Assignment and Immediate Assignment.pdf

Assignment and Immediate Assignment Feature Parameter Description

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Issue 02 (2009-09-30) Huawei Proprietary and Confidential

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BSS Assignment and Immediate Assignment Contents

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Contents 1 Introduction to This Document .............................................................................................1-1

1.1 Scope ............................................................................................................................................ 1-1 1.2 Intended Audience ........................................................................................................................ 1-1 1.3 Change History.............................................................................................................................. 1-1

2 Overview of Assignment and Immediate Assignment....................................................2-1

3 Technical Description ..............................................................................................................3-1 3.1 Immediate Assignment.................................................................................................................. 3-1

3.1.1 Immediate Assignment Procedure ....................................................................................... 3-1 3.1.2 Immediate Assignment Combination.................................................................................... 3-2

3.2 Assignment.................................................................................................................................... 3-2 3.2.1 Assignment Procedure ......................................................................................................... 3-2 3.2.2 Assignment Classification..................................................................................................... 3-4

4 Parameters .................................................................................................................................4-1

5 Counters......................................................................................................................................5-1

6 Glossary ......................................................................................................................................6-1

7 Reference Documents .............................................................................................................7-1

BSS Assignment and Immediate Assignment 1 Introduction to This Document


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1 Introduction to This Document 1.1 Scope This document describes the assignment procedure, immediate assignment procedure, and assignment classification.

1.2 Intended Audience It is assumed that users of this document are familiar with GSM basics and have a working knowledge of GSM telecommunication.

This document is intended for:

Personnel working on Huawei GSM products or systems System operators who need a general understanding of this feature

1.3 Change History This section provides information on the changes in different document versions.

There are two types of changes, which are defined as follows:

Feature change Feature change refers to the change in the Assignment and Immediate Assignment feature of a specific product version.

Editorial change Editorial change refers to the change in wording or the addition of the information that was not described in the earlier version.

Document Issues The document issues are as follows:

01 (2009-11-20)

01(2009-11-20) This is the first commercial release of GBSS9.0.

BSS Assignment and Immediate Assignment

2 Overview of Assignment and Immediate Assignment


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2 Overview of Assignment and Immediate Assignment When an MS initiates a call or needs to switch from a signaling channel to a TCH, the BSC needs to assign a channel to the MS.

When the MS initiates a call, the BSC needs to assign an SDCCH or a TCH (the TCH is used for signaling) according to the specific call establishment cause. This procedure is called immediate assignment.

After receiving a channel request from the MS, the MSC sends the BSC an Assignment Request message, instructing the BSC to assign a suitable channel to the MS. The channel to be assigned must meet the requirements of the MSC and MS, such as the channel type, speech version, and MS frequency capability. This procedure is called assignment.

The immediate assignment and assignment procedures are very important for call establishment. Proper immediate assignment and assignment algorithms ensure optimal KPIs, thus improving the performance of radio networks.

Through the immediate assignment procedure, a radio resource (RR) connection is established between the MS and the network.

Through the assignment procedure, the MSC assigns a specific TCH to the MS so that a stable connection is established between the MS and the network.

The processing during the immediate assignment and assignment procedures varies based on different conditions. For details, see Channel Management Parameter Description.

BSS Assignment and Immediate Assignment 3 Technical Description


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3 Technical Description 3.1 Immediate Assignment 3.1.1 Immediate Assignment Procedure The immediate assignment procedure is initiated by an MS, with the purpose of establishing an RR connection between the MS and the network.

The immediate assignment procedure is shown in Figure 3-1.

Figure 3-1 Immediate assignment procedure

Channel Request(1)

RACH

Channel Required(2)

Channel Activation(3)

MS BTS BSC

Channel Activation Acknowledge(4)

Immediate Assignment Command(5)

AGCH

Start T3101SABM(6)

main DCCH

UA(7)

main DCCHEstablish Indication(8)

Stop T3101

1. The MS sends a Channel Request message to the BTS on the RACH. After initiating the immediate assignment procedure, the MS always listens to the BCCH and the corresponding CCCH. If the MS does not receive the Immediate Assignment Command message or Immediate Assignment Extended message, it resends the Channel Request message at a specified interval. When the number of times that the Channel Request message is resent exceeds MS MAX Retrans, the immediate assignment procedure fails.

