g-tch congestion rate optimization delivery guide 20070115-a-1.1.doc
TRANSCRIPT
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GSM TCH Congestion Rate Optimization Delivery Guide For internal use
Reference code Product name GSM RNP
Target readers Product version V1.0
Edited by Document version
GSM TCH Congestion Rate Optimization
Delivery Guide
(For internal use only)
Prepared by Wang Weiji, Yang Haiquan Date: 2006-12-20
Reviewed by Network Planning GSM TechnicalSupport Team
Date: 2006-12-29
Reviewed by Date:
Approved by Date:
Huawei Technologies Co., Ltd.
All rights reserved
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Revision Record
Date Revised version Description Author
2006-12-20 V1.0 Completed the initial draft Wang Weiji, Yang
Haiquan
2007-01-15 V1.1 Modified the level of indexes of
Table 1 and Table 2
Wang Weiji
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Contents
1 Overview..................................................................................................................................... 5
2 Definition of TCH Congestion Rate ......................................................................................... 5
3 Application Strategy ................................................................................................................. 6
4 Optimization Strategy of TCH Congestion Rate ..................................................................... 8
5 Appendix: TCH Channel Rate Signaling Process ................................................................19
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GSM TCH Congestion Rate OptimizationDelivery Guide
Keywords: GSM, TCH congestion rate, application strategy, and optimization strategy
Abstract: This document defines the current key TCH congestion rates, and provides the
references for KPI index clarifications and index commitment related to the
project in China. In addition, this guide provides the optimization methods
briefly for the TCH congestion caused by various reasons.
Reference document
SN Document name Author Publishing house Date
1 GSM Radio Network
Planning and Optimization
Huawei People's Posts and
Telecommunications
Publishing House
June 2004
2 GSM Principles and
Network Optimization
Han Binjie Mechanical Industry
Publishing House
August 2001
3 GSM Wireless Network
Optimization Procedures
Si Fazhong 2001-03-09
5 Traffic Statistic Analysis
Guide
Bai Xiaobin 2002-04-20
6 M900/M1800 Base
Station Controller Traffic
Statistic Manual (v6.06)
Huawei
7 GSM Wireless Network
KPI Baseline (v1.38)
Huawei
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1 Overview
The TCH congestion rate is an important index for measuring the network operation
quality in the GSM network optimization. It indicates the access performance of a
mobile network. The TCH congestion rate influences on the network indexes such as
wireless put-through rate, handover success rate, and worst cell rate.
This document defines the various TCH congestion rates and introduces the
optimization strategy. Competitors and customers have different understandings on
the KPI indexes; therefore, TCH congestion rate varies with competitors and
customers.
Abstract: This document defines the current key TCH congestion rates, and provides
the references for KPI index clarifications and index commitment related to the project
in China. In addition, this guide provides the optimization methods briefly for the TCH
congestion caused by various reasons, and is helpful for the on-site handling.
The description of this document is based on GSM BSC V300R002C13.
2 Definition of TCH Congestion Rate
At present, the definitions of the TCH congestion rate are as follows:
1) TCH congestion rate (TCH overflow) (%) = [2124 Attempted TCH seizures
meeting TCH overflow/2089 Attempted TCH seizures (all)]*100%
This index indicates the percentage of the TCH allocations in the attempted TCH
seizures when there is no idle TCH for allocation in the application.
2) TCH congestion rate (including handover)(%) = [2126 TCH seizure failures for
call + 2127 TCH seizure failures for very early assignment + 2131 TCH seizure
failures for intraBSC incoming cell handover(no radio resource) +2132 TCH
seizure failures for interBSC incoming cell handover(no radio resource)]/[2090
Attempted TCH seizures for call + 2091 Attempted TCH seizures for very early
assignment + 2096 Attempted TCH seizures for intraBSC incoming cell
handover + 2097 Attempted TCH seizures for interBSC incoming cell handover].
3) TCH congestion rate (excluding handover) (%) = [2126 TCH seizure failures for
call + 2127 TCH seizure failures for very early assignment]/[2090 Attempted
TCH seizures for call + 2091 Attempted TCH seizures for very early assignment]
This index indicates the percentage of TCH seizure failures for call excluding the
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handover procedure in attempted TCH seizures for call (excluding handover).
