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Call Delay Optimization
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Revision History
Product Version Document Version Serial Number Reason for Revision
R1.0 First published
Author
Date Document Version Prepared
by Reviewed by Approved by
2011-12-07 R1.0 Wang Xiaohui
Zheng Hao Wang Zhenhai
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Intended audience: GSM network optimization engineers
Proposal: Before reading this document, you had better have the following knowledge and skills.
SEQ Knowledge and skills Reference material
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2
3
Follow-up document: After reading this document, you may need the following information.
SEQ Reference material Information
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About This Document
Summary
Chapter Description
1 GSM Call Delay Definition Introduces the call delay definition.
2 GSM Call Delay Analysis Introduces the origination and termination signaling flow related to the call delay and analyze the factors affecting the call delay.
3 GSM Call Delay Optimization Scheme
Describes the measures of call delay optimization.
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TABLE OF CONTENTS
1 GSM Call Delay Definition ........................................................................... 1
2 GSM Call Delay Analysis ............................................................................. 1 2.1 GSM Call Flow .............................................................................................. 1 2.1.1 Origination Signaling Flow ............................................................................. 1 2.1.2 Termination Signaling Flow ............................................................................ 2 2.2 Comparison of Call Delays of Different Service Models ................................... 3 2.3 Comparison of Time Delays of All the GSM Sites............................................ 4
3 GSM Call Delay Optimization Scheme ........................................................ 6 3.1 Call Flow Optimization ................................................................................... 6 3.1.1 Simplest Call Flow ......................................................................................... 6 3.1.2 Influence on Delay of Optional Processes....................................................... 6 3.2 CN Assignment Flow Optimization ................................................................. 9 3.2.1 Early Assignment Flow .................................................................................. 9 3.2.2 Late Assignment Flow (The Function Against Missing Call not Being
Enabled) ..................................................................................................... 11 3.2.3 Late Assignment Flow (The Function Against Missing Call Being Enabled) .... 13 3.3 Parameter Optimization ............................................................................... 15 3.3.1 Number of Paging Multi-Frames ................................................................... 15 3.3.2 Number of Reserved AGCH Blocks .............................................................. 17 3.3.3 Interval Between Two Paging Times of the CN ............................................. 17 3.3.4 Assignment Queuing ................................................................................... 18 3.4 System Version Optimization ....................................................................... 18 3.4.1 Optimization of Immediate Assignment Flow................................................. 18 3.4.2 Optimization of Connection Flow at the Abis Interface ................................... 19 3.4.3 BSC Packing Delay Optimization ................................................................. 21 3.4.4 BTS Packing Delay Optimization .................................................................. 22
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FIGURES
Figure 1-1 The Signaling Flow Related to Call Delay .........................................................1
Figure 2-1 Origination Signaling Flow ................................................................................1
Figure 2-2 Termination Signaling Flow ..............................................................................2
Figure 2-3 Call Delays of Different Termination Objects .....................................................4
Figure 3-1 Paging Responding Time ............................................................................... 15
Figure 3-2 Paging Success Rate ..................................................................................... 16
Figure 3-3 Paging Success Rate Min Value Per Day ....................................................... 16
Figure 3-4 Flow of Two-Paging Mechanism ..................................................................... 17
Figure 3-5 Flow of Assignment Queuing .......................................................................... 18
Figure 3-6 Immediate Assignment Flow Before Optimization ............................................ 18
Figure 3-7 Immediate Assignment Flow After Optimization............................................... 19
The Figure 3-8 Connection Flow at the Abis Interface Before Optimization ....................... 19
Figure 3-9 Connection Flow at the Abis Interface After Optimization ................................. 20
Figure 3-10 BSC Packing Principle ................................................................................. 21
TABLES
Table 2-1 Intervals Between Signaling Points of Call Delay ................................................4
Table 3-1 Simplest Origination Flow ..................................................................................6
Table 3-2 Simplest Termination Flow ................................................................................6
Table 3-3 Delay of Authentication Flow (1 s)......................................................................7
Table 3-4 Delay of IMEI Query flow (0.7 s) ........................................................................7
Table 3-5 Delay of Encryption Flow (0.7 s) ........................................................................7
Table 3-6 Delay of Classmark Query Flow (0 s) .................................................................8
Table 3-7 Influence on the Call Delay of Different Flows ....................................................8
Table 3-8 Call Delays of These Assignment Flows ............................................................9
Table 3-9 Early Assignment Flow ......................................................................................9
Table 3-10 Late Assignment Flow (The Function Against Missing Call not Being Enabled) 11
Table 3-11 Late Assignment Flow (The Function Against Missing Call Being Enabled) ..... 13
Table 3-12 Test Effects Comparison ............................................................................... 21
Table 3-13 Call Delay Test Comparision Result ............................................................... 22
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1 GSM Call Delay Definition
Call delay is used to evaluate the time from the call initiation to alerting. It is one of the
KPIs reflecting the user’s perception. On the signaling point, the statistics of process from
the originating MS sending the CHANNEL REQUEST message to receiving the
ALERTING message is made, as shown in the following figure (the red arrow).
