GO_NA11_E1_1 GSM Paging Problems & Solutions-36

GSM Paging Problems & Solutions

ZTE university

Training goals

To master the definition of paging indicators To master optimization strategy of paging problems To know relevant counters and key parameters

Contents

Indicator definition Optimization strategy Key parameters Typical cases

Indicator definition The relevant counter of ZTE BSS side

C900060002

MTC access success number C900060152

ABIS_INTER_PAGING_CMD

message number

Paging success rate （ BSC ） = ∑C900060002 / C900060152

Indicator definition

Paging principle

Indicator definition

Basic signaling flow of radio paging

Contents


Optimization strategy Reasons for low paging success rate

Paging failure usually concentrate on these aspects

PAGING message can’t be sent on radio channel

MS don’t receive

PAGING message

Related messages aren’t sent to MSC when MS is

responding PAGING

Special situation

LINK load is so high that it makes bottom layer SCCP message lost.

MSC/VLR, BSC flux control makes message be discarded.

When the load is high, message queuing time gets longer so that

the message can’t be sent to MS in time 。 Unfavorable transmission link quality makes bottom layer LAPD message lost.

T3212 is set unreasonably.

Too many paging messages make message lost on radio interface

(such as sending sms to multi subscribers, and so on)

MSC redundant cell data makes BSC paging times abnormal.

Optimization strategy Causes which affect paging success rate

手没有收到PAGING消息

Coverage reason .

Frequent MS reselection.

Frequent Location update.

MS can’t monitor messages on BCCH while doing GPRS services.

Paging group is set unreasonably that makes paging time too long or

paging lost; especially two adjacent cells’ paging groups are different.

Twice paging time is set unreasonably.

Frequencies of adjacent cells differ greatly so there are frequent

reselections; different monitor time makes paging lost easily.

PAGING message can’t be sent on

radio channel

MS don’t receive

PAGING message

Related messages aren’t sent to MSC

when MS is responding PAGING

Special situation

Paging failure usually concentrate on these aspects


SDCCH congestion.

SDCCH assign failure.

Unbalanced uplink and downlink; weak uplink.

Bad transmission link makes message lost

PAGING message fails to give off via

radio channel

MS doesn’t receive

PAGING message



Special situation

Paging failure usually concentrates on these aspects


特殊情况手机响应 PAGING时，相关信息未能发送到MSC

two MS are calling one mobile phone at the same time, MSC connects

one MS as MOC and replies another MS no paging response.

MSC Paging message sending time is unreasonable: MSC releases the

call before MS releases it and MSC sends new paging at the same time,

consequently gets a reply of no paging response.

PAGING message can’t be sent on radio channel

MS don’t receive

PAGING message



Special situation

Paging failure usually concentrates on these aspects

Optimization strategy Optimization steps and methods

step1 step2 step3 step4 step5 step6 step7

Expel the

abnormal

phenomeno

n caused by

system

Check MS

latest

activity

status

Eliminate

GPRS

influence

Indicator

analysis

Radio parameter checking and optimization

MSC paging strategy analysis

Field test

Check flux control alarm and see whether MSC/VLR/BSC has Flow control alarm. Maintain trunk link on A/Abis

interface, observe signaling load on A/Abis interface, increase signaling link in time and decrease paging failure

caused by too high signaling load.

Check whether BTS has transmission transient interruption alarm. Observe whether it is multifarious to reselect

phenomenon, if it is already needed to modify reselection parameters (CRO, TMO and PT etc.).

Check whether MSC database has redundant data.



Expel the

abnormal

phenome

non

caused by

system

Check MS

latest

activity

status

Eliminate

GPRS

influence

Indicator

analysis



Field test

Presently only VLR probe can be used to check MS latest activity status.

Record signaling on SGSN, MSC, and ABIS interface in the test to judge MS activity.



Expel the

abnormal

phenome

non

caused by

system

Check MS

latest

activity

status

Eliminate

GPRS

influence

Indicator

analysis



Field test

Check whether GPRS routing area is set reasonably. Routing areas of one site shall be the

same, routing areas of cells where frequent reselections occur shall be the same.

Check whether routing area update cycle time is set reasonably.

Use mobile phone that has no GPRS function to test.



Expel the

abnormal

phenome

non

caused by

system

Check MS

latest

activity

status

Eliminate

GPRS

influence

Indicator

analysis



Field test

Check SDCCH congestion status, check indicators in traffic statistic such as SDCCH congestion rate

which shall be 0 or close to 0 generally. Eliminate No Paging Response caused by SDCCH

congestion.

Analyze whether MTC success rate is abnormal.

Analyze whether cell location update times is abnormal.

