Huawei PCU Signaling Analysis Guide

7/30/2019 Huawei PCU Signaling Analysis Guide

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PCU Signaling Analysis Guide Internal use

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PCU Signaling Analysis Guide

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Huawei Technologies Co., Ltd

All Rights Reserved

2013-8-25 HUAWEI Proprietary and Confidential. Page 1 of 50


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Revision Record

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Guide to the Survey of GSM BSC6000 Products V5.2 Internal use

Table of Contents

1 Messages on the Pb Interface.................................................................................................1

1.1 Overview of the Pb Interface...............................................................................................1

1.2 Procedures on the Pb Interface...........................................................................................2

1.3 Cell Activation/Deactivation Procedure...............................................................................2

1.4 Cell Initialization Procedure.................................................................................................2

1.5 Normal Procedure...............................................................................................................3

1.6 Abnormal procedure............................................................................................................4

1.7 Cell Reset Procedure Initiated by the PCU.........................................................................7

1.8 Cell Reset Procedure Initiated by the BSC.........................................................................7

1.9 Procedure for Requesting Dynamic Channels....................................................................8

1.10 Active/Passive Release Procedure of the Dynamic Channels..........................................9

1.11 Active Release Procedure.................................................................................................9

1.12 Passive Release Procedure............................................................................................10

1.13 Resource Verification Procedure.....................................................................................10

1.14 Procedure for Maintaining PCIC and Packet Resources.................................................12

1.15 Maintenance Initiated by the PCU...................................................................................12

1.16 Maintenance Initiated by the PCU ..................................................................................13

1.17 Acknowledgment Procedure for the Dynamic Adjustment of Channel Coding Schemes 14

2 Messages on the Um Interface.............................................................................................15

2.1 Title................................................................................................................................... 15

2.2 Basic Concepts for the RLC/MAC Protocol.......................................................................16

2.3 Main Procedures on the Um Interface...............................................................................17

2.4 Uplink One-Phase Access on the CCCH..........................................................................17

2.5 Uplink Two-Phase Access on the CCCH..........................................................................19

2.6 Uplink Access on the PACCH...........................................................................................21

2.7 Abnormal Uplink Access ..................................................................................................22

2.8 Setup of Downlink TBF on the CCCH...............................................................................22

2.9 Setup of Downlink TBF on the CCCH Failed ....................................................................24

2.10 Setup of Downlink TBF on the PACCH...........................................................................24

2.11 Setup of Downlink TBF on the PACCH Failed ...............................................................27

2.12 Normal Release of the Uplink TBF .................................................................................28

2.13 Abnormal Release of the Uplink TBF .............................................................................30



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2.14 Normal Release of the Downlink TBF ............................................................................30

2.15 Enable the Downlink Delay Release...............................................................................32

2.16 Abnormal Release Procedure of the Downlink TBF........................................................34

3 Messages on the Gb Interface..............................................................................................35

3.1 Overview of the Gb Interface.............................................................................................35

3.2 Tracing Messages on the Gb Interface ............................................................................37

3.3 Overview of the Pb Interface.............................................................................................37

Appendix Tracing Signaling Messages.....................................................................................1

3.4 Tracing Signaling Messages on the Interfaces.................................................................... 1

3.5 Tracing Signaling Messages on the Um Interface...............................................................1

3.6 Tracing Signaling Messages on the Pb Interface................................................................2

3.7 Tracing Signaling Messages on the Gb Interface................................................................ 3



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1 Messages on the Pb Interface

1.1 Overview of the Pb Interface

Pb interface is an internal interface between the PCU and the BSC from Huawei. It manages

radio packet resources.

Some basic concepts associated with the Pb interface are as follows:

Packet Circuit Identification Code (PCIC)

The PCIC derives from the Circuit Identification Code (CIC). The CIC is on the A interface of the

Global System for Mobile communications (GSM) and the PCIC is on the Pb interface of the

General Packet Radio Service (GPRS). The PCIC is coded uniquely in a BSC. Each PCIC maps

with one 16 kbit/s trunk circuit that lies between the PCU and the BSC.

Logical cell ID

The logical cell ID is coded uniquely in a PCU subrack. Each logical cell ID maps with one Cell

Global Identifier (CGI). A cell is identified by its logical cell ID among the internal modules of the

PCU and by its CGI between the PCU and the BSC.

Logical channel ID

A logical channel is a uniquely coded Packet Data Channel (PDCH) in a cell. The logical channel

ID helps the internal modules of the PCU and the O&M module to identify a channel.

Static channels and dynamic channels

The static channels refer to the PDCHs that are converted from the TCHs when the system is

initialized and which will not be released even though there are services with higher priorities in a

cell until the cell is reset.

The dynamic channels refer to the channels that switch between the TCHs and the PDCHs. That

is, these channels serve as the TCHs when the system is initialized. These TCHs, however, are

converted to PDCHs when the packet service is busy. When services with higher priorities need

to be processed by the BSC, these PDCHs can be converted back to TCHs.



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1.2 Procedures on the Pb Interface

The main procedures on the Pb interface are as follows:

Cell activation/deactivation procedure

Cell initialization procedure

Cell reset procedure

Procedure for requesting dynamic channels

Active/passive release procedure of the dynamic channels

Resource verification procedure

Procedure for maintaining PCIC and packet resources

Acknowledgment procedure for the dynamic adjustment of the channel coding

schemes

1.3 Cell Activation/Deactivation Procedure

1.3.1 Cell Activation Procedure

A cell is deactivated when you add or modify the data in the ATTR table of the cell.

To activate the cell, you should activate the cell through the PCU O&M terminal

(Telnet).

The PCU initiates a cell reset procedure after the cell is activated. Upon receipt of an

acknowledgment message from the BSC, the PCU initiates the cell initialization

procedure.

1.3.2 Cell Deactivation Procedure

To delete or modify the data in the ATTR table of the cell, you should deactivate the

cell.

The PCU releases the static and dynamic channels after the cell is deactivated.

1.4 Cell Initialization Procedure

You should initialize a cell under the following situations:



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The LAPD links are recovered from the blocked state.

The cell is recovered from the deactivation state.

The PCU or BSC initiates a cell reset procedure.

The PCU obtains the detailed information about the cell during the cell initialization. If the

channel information indicates that the BSC has allocated static channels, the PCU

immediately requests these static channels to process packet services.

1.5 Normal Procedure

lists the signaling exchanged between the PCU and the BSC in a normal cell initialization

procedure.

