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PCU Signaling Analysis Guide Internal use
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PCU Signaling Analysis Guide
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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
7 15:19:51.600 PCUBSC MT_PCU_BSC_CHAN_INFO_CNF
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
4 17:13:2.860 BSCPCU MT_BSC_PCU_CHAN_INFO
5 17:13:2.860 PCUBSC MT_PCU_BSC_CHAN_INFO_CNF
6 17:13:2.970 BSCPCU MT_BSC_PCU_CHAN_INFO
7 17:13:2.970 PCUBSC MT_PCU_BSC_CHAN_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
BSC management state : blocked
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Cause of BSC being blocked : unknown
Management state of maintenance: unblocked
Management state of Gb : blocked
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
2 16:40:15.650 PCUBSC MT_PCU_BSC_CELL_RESET
3 16:40:16.700 PCUBSC MT_PCU_BSC_CELL_RESET
4 16:40:17.690 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
BSC management state : blocked
Cause of BSC being blocked : unknown
Management state of maintenance : unblocked
Management state of Gb : blocked
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
1 15:19:49.240 PCUBSC MT_PCU_BSC_CELL_RESET
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
5 15:19:53.360 BSCPCU MT_BSC_PCU_CHAN_REQ
6 15:19:53.360 PCUBSC MT_PCU_BSC_IMM_ASS
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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Cell state verification
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.
Cell state verification
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
3 17:13:24.840 PCUBSC MT_PCU_BSC_PCIC_CHECK
4 17:13:29.830 PCUBSC MT_PCU_BSC_PCIC_CHECK
5 17:13:29.830 PCU
BSC MT_PCU_BSC_PCIC_CHECK
6 17:13:29.830 PCUBSC MT_PCU_BSC_PCIC_CHECK
7 17:13:29.830 PCUBSC 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
1 17:18:22.810 BSCPCU MT_BSC_PCU_CHAN_REQ
2 17:18:22.810 PCUBSC MT_PCU_BSC_IMM_ASS
Um interface signaling in the uplink one-phase access on the CCCH
1 17:18:22.810 BSCPCU MT_BSC_PCU_CHAN_REQ
2 17:18:22.810 PCUBSC MT_PCU_BSC_IMM_ASS
3 17:18:22.420 PCUMS PACK_PSI13
4 17:18:22.140 MSPCU Uplink Data Block
5 17:18:22.140 MSPCU Uplink Data Block
6 17:18:22.140 PCUMS PACK_UL_ACKNACK
7 17:18:22.140 MSPCU Uplink Data Block
8 17:18:22.140 PCUMS PACK_UL_ACKNACK
9 17:18:22.190 MSPCU Uplink Data Block
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
1 17:18:22.810 BSCPCU MT_BSC_PCU_CHAN_REQ
2 17:18:22.810 PCUBSC MT_PCU_BSC_IMM_ASS
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
6 17:19:41.400 MSPCU Uplink Data Block
7 17:19:41.400 MSPCU Uplink Data Block
8 17:19:41.460 MSPCU Uplink Data Block
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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
4 10:52:22.590 MSPCU Uplink Data Block
5 10:52:22.590 MSPCU Uplink Data Block
6 10:52:22.590 MSPCU Uplink Data Block
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
1 10:52:5.570 PCUBSC MT_PCU_BSC_IMM_ASS
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
6 10:52:6.440 PCUMS Downlink Data Block
7 10:52:6.440 PCUMS Downlink Data Block
8 10:52:6.500 PCUMS Downlink Data Block
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
1 17:19:41.510 MSPCU Uplink Data Block
2 17:19:41.510 MSPCU Uplink Data Block
3 17:19:41.510 PCUMS PACK_DL_ASSI
4 17:19:41.570 MSPCU Uplink Data Block
5 17:19:41.620 MSPCU Uplink Data Block
6 17:19:41.620 MSPCU Uplink Data Block
7 17:19:41.730 MSPCU PACK_CONTRL_ACK
8 17:19:41.840 PCUMS Downlink Data Block
9 17:19:41.120 MSPCU PACK_DL_ACK_NACK
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)
1 17:19:41.510 MSPCU Uplink Data Block
2 17:19:41.510 MSPCU Uplink Data Block
3 17:19:41.510 PCUMS PACK_DL_ASSI
4 17:19:41.570 MSPCU Uplink Data Block
5 17:19:41.620 MSPCU Uplink Data Block
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
9 17:19:41.120 MSPCU PACK_DL_ACK_NACK
The signaling on the Um interface 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 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
1 17:19:41.460 MSPCU Uplink Data Block
2 17:19:41.460 PCUMS PACK_UL_ACKNACK
3 17:19:41.460 MSPCU Uplink Data Block
4 17:19:41.510 MSPCU Uplink Data Block
5 17:19:41.510 MSPCU Uplink Data Block
6 17:19:41.570 MSPCU Uplink Data Block
7 17:19:41.570 MSPCU Uplink Data Block
8 17:19:41.570 MSPCU Uplink Data Block
9 17:19:41.620 MSPCU PACK_CONTRL_ACK
The signaling on the Um interface is as follows:
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
1 10:52:21.990 PCUMS Downlink Data Block
2 10:52:21.990 PCUMS Downlink Data Block
3 10:52:22.40 PCUMS Downlink Data Block
4 10:52:22.320 MSPCU PACK_DL_ACK_NACK
The signaling on the Um interface is as follows:
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)
1 17:19:41.460 PCUMS Downlink Data Block
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2 17:19:41.460 PCUMS Downlink Data Block
3 17:19:41.460 PCUMS Downlink Data Block
4 17:19:41.510 MSPCU PACK_DL_ACKNACK
5 17:19:41.510 PCUMS Downlink Data Block
6 17:19:41.570 MSPCU PACK_DL_ACKNACK
7 17:19:41.570 PCUMS Downlink Data Block
8 17:19:43.860 MSPCU PACK_DL_ACKNACK
The signaling on the Um interface is as follows:
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.