Figure 1-1 The Signaling Flow Related to Call Delay
The call delay relates to the origination and termination signaling flow, equipment type,
assignment mode of the CN, and test method. The analysis and comparison of the
factors affecting the call delay are demonstrated in the following contents.
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2 GSM Call Delay Analysis
2.1 GSM Call Flow
2.1.1 Origination Signaling Flow
In the origination flow, the process from sending the CHANNEL REQUEST message to
receiving the ALERTING message is relevant to the call delay. This process includes the
origination SD assignment, classmark query, authentication, encryption, IMEI query, call
establishment, and TCH channel assignment. During these processes, the four
processes of classmark query, authentication, encryption, and IMEI query are optional.
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Figure 2-1 Origination Signaling Flow
MS BTS BSC MSC
CHANNEL REQCHANNEL RQD
CHANNEL ACT
CHANNEL ACT ACK
CM SERVICE ACCEPTED
SETUP
IMM ASSIGNMENT CMD
SABM
UAEST IND(CM SERVICE REQ)
CR
CC
CALL PROCEEDING
CLEAR CMD
CLEAR CMP
CHANNEL REL
DEACTIVE SACCHDISC
UA RELEASE INDICATION
RF CHANNEL REL
RF CHANNEL REL ACK
RLSD
RLSD CMP
SABM
UA
ASSIGNMENT REQCHANNEL ACT
CHANNEL ACT ACK
ASSIGNMENT CMD
EST IND
ASSIGNMENT CMPASSIGNMENT CMP
ALERTING
CONNECT
CONNECT ACK
DISCONNECT
RELEASE
RELEASE CMP
TALKING
AUTHENTICATION REQUEST
AUTHENTICATION RESPONSE
CIPHER MODE CMD
CIPHER MODE CMP
CIPHER MODE CMD
IDENTITY REQUEST
IDENTITY RESPONSE
CLASSMARK REQUEST
CLASSMARK UPDATE
2.1.2 Termination Signaling Flow
After the origination SETUP message is received by the CN, the CN starts the
termination paging. After the termination alerting, the MS receives the Alerting message.
Therefore, the termination flow should be considered.
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In the termination flow, the process from paging message to alerting is relevant to the call
delay. This process includes the origination SD assignment, classmark query,
authentication, encryption, IMEI query, call establishment, and TCH channel assignment.
During these processes, the four processes of classmark query, authentication,
encryption, and IMEI query are optional.