4) Time congestion rate (%) = [2169 TCHF busy time (second) 2283 Cell
unavailable duration]/3600. This index indicates the time ratio of TCHF busy time
in the statistic duration.
5) Times congestion rate (including handover) = [[2120 TCH seizure failures for
call(no radio resource) + 2131 TCH seizure failures for intraBSC incoming cell
handover(no radio resource) + 2132 TCH seizure failures for interBSC incoming
cell handover(no radio resource) +2161 TCH seizure failures for intracell
handover (no radio resource)] /[2090 Attempted TCH seizures for call + 2091
Attempted TCH seizures for very early assignment + 2096 Attempted TCH
seizures for intraBSC incoming cell handover + 2097 Attempted TCH seizures
for interBSC incoming cell handover + 2101 Attempted TCH seizures duringintracell handover]]
This index indicates the voice channel attempted call congestion rate (including
handover).
6) Times congestion rate (excluding handover) = 2120 TCH seizure failures for call
(no radio resource)/2090 Attempted TCH seizures for call
This index indicates the voice channel attempted call congestion rate (excluding
handover).
3 Application Strategy
3.1 Distinguishing according to Index Statistic Object
It can be divided into BSC level, Cluster level, and cell level, that is, the TCH
congestion rate of the whole BSC, the TCH congestion rate of the Cluster consisting
of a series of cells, and the TCH congestion rate of each cell. In the acceptance of
TCH congestion rate index, the object requirements of the index statistic vary with
operators. In general, it is BSC level or Cluster level. The selection of BSC level or
Cluster level is subject to the specific networks and operators practical requirements.
3.2 Distinguishing according to Congestion Rate Definition
Signaling processes related to TCH congestion rate definitions are different. The
calculation value is also different. Numerator statistic reasons are different also, for
example, Attempted TCH seizures meeting TCH overflow, and seizure failure.
Attempted TCH seizures meeting TCH overflow: It is the channel request failure
caused by the real channel allocation failure. TCH seizure failure: It is the assignment
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failure caused by various causes after the assignment commands are issued.
The processes and causes of numerator TCH seizure failures are listed in the table
below:
Definition of
congestion rate
Related process Index meaning
TCH congestion rate
(TCH overflow) (%)
Call, early assignment, intra-BSC
incoming inter cell handover, inter-
BSC incoming cell handover
Indicate the idle degree of
the channel resources
TCH congestion rate
(including handover)
Call, early assignment, intra-BSC
incoming inter cell handover, inter-
BSC incoming cell handover
In the numerator, some
items indicate the idle
degree of the TCH channel
resource, and some items
indicate the TCH seizure
failure.
TCH congestion rate
(excluding handover)
Call, early assignment Indicate the TCH seizure
failure rate
Times congestion
rate (excluding
handover)
Call Indicate the TCH seizure
failure rate owing to
unavailable channel
resources. It indicates the
idle degree of channel
resources.
Times congestion rate
(including handover)
Call, intra-BSC incoming inter-cell
handover, inter-BSC incoming inter-
cell handover, and intra-BSC intra-
cell handover
Indicate the TCH seizure
failure rate owing to
unavailable channel
resources. It indicates the
idle degree of channel
resources.
In the definition of the acceptance index, TCH congestion rate (TCH overflow) (%)
and Times congestion rate (%) are used most frequently. The numerator of the time
congestion rate indicates the seizure failures owing to the unavailable TCH channel
resources. The index calculation results are better than TCH congestion rate (TCH
overflow) (%). It is the formula selected with preference in the relocation project.
Other competitors use the times congestion rate frequently in the acceptance.
The process in the times congestion rate (including handover) differs from that in the
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times congestion rate (excluding handover). The times congestion rate (excluding
handover) includes the call process only.
3.3 Time Congestion Rate
The meaning of statistic point TCHF busy time (second) of the competitor Ericsson
differs from that of Huawei.
Huawei TCHF busy time (second) indicates the no TCH allocation caused by
unavailability of TCH channel resources or BTS unavailability of a cell in the statistic
period.
Ericsson TCHF busy time (second) does not include the time of TCH channel
unavailability caused by the BTS unavailability, and only include the time of theunavailable TCH channel resources.