2. The BTS sends a Channel Required message to the BSC. 3. After the reception of the Channel Required message, the BSC assigns a signaling channel and

sends the BTS a Channel Activation message, which carries information elements (IEs) such as Activation Type, Channel Description, Level, and Time Advance (TA).

4. After the reception of the Channel Activation message, if the IEs carried in the message are correct, the BTS turns on the power amplifier on the specified channel to receive uplink messages. At the

3 Technical Description BSS

Assignment and Immediate Assignment

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same time, the BTS sends the BSC a Channel Activation Acknowledge message carrying the absolute frame number, which is used by the BSC to determine Starting Time.

5. The BSC sends the MS an Immediate Assignment Command message, instructing the MS to access the specified channel. The specified channel can be either an SDCCH or a TCH.

Huawei BSC supports the immediate assignment of an SDCCH and a TCH at the cell level. The parameter TCH Immediate Assignment specifies whether the immediate assignment of a TCH is supported. The IMMEDIATE ASSIGNMENT COMMAND message can be resent only when Use IMM ASS Retransmit Parameter is set to Yes and the delay time is within the Max Delay of IMM ASS Retransmit. When the number of times that the Immediate Assignment Command message is resent exceeds Max Transmit Times of IMM ASS, the Immediate Assignment Command message is not resent.

6. The MS sends a Set Asynchronous Balanced Mode (SABM) frame on the main DCCH to access the network.

7. The BTS answers with a Unnumbered Acknowledge (UA) frame on the main DCCH. 8. The BTS sends an Establish Indication message to the BSC.

The MS may send several Channel Request messages during one RR connection establishment attempt. In this case, the BSS activates multiple signaling channels, whereas the MS uses only one channel. The other channels cannot receive the Establish Indication message from the BTS for a long time. As a result, the BSC releases the channels at expiry of timer T3101.

3.1.2 Immediate Assignment Combination Generally, the Immediate Assignment Command message from the BSC to the BTS contains the response to the channel request from only one MS. On the UM interface, however, the response to the Channel Request message are of three types: Immediate Assignment Command, Immediate Assignment Extended, and Immediate Assignment Reject. One Immediate Assignment Extended message contains the contents of the Immediate Assignment Command message (for acknowledgement) sent to two MSs over the Abis interface. One Immediate Assignment Reject message contains the contents of the Immediate Assignment Command message (for rejection) sent to four MSs. Therefore, to improve the message sending efficiency, the BTS encapsulates multiple Immediate Assignment Command messages received from the BSC into one Immediate Assignment Extended or Immediate Assignment Reject message before sending them to MSs. This procedure is called immediate assignment combination.

The Wait Indication IE in the Immediate Assignment Reject message from the BSC to the MS carries timer T3122.

Upon receiving the Immediate Assignment Reject message, the MS attempts to access the network at expiry of timer T3122.

3.2 Assignment 3.2.1 Assignment Procedure In the assignment procedure, the network assigns a TCH to an MS.

The assignment procedure is shown in Figure 3-2.



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Figure 3-2 Assignment procedure

Channel Activation(2)

Channel ActivationAcknowledge(3)

MS BTS MSC

Assignment Command(4)

Start T10

SABM(5)

main DCCH

UA(6)

FACCH Establishment Indication(7)

BSC

AssignmentRequest(1)

Start T3107

FACCH

AssignmentComplete(8)

FACCHStop T3107

AssignmentComplete(9)

Stop T10

1. The MSC sends an Assignment Request message to the BSS based on the service request and then starts timer T10. Upon receiving the Assignment Request message from the MSC, the BSC checks the channel type. If a PS service is requested, the BSC determines whether the requested service is supported according to the setting of the parameter Data Service Allowed.

