

with Time slot 0.Just because of this deviation, the TX changed periodically.

Besides, the interference signal just affected Time slot 0.Therefore, the adjustment

on the TA access threshold can only relieve the problem, but cannot solve it

completely.



There was army garrisoning in the area and the interference signals were probably

sent from the army.

8.3 Paging Cases

8.3.1 No Paging Response due to the SDCCH Congestion

Table 8-4 SDCCH Congestion Information

问

题

描

述

：

某

1

Fault description

No paging response occurred continuously in an office in XX country on XX date.

Fault analysis

After the check, it was found that a micro cell debugging was being conducted and

the signals at this site were too strong, which led to many mobile phones staying

within the site. The serious SDCCH congestion led to no paging response.

8.3.2 Call Failure due to the MSC Flow Control

Fault description

The call complete rate was low (about 60%) in the busy hours in a certain location.

Fault analysis

According to the signaling analysis recorded in the CQT on site, it was found that no

PAGING message was sent by the MSC.

The signaling flow is shown in the following figure.

BSC SITE CELL Time Alias 11603 (SDCCH Attempt Total

Number)

11604 (SDCCH Overflow Total

Number)

80 11 1 2006-3-14 16:30 POF1 271 0

80 11 2 2006-3-14 16:30 POF2 293 0

80 11 3 2006-3-14 16:30 POF3 345 0

80 611 1 2006-3-14 16:30 POF7 100 61

Notes: Site 611 was commissioning and the signal of the site was very strong




According to the above figure, the MSC sent less PAGING messages than it should

do.

Due to the MSC flow control in busy hours, the flow control of messages happened,

leading to no paging response.

8.3.3 No Paging Response due to Wrong T3212 Setting

Fault description

In XX city, it occurred suddenly that many MSs under a BSC cannot be paged. After

the power on/off operation, the paging became normal.

Fault description

The signaling tracing showed that the MSC did not send the PAGING messages.

After checking, it turned out the location update time in MSC was changed from 2

hours to 1 hour, but that in BSC was set to one hour. Thus, many MSs, before the

periodic location update, had been marked as inactive status at the MSC side.

Therefore, the MSs could not be paged.

8.3.4 Low Paging Success Rate due to Location Area Division

Fault description



After the original 3 location areas under a BSC of the ISB were divided into 8 ones,

the paging success rate calculated in the MSC decreased by about 5%.

Fault analysis

Due to the location area division, the location update became more frequent.

According to the following figure, the number of location update times doubled,

which indicated serious cross location area. As a result, the paging failure

happened.

Figure 8-13 Number of Location Update Times

8.3.5 GSM Paging Success Rate Optimization of a China Unicom Branch

Fault description

In a certain area, all the BTSs in XX area were ZTE equipment, in which there were

two BSCs and a location area LAC 21088. Under BSC1, there were four isolated

sites in a forest which were set as separate location area, LAC21136 and the

Ericsson switch was used. In this area, the paging success rate of LAC 21088

remained as 92%, being middle-level or below in the whole province. And the

provincial company requires the KPI to be increased to the maximum score of 94%.

Fault analysis

0

10000

20000

30000

40000

50000

60000

70000

03-01-2006 20:00

03-03-2006 20:00

03-05-2006 20:00

03-07-2006 20:00

03-09-2006 20:00

03-11-2006 20:00

03-13-2006 20:00

03-15-2006 20:00

03-17-2006 20:00

03-19-2006 20:00

Times of general location update

Times of periodic location update



According to MSC SY01 statistics, LAC 21088 uses the TMSI paging and the

second paging mode with an interval of 8 s. In the existing network, the number of

the first paging times in the busy hours was 53653, with 49192 succeeded and 4461

failed; the number of the successful second paging times was 1009. The statistical

analysis indicated the second paging success rate was only 1009/4461 × 100% =

22.61%, being relatively low.

Through a systematical DT in the urban district in this area, it was found that this

area was a typical mountainous area, in which there were coverage holes even in

urban areas due to lack of sites. Now, there were totally 211 sites in this area, with

about 70 sites in urban areas, and many other sites are marginal isolated ones.