Analyze system average TA and maximum TA to judge whether overlapping exists.



Expel the

abnormal

phenome

non

caused by

system

Check MS

latest

activity

status

Eliminate

GPRS

influence

Indicator

analysis



Field test

Check parameter setting related to paging, access, immediate assignment.

Check whether T3212 , RxLev Access Min IDETTIM are set reasonably.

Whether LAC division is reasonable, whether overlapping area of several LAC is reasonable. BTS

maximum paging capacity shall not be exceeded; once the paging capacity is not enough, we shall

consider splitting LAC.



Expel the

abnormal

phenome

non

caused by

system

Check MS

latest

activity

status

Eliminate

GPRS

influence

Indicator

analysis



Field test

Check whether system capacity supports multi paging; if yes, analyze influence of multi paging to the system.

MSC is in charge of forming paging message and resending the message if there is no response.

The interval between two paging is a very important parameter. In radio aspect, the longer is the interval

between two paging, the smaller is the relativity with radio environment for MS while responding paging, the

easier for MS to respond paging message successfully. But if the interval between two

paging is set too long, then MOC subscriber will be at a waiting status for a long time and MOC subscriber

may hang up.



Expel the

abnormal

phenome

non

caused by

system

Check MS

latest

activity

status

Eliminate

GPRS

influence

Indicator

analysis


MSC

paging

strategy

analysis

Field test

Field test is the most important step, from which we can only capture the real phenomenon.

If the problem is easily to be discovered in common mobile phone rather than test mobile phone, we need to test two SIM cards that belong to the same paging group and then we can judge whether common mobile phone can’t respond the paging message correctly after paging message has been sent.

Observe whether frequent reselection occurs, modify reselection parameter (CRO, TMO, PT, etc.) if necessary.

Test whether blind area exists.

Contents


Key parameters

Calculation of paging group that mobile phone belongs to Principle

In GSM system, paging messages are sent in groups; each MS can only monitor the paging group which it belongs to while monitoring paging message and ignoring other paging group. MS even turns off some hardware power to save power consumption during the period when other paging groups are sending paging message (that’s the reason of DRX).

Calculation method We can ascertain MS paging group according to its IMSI, system’s

CCCH number, multiplexing frame number that paging group occupies, AGCH reserved blocks as well as the combination of BCCH and SDCCH. Detailed calculation method is as follows (the result is determined by two parameters CCCH_GROUP and PAGING_GROUP):

CCCH_GROUP=((IMSI mod 1000) mod (BS_CC_CHANS*N)) div N PAGING_GROUP=((IMSI mod 1000) mod (BS_CC_CHANS*N)) mod

N

Key parameters

Calculation of paging duration

BS PA MFRMS （ Tx-integer）

relevant

parameters

RACH

Max Retrans

Key parameters

Multi-frame number of paging channel BsPaMframs

This parameter indicates the number of multi-frames of 51 TDMA frame of MSes in the same paging group, to which the paging message is transmitted. (BS-PA-MFRMS )

BsPaMframs means the number of multi-frames which can form a cycle of paging subchannel.

This parameter is mainly calculated for MS to judge which paging group it belongs to so as to monitor the corresponding paging sub-channel.

BsPaMframs makes a broadcast to the MS in a cell by RIL3_RR SYSTEM INFORMATION TYPE3.

Parameter value

BS_PA_MFRMS

Original DSC value in idle mode of circuit switch

2 2 45

3 3 30

4 4 23

5 5 18

6 6 15

7 7 13

8 8 11

9 9 10

Key parameters

Configuration principles: On condition that there

is no paging channel overload, this parameter should be as small as possible.

It is suggested that cells in one location area should have the same value.

areas Parameters values

high traffic location areas

8/9

medium traffic location areas

6/7

low traffic location areas

4/5

default value 5.

Multi-frame number of paging channel (BsPaMframs)

Key parameters

Description: RACH is an ALOHA channel. In order to

improve the success rate of MS access, the

network allows MS to send several channel

request messages before it receives an

immediate assignment message. The

maximum number of allowed retransmission is

decided by MaxRetran.

This parameter notifies MS in a cell by RIL3_R

R SYSTEM INFORMATION TYPE1, 2, 2bis, 3

and 4.

MaxRetransThe maximum

number of retransmission

0 1

1 2

2 4

3 7

The maximum retransmission number (MaxRetrans)

Key parameters

The maximum number of retransmission (MaxRetrans)

radius times

more than 3 kilometers, and which has a relatively low traffic

7

less than 3 kilometers, and which has a medium traffic 4

micro cells 2

micro cells with a high traffic or cells 1

default value 2

Key parameters

TxIntegerDescription: TxInteger parameter is used to calculate the number of time slot

between every two transmissions, when MS continuously send several channel requests. This parameter is used to decide the random delay time.