2. The BSC sends the BTS a Channel Activation message to activate the corresponding terrestrial resources. The message carries IEs such as Activation Type, Channel Description, Level, and TA.

3. Upon receipt of the Channel Activation message, if the IEs carried in the message are correct, the BTS turns on the power amplifier on the specified channel to receive uplink messages. At the same time, the BTS sends the BSC a Channel Activation Acknowledge message carrying the absolute frame number, which is used by the BSC to determine Starting Time.

4. After receiving the Channel Activation Acknowledge message, the BSC sends the Assignment Command message on the signaling channel to the MS and starts timer T3107. The Assignment Command message carries IEs such as Channel Description, Power Command, and Channel Mode.

5. After receiving the Assignment Command message, the MS starts to transmit and receive signaling over the TCH. The MS sends an SABM message to the network over the FACCH through frame stealing. The SABM frame is the first frame for establishing the asynchronous balanced mode. Compared with the immediate assignment procedure, the assignment procedure does not have layer 3 messages.




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6. After receiving the SABM message, the BTS sends a UA frame to the MS over the FACCH. The layer 3 messages are not carried.

7. At the same time, the BTS sends the BSC an ESTABLISH INDICATION message without the layer 3 messages. Then, the BSC responds with a UA frame for acknowledgement.

8. After receiving the UA frame, the MS sends an Assignment Complete message to the network over the FACCH, indicating that the TCH is established successfully. When receiving the Assignment Complete message, the BSC stops timer T3107.

9. In addition, the BSC fills the message with the corresponding information indicated by the parameter A Interface Tag and sends the message to the MSC. Upon receiving the Assignment Complete message, the MSC stops timer T10.

3.2.2 Assignment Classification In different scenarios, the assignment procedure may play different roles during the call. The assignment type has certain impacts on allocation and seizure of the network resources. According to the roles of the assignment procedure in the call, the assignment procedure is classified into mobile originating call establishment without OACSU (early assignment), mobile originating call establishment with OACSU (late assignment), mobile originating call establishment with very early assignment, mobile terminating call establishment without OACSU (early assignment), mobile terminating call establishment with OACSU (late assignment), and mobile terminating call establishment with very early assignment.

Mobile Originating Call Establishment Without OACSU (Early Assignment) Mobile originating call establishment without OACSU (early assignment) refers to the procedure in which the calling MS is assigned a TCH before the call is established.

After the immediate assignment is complete, the network sends the MS an Assignment Command message that requests the calling MS to occupy the TCH even if the Altering message is not received. In this case, the ringing tone is generated by the network. The mobile originating call establishment without OACSU (early assignment) procedure is shown in Figure 3-3.



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Figure 3-3 Mobile originating call establishment without OACSU (early assignment)

MS BTS MSC

Setup(5)

BSC

FACCH

SDCCH

Immediate Assignment Procedure

Establish Indication(CM Service Request)(1)

CC(3)

CR(L3:CMService Request)(2)

CM Service Accepted(4)

Call Proceeding(6)SDCCH

TCH Assignment Procedure

FACCH

Alerting(7)

FACCH

Connect(8)

Connect Acknowledge(9)SDCCH

Talking(10)

Release Procedure

Mobile Originating Call Establishment with OACSU (Late Assignment) In this mode, the network sends the MS an Assignment Command message that requests the calling MS to occupy a TCH only after the network receives the Alerting message from the called party. In this case, the ringing tone is generated by the MS because no TCH is available before the RR connection is established. The mobile originating call establishment with OACSU (late assignment) procedure is shown in Figure 3-4.




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Figure 3-4 Mobile originating call establishment with OACSU (late assignment)

MS BTS MSC

Setup(5)

BSC

SDCCH

SDCCH

Immediate Assignment Procedure


CC(3)



Call Proceeding(6)SDCCH

TCH Assignment Procedure

SDCCHAlerting(7)

FACCH

Connect(8)

Connect Acknowledge(9)SDCCH

Talking(10)

Release Procedure

Mobile Originating Call Establishment with Very Early Assignment Mobile originating call establishment with very early assignment refers to the procedure in which a TCH instead of an SDCCH is assigned to the calling MS during the immediate assignment procedure.