Normal cell initialization procedure

1 15:19:51.330 PCUBSC MT_PCU_BSC_CELL_CONFIG_REQ

2 15:19:51.440 BSCPCU MT_BSC_PCU_CELL_INFO

3 15:19:51.440 PCUBSC MT_PCU_BSC_CELL_INFO_CNF

4 15:19:51.490 BSCPCU MT_BSC_PCU_CHAN_INFO

5 15:19:51.490 PCUBSC MT_PCU_BSC_CHAN_INFO_CNF

6 15:19:51.600 BSC

PCU MT_BSC_PCU_CHAN_INFO


8 15:19:51.660 BSCPCU MT_BSC_PCU_CELL_CONFIG_ACK

9 15:19:51.660 PCUBSC MT_PCU_BSC_PDCH _REQ

10 15:19:51.710 BSCPCU MT_BSC_PCU_PDCH_ACK

The PCU sends an MT_PCU_BSC_CELL_CONFIG_REQ message to the BSC, as shown

in item 1.

This message contains the logical cell ID of the cell to be initialized.

Upon receipt of the MT_PCU_BSC_CELL_CONFIG_REQ message, the BSC sends an

MT_BSC_PCU_CELL_INFO message to the PCU, as shown in item 2.

This message contains the hopping information of the cell and the parameters about

system information.

The PCU responds with an MT_PCU_BSC_CELL_INFO_CNF message, as shown in item

3.

Upon receipt of the MT_PCU_BSC_CELL_INFO_CNF message, the BSC sends an

MT_BSC_PCU_CHAN_INFO message to the PCU. See items 4 and 6.



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This message contains the absolute radio frequency channel numbers (without frequency

hopping) and the TSC. This message also contains the HSN, MAIO, and the frequency list

if frequency hopping is applied.

Upon receipt of the MT_BSC_PCU_CHAN_INFO message, the PCU responds with anMT_PCU_BSC_CHAN_INFO_CNF message. See items 5 and 7.

By sending an MT_BSC_PCU_CELL_CONFIG_ACK message to the PCU, the BSC

notifies the PCU that the cell initialization is complete and that the cell can work normally.

See item 8.

If a static channel is available, the PCU initiates a channel request procedure by sending

an MT_PCU_BSC_PDCH _REQ message to the BSC.

The BSC responds with an MT_BSC_PCU_PDCH_ACK message, as shown in item 10.

shows the Pb interface signaling traced in the normal cell initialization procedure.

Pb interface signaling traced in the normal cell initialization procedure

1.6 Abnormal procedure

1.6.1 Cell not configured in the BSC

shows the cell initialization procedure that occurs when the cell is not configured in the

BSC.

Cell initialization procedure (cell not configured in the BSC)

1 PCUBSC MT_PCU_BSC_CELL_CONFIG_REQ

2 BSCPCU MT_BSC_PCU_RF_RES_BLOCK

The PCU initiates a cell configuration procedure by sending an

MT_PCU_BSC_CELL_CONFIG_REQ message to the BSC, as shown in item 1. The BSC

responds with an MT_BSC_PCU_RF_RES_BLOCK message if the cell is not configured in the

BSC, as shown in item 2. This message contains the cause value Cell Not Exit.

You can view the states of the cell through the PCU O&M terminal (Telnet) as follows:



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RPPU : 1

Cell : 37

Operation state : disabled

Availability state : inside fail

BSC management state : blocked

Cause of BSC being blocked : unknown

Management state of maintenance: unblocked

Management state of Gb : blocked

1.6.2 Abnormal state of the cell in the BSC

shows the cell initialization procedure that occurs when the cell is abnormal in the BSC.

Cell initialization procedure (cell abnormal in the BSC)

1 17:13:2.650 PCUBSC MT_PCU_BSC_CELL_CONFIG_REQ

2 17:13:2.750 BSCPCU MT_BSC_PCU_CELL_INFO

3 17:13:2.750 PCUBSC MT_PCU_BSC_CELL_INFO_CNF





8 17:13:3.30 BSCPCU MT_BSC_PCU_CELL_CONFIG_ACK

9 17:13:2.30 PCUBSC MT_PCU_BSC_PDCH_REQ

10 17:13:2.140 BSCPCU MT_BSC_PCU_PDCH_NACK

The BSC_PCU_CELL_CONFIG_ACK message indicates that the cell is blocked. The BSC

rejects the request for the static channels.

You can view the states of the cell through the PCU O&M terminal (Telnet) as follows:

RPPU : 1

Cell : 35

Operation state : enabled

Availability state : no exception




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Management state of maintenance: unblocked


To view the operation status of the cell, you can start the Site Maintenance TerminalSystem.

1.6.3 No response from the BSC

shows the cell initialization procedure that occurs when there is no response from

the BSC.

Cell initialization procedure (no response from the BSC)

1 16:40:12.690 PCUBSC MT_PCU_BSC_CELL_RESET




As shown , the PCU keeps sending cell reset messages; but there is no response

from the BSC.

You can view the states of the cell through the PCU O&M terminal (Telnet) as

follows:

Operation successful

RPPU : 4

Cell : 51

Operation state : disabled

Availability state : device has not been initialized



Management state of maintenance : unblocked


In this case, you should check whether the BSC is operating normally.



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1.7 Cell Reset Procedure Initiated by the PCU

The PCU initiates a cell reset procedure in the following situations:

The maintenance engineer resets a cell through the PCU O&M terminal (Telnet).

A cell is recovered from the deactivation state.

lists the cell reset procedure initiated by the PCU.

Cell reset procedure initiated by the PCU


2 15:19:49.350 BSCPCU MT_BSC_PCU_CELL_RESET_ACK

The PCU initiates a cell reset procedure by sending an

MT_PCU_BSC_CELL_RESET message to the BSC, as shown in item 1.

The BSC responds with an MT_BSC_PCU_CELL_RESET_ACK message, as

shown in item 2.

After the cell is reset, the PCU immediately initiates the cell initialization

procedure.

shows the Pb interface signaling traced in the PCU-initiated cell reset procedure.

Pb interface signaling traced in the PCU-initiated cell reset procedure

1.8 Cell Reset Procedure Initiated by the BSC

The BSC initiates a cell reset procedure in the following situations:

When the dynamic data configuration takes effect, the BSC notifies the PCU of



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obtaining the information about the cell configurations.

The BSC issues a cell reset command to the general radio resource management module

(GRRM) after the BSC is powered on.

1.9 Procedure for Requesting Dynamic Channels

Upon receipt of the access request from the MS, the PCU decides whether to request a dynamic

channel from the BSC based on the following conditions:

Multi-timeslot capability of the MS

Information about channel configurations during the cell initialization

Seized channels

Number of MSs multiplexed on each channel

If the PCU decides to request a dynamic channel from the BSC, it shall also specify which

channel to be used.

The PCU initiates a dynamic channel request procedure to request a dynamic channel from the

BSC in a designated way.

shows the Pb interface signaling in the dynamic channel request procedure.