Therefore, Huawei TCH time congestion rate is the difference of two parts, which
subtracts the time of the unavailable TCH channel (Cell unavailable duration
(second)). Ericsson time congestion rate includes TCHF busy time (second) only.
3.4 TCH Times Congestion Rate (%)
In the numerator, TCH seizure failure in each process is caused by the unavailable
resources.
4 Optimization Strategy of TCH Congestion Rate
4.1 Optimization Analysis
The TCH congestion includes the congestion owing to TCH seizure failure caused by
Attempted TCH seizures meeting TCH overflow and other causes. Figure 1 shows the
analysis process.
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Figure 1 Analysis process of high TCH congestion rate
Check whether the TCH congestion occurs in all cells or certain cell of the BSC. If it
occurs in all cells, perform the troubleshooting from the aspects such as capacity,
transmission, and hardware. If it occurs in a certain cell, troubleshoot the specific cell.
For the TCH congestion occurred in a specific cell, locate the causes from the
aspects such as traffic load, equipment fault or transmission problem, interference,
coverage, and data configuration.
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The traffic statistic items needed for locating the TCH congestion rate problem are
listed as follows:
Table 1 TCCH congestion rate traffic statistic
Cause
classification
BSC-level traffic statistic Cell-level traffic statistic Carrier-level
traffic statistic
Attempted
TCH seizures
meeting TCH
overflow
BSC measurement
function -> Access
measurement function ->
Percentage of TRX in
good condition (%)
TCH traffic volume
(excluding very early
assignment) (ERL) ->
TCH congestion rate
(TCH overflow) (%)
Unsuccessful
assignments (no radio
resource available)
Attempted TCH seizures
(all)
TCH measurement function ->
Attempted TCH seizures meeting TCH overflow
Percentage of TRX in Good Condition (%)
TCH usability (%)
TCH traffic volume (excluding very early
assignment) (ERL)
Attempted TCH seizures (all)
None
Seizure failure BSC measurement
function -> Access
measurement function ->
Attempted TCH seizures
(all)
TCH congestion rate
(including handover)(%)
TCH Seizure failures (all)
Attempted TCH seizures (all)
N/A.
Very early
assignment
TCH measurement function ->
TCH seizure failures for very
early assignment
Attempted TCH seizures for
very early assignment
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Cause
classification
BSC-level traffic statistic Cell-level traffic statistic Carrier-level
traffic statistic
TCH congestion rate
(excluding handover)(%)
Unsuccessful
assignments (radio
interface failure,
reversion to previous
channel)
Unsuccessful
assignments (equipment
failure)
Unsuccessful
assignments (requested
terrestrial resource
unavailable)
Unsuccessful
assignments (terrestrial
circuit already allocated)
Unsuccessful channel
activation duringassignment (NACK)
Channel activation
timeout during
assignment (TIMEOUT)
Assignment TCH measurement function ->
TCH Queue failures for queue
full
TCH queue failures for timeout
Directed retry after queue
failure
TCH seizure failures
(equipment failure)
TCH seizure failures (requested
terrestrial resource unavailable)
TCH seizure failures (terrestrial
circuit already allocated)
TCH seizure failures (invalid
message contents)
Incoming
BSC
handover or
intra-BSC
handover
TCH measurement function ->
TCH Queue failures for queue
full
TCH queue failures for timeout
Attempted TCH seizures during
intraBSC incoming cell
handover
Attempted TCH seizures for
interBSC incoming cell
handover
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Table 2 TCH congestion rate cause
Causeclassification
BSC level Cell level Carrier level
Traffic load BSC measurement
function -> Access
measurement function ->
TCH congestion rate
(including handover)(%)
TCH congestion rate
(excluding handover)(%)
TCH congestion rate (TCHoverflow) (%)
Percentage of TRX in
good condition (%)
TCH traffic volume
(excluding very early
assignment) (ERL) ->
Unsuccessful assignments
(no radio resource
available)
Percentage of TRX in good
condition (%)
TCH usability
TCH traffic volume
(excluding very early
assignment) (ERL)
Full rate traffic volume
(excluding very earlyassignment) (ERL)
Half rate traffic volume
(excluding very early
assignment) (ERL)
1800/1900 cell TCH traffic
volume (excluding very early
assignment) (ERL)
Radio
environment
and
interference
BSC measurement
function -> Access
measurement function
->Unsuccessful
assignments (radio