If TCH Immediate Assignment is set to Yes and no SDCCH is available in the serving cell of the calling MS, a TCH is allocated during the immediate assignment procedure.

Mobile originating call establishment with very early assignment can speed up connection establishment. The network performs authentication, ciphering, other signaling exchanges, and follow-up call connection procedures on the TCH. In this case, the TCH is used for signaling. Upon receiving the Assignment Request message from the MSC, the BSC changes the TCH used for signaling to a real TCH through the Mode Modify command. The mobile originating call establishment with very early assignment procedure is shown in Figure 3-5.



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Figure 3-5 Mobile originating call establishment with very early assignment

MS BTS MSC

Setup(5)

BSC

FACCH

FACCH

Immediate Assignment TCH Procedure


CC(3)



Call Proceeding(6)FACCH

TCH Mode Modify

FACCHAlerting(7)

FACCH

Connect(8)

Connect Acknowledge(9)FACCH

Talking(10)

Release Procedure

Mobile Terminating Call Establishment Without OACSU (Early Assignment) Mobile terminating call establishment without OACSU (early assignment) refers to the procedure in which the called MS is assigned a TCH before the call is established.

Mobile terminating call establishment is initiated by the network sending a Paging Request message. After the immediate assignment procedure is complete, the network sends an Assignment Command message to the called MS to require the MS to occupy a TCH before answering the phone. In this case, the ringing tone is generated by the network.

The mobile terminating call establishment without OACSU (early assignment) procedure is shown in Figure 3-3.




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Mobile Terminating Call Establishment with OACSU (Late Assignment) In this mode, the network sends the MS an Assignment Command message that requests the called MS to occupy a TCH only after the network receives the Alerting message. In this case, the ringing tone is generated by the MS because no TCH is available before the RR connection is established.

The mobile terminating call establishment with OACSU (late assignment) procedure is shown in Figure 3-4.

Mobile Terminating Call Establishment with Very Early Assignment Mobile terminating call establishment with very early assignment refers to the procedure in which a TCH instead of an SDCCH is assigned to the called MS during the immediate assignment procedure.

If TCH Immediate Assignment is set to Yes and no SDCCH is available in the serving cell of the called MS, a TCH is allocated during the immediate assignment procedure.

Mobile terminating call establishment with very early assignment can speed up connection establishment. The network performs authentication, ciphering, other signaling exchanges, and follow-up call connection procedures on the TCH. Upon receiving the Assignment Request message from the network, the BSC changes the TCH used for signaling to a real TCH through the Mode Modify command.

The mobile terminating call with very early assignment procedure is shown in Figure 3-5.

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4 Parameters This chapter describes the parameters related to assignment and immediate assignment.

For the meaning of each parameter, see Table 4-1. For the default value, value ranges, and MML commands of each parameter, see Table 4-2.

Table 4-1 Parameter description (1)

Parameter Description

MS MAX Retrans

Maximum number of Channel Request messages that can be sent by an MS in an immediate assignment procedure. After the MS initiates the immediate assignment procedure, it always listens to the messages on the BCCH and all the common control channels (CCCHs) in the CCCH group to which the MS belongs. If the MS does not receive Immediate Assignment or Immediate Assignment Extend messages, it retransmits Channel Request messages at a specified interval. If the downlink quality is poor, the MS may send SABM frames to the BTS multiple times.

TCH Immediate Assignment

Whether to allow immediate TCH assignment. If this parameter is set to YES, the BSC can assign a TCH immediately when there is no available SDCCH for a channel request. If this parameter is set to NO, the BSC can assign only an SDCCH when processing a channel access request.

Use IMM ASS Retransmit Parameter

Whether the BSC6900 sends immediate assignment retransmission parameters to the BTS

Max Delay of IMM ASS Retransmit

Maximum time delay in resending an immediate assignment message. Within the period specified by this parameter, an immediate assignment message can be dispatched and retransmitted. Otherwise, the message is not dispatched or retransmitted.