Pb interface signaling in the dynamic channel request procedure

1 15:19:51.880 BSCPCU MT_BSC_PCU_CHAN_REQ

2 15:19:51.880 PCUBSC MT_PCU_BSC_IMM_ASS

3 15:19:52.260 PCUBSC MT_PCU_BSC_PDCH_REQ

4 15:19:52.650 BSCPCU MT_BSC_PCU_PDCH_ACK



The signaling exchanged on the Pb interface is as follows:The BSC sends a channel request message (MT_BSC_PCU_CHAN_REQ, sent from the

MS) to the PCU, as shown in item 1.

The PCU requests a dynamic channel from the BSC according to the multi-timeslot

capability of an MS, channel configuration information upon cell initialization, seized

channels, and the number of MSs multiplexed on each channel.

Item 3 shows the MT_PCU_BSC_PDCH_REQ message sent by the PCU.

The BSC allocates the PDCHs to the PCU when the circuit service is idle.

Item 4 shows the MT_BSC_PCU_PDCH_ACK message sent by the BSC.

The PCU assigns these PDCHs to the MS for processing data services.



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Item 6 shows the MT_PCU_BSC_IMM_ASS message sent by the PCU.

shows the Pb interface signaling in the dynamic channel request procedure.

Pb interface signaling in the dynamic channel request procedure

1.10 Active/Passive Release Procedure of the Dynamic Channels

The release procedure of dynamic channels can be classified into active release procedure and

passive release procedure. The active release procedure of dynamic channels is initiated by the PCU under

the following situations:

The channels are in idle state for a long period.

The channels are dynamically adjusted between cells.

The PCIC is blocked.

The passive release procedure of dynamic channels in initiated by the PCU

under the following situation:

There are few TCHs on the BSC side. Thus, the BSC requests the PCU to release the PDCHs.

1.11 Active Release Procedure

shows the Pb interface signaling in the active release procedure of dynamic

channels.

Pb interface signaling in the active release procedure of dynamic channels

1 15:10:32.20 PCUBSC MT_PCU_BSC_PDCH_REL

2 15:10:32.130 BSCPCU MT_BSC_PCU_PDCH_REL_CNF

shows the Pb interface signaling traced in the active release procedure of dynamic

channels.



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Pb interface signaling traced in the active release procedure of dynamic channels

1.12 Passive Release Procedure

When the circuit service is busy, the BSC sends a TCH Request message to the

PCU so that more dynamic channels can be used for the circuit services with higher

priority. The PCU releases the dynamic channels unconditionally.

shows the Pb interface signaling in the passive release of dynamic channels.

Pb interface signaling in the passive release of dynamic channels

1 15:10:32.20 BSCPCU MT_BSC_PCU_TCH_REQ

2 15:10:32.130 PCUBSC MT_PCU_BSC_TCH_ACK

shows the Pb interface signaling traced in the passive release procedure of dynamic

channels.

Pb interface signaling traced in the passive release procedure of dynamic channels

1.13 Resource Verification Procedure

Resource verification is performed to check whether the status of the resources

between the PCU and the BSC is consistent. This process is necessary as some

abnormal cases may (such as loss of messages) occur in the long operation of the

equipment. The resource verification can be classified into the following types:

Cell state verification

This procedure checks whether the cell state is consistent between the PCU and

the BSC.



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This operation checks the combination type and management status of the

channels. The PCU periodically sends the Channel Check message to the BSC.

Upon receipt of this message, the BSC compares the channel state between the

BSC and the PCU, and takes measures accordingly.


This operation is initiated by the PCU. It only checks the O&M state

(Blocked/Unblocked) of the PCIC. When the BSC detects that the state of the

PCIC is inconsistent between the PCU and the BSC, it takes measures

accordingly.

shows the Pb interface signaling in the resource verification procedure.

Pb interface signaling in the resource verification procedure

1 17:13:24.840 PCUBSC MT_PCU_BSC_CHAN_CHECK

2 17:13:24.840 PCUBSC MT_PCU_BSC_PCIC_CHECK



5 17:13:29.830 PCU

BSC MT_PCU_BSC_PCIC_CHECK



shows the Pb interface signaling traced in the resource verification procedure.



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Pb interface signaling traced in the resource verification procedure

1.14 Procedure for Maintaining PCIC and Packet Resources

You can maintain the PCIC and packet resources through the PCU O&M terminal

(Telnet) or the BSC Maintenance System.

1.15 Maintenance Initiated by the PCU

The maintenance initiated by the PCU consists of the following types:

Block/Unblock of PCIC

PCIC Block command from the PCU O&M terminal

If the packet channel mapping with the PCIC is idle, only the PCIC block state

is recorded.

If the PCIC is assigned and used by a dynamic PDCH, the PCU will initiate

PDCH release procedure and record the block state.

If the PCIC is used by a static PDCH, the PCU will only record the block

state.

PCIC Unblock command from by the PCU O&M terminal

The PCU modifies the state of the PCIC and the BSC responds with an

acknowledgment.

If the PCIC is used by a static PDCH, you should change the state of the

PDCH first.

Lock/Unlock of packet resources

The Cell Management State is Locked when the PCU initiates the Cell Lock



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command.

The MS cannot access the cell when the cell is locked.

The Cell Management State is Unlocked when the PCU initiates the Cell Unlock

command.

The MS can access the cell when the cell is unlocked.

The Channel Management State is Locked when the PCU initiates the Channel

Lock command.

The channel cannot be assigned to an MS to process data service when the

channel is locked.

The Channel Management State is Unlocked when the PCU initiates theChannel Unlock command.

The channel can be assigned to an MS to process data service when the

channel is unlocked.

1.16 Maintenance Initiated by the PCU

The maintenance initiated by the BSC consists of the following types:

Block/Unblock of the PCIC

PCIC Block command initiated by the BSC

The PCU sets the management state of the PCIC to Blocked. If the PCIC is used

by a dynamic PDCH, the PDCH is released.

The BSC unblocks the PCIC by setting the management state of the PCIC to

Unlocked.

PCIC Reset command initiated by the BSC

When the BSC detects that the state of the PCIC is inconsistent between the

BSC and the PCU during the state verification, the BSC will reset the PCICs that

are labeled as PDCH on the BSC side and the PCICs that are labeled as TCH

on the PCU side.

This reset might lead to the release of the PDCH.

The Site Maintenance System of the BSC can also initiate the reset of PCIC.

Lock/Unlock of packet resource



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If the lock command initiated by the BSC locks the dynamic channel, the PCU

releases the channel and responds with an acknowledgment.

The BSC initiates an unlock command and the PCU responds with an

acknowledgment.

1.17 Acknowledgment Procedure for the Dynamic Adjustment of Channel

Coding Schemes

When the coding scheme is changed from CS-1 or CS-2 to CS-3 or CS-4, the PCU

must notifies the BSC to add 16 kbit/s E1 links on the Abis interface and Pb interface.

You cannot adjust the coding scheme until a positive acknowledgment is received

from the BSC. See .