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Figure 2-2 Termination Signaling Flow
MS BTS BSC MSC
CHANNEL REQCHANNEL RQD
CHANNEL ACT
CHANNEL ACT ACK
CM SERVICE ACCEPTED
SETUP
IMM ASSIGNMENT CMD
SABM
UAEST IND(PAGING RESPONSE)
CR
CC
CALL CONFIRMED
CLEAR CMD
CLEAR CMP
CHANNEL REL
DEACTIVE SACCHDISC
UA RELEASE INDICATION
RF CHANNEL REL
RF CHANNEL REL ACK
RLSD
RLSD CMP
SABM
UA
ASSIGNMENT REQCHANNEL ACT
CHANNEL ACT ACK
ASSIGNMENT CMD
EST IND
ASSIGNMENT CMPASSIGNMENT CMP
ALERTING
CONNECT
CONNECT ACK
DISCONNECT
RELEASE
RELEASE CMP
TALKING
PAGINGPAGING CMD
PAGING REQ
AUTHENTICATION REQUEST
AUTHENTICATION RESPONSE
CIPHER MODE CMD
CIPHER MODE CMP
CIPHER MODE CMD
IDENTITY REQUEST
IDENTITY RESPONSE
CLASSMARK REQUEST
CLASSMARK UPDATE
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2.2 Comparison of Call Delays of Different Service
Models
In the actual test, because the handing methods for different termination objects of the
CN are different, the call delays of different termination objects are different. In the
following figure, the delays of mobile phone calling mobile phone, mobile phone calling
the fixed-line telephone, and mobile phone calling the virtual number are described.
Figure 2-3 Call Delays of Different Termination Objects
2.3 Comparison of Time Delays of All the GSM Sites
The equipment in the existing network has the following three kinds of configuration.
ZTE CN + iBSC + BTS V3
ZTE CN + BSC + BTS V3
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ZTE CN + iBSC + SDR
The engineers make the dialing test in three kinds of configuration respectively and the
intervals between the signaling points of call delay are shown in the following table.
Table 2-1 Intervals Between Signaling Points of Call Delay
iBSC + SDR iBSC + B8018 BSC + B8018
CHANNEL REQUIRED
CHANNEL ACTIVATION 0.000 0.000 0.0031
CHAN ACTIV ACK 0.024 0.109 0.0235
IASS IMME ASSIGN 0.000 0.000 0.0016
EIND 0.262 0.340 0.2966
CIPH MODE CMD 0.024 0.051 0.0501
CLASSM CHANGE 0.193 0.184 0.1845
CIPH MODE COMP 0.488 0.471 0.4686
SETUP 0.471 0.473 0.575
CALL PROCEED 0.025 0.042 0.0438
CHANNEL ACTIVATION 3.317 3.986 2.9736
CHAN ACTIV ACK 0.026 0.116 0.0232
ASSIGNMENT CMD 0.000 0.000 0
EIND 0.571 0.380 0.4299
ASSIGN COMPL 0.104 0.099 0.2046
ALERTING 0.313 0.172 0.2967
Average time of the originating call
5.818 6.423 5.5748
PAGING CMD 0.000 0.101 0
CHANNEL REQUIRED 1.238 1.429 0.66
CHANNEL ACTIVATION 0.001 0.001 0.0046
CHAN ACTIV ACK 0.026 0.105 0.0363
IMME ASSIGN 0.000 0.000 0.0078
PAGE RESPONSE 0.288 0.370 0.278
CIPH MODE CMD 0.030 0.048 0.0891
CLASSM CHANGE 0.204 0.187 0.1732
CIPH MODE COMP 0.470 0.466 0.4862
SETUP 0.031 0.050 0.0609
CALL CONFIRMED 0.678 0.896 0.6155
CHANNEL ACTIVATION 0.139 0.236 0.1313
CHAN ACTIV ACK 0.023 0.095 0.0546
ASSIGNMENT CMD 0.001 0.000 0.0157
EIND 0.620 0.428 0.3188
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iBSC + SDR iBSC + B8018 BSC + B8018
ASSIGN COMPL 0.163 0.088 0.1936
ALERTING 0.179 0.101 0.3173
Average time of terminating call
4.091 4.500 3.4429
The main differences of the three kinds of configuration are described as follows.
Delay between the channel activation and activation response
The delays of the B8018s in the SDR and BSC are similar and the delay of the
B8018 in the iBSC is long.