Therefore, weak coverage was one of the main reasons resulting in lower paging

success rate.

Fault handling

Adjusting the BS_AG_BLK_RES parameter

Currently, this parameter was set to 2, combined with the CCCH_CONF

parameter (0 indicates the CCCH used a basic physical channel and was not

combined with the SDCCH; there were nine blocks of CCCH messages in a 51

multi-frame), that is to say. Two blocks were reserved for the AGCH in each

BCCH multi-frame. Correspondingly, the number of PCH blocks was 9-2=7;

According to the KPIs in the existing network, the maximum number of SDCCH

requests in busy hours was below 2,500. If it was taken as 3,000, the number

of SDCCH allocation requests in each paging period was (3000/3600) ×

0.2354 = 0.2, less than one user. Therefore, the engineers modified the value

of the BS_AG_BLK_RES parameter from 2 to 1 and then the number o f PCH

blocks may reach 8 accordingly.

Adjusting the BS_PA_MFRAMS parameter

Currently, this parameter was set to 3, that is to say the same paging group

was transmitted every 3 51 multi-frames, hence the following calculation can

be made.

The number of paging blocks in a paging period: 8 × 3 = 24

The maximum number of subscribers in each paging block: 1000/24 = 42

According to statistics at the MSC side, the number of radio paging times in

LAC 21088 was 53653 + 4461 = 58114, thus, in the existing network the

number of subscribers in each paging period was 58114/3600 ×0.2354 = 3.8.

In the existing network, the TMSI paging was adopted. The maximum number

of each paging block in the TMSI paging was 4. As 3.8 was close to 4, it was

suggested to increase the value of the BS_PA_MFRAM parameter from 3 to 5.



Then, the maximum number of subscribers carried in each paging blocks

would change to 1000/(8*5) = 25. Though paging messages would delay

longer in the air section, users in each paging sub-channel would be

decreased, paging channel would be strengthened in bearing capacity, and

interruptions will also be reduced in probability of happening.

Adjusting the TX_INTEGER parameter

Currently, this parameter was set to 14, indicating that the number of time slots

was 32 and the value of S was 217; in existing network the MAX_RETRAN

parameter was set to 7, hence the following calculation can be made.

The maximum number of time slots for sending messages was 32 – 1 = 31, the

maximum resending interval was 217 + 32 – 1 = 248; and the time consumed

for resending seven times was (31 + 217) × 4.615/1000 × 7 + 31 × 4.615/1000

= 8.154705 s.

At the switch side, the second paging mode was adopted. If the paging period

was 5 × 0.2354 = 1.177S, it could be concluded that the maximum time

consumed in radio paging was 8.154705 + 1.177 = 9.331705s. As the interval

between two paging defined at switch side was 8 s < 9.331705 s, the

TX_INTEGER parameter would be reduced to 12.

The value of 12 indicated that the number of time slots was 20 and the value of

S was 109. Through the recalculation, the maximum time consumed in radio

paging was (19 + 109) × 4.615/1000 × 7 + 19 × 4.615/1000 + 1.177 =

5.399725S < 8s.

But this parameter should not be configured too samll; otherwise, the waiting

time may be too short, increasing both the possibility of collision and the

network load, and then the KPIs would be worsened. Slight modification was

needed to be made according to actual KPIs after the calculation.

Adjusting the RXLEV_ACCESS_MIN parameter

In the existing network, this parameter was set to 10, indicating the

RXLEV_ACCESS_MIN parameter was –100 dBm. If the threshold was

lowered to 8, the RXLEV_ACCESS_MIN parameter was –102 dBm.

Note:

This parameter helps to enlarge the BTS coverage and increase the paging success rate,

but it can affect the KPIs such as the call drop negatively.

Adjusting T3212



This timer is set to 72 min at the switch side and 10 (60 min) at the radio side.

The engineers modified it to 8 (48 min) at the radio side.

Note:

This parameter should not be configured to be too small; otherwise, the network signaling

flow would be increased and the stand-by time of MS would be shortened.