Acknowledgment procedure in the dynamic adjustment of channel coding schemes

1 17:13:24.840 PCUBSC MT_PCU_BSC_CS_MOD

2 17:13:24.840 BSCPCU MT_BSC_PCU_CS_ACK

3 17:13:24.840 BSCPCU MT_BSC_PCU_CS_NACK

The PCU sends an MT_PCU_BSC_CS_MOD message before adjusting the

coding scheme from CS-1 or CS-2 to CS-3 or CS-4.

The BSC responds with a positive acknowledgment when it successfully adjusts

the coding scheme.

The PCU assigns the PCICs to the PDCHs that support CS-3 or CS-4.

shows the Pb interface signaling traced in the dynamic adjustment of coding

scheme.



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Pb interface signaling traced in the dynamic adjustment of coding scheme

2 Messages on the Um Interface

2.1 Title

2.1.1 Protocol Stack on the Um Interface

shows the protocol stack of the GPRS.

Protocol stack of the GPRS

Relay

Network

Service

GTP

Application

IP / X.25

SNDCP

LLC

RLC

MAC

GSM RF

SNDCP

LLC

BSSGP

L1bis

RLC

MAC

GSM RF

BSSGP

L1bis

Relay

L2

L1

IP

L2

L1

IP

GTP

IP / X.25

Um Gb Gn Gi

MS BSS SGSN GGSN

Network

Service

UDP /

TCP

UDP /

TCP

Um interface is an interface between the BSS and the MS.

GSM Rec. 03.64 introduces the Um interface in the GPRS.

GSM Rec. 05.02 describes the radio channels of the GSM/GPRS.

GSM Rec. 04.60 and 04.08 describe the signaling on the Um interface of the

GPRS.

The main Um interface protocol processed by the PCU is the Radio Link

Control/Medium Access Control (RLC/MAC) layer protocol.



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The function of tracing the messages on the Um interface is to trace the signaling

and data on the RLC/MAC layer between the PCU and an MS. The tracing function

can be used to solve some abnormal cases concerning the

2.2 Basic Concepts for the RLC/MAC Protocol

2.2.1 Functions of the RLC/MAC Layer

The RLC/MAC layer provides the LLC PDUs with transmission channels, which help

the transmission of LLC PDUs between the MS and the SGSN.

To achieve this purpose, the PCU should accomplish the following operations:

Set up a data transmission link on the Um interface, namely, TBF.

Allocate resources (channels and radio blocks) for links; adjust, and release the

allocated resources.

2.2.2 Link in the RLC/MAC LayerTBF

The Temporary Block Flow (TBF) is a physical connection used for transferring data

between the MS and the BSS. The TBF does not exist until there is data

transmission.

The TBF comprises the following information:

TFI

The Temporary Flow Identity (TFI) is the identity of TBF. The TBF is identified by

the TFI and the transfer direction of data.

Allocated channels

The allocated channels refer to the channels on which the data blocks of the

TBF are transferred.

Control channels

The control channels refer to the channels on which the control blocks of the

TBF are transferred.

RLC mode

The RLC mode consists of acknowledged mode and unacknowledged mode.

Acknowledged mode



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The receiver should acknowledge each data block transferred by the TBF; otherwise, the TBF

should retransfer the data block. The TBF will not be released until all the data blocks are

transferred and acknowledged.

Unacknowledged modeThe receiver need not acknowledge the transferred data blocks and the TBF need not retransfer

the lost data blocks. The TBF is released when all the data blocks are transferred.

MAC mode (uplink TBF)

The MAC mode consists of three modes: fixed allocation, dynamic allocation, and extended

dynamic allocation.

Fixed allocation

The BSS allocates the radio blocks for the MS in advance by sending a Resource Bit Map to the

MS in the assignment message. If the radio blocks are used up while there are still data to be

transferred, the BSS should re-allocate radio blocks.

Dynamic allocation

When the BSS allocates radio resource to the MS, it not only allocates radio channels but also

allocates the Uplink State Flag (USF) values for the radio channels. The MS monitors the USF

value in the downlink radio block of the assigned channel. If the USF value is the same with the

assigned USF, the MS transfers data on the corresponding uplink radio block.

Extended dynamic allocation

The resource allocation mechanism of the extended dynamic allocation mode is nearly the same

with that of the dynamic allocation mode. In the extended dynamic allocation mode, however,after receiving the USF value in a channel, the MS can transfer data on the channel or other

channels with higher numbering.

2.3 Main Procedures on the Um Interface

Because the network operators do not configure PCCCH at present, the following sections

introduce the procedures only when the system is configured with CCCH instead of PCCH.

2.4 Uplink One-Phase Access on the CCCH

If no PCCCH is configured in a cell, the packet service is initiated on the CCCH. The packet

access request on the CCCH is first sent to the BSC and then forwarded to the PUC by the

BSC. Thus, you cannot view the packet channel request message and immediate

assignment message on the Um interface.

shows the Pb interface signaling in the uplink one-phase access on the CCCH and

shows the Um interface signaling in the uplink one-phase access on the CCCH.



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Pb interface signaling in the uplink one-phase access on the CCCH



Um interface signaling in the uplink one-phase access on the CCCH



3 17:18:22.420 PCUMS PACK_PSI13

4 17:18:22.140 MSPCU Uplink Data Block


6 17:18:22.140 PCUMS PACK_UL_ACKNACK




Take for instance, the Um interface signaling in the uplink one-phase access on the CCCH is as

follows:

The MS initiates a packet channel request on the CCCH by sending an

MT_BSC_PCU_CHAN_REQ message to the BSC, which forwards the message to the

PCU. See item 1.

The PCU processes the packet channel request and sends an MT_PCU_BSC_IMM_ASS

message to the MS through the BSC, as shown in item 2. This message assigns a channel

for the MS.

The MS sends uplink data blocks on the channels assigned by PCU, as shown in items 4, 5,

7 and 9.

After receiving the uplink data blocks, the PCU sends a PACK_UL_ACKNACK message to

the MS. See items 6 and 8.

Thus, the conflict settlement is complete. The conflict settlement is necessary as this is the

one-phase access on the CCCH.

The setup of an uplink TBF is complete once the conflict is settled.

shows the Pb interface signaling traced in the uplink one-phase access on the CCCH.



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Pb interface signaling traced in the uplink one-phase access on the CCCH

shows the Um interface signaling traced in the uplink one-phase access on the

CCCH.

Um interface signaling traced in the uplink one-phase access on the CCCH

2.5 Uplink Two-Phase Access on the CCCH

shows the uplink two-phase access procedure on the Pb interface and Table 2-4

shows the uplink two-phase access procedure on the Um interface.

Pb interface signaling in the uplink two-phase access on the CCCH



Um interface signaling in the uplink two-phase access on the CCCH

3 17:19:36.790 PCUMS PACK_PSI13

4 17:19:41.130 MSPCU PACK_RES_REQ

5 17:19:41.130 PCUMS PACK_UL_ASSI






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Take for instance, the Um interface signaling in the uplink two-phase access on the CCCH is

as follows:

The MS initiates a packet channel request on the CCCH by sending an

MT_BSC_PCU_CHAN_REQ message to the BSC, which forwards the message to thePCU. See item 1.