Paging responding time
The paging response time of the B8010 in the BSC is the shortest and the paging
response time of the B8018s in the SDR and iBSC is long.
The causes of the differences are listed as follows.
The signaling interaction delay of the B8018 in the iBSC is long, which is caused by
the CMB forwarding the signaling.
Because of using the IP mode, the signaling transmission is fast in the SDR.
Because the signaling is transferred between the BSC and FUC and it is not
forwarded by the CMB, the signaling transmission is fast in the BSC.
Because the B8018 adopts the central paging mode in the iBSC and the signaling is
forwarded by the CMB, the paging responding time is quite long.
The SDR also adopts the central paging and the signaling is forwarded by CC.
Before of the advantage of the IP transmission method, the paging responding time
in the SDR is shorter than that of the B8018 in the iBSC.
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3 GSM Call Delay Optimization Scheme
3.1 Call Flow Optimization
3.1.1 Simplest Call Flow
The call flow optimization means to delete the optional flows (Classmark query,
authentication, encryption, and IMEI query) in the call initiation process. The simplest
flow is shown as follows.
Table 3-1 Simplest Origination Flow
Time Direction Protocol Message
09:10.3 UL MM The CM SERVICE REQUEST
message
09:10.4 UL RR The CHANNEL REQUEST message
09:10.6 DL RR The IMMEDIATE ASSIGNMENT
message
09:10.8 UL RR The CLASSMARK CHANGE
message
09:11.1 DL MM The CM SERVICE ACCEPT message
09:11.1 UL CC The SETUP message
09:12.0 DL CC The CALL PROCEEDING message
09:14.6 DL RR The ASSIGNMENT COMMAND
message
09:14.7 UL RR The ASSIGNMENT COMPLETE
message
09:15.3 DL CC The ALERTING message
Table 3-2 Simplest Termination Flow
Time Direction Protocol Message
09:12.2 DL RR The PAGING REQUEST TYPE 1
message
09:12.8 UL RR The CHANNEL REQUEST message
09:13.0 DL RR The IMMEDIATE ASSIGNMENT
message
09:13.0 UL RR The PAGING RESPONSE message
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Time Direction Protocol Message
09:13.3 UL RR The CLASSMARK CHANGE message
09:13.7 DL CC The SETUP message
09:13.7 UL CC The CALL CONFIRMED message
09:14.7 DL RR The ASSIGNMENT COMMAND message
09:14.8 UL RR The ASSIGNMENT COMPLETE
message
09:15.0 UL CC The ALERTING message
3.1.2 Influence on Delay of Optional Processes
The optional processes, including Classmark query, authentication, encryption, and IMEI
query, are controlled at the CN. The delays of these processes in the CN statistics are
accurate, as shown in the following tables.
Table 3-3 Delay of Authentication Flow (1 s)
Time Tracing
Entity Type Message Delay
14:53:10 BSSAP The AUTHENTICATION REQUEST message
00:01.0
14:53:11 BSSAP The AUTHENTICATION RESPONSE message
14:55:23 BSSAP The AUTHENTICATION REQUEST message
00:01.0
14:55:24 BSSAP The AUTHENTICATION RESPONSE message
14:57:35 BSSAP The AUTHENTICATION REQUEST message
00:01.0
14:57:36 BSSAP The AUTHENTICATION RESPONSE message
14:59:48 BSSAP The AUTHENTICATION REQUEST message
00:01.0
14:59:49 BSSAP The AUTHENTICATION RESPONSE message
15:02:00 BSSAP The AUTHENTICATION REQUEST message
00:01.0
15:02:01 BSSAP The AUTHENTICATION RESPONSE message
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Table 3-4 Delay of IMEI Query flow (0.7 s)
Time Tracing
Entity Type Message Delay
09:46.4 BSSAP The IDENTITY REQUEST message
00:00.7
09:47.2 BSSAP The IDENTITY RESPONSE message
09:49.9 BSSAP The IDENTITY REQUEST message
00:00.7
09:50.6 BSSAP The IDENTITY RESPONSE message
10:25.2 BSSAP The IDENTITY REQUEST message
00:00.7
10:26.0 BSSAP The IDENTITY RESPONSE message
11:00.7 BSSAP The IDENTITY REQUEST message
00:00.7
11:01.3 BSSAP The IDENTITY RESPONSE message