This parameter notifies MS in a cell by RIL3_RR SYSTEM INFORMATION TYPE1, 2, 2bis, 3 and 4.

MS sends a channel request message to the network as follows: The interval between the time when MS sends an immediate

assignment message and the time when the first channel request message is sent (time slot number ) is a random number among { 0,1,…,Max （ T,8 ） -1 };

The interval (time slot number) between two continuous channel request messages is a random number among {S,S+1,…,S+T-1}.

T is the slot time number represented by TxInteger parameter （ Note: It isn’t TxInteger itself）， the values of S are in the following table:

Key parameters

The values of S and T

Number of time slot represented by TxInteger

S （ CCCH doesn’t combine with SDCCH）

S （ CCCH doesn’t combine with SDCCH）

3, 8, 14,50 55 41

4, 9, 16 76 52

5,10,20 109 58

6,11,25 163 86

7,12,32 217 115

TxIntegerNumber of time slot represented

0 3

1 4

2 5

3 6

4 7

5 8

6 9

7 10

8 11

9 12

10 14

11 16

12 20

13 25

14 32

15 50

Contents


Cases1:indicator optimization of some area

Malfunction description Paging success rate keeps 92% ， which is in a low

position in the whole province. The operator demands a full mark indicator that is 94 ％ .

Malfunction analysis According to MSC SY01 statistic, LAC21088 uses TMSI

paging and second paging mode with an interval of 8 seconds. The number of first paging times on busy hour on the existing network is 53653, the number of success paging times is 49192 and the number of failure times is 4461; the number of second paging success times is 1009. From the statistic analysis we can see that the second paging success ratio is only 1009/4461*100%=22.61%, which is relatively low.


Malfunction analysis Do system DT in this area city and we find out in the

test that area is a typical mountainous area; due to lack of sites, there are blind areas in an urban area. Now there are totally 211 sites in this area with 70 sites in the urban area. Most sites are isolated on the edge, therefore bad coverage is a main reason for low paging success rate.


Malfunction solution Modify the value of parameter BS_AG_BLK_RES from

2 to 1, and the number of corresponding blocks for PCH is 8.;

Increase the value of BS_PA_MFRAMS from 3 to 5; Modify the value of parameter TX_INTEGER from 14 to

12 Modify the value of parameter RXLEV_ACCESS_MIN

from 10 to 8 Modify the value of timer T3212 RXLEV_ACCESS_MIN

from 10 to 8


The result After adjusting the upper parameters on June 23rd, the paging

success rate in this area increases by 1% and it is close to 94%, which is shown in the following figure.

Cases2:T3212 set wrong lead to the paging no response problem description:

somewhere under a BSC suddenly appeared a lot of mobile phones paging less than phenomenon, mobile phone switch machine, paging, no problem.

problem analysis: tracking signaling found MSC not issued paging

message, examination revealed that the MSC oneself to update time change position from two hours to 1 hour, and BSC Settings for 1 hour. Cause a lot of mobile phones in no position periodically update, MSC side had will sign for mobile phone is inactive, resulting in less than mobile phone subscribers.

Cases3:location area compartmentalize cause paging success rate lower problem Description:

the location area BSC somewhere, from 3 is divided into 8, MSC statistical paging success rate dropped about five percentage points.

010000200003000040000500006000070000

03- 0

1-20

06 2

0:00

03- 0

3-20

06 2

0:00

03- 0

5-20

06 2

0:00

03- 0

7-20

06 2

0:00

03- 0

9-20

06 2

0:00

03- 1

1-20

06 2

0:00

03- 1

3-20

06 2

0:00

03- 1

5-20

06 2

0:00

03- 1

7-20

06 2

0:00

03- 1

9-20

06 2

0:00

Ti mes of general l ocat i on updateTi mes of per i odi c l ocat i on update

problem analysis:

because the location area compartmentalize, resulting in location update increased, in the following location update can be seen general

location update doubled. indicates that the phenomenon is very serious, such frequent cross-culture mobile location area, Inevitably led to the paging less than.

Cases4:MSC flow control leads to the paging low success Problem Description:

When a place is busy phone cell phone connection rate is low. Busy through rate about 60%.

Problem Analysis: The test recorded on-site call signaling analysis and

found that MSS PAGING message is not issued. MSC issued less PAGING message. MSC produced the busy flow control, resulting in the

message is flow control, caused no response to paging.

GO_NA11_E1_1 GSM Paging Problems & Solutions-36

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