The PCU processes the packet channel request and sends an MT_PCU_BSC_IMM_ASS

message to the MS through the BSC, as shown in item 2. This message assigns a single

block resource for the MS.

The MS sends a PACK_RES_REQ message on the block resource assigned by the PCU,

as shown in item 4.

The PCU processes the packet resource request and assigns a channel for the MS by

sending a PACK_UL_ASSI message to the MS, as shown in item 5.

The MS sends uplink data on the channels assigned by PCU, as shown in items 6, 7 and

9. The setup of the uplink TBF is complete.

shows the Pb interface signaling traced in the uplink two-phase access on the CCCH.

Pb interface signaling traced in the uplink two-phase access on the CCCH

shows the Um interface signaling traced in the uplink two-phase access on the

CCCH.

Um interface signaling traced in the uplink two-phase access on the CCCH

shows the PACK_RES_REQ message, which contains the information about the

multi-slot capability of an MS.



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PACK_RES_REQ message traced on the Um interface

2.6 Uplink Access on the PACCH

In the downlink TBF transmission process, the MS can request for the setup of uplink

TBF by carrying uplink channel request in the PACK_DL_ACK_NACK message.

shows the uplink access procedure on the PACCH.

Uplink access procedure on the PACCH

1 10:52:22.40 PCUMS Downlink Data Block

2 10:52:22.320 MSPCU PACK_DL_ACK_NACK

3 10:52:22.320 PCUMS PACK_UL_ASSI




The signaling exchanged on the Um interface is as follows:The MS requests to set up an uplink TBF by sending a PACK_DL_ACK_NACK message,

which contains the channel request description, as shown in item 2.

The PCU processes the packet channel request and assigns the channel resource for the

MS by sending a PACK_UL_ASSI message on the PACCH, as shown in item 3.

The MS sends uplink data blocks on the channels assigned by PCU, as shown in items 4, 5,

and 6. The setup of the uplink TBF is complete.

shows the signaling traced for the uplink access on the PACCH.



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Signaling traced for the uplink access on the PACCH

shows the Channel Request Description field in the EGPRS_DL_ACK_NACK

message, the counterpart PACK_DL_ACK_NACK in the GPRS.

Channel request description

2.7 Abnormal Uplink Access

After sending an assignment message (uplink immediate assignment or packet

uplink assignment) to the MS in the uplink access procedure, the PCU shall set the

USF field to the downlink block on the assigned PDTCH. If the PCU fails to receive

an uplink data block from the MS after sending a maximum of downlink blocks with

the USF field, the setup of the uplink TBF fails. The maximum value generated by the

N3101 is decided by the system.

decided by the system.

2.8 Setup of Downlink TBF on the CCCH

If no TBF exists when the PCU receives the LLC PDUs, the PCU needs to set up a

downlink TBF to transfer data.



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The MS monitors the PCH when it is in the packet idle mode. In this case, the

downlink assignment message is sent on the CCCH.

The MS monitors the PDCH when it is in the uplink TBF transmission process or

timer T3192 has not expired. In this case, the downlink assignment message is

sent on the PACCCH. For detailed information, see section 2.2.5.

and show the procedure for setting up a downlink TBF on the CCCH.

Pb interface signaling in setting up a downlink TBF on the CCCH


Um interface signaling in setting up a downlink TBF on the CCCH

2 10:52:6.120 PCUMS PACK_POLL_REQ

3 10:52:6.390 MSPCU ACCESS BURST MESSAGE

4 10:52:6.390 PCUMS PACK_POW_CTRL

5 10:52:6.440 PCUMS PACK_DL_ASSI




The signaling exchanged is as follows:

After receiving a downlink LLC PDUs on the Gb interface, the PCU initiates the

procedure for setting up a downlink TBF.

The downlink assignment messages are sent on the CCCH since the MS is in

packet idle mode. As shown in item 1, the PCU assigns a channel to the MS by

sending an MT_PCU_BSC_IMM_ASS message to the MS through the BSC.

To obtain the timing advance (TA) of the MS, the PCU sends a

PACK_POLL_REQ message to the MS on the assigned packet channel. See

item 2.

The MS responds with an ACCESS BURST message, as shown in item 3. The

PCU obtains the timing advance (TA) of the MS through this response and then

sends a PACK_POW_ CTRL message to the MS. See item 4.

If the channel assigned for the MS in the immediate assignment message does

not meet the multi-slot capability of the MS, the PCU will re-initiate a channel



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assignment procedure. See item 5.

The downlink TBF setup succeeds and the PCU begins to send downlink data

blocks as shown in items 6, 7, and 8.

shows the Pb interface signaling in setting up a downlink TBF on the CCCH. Pb

interface signaling traced in setting up a downlink TBF on the CCCH

shows the polling request and packet resource assignment on the Um interface.

Um interface signaling traced in setting up a downlink TBF

2.9 Setup of Downlink TBF on the CCCH Failed

If the MS does not respond to the Polling Request message from the PCU with an

Access Burst message, the setup of downlink TBF on the CCCH fails.

shows the Um interface signaling traced in an unsuccessful downlink TBF setup

procedure.

Um interface signaling traced in an unsuccessful downlink TBF setup procedure

2.10 Setup of Downlink TBF on the PACCH

2.10.1 Disable Sending Downlink Data Blocks Ahead of Schedule

shows the Um interface signaling in setting up a downlink TBF on the PACCH.



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Um interface signaling in setting up a downlink TBF on the PACCH







7 17:19:41.730 MSPCU PACK_CONTRL_ACK



The signaling on the Um interface is as follows:

Upon receipt of the downlink LLC PDUs on the Gb interface, the PCU initiates a

procedure for setting up a downlink TBF. The downlink assignment message is

sent on the PACCH because the uplink TBF is in transfer state, as shown in item

3.

Upon receipt of the PACK_CONTRL ACK (or Access Burst message, depending

on the actual configuration) from the MS in response to the downlink packetassignment, the PCU assumes that the downlink TBF is successfully setup and

begins to transfer data. See item 8.

shows the Um interface signaling traced in setting up a downlink TBF on the

PACCH.

Um interface signaling traced in setting up a downlink TBF on the PACCH

2.10.2 Enable Sending Downlink Data Blocks Ahead of Schedule

shows the signaling in the setting up a downlink TBF on the PACCH when the

downlink data block is sent ahead of schedule.



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Signaling in setting up a downlink TBF (downlink data blocks sent ahead of schedule)






6 17:19:41.620 MSPCU Downlink Data Block

7 17:19:41.730 MSPCU Downlink Data Block

8 17:19:41.840 PCUMS PACK_CONTRL_ACK



After receiving a downlink LLC PDUs on the Gb interface, the PCU initiates the

procedure for setting up a downlink TBF. The downlink assignment message is

sent on the PACCH because the uplink TBF is in transfer state, as shown in item

3.