interface failure, reversion
to previous channel)
TCH call drop rate (%)
Cell measurement function ->
Inter-cell handover
measurement function ->
Attempted handovers for
uplink quality
Attempted handovers for
downlink quality
Attempted handovers for
uplink strength
Attempted handovers for
downlink strength
Cell frequency scan
Channel allocation
measurement function -> TCH
allocation measurement function
Average num. of idle TCHs in
Interf. band 1
Average num. of idle TCHs in
Interf. band 2
Average num. of idle TCHs in
Interf. band 3
Average num. of idle TCHs in
Interf. band 4
Average num. of idle TCHs in
Interf. band 5
Receive quality measurement
function
Receive level measurement
function
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Cause
classification
BSC level Cell level Carrier level
Hardware fault
and
transmission
problem
BSC measurement
function -> Access
measurement function ->
Unsuccessful assignments
(equipment failure)
Unsuccessful assignments
(requested terrestrial
resource unavailable)
Unsuccessful assignments
(terrestrial circuit already
allocated)
Unsuccessful channel
activation during
assignment (NACK)
Channel activation timeout
during assignment
(TIMEOUT)
Cell measurement function ->
TCH measurement function
Cell measurement function 2-
> TCHF/H measurement
function (2)
TCH seizure failures
(requested terrestrial
resource unavailable)
TCHH channel activationfailures during very early
assignment (NACK)
TCHH channel activation
failures during assignment
(TIMEOUT)
TCHF channel activation
failures during assignment
(NACK)
TCHF channel activation
failures during assignment
(TIMEOUT)
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Cause
classification
BSC level Cell level Carrier level
Coverage Cell measurement function ->
Inter-cell handover
measurement function->
Attempted handovers for
uplink quality
Attempted handovers for
downlink quality
Attempted handovers for
uplink strength
Attempted handovers for
downlink strength
Attempted handovers for
timing advance
Attempted handovers for
better cell
TCH measurement function
->
TCH lost radio connections
(connection failure)TCH lost radio connections
(error indication)
Power control measurement
function ->
Up-Down Link Balance
Measurement Function
Call Allocation by TA
Measurement Function
4.2 Congestion Caused by Traffic Load
If the network capacity is deficient or the radio capacity in each position of thenetwork differs from the practical traffic allocation, the TCH congestion occurs in the
cell where there are a lot of subscribers. Through the traffic statistic cell TCH
measurement task, check whether the TCH congestion rate is caused by the TCH
overflow. If the congestion rate is caused really by the too large traffic volume,
forecast its real traffic volume, and check whether the traffic can be shared by other
cells. If it exceeds the optimization adjustment capabilities, the operator should be
suggested to expand the capacity. The traffic balance measures may not conform to
the minimum radio path loss principle. The methods include the adjustment of
coverage range, adjustment of access threshold, CRO, handover threshold, and
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enabling the load handover.
4.3 Congestion Caused by Hardware Problem
The TCH channel seizure failure may be caused by hardware (carrier) or
transmission problem. As a result, the congestion may occur. The specific analysis is
as follows:
1) Check alarm information such as transmission alarm, board communication
alarm, CDU Standing Wave Ratio alarm, and clock alarm to make sure whether
the equipment is faulty.
2) Query the indexes such as Percentage of TRX in good condition (%), TCH
usability, and [TCH channel activation (NACK)]/[TCH channel activation
(TIMEOUT)] of the target cell to check whether the equipment is faulty.
3) Query the indexes such as TCH seizure failures due to A-interface failures and
TCH seizure failures due to terrestrial link failures to analyze whether the
terrestrial link is broken.
4) If the uplink channel is damaged or performance decreases, the MS resides in
the cell and cannot be accessed. As a result, the congestion occurs owing to a
lot of seizure failures. Through Incoming Inter Cell Handover Measurement
Function, you can find that handovers towards this cell fail. Through Receiving
Quality Measurement or Receiving Level Measurement Function, query each
TRX status of the cell. Query whether the uplink/downlink measurement report ofthe same TRX is abnormal to determine which carrier is associated with.