Max Transmit Times of IMM ASS

Maximum number of retransmissions of an immediate assignment message. When the value of this parameter is reached, the immediate assignment message is not retransmitted even if the value of "Max Delay of IMM ASS Retransmit" is not exceeded.

T3101

Timer for the BSC waiting for an Establish Indication message after sending an Immediate Assignment message. If T3101 expires before the BSC receives an Establish Indication message, the BSS releases the seized SDCCH.

T3122

Timer carried by the Wait Indication information element when the BSC6900 sends an immediate assignment reject message to an MS. After the MS receives the immediate assignment reject message, the MS reattempts to access the network after the timer expires.

Data Service Allowed Data service supported by the BSC6900. You can set this parameter according to actual requirements.

T3107

After the BSC6900 delivers an assignment command, the T3107 timer starts. If the BSC6900 receives an assignment complete message within the scheduled time, the T3107 timer stops. If the timer expires, the BSC6900 sends an assignment failure message.

A Interface Tag Phase tag for GSM protocols supported by the A interface. The value of this parameter is chosen according to the A interface phase tag provided by the MSC.

4 Parameters BSS



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Table 4-2 Parameter description (2)

Parameter Default Value

GUI Value Range

Actual Value Range Unit MML

Command Impact

MS MAX Retrans 4_Times

1_Times(1_Times), 2_Times(2_Times), 4_Times(4_Times), 7_Times(7_Times)

1_Times, 2_Times, 4_Times, 7_Times None

SET GCELLCCBASIC(Optional) Cell

TCH Immediate Assignment NO

NO(No), YES(Yes) NO, YES None

SET GCELLBASICPARA(Optional) Cell

Use IMM ASS Retransmit Parameter NO

NO(No), YES(Yes) NO, YES None

SET GCELLCCTMR(Optional) Cell

Max Delay of IMM ASS Retransmit 4 0~254 0~254 ms


Max Transmit Times of IMM ASS 2 1~5 1~5 None


T3101 3000 500~60000 500~60000 ms

SET GCELLTMR(Optional) Cell

T3122 10 0~255 0~255 s


Data Service Allowed

NT14_5K-0&NT12K-1&NT6K-1&T14_4K-0&T9_6K-1&T4_8K-1&T2_4K-1&T1_2K-0&T600_BITS-0&T1200_75-0

NT14_5K~0 NT12K~1 NT6K~2 T14_4K~3 T9_6K~4 T4_8K~5 T2_4K~6 T1_2K~7 T600_BITS~8 T1200_75

NT14_5K, NT12K, NT6K, T14_4K, T9_6K, T4_8K, T2_4K, T1_2K, T600_BITS, T1200_75 None

SET GCELLOTHEXT(Optional) Cell

T3107 10000 500~60000 500~60000 ms


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Default GUI Value Actual Value MML Parameter Unit Impact Value Range Range Command

A Interface Tag

GSM_PHASE_2

GSM_PHASE_1, GSM_PHASE_2, GSM_PHASE_2Plus

GSM_PHASE_1, GSM_PHASE_2, GSM_PHASE_2Plus None

SET BSCBASIC(Optional) BSC

BSS Assignment and Immediate Assignment 5 Counters


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5 Counters For the counters, see the BSC6900 GSM Performance Counter Reference.

BSS Assignment and Immediate Assignment 6 Glossary


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6 Glossary For the acronyms, abbreviations, terms, and definitions, see the Glossary.

BSS Assignment and Immediate Assignment 7 Reference Documents


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7 Reference Documents 3GPP TS 48.008 Mobile Switching Centre - Base Station system (MSC-BSS) interface; Layer 3 specification

3GPP TS 44.018 Mobile radio interface layer 3 specification; Radio Resource Control (RRC) protocol

BSC6900 Feature List BSC6900 Basic Feature Description BSC6900 GSM Parameter Reference BSC6900 GSM MML Command Reference BSC6900 GSM Performance Counter Reference

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