The PCU begins to transmit downlink data blocks before receiving the

PACK_CONTRL ACK message (or Access Burst Message) from the MS (inresponse to the packet assignment message). See items 6 and 7.

The setup of the downlink TBF fails if the PCU does not receive a

PACK_CONTRL ACK message from the MS for a long period. The abnormal

downlink release is initiated.

shows the Um interface signaling traced in setting up a downlink TBF when the

downlink data block is sent ahead of schedule.



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Um interface signaling traced in setting up a downlink TBF (downlink data block sent ahead of

schedule)

shows the abnormal procedure that occurs when the MS does not respond to the

PCU with a PACK_CONTRL ACK message.

Abnormal procedure for setting up a downlink TBF (downlink data block sent ahead of schedule)

2.11 Setup of Downlink TBF on the PACCH Failed

If the MS does not respond to the packet assignment message sent by the PCU with

a PACK_CONTRL_ACK message, the setup of the downlink TBF on the PACCH

fails.



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2.12 Normal Release of the Uplink TBF

shows the Um interface signaling in the normal release of an uplink TBF.

Um interface signaling in the normal release of an uplink TBF









9 17:19:41.620 MSPCU PACK_CONTRL_ACK


When the PCU receives the last uplink RLC data block (CV=0) from the MS, as

shown in item 1:

If all the other uplink RLC data blocks are received, as shown in item 1, the PCU

responds with a packet uplink acknowledgment message

(PACK_UL_ACKNACK, FAI=1).

If not all the uplink RLC data blocks are received, the PCU responds with a

packet unlink acknowledgment message (PACK_UL_ACKNACK, FAI=0) and

requests the MS to retransmit the missed data blocks, as shown in item 2.

Upon receipt of the packet uplink acknowledgment message (PACK_UL_ACKNACK,FAI=1), the MS assumes that the uplink TBF is terminated.

The uplink TBF of the PCU is normally terminated when the PCU receives a packet

uplink acknowledgment message (PACK_CONTRL ACK, FAI=1) from MS, as shown

in item 9

shows the Um interface signaling traced in the the normal release of an uplink TBF.



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Um interface signaling traced in the the normal release of an uplink TBF

The last uplink block in the signaling is set with a RRBP field and labeled with .

This setting requests the MS to respond with a PACK_CTRL_ACK message or an

Access Burst message.

shows the Uplink Data Block (BSN=02) whose Countdown Value (CV) equals 0.

Uplink Data Block (CV=0)

CV=0 indicates that this block is the last block from the MS. If the PCU has received

all the uplink data blocks, it will set field FAI=1 in the PACK_UL_ACKNACK

message. Otherwise, the PCU will set field FAI=0 and request the MS to retransmit

the missed data block, as shown in .



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PACK_UL_ACKNACK (FAI=1)

Upon receipt of the PACK_CONTRL ACK message or the Access Burst message

from the MS, the PCU releases the uplink TBF.

2.13 Abnormal Release of the Uplink TBF

2.13.1 Abnormal release of uplink TBF due to overflow of N3101

If the PCU has received the uplink data blocks from the MS, the setup of the uplink

TBF is successful. In the transmission process of the TBF, if the PCU fails to receive

an uplink data block from the MS after setting a maximum of Packet Downlink

Acknowledgment messages (countered by N3101) with the USF field, the uplink TBF

is abnormally released.

2.13.2 Abnormal release of uplink TBF due to overflow of N3103

After receiving all the uplink RLC data blocks from the MS, the PCU sends a Packet

Uplink Acknowledgment message with the field FAI=1 to the MS. If the PCU does not

receive the ACK_CONTRL ACK message responded by the MS, counter N3103 is

increased by 1. If the PCU fails to receive a Packet Control Acknowledgment

message from the MS after transmitting a maximum of downlink blocks (countered by

N3103) with the field FAI=1, counter N3103 overflows, and the uplink TBF is

abnormally released.

2.14 Normal Release of the Downlink TBF

2.14.1 Disable the Downlink Delay Release

shows the Um interface signaling in the normal release of a downlink TBF.



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Um interface signaling in the normal release of a downlink TBF






The PCU sets the Final Block Indicator (FBI) to 1 while transmitting the last

downlink RLC data block, as shown in item 3. If the MS has received all the

downlink RLC data blocks, it responds with a PACK_DL_ACK_NACK message

with the field FAI=1; otherwise, it responds with a PACK_DL_ACK_NACK

message with the field FAI=0, asking the network to retransmit the missed data

blocks.

The downlink TBF is normally terminated when the network receives the

PACK_DL_ACK_NACK message with the field FAI=1.

shows the Um interface signaling traced in the normal release of a downlink TBF.

Um interface signaling traced in the normal release of a downlink TBF

The last downlink data block in the signaling is set with a RRBP field and labeled with

. This setting requests the MS to respond with a PACK_DL_ACK_NACK (labeled

with in the preceding figure).

shows the last downlink data block with the field FBI=1.



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Downlink data block (FBI=1)

shows the acknowledgment message (PACK_DL_ACK_NACK, labeled with )

responded by the MS with the field FAI=1. The downlink TBF is normally terminatedin this case.

PACK_DL_ACK_NACK (FAI=1)

2.15 Enable the Downlink Delay Release

The downlink delay release optimizes the normal downlink release procedure. If

downlink data need to be transferred in the downlink delay release process, the

transmission could be performed on the original downlink TBF instead of setting up

another TBF on the CCCH. If uplink data need to be transferred in the downlink delay

release process, the procedure for setting up the uplink TBF could be initiated on the

PACCH in order to increase the uplink access speed. The downlink delay release

lasts 2.4 seconds in normal.

shows the Um interface signaling in the normal release of TBF when the delay

release mechanism is enabled.

Um interface signaling in the normal release of TBF (delay release mechanism enabled)




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4 17:19:41.510 MSPCU PACK_DL_ACKNACK






The PCU sets the Final Block Indicator (FBI) to 1 when the downlink delay

release mechanism is disabled. If the downlink delay release mechanism is

enabled, the PCU will not set the FBI in the last downlink RLC data block to 1.

See item 3. Instead, the PCU will retransmit the last data block with the fieldFBI=0, as shown in item 5. The MS responds with a PACK_DL_ACKNACK

message with the field FAI=0, as shown in item 6.

If no uplink or downlink data need to be transferred, the PCU sets the FBI in the

last downlink data block to 1 after the timer (2.4 seconds) in the downlink delay

release expires. The MS responds with a PACK_DL_ACKNACK message with

the field FAI=1.

The downlink TBF is normally released when the network receives a

PACK_DL_ACK_NACK message with the field FAI=1.

shows the Um interface signaling traced in the delay release of downlink TBF.