The carrier is faulty but without the fault alarm on the alarm console. This problem
can be solved by using the signaling analyzer to trace the messages of the Abis in the
cell with high TCH congestion rate. Through the analysis of the signaling, locate the
fault at the carrier.
After the fault is located at the carrier, the fault can be cleared through replacing the
carrier or temporarily disabling the carrier.
4.4 Congestion Caused by CoverageThe coverage problems such as wrong installation of BTS antenna feeder and
incorrect configuration may result in the TCH seizure failure.
1) TCH seizure failure caused by inappropriate installation of antenna feeder
The cell antenna is reversely connection, that is, the cell transmit antenna and receive
antenna are wrongly connected. As a result, the signals of the uplink and downlink
channel are severely unbalanced.
Solution: Analyze the uplink/downlink signal level and quality of the target cell by
using the DT or CQT test or using the signaling analyzer. Focus on the unbalance
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symptom.
2) TCH seizure failure caused by antenna feeder fault
The standing wave ratio of the antenna feeder may increase owing to damage,
water, and loose of the connector. The practical transmit power and receive sensitivity
decrease. As a result, the TCH channel seizure fails and the TCH congestion occurs.
This kind of problem can be located through carefully checking the antenna feeders
such as tower amplifier, power amplifier, combiner, and feeder, and check whether the
standing wave ratio alarm exists. For the cell with problem, perform the DT and CQT
test. The simple method is: Test the BTS practical transmit signals by using the test
MS at the foot of the BTS. If the signal strength is -30 to -50dBm, it is normal.
Otherwise, it is problematic.
3) TCH seizure failure caused by CDU/SCU configuration
For the BTS configuration reason, the difference of the combiner loss between the
channels passed by the BCCH and the channels passed by non-BCCH is large;
therefore, the transmit power of the channel where the non-BCCH is located is
smaller than that of the channel where the BCCH is located. If a MS originates a call
(especially, it is far away from the BTS), when the system assigns the MS with the
TCH channel of the TRX where the non-BCCH is located, the TCH channel seizure
fails owing to the low transmit power.
Solutions:
Configure the TRX of the BCCH on the channel with high combiner loss.
Optimize the configuration, to avoid the big difference of the combiner loss
between the channel where the BCCH passes and the channel where the non-
BCCH passes.
4) Congestion caused by too large coverage
Query the average level of the power control, the average level in case of the call
drop, and TA to analyze the TA value and the relation with the receive level. Judge the
coverage range by using the driving test. Query the TCH usability of the neighbor cell
to check whether the fault of the neighbor cell results in the congestion. Query the
uplink and downlink balance performance to check whether the downlink value is
greater than the uplink value, as a result, the MS cannot normally occupy the TCH.
4.5 Congestion Caused by Interference
The TCH congestion rate may be related to the interference. The call drops of the cell
occur frequently, and the SDCCH congestion rate is high. In the random access
measurement function, the RACH congestion occurs, and the immediate assignment
success rate decreases.
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1. Inter-network interference
The transmit power of illegal frequency from other networks results in theinterferences on the network. When the system assigns the TCH channel for a call,
the channel is affected by the interference. As a result, the assignment fails, and the
TCH congestion occurs.
Query Average num. of idle TCHs in Interf. band 4 and 5 to check whether it is the
uplink interference. It is used as a reference only.
To clear the interference, use the spectrum analyzer and high gain directional
antenna to search the position of the interference source, and then shut off the
interference source.
2. Intra-network interference
If the frequency plan is inappropriate, the same-/adjacent-frequency carrier-to-
Interference ratio cannot be met in some positions in the network. The
same-/adjacent-frequency interference occurs. Meanwhile, the TCCH congestion
occurs owing to the TCH seizure failure.
The uplink and downlink of the cell frequency in the network appears in pairs. The
interference band of the traffic statistic can be used as the fundament. Query the
interference band in the traffic statistic, and locate the cells with high interference
band 4 and interference band 5 values. Then, check the network frequency plan.
Locate the cell with problem, and adjust the frequency plan to solve the interference.
For the intra-network interference, the driving test should be performed in a lot of
places, to find the downlink interference and cross-cell coverage interference
according to the practical quality allocation, so as to adjust the antenna or frequency
plan specifically.