13:18.6 BSSAP The IDENTITY REQUEST message
00:00.7
13:19.3 BSSAP The IDENTITY RESPONSE message
Table 3-5 Delay of Encryption Flow (0.7 s)
Time Tracing Entity Type Message Delay
15:29.2 BSSAP The CIPHER MODE COMMAND message
00:00.7
15:30.0 BSSAP The CIPHER MODE COMPLETE message
16:08.8 BSSAP The CIPHER MODE COMMAND message
00:00.7
16:09.5 BSSAP The CIPHER MODE COMPLETE message
16:24.6 BSSAP The CIPHER MODE COMMAND message
00:00.7
16:25.3 BSSAP The CIPHER MODE COMPLETE message
16:38.5 BSSAP The CIPHER MODE COMMAND message
00:00.7
16:39.2 BSSAP The CIPHER MODE COMPLETE message
17:40.2 BSSAP The CIPHER MODE COMMAND message 00:00.7
17:40.9 BSSAP The CIPHER MODE
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Time Tracing Entity Type Message Delay
COMPLETE message
Classmark query can be made at the same with authentication and IMEI query and its
delay is quite short, 0 s.
Table 3-6 Delay of Classmark Query Flow (0 s)
Time Tracing Entity
Type Message Delay
14:53:10 BSSAP The CLASSMARK REQUEST message
00:00.0
14:53:10 BSSAP The CLASSMARK UPDATE message
14:53:15 BSSAP The CLASSMARK REQUEST message
00:00.0
14:53:15 BSSAP The CLASSMARK UPDATE message
14:55:23 BSSAP The CLASSMARK REQUEST message
00:00.0
14:55:23 BSSAP The CLASSMARK UPDATE message
14:55:27 BSSAP The CLASSMARK REQUEST message
00:00.0
14:55:27 BSSAP The CLASSMARK UPDATE message
14:57:40 BSSAP The CLASSMARK REQUEST message
00:00.0
14:57:40 BSSAP The CLASSMARK UPDATE message
Judging from the above comparison, the influence on the call delay of different flows is
demonstrated in the following table.
Table 3-7 Influence on the Call Delay of Different Flows
Flow Corresponding Signaling Point Delay (s)
Authentication Authentication Request -> Authentication Response
1.0
Encryption Cipher Mode Command -> Cipher Mode Complete
0.7
IMEI query Identity Request -> Identity Response 0.7
Classmark query
Classmark Enquiry -> Classmark Change 0.0
Judging from the above table, the authentication, encryption, and IMEI query flows affect
the delay greatly. The specific value differs because of different equipment and
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environments. The delays in the above table are the single-flow delays. If the flow is
included in both the origination and termination, the affected delay will be two times of the
affected delay of single flow. The IMEI query flow can be set to be periodical in the CN.
This flow is not made for each call and it needs the support from the CN.
3.2 CN Assignment Flow Optimization
There are three kinds of common assignment flows: early assignment flow, late
assignment flow (the function against missing call not being enabled), and late
assignment flow (the function against missing call being enabled). The call delays of
these assignment flows are shown in the following table.
Table 3-8 Call Delays of These Assignment Flows
Signaling point
Early Assignment
Flow
Late Assignment Flow (The Function Against Missing Call not Being
Enabled)
Late Assignment Flow (The Function Against
Missing Call Being Enabled)
Setup 14:53:12 16:09:13 23:49:15
Alerting 14:53:16 16:09:17 23:49:20
Delay 0:00:04 0:00:04 0:00:05
The differences of the CN flows mainly lay between the setup and alerting. Therefore, the
delays of different assignment flows of this process are compared. The delay of late
assignment flow (the function against missing call being enabled) is 1 s longer than that
of early assignment and late assignment (the function against missing call not being
enabled).Therefore, from the aspect of delay reduction, it is suggested that the early
assignment flow or late assignment flow (the function against missing call not being
enabled) should be adopted.