Um interface signaling traced in the delay release of downlink TBF

The last downlink data block in the signaling is set with a RRBP field and labeled with

. This setting requests the MS to respond with a PACK_DL_ACK_NACK (labeled

with in the preceding figure.

shows the last downlink data block with the field FBI=1.



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Downlink Data Block (FBI=1)

shows the acknowledgment message (PACK_DL_ACK_NACK, labeled with )

responded by the MS with the field FAI=1. The downlink is normally TBF terminatedin this case.

PACK_DL_ACK_NACK (FAI=1)

2.16 Abnormal Release Procedure of the Downlink TBF

The abnormal release of the uplink TBF is caused by the overflow of N3101.

In the TBF transfer process (Downlink TBF successfully established.), the PCU sets

a RRBP field in the downlink RLC data block, requiring the MS to respond with a

Packet Downlink Acknowledgment message if the MS has received the downlink

RLC data block. If the PCU does not receive a Packet Downlink Acknowledgment

message responded by the MS, counter N3105 is increased by 1. If no Packet

Downlink Acknowledgment is received from the MS after a maximum of downlink

RLD data blocks (countered by N3105) with the field RRBP are sent by the PCU,

counter N3105 overflows. Thus, the downlink TBF of the PCU is released

abnormally.



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3 Messages on the Gb Interface

3.1 Overview of the Gb Interface

3.1.1 Protocol Stack on the Gb Interface

shows the protocol stack on the Gb interface.

Protocol stack on the Gb interface

Gb

BSS

LLC

BSSGP

L1

SGSN

NS

L1

MAC

BSSGPRLC

RELAY

NS

Layer 1 is the physical layer at the bottom of the protocol stack. The point-to-point

physical lines or frame relay network can be implemented for the connection on layer

1. Layer 1 provides telecommunications service for the network service layer.

Network service layer provides telecommunications service for the BSSGP layer.

The NS layer is described in GSM Rec. 08.16 while the BSSGP layer is described in

GSM Rec. 08.18.

3.1.2 Functions of the BSSGP Layer

The service model of the BSSGP is described in GSM Rec. 08.18. As shown in , the

service model of the BSSGP for a BSS and an SGSN is asymmetric.



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Service model on the BSSGP layer

GSM 03.64 BSSGP

Service model in an SGSN

LLC

BSSGP

Network service

NM

NM

GMM

GMM

BSSGPRLC/MAC

RELAY

Network service

GSM 08.16

NM

NM

GMM

GMM

Service model in a BSS

GSM 08.16

RL

The functions of the BSSGP on the BSS side are classified into three parts: Relay,

GPRS mobility management (GMM), and network management (NM). The BSSGP

transacts the packet data unit (PDU) with the RLC/MAC by means of Relay, and then

transacts data packets with the peer end by means of unacknowledged transmission

on the Gb interface.

The network management module (NM) on the BSSGP layer performs the following

operations:

BVC management

The BVC management consists of the operation of BVC reset, BVC block, and

BVC unblock.

Flow control management

The flow control on the Gb interface is mandatory as the transmission rate on

the Gb interface is greater than that on the Um interface. The flow control is

implemented through cell flow control and MS flow control.

LLC_DISCARD

This message notifies the SGSN that the BSS has discarded the data packet

due to transmission timeout. The transmission timeout of the data packet is

caused by the poor transmission quality on the Um interface.

The GPRS mobility management module (GMM) on the BSSGP layer performs the

following operations:

Paging



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After receiving the paging message (including circuit paging and packet paging)

from the SGSN, the BSS analyzes the message according to its paging area.

Once the analysis is complete, a paging message that corresponds to the target

cell is generated and sent on the Um interface.

Suspending and resuming of the packet service

A Class B MS uses this function to stop the ongoing packet service if the circuit

service is requested. When the circuit service is complete, the BSS notifies the

SGSN to resume the suspended packet service.

Notification and update of radio capability

The BSS uses this function to acquire the radio capability parameters from the

SGSN.

3.1.3 Functions of the NS Layer

The network service (NS) layer is symmetric between the BSS and the SGSN. The

NS layer sends the NS SDUs between the SGSN and the BSS. The NS layer

provides the following services for the upper layer:

Transmission of NS SDUs, which is of unacknowledged data transmission

Network congestion indication and load-sharing among NSVCs

NS state indication, such as the variation of available transmission capacity

3.2 Tracing Messages on the Gb Interface

3.2.1 Functions of the NS Layer

3.3 Overview of the Pb Interface

The procedures on the Gb interface consist of cell initialization procedure, data

transmission procedure, and MS suspending/resume procedure.

3.3.1 Cell Initialization Procedure

Normal Procedure

On the Gb interface, the point-to-point BSSGP Virtual Connection (PTP BVC) maps

with the connection on the Um interface as far as the cell is concerned. The cell



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initialization procedure consists of three processes: BVC Block, BVC Unblock, and

BVC flow control.

shows the Gb interface signaling in resetting a cell.

Gb interface signaling in resetting a cell

1 17:53:57.430 PCUSGSN BSSGP_PDU_BVC_BLOCK

2 17:53:57.490 SGSNPCU BSSGP_PDU_BVC_BLOCK_ACK

3 17:54:10.500 PCUSGSN BSSGP_PDU_BVC_UNBLOCK

4 17:54:10.500 SGSNPCU BSSGP_PDU_BVC_UNBLOCK_ACK

5 17:54:10.500 PCUSGSN BSSGP_PDU_FLOW_CONTROL_BVC

6 17:54:10.500 SGSNPCU BSSGP_PDU_FLOW_CONTROL_BVC_ACK

The signaling on the Gb interface is as follows:

The PCU initiates a cell reset procedure in which the relevant PTP BVC cannot

process any services. Thus, the BSSGP on the BSS side sends a BVC_BLOCK

message to its counterpart on the SGSN side, as shown in item 1.

The parameter BVCI in the After transmitting the BVC_BLOCK message, the

PCU blocks the BVC on the local side and waits for the response from the

SGSN.

Upon receipt of the BVC_BLOCK_ACK message. See item 2.

If the PUC receives an acknowledgment from the SGSN, the BVC BLOCK

procedure is complete. If the PCU does not receive an acknowledgment from the

SGSN, it will retransmit the

If the cell reset procedure is successful, the PCU will initiate the

BVC_UNBLOCK procedure.

If the cell reset procedure fails, the PCU will not initiate the BVC_UNBLOCK

procedure. In this case, the BVC is in BLOCKED state. Item 3 shows the BVC

UNBLOCK procedure initiated by the PCU with the specified BVCI.

Upon receipt of the BVC_UNBLOCK_ACK message. See item 4.