For specific troubleshooting, see G- Interference Problem Handling Guide-20050311-
A-1.0
1) Hardware fault interference: Features of the interference caused by hardware
and equipment problems: Strong interference signals and lasting for a long time.
For the interference caused by the adjustment, it may be related to the traffic
volume obviously. When the traffic volume is small, you can send the idle
BURST for verification.
2) Intra-network interference: It is the intra-frequency interference or inter-frequency
interference caused by inappropriate frequency planning, frequent frequency
multiplexing, and cross-cell coverage. In general, the intra-network interference
increases with the increase of the traffic volume.
3) For specific troubleshooting, see G- Interference Problem Handling Guide-
20050311-A-1.0
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4.6 Congestion Caused by Frequent Handover
The frequent handovers may result in the TCH channel congestion. Query thehandover times and successful call seizures, and check whether the ratio is
appropriate. Check whether the ratio of the handover-in and handover-out, and check
whether the cell congestion is caused by the inappropriate handovers.
4.7 Congestion Caused by Data Configuration
When the cell is activated with the half rate and overlaid/underlaid functions, the
congestion may be caused by the inappropriate setting of parameters. When the
GPRS service is activated, the TCH congestion occurs owing to the inappropriate
allocation of speech channel and traffic channel. In addition, the TCH channel
congestion may be caused by the wrong setting of circuit pool number.
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5 Appendix: TCH Channel Rate Signaling Process
5.1 Immediate Assignment and Assignment Channel SeizureProcess
Channel Activation Acknowledge
MS BTS BSC
Channel Request
Channel Activation
Immediate assignment Command
SABM
Channel Requiredt
UA EST IND
MSC
CR CMP Lay3 information
CCCM Service Accept
Setp
Call Proceeding
Assinnment Request
Channel Activation
Channel Activation Acknowledge
SABM
UAEST IND
Assignment Complete
Channel Activation Acknowledge
MS BTS BSC
Channel Request
Channel Activation
Immediate assignment Command
SABM
Channel Requiredt
UA EST IND
MSC
CR CMP Lay3 information
CCCM Service Accept
Setp
Call Proceeding
Assinnment Request
Channel Activation
Channel Activation Acknowledge
SABM
UAEST IND
Assignment Complete
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5.2 BSC Intra-handover Channel Seizure Process
MS BTS2 BSC BTS1 MSC
Measurement Report from MS(1)
MS
Channel ACT(2)
Channel ACT ACK(3)
Handover CMD(4)
Handover Access(5)
Handover Detect(6)
PHY INFO(7)
UA(10)
SABM(8)
EST IND(9)
Handover Complete(11) Handover Performed(12)
MS BTS2 BSC BTS1 MSC
Measurement Report from MS(1)
MS
Channel ACT(2)
Channel ACT ACK(3)
Handover CMD(4)
Handover Access(5)
Handover Detect(6)
PHY INFO(7)
UA(10)
SABM(8)
EST IND(9)
Handover Complete(11) Handover Performed(12)
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GSM TCH Congestion Rate Optimization Delivery Guide For internal use
5.3 Incoming BSC Handover Channel Seizure Process
MS Other BTS Other BSC HUWEI BSC
Measurement Report
from MS(1)
HUAWEI BTS
Channel ACT ACK(5)
Handover RQD(2)Handover REQ(3)
MSC
Channel ACT(4)
Handover REQ
ACK (6)Handover CMD(7)
HANDOVER COMMAND(8)Handover Access(9)
Handover Detect(10)Handover Detect(11)
PHY INFO(12)
PHY INFO(13)
SABM(14)Establish IND(15)
UA(16)
HANDOVER CMP(17)Handover CMP(18)Clear CMD(19)
MS
Clear CMP(20)
MS Other BTS Other BSC HUWEI BSC
Measurement Report
from MS(1)
HUAWEI BTS
Channel ACT ACK(5)
Handover RQD(2)Handover REQ(3)
MSC
Channel ACT(4)
Handover REQ
ACK (6)Handover CMD(7)
HANDOVER COMMAND(8)Handover Access(9)
Handover Detect(10)Handover Detect(11)
PHY INFO(12)
PHY INFO(13)
SABM(14)Establish IND(15)
UA(16)
HANDOVER CMP(17)Handover CMP(18)Clear CMD(19)
MS
Clear CMP(20)
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