3.2.1 Early Assignment Flow
The early assignment flow means that the originating call is assigned after the
terminating paging is delivered. Compared with the late assignment flow (the function
against missing call being enabled), the delay of early assignment flow is 1 s shorter.
Table 3-9 Early Assignment Flow
Time Direction Message Remarks
14:53:10
>TRC_MI_FROM_A
The CM_SERVICE_REQUEST message
Receiving the first message from the radio side
14:53:10
<TRC_MI_TO_A
The CLASSMARK_REQUEST
message
14:53:10
<TRC_MI_TO_A
The AUTHENTICATION_REQUES
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Time Direction Message Remarks
T message
14:53:10
>TRC_MI_FROM_A
The CLASSMARK_UPDATE
message
14:53:10
>TRC_MI_FROM_A
The CLASSMARK_UPDATE message
14:53:11
>TRC_MI_FROM_A
The AUTHENTICATION_RESPONSE message
14:53:11
<TRC_MI_TO_A
The CM_SERVICE_ACCEPT message
14:53:12
>TRC_MI_FROM_A
The SETUP message Starting the internal flow
14:53:12
<TRC_MI_TO_A
The CALL_PROCEEDING
message
14:53:12
<TRC_MI_TO_C_D_F
The MAP_OPEN_REQ message
14:53:12
<TRC_MI_TO_C_D_F
The MAP_SEND_ROUTING_
INFORMATION_REQ
message
14:53:12
<TRC_MI_TO_C_D_F
The MAP_DELIMITER_REQ message
14:53:13
>TRC_MI_FROM_C_D_F
The MAP_PROVIDE_ROAMING_NUMBER_IND message
14:53:13
<TRC_MI_TO_C_D_F
The MAP_PROVIDE_ROAMING_NUMBER_RSP message
14:53:13
<TRC_MI_TO_C_D_F
The MAP_CLOSE_REQ message
14:53:12
<TRC_MI_TO_H248
The ADD_REQ message
14:53:13
>TRC_MI_FROM_H248
The ADD_REPLY message
14:53:12
>TRC_MI_FROM_C_D_F
The MAP_OPEN_CNF message
14:53:12
>TRC_MI_FROM_C_D_F
The MAP_SEND_ROUTING_
INFORMATION_CNF message
14:53:12
>TRC_MI_FROM_C_D_F
The MAP_CLOSE_IND message
14:53: <TRC_MI_ The Paging message Terminating paging
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Time Direction Message Remarks
13 TO_A
14:53:12
<TRC_MI_TO_A
The ASSIGNMENT_REQUEST
message
Assigning the originating call after the terminating paging
14:53:13
>TRC_MI_FROM_A
The ASSIGNMENT_COMPLETE
message
The assignment of originating call is completed.
14:53:15
>TRC_MI_FROM_A
The PAGING_RESPONSE
message
14:53:15
<TRC_MI_TO_A
The CLASSMARK_REQUEST message
14:53:15
<TRC_MI_TO_A
The SETUP message
14:53:15
>TRC_MI_FROM_A
The CLASSMARK_UPDATE
message
14:53:16
>TRC_MI_FROM_A
The CLASSMARK_UPDATE message
14:53:16
>TRC_MI_FROM_A
The CALL_CONFIRMED
message
14:53:15
<TRC_MI_TO_H248
The ADD_REQ message
14:53:16
<TRC_MI_TO_A
The ASSIGNMENT_REQUEST
message Assigning the terminating call
14:53:15
>TRC_MI_FROM_H248
The ADD_REPLY message
14:53:17
<TRC_MI_TO_H248
The ADD_REQ message
14:53:17
>TRC_MI_FROM_A
The ASSIGNMENT_COMPLETE
message
The assignment of terminating call is completed.