After adjusting the above parameters on June 23th, the paging success rate in

this area was increased by about 1%, close to 94%, as shown in the following

figureError! No bookmark name given..

Figure 8-14 Paging Success Rate

8.4 V4 Cases

Fault description

In a certain area, during the V4 BSC and the SDR BTS swap, the TCH congestion

happened and the service cannot be made normally.

Version information:

iBSCV6.50.100f

SDR V4.11.10.14P05

Networking condition:



ABIS: IPOE

A: STM-1

Gb: IP

After the swap, according to the KPI condition, the traffic was not large, but the TCH

congestion rate was quite high.

Table 8-5 TCH Congestion KPIs

Start Time SUBNETWORK

Name

Call Setup

Success Rate

Call Setup TCH

Blocking

TP2-SDCCH Blocking

306024:TCH Total Traffic

Number (erl)

2012-10-19 14:00:00

PSH751_ZXB01 (3)

80.66% 13.80% 5.35% 231

2012-10-19 15:00:00

PSH751_ZXB01 (3)

84.31% 12.68% 2.04% 227

2012-10-19 16:00:00

PSH751_ZXB01 (3)

85.63% 12.60% 0.41% 207

2012-10-19 17:00:00

PSH751_ZXB01 (3)

85.46% 12.58% 0.62% 203

2012-10-19 18:00:00

PSH751_ZXB01 (3)

83.15% 13.31% 2.61% 225

2012-10-19 19:00:00

PSH751_ZXB01 (3)

80.31% 14.51% 4.51% 150

2012-10-19 20:00:00

PSH751_ZXB01 (3)

84.21% 13.29% 1.11% 138

In the field test, the engineers found that it was difficult to complete the call.

Fault analysis

The engineers made the CQT on the field and found that it was difficult to

occupy the channel. However, many idle channels existed according to the

channel occupation dynamic observation from the OMC.

All the swap cells had this problem and there was no alarm.

The RQ and interference were normal.

There was no wrong configuration of the swap data.

The engineers found the following abnormalities in the TCH measurement

analysis.



Table 8-6 TCH Measurement Analysis

Start Time

Number of

TCH/F Allocat

ion Failure due to Apply Abis

Resource

Failure for

Assignment

(Speech

Version

2)(Times)

Number of

TCH/F Allocat


Resource

Failure for

Assignment

(Speech

Version3)

(Times)

Number of

TCH/F Allocation Failure due

to Apply Abis Resource

Failure for Handover

(Speech

Version2) (Time

s)

Number of TCH/F

Allocation Failure due to apply Abis

resource failure for handover (speech

version3)(Times)

Number of

TCH/H Allocat


Resource

Failure for

Assignment

(Speech

Version1)

(Times)

Number of

TCH/H Allocat


Resource

Failure for

assignment

(Speech

Version

3)(Times)

Number of TCH/

H Allocation Failure due



(Speech

Version

1)(Times)

Number of TCH/

H Allocation Failure due



(Speech

Version

3)(Times)

14:00:00

2449 74701 613 11278 0 0 0 0

15:00:00

2598 73667 709 15269 0 0 0 0

16:00:00

2331 51398 706 10612 362 14965 152 3863

17:00:00

2088 48746 442 8670 353 16523 113 3786

18:00:00

2277 52048 653 8840 464 20316 131 4811

19:00:00

1532 35065 795 9933 245 12885 126 4437

20:00:00

1162 35029 762 9314 151 9503 15 2329

The counters in the above tables are the newly added V4 counters (TCH2/F

and TCH2/H). And the engineers found that the problems were mainly the Abis

resource application failure. It was necessary to troubleshoot the configuration

of the acceptance and control.

The field BSC engineers made further troubleshooting and found that the IP

address configuration of the transmission path at the BSC side was wrong.

Then the transmission path matching the IP address cannot be found in the

corresponding office according to the BTS service address at the time of

bandwidth acceptance.