If the PCU does not receive an acknowledgment from the SGSN, it will

retransmit the If still no response is received upon the retransmission of the

After the PCU receives the BVC_UNBLOCK_ACK message, the cell begins to

process services. As specified in the GSM protocols, the PCU should also



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The signaling and data on the higher layers make no distinguish on the Gb interface

as far as the content of the data is concerned. Both of them are sent in the form of

UNITDATA data packet. That is, there is no difference between the MS Attach

procedure and the WAP interaction procedure for the transmission on the Gbinterface. If the buffered PDUs in the PCU are discarded due to timeout, the PCU

shall notify the SGSN about the size and bytes of the PDU packet by sending a

LLC_DISCARD message.

shows the signaling traced for the attach procedure.

Signaling traced for the attach procedure

shows the signaling traced for the PDP activation procedure.

Signaling traced for the PDP activation procedure

3.3.3 MS Suspending/Resuming Procedure

Normal Procedure

If a class B MS switches from packet data service to speech service, it shall notify the

SGSN to suspend the transmission of packet service through the SUSPEND

procedure. After the speech service is complete, the MS shall notify the SGSN to

resume the transmission of packet service through the RESUME procedure. After the

GPRS ATTACH procedure is complete, some MSs will initiate the SUSPEND

procedure once they enter the speech services.

shows the Gb interface signaling in suspending and resuming an MS.

Gb interface signaling in suspending and resuming an MS

1 10:53:46.80 PCUSGSN BSSGP_PDU_SUSPEND

2 10:53:46.130 SGSNPCU BSSGP_PDU_SUSPEND_ACK



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3 10:53:49.160 PCUSGSN BSSGP_PDU_RESUME

4 10:53:49.210 SGSNPCU BSSGP_PDU_RESUME_ACK

The signaling on the Gb interface is as follows:

Before switching to speech service, the MS initiates a SUSPEND procedure by

sending a PDU_SUSPEND message to the network. The PCU forwards the

PDU_SUSPEND message to the SGSN and notifies it to stop transmitting

packet data. See tem 1.

Upon receipt of the PDU_SUSPEND messageSUSPEND_ACK message. See

item 2.

If the PCU does not receive an acknowledgment from the SGSN, it will

retransmit the PDU_SUSPEND message

When the speech service of the MS is over, the PCU shall send a

PDU_RESUME message to the SGSN and notify it to resume the packet

service. See item 3.

Upon receipt of the PDU_RESUME message, the SGSN responds with a

RESUME_ACK message (item 4) and sends the suspended data packet to the

MS. The PCU will forward the RESUME Completed message to the MS throughthe BSC.

If the MS does not receive a RESUME Completed message, it will initiate an

updating procedure in the route area when the speech service is over. This

procedure notifies the SGSN to resume the suspended PDUs.

Abnormal Procedure

The abnormal cases in the SUSPEND/RESUME procedure are as follows:

The PCU resends the PDU_SUSPEND message four times but fails to receive a

SUSPEND_ACK message from the SGSN. The SUSPEND procedure fails and

a RESUME procedure shall not follow. This symptom happens when the SGSN

product does not support SUSPEND procedure.

Upon receipt of the PDU_SUSPEND message, the SGSN responds with a

SUSPEND NACK message. This happens when the SGSN fails to suspend the

packet service due to some abnormal cases. For example, the subscriber's

information is unavailable. Thus, the SUSPEND procedure fails and a RESUME

procedure shall not follow.



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The PCU resends the PDU_RESUME message four times but fails to receive a

PDU_RESUME_ACK message from the SGSN. Thus, the RESUME procedure

fails.

Upon receipt of the PDU_RESUME message, the SGSN responds with a

RESUME NACK message. This happens when the SGSN fails to resume the

packet service due to some abnormal cases. For example, the subscriber's

information is unavailable.

The SUSPEND/RESUME procedure is a rather complicated one as it involves

the MS, BSC, PCU, and SGSN. Though the procedure on the Gb interface is

normal, the MS might fail to receive the RESUME Succeed message due to

some abnormal cases. Thus, the entire procedure fails.

After acknowledging that the SUSPEND/RESUME procedure has failed, the MS

shall initiate an updating procedure in the route area. After the updating

procedure in the route area is complete, the SGSN can resume the suspended

downlink PDUs.

shows the Gb interface signaling traced in the SUSPEND/RESUME procedure.

Gb interface signaling traced in the SUSPEND/RESUME procedure



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Appendix Tracing Signaling Messages

3.4 Tracing Signaling Messages on the Interfaces

The signaling tracing is currently performed on the PCU-OMC maintenance

system. The interfaces include Um interface, Pb interface, and Gb

interface.

3.5 Tracing Signaling Messages on the Um Interface

Launch the PCU-OMC maintenance system and choose Tracing > Um

Interface Tracing. On the Um interface tracing Setting window, set the

relevant parameters to create a tracing task on the Um interface. See .

Note leave the Filter data block option unchecked.

Um interface tracing setting

You can view the Cell No. and TRX No. in Figure 3-6 by typing mt pdch

show attr all in the Telnet window. The relevant command and

results are shown below.

809_PCU1(maintenance)#mt pdch show attr 601 all



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Operation successful

4 PDCH(s) processed

Cell : 601

PDCHNo : 0

Channel combination : CH_COMB_PDTCH

PCIC Number : 1

PCIC list : 129

TRX : 5

TN : 4

TSC : 0

No hop. Absolute frequency : 750

PDCH timeslot type : Normal PDCH

Support EGPRS : yes

3.6 Tracing Signaling Messages on the Pb Interface

Launch the PCU-OMC maintenance system and choose Tracing > Pb

Interface Tracing. On the Pb interface tracing Setting window, set the

relevant parameters to create a tracing task on the Pb interface. See .

The setting of the Cell No. is the same with that for the Um interface tracing

setting.



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Pb interface tracing setting

3.7 Tracing Signaling Messages on the Gb Interface

Launch the PCU-OMC maintenance system and choose Tracing > BSSGP

Cell Message Tracing. On the BSSGP cell information tracing Setting

dialog box, set the relevant parameters to create a tracing task on the Gb

interface. See .

BSSGP cell information tracing Setting

You can view the Cell No. in Figure 3-8 by typing pcu show lcc

in the Telnet window. The relevant command and results are shown below.

809_PCU1(maintenance)#pcu show lcc 601

LCNo : 601

CellID : 460606060330001

3.7.1 Saving Signaling Messages

After creating a tracing task for one of the three interfaces (Um, Pb, and

Gb), you should right-click in the display area of the task and choose

Autosave Message. See .



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Autosave signaling messages on the Um, Pb, and Gb interfaces

You should trace the signaling on the three interfaces simultaneously. After

a test is complete, it is better to pack the signaling traced on the three

interfaces, as well as the test items and results. Then you should turn off

the tracing tasks on the three interfaces. Once done, a test with signaling

tracing is complete.

You could launch the signaling tracing window with the default values

before performing another round of test on the Um, Pb, and Gb interfaces.

Documents

Huawei PCU Signaling Analysis Guide