14:53:17
>TRC_MI_FROM_A
The ALERT message
14:53:16
<TRC_MI_TO_A
The ALERT message Originating call alerting
3.2.2 Late Assignment Flow (The Function Against Missing Call not Being
Enabled)
The late assignment flow adopted for the CN of ZTE is described as follows. In the TCH
assignment stage, the origination and termination are made at almost at the same time.
Compared with the late assignment flow (the function against missing call being enabled),
the delay of the late assignment flow (the function against missing call not being enabled)
is 1 s shorter.
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Table 3-10 Late Assignment Flow (The Function Against Missing Call not Being Enabled)
Time Entity Type
Message Directio
n Remarks
16:09:12.17
BSSAP The CM SERVICE REQUEST message
Receive
Receiving the first message from the radio side
16:09:12.18
BSSAP The COMMON ID message Send
16:09:12.18
BSSAP The CM SERVICE ACCEPT message
Send
16:09:12.41
BSSAP The CLASSMARK UPDATE
message Receive
16:09:13.11
BSSAP The SETUP message Receive Starting the internal flow
16:09:13.12
MSCMAP
The MAP OPEN REQUEST message
Send
16:09:13.12
BSSAP The CALL PROCEEDING
message Send
16:09:13.12
MSCMAP
The SEND ROUTING INFO REQUEST message
Send
16:09:13.12
MSCMAP
The MAP DELIMITER REQUEST message
Send
16:09:13.30
VLRMAP The MAP OPEN INDICATION message
Receive
16:09:13.30
VLRMAP The MAP OPEN RESPONSE message
Send
16:09:13.30
VLRMAP
The PROVIDE ROAM NUMBER REQUEST
message Receive
16:09:13.30
VLRMAP
The PROVIDE ROAM NUMBER RESPONSE
message Send
16:09:13.30
VLRMAP The MAP CLOSE REQUEST message
Send
16:09:13.43
MSCMAP
The MAP OPEN CONFIRM
message Receive
16:09:13.43
MSCMAP
The SEND ROUTING INFO RESPONSE message
Receive
16:09:13.43
BSSAP The PAGING message Send Terminating paging
16:09:13.43
BSSAP The PAGING message Send
16:09:13.43
BSSAP The PAGING message Send
16:09:14.6 BSSAP The PAGE RESPONSE Receive
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Time Entity Type
Message Directio
n Remarks
6 message
16:09:14.67
BSSAP The COMMON ID message Send
16:09:14.67
BSSAP The SETUP message Send
16:09:14.90
BSSAP The CLASSMARK UPDATE
message Receive
16:09:15.60
BSSAP The CALL CONFIRMED message
Receive
16:09:15.61
H248 The EVT_H248S_ADD_REQ message
Send
16:09:15.67
H248 The EVT_H248S_ADD_RPL
message Receive
16:09:15.67
BSSAP The ASSIGNMENT REQUEST message
Send Assigning the terminating call
16:09:15.68
H248 The EVT_H248S_ADD_REQ
message Send
16:09:15.72
H248 The EVT_H248S_ADD_RPL
message Receive
16:09:15.72
BSSAP The ASSIGNMENT REQUEST message
Send Assigning the originating call
16:09:16.30
BSSAP The ASSIGNMENT COMPLETE message
Receive The assignment of terminating call is completed.
16:09:16.44
BSSAP The ASSIGNMENT COMPLETE message
Receive The assignment of originating call is completed.
16:09:16.56
BSSAP The ALERTING message Receive
16:09:16.56
H248 The EVT_H248S_MODIFY_REQ
message Send
16:09:16.62
H248 The EVT_H248S_MOD_RPL message
Receive
16:09:16.62
BSSAP The ALERTING message Send Originating call alerting
3.2.3 Late Assignment Flow (The Function Against Missing Call Being
Enabled)
The late assignment flow (the function against missing call being enabled) means that the
terminating call is assigned after the originating call is successfully assigned. Compared
with the late assignment flow with the function against missing call not being enabled, the
delay of this late assignment flow is 1