On the field, the temporary avoiding measure was adopted. After the

bandwidth acceptance switch was turned off temporarily, this problem

disappeared. Then, the engineers modified the wrongly configured IP address

and the problem was solved.

Solution:

After the acceptance control adjustment, the field test became normal and the KPIs

in the OMC statistics were restored, as shown in the following table.

Table 8-7 KPIs in the OMC Statistics

Start Time Sub-Network

Name

Call Set up

Success Rate

Call Setup TCH

Blocking

TP2-SDCCH Blocking

306024:TCH Total Traffic

Number (erl)

2012-10-19 14:00:00

PSH751_ZXB01(3)

80.66% 13.80% 5.35% 231

2012-10-19 15:00:00

PSH751_ZXB01(3)

84.31% 12.68% 2.04% 227

2012-10-19 16:00:00

PSH751_ZXB01(3)

85.63% 12.60% 0.41% 207

2012-10-19 17:00:00

PSH751_ZXB01(3)

85.46% 12.58% 0.62% 203

2012-10-19 18:00:00

PSH751_ZXB01(3)

83.15% 13.31% 2.61% 225

2012-10-19 19:00:00

PSH751_ZXB01(3)

80.31% 14.51% 4.51% 150

2012-10-19 20:00:00

PSH751_ZXB01(3)

84.21% 13.29% 1.11% 138

2012-10-19 21:00:00

PSH751_ZXB01(3)

88.62% 8.30% 2.16% 328

2012-10-19 22:00:00

PSH751_ZXB01(3)

96.59% 0.38% 2.64% 545

2012-10-19 23:00:00

PSH751_ZXB01(3)

98.37% 0.47% 0.75% 404

The TCH 2 measurement is displayed as follows.



Figure 8-15 TCH 2 Measurement

Start Time

Number of

TCH/F Allocati

on Failure due to Apply Abis

Resource

Failure for

Assignment

(Speech

Version 2)(Time

s)

Number of

TCH/F Allocati


Resource

Failure for

Assignment

(Speech

Version 3)

(Times)

Number of

TCH/F Alloca

tion Failure due

to Apply Abis

Resource

Failure for

Handover

(Speech

Version 2)

(Times)

Number of

TCH/F Alloca

tion Failure due

to Apply Abis

Resource

Failure for

Handover

(Speech

Version 3)

(Times)

Number of

TCH/H Allocati


Resource

Failure for

Assignment

(Speech

Version 1)

(Times)

Number of

TCH/H Allocati


Resource

Failure for

Assignment

(Speech

Version 3)

(Times)

Number of

TCH/H Alloca

tion Failure due

to Apply Abis

Resource

Failure for

Handover

(Speech

Version 1)

(Times)

Number of

TCH/H Alloca

tion Failure due

to Apply Abis

Resource

Failure for

Handover

(Speech

Version 3)

(Times)

14:00:00

2449 74701 613 11278 0 0 0 0

15:00:00

2598 73667 709 15269 0 0 0 0

16:00:00

2331 51398 706 10612 362 14965 152 3863

17:00:00

2088 48746 442 8670 353 16523 113 3786

18:00:00

2277 52048 653 8840 464 20316 131 4811

19:00:00

1532 35065 795 9933 245 12885 126 4437

20:00:00

1162 35029 762 9314 151 9503 15 2329

21:00:00

374 11672 325 5375 51 2954 38 1212

22:00:00

0 0 0 0 0 0 0 0

23:00:00

0 0 0 0 0 0 0 0

Summary:

For V4, when the TCH congestion and occupation are abnormal in the condition of

service channel resource sufficiency, it is necessary to troubleshoot the

measurement of the newly-added counter TCH 2, so as to judge whether the

congestion is caused by the Abis interface resource application failure.



On the field, the engineers can adopte the method of turning off the acceptance and

control switches for observation and problem avoiding. At the same time, they

should check whether the IP setting is wrong.

GSM RNO Subject-Troubleshooting of Problems in Stages of Call Setup_R1.0_20130311

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Transcript of GSM RNO Subject-Troubleshooting of Problems in Stages of Call Setup_R1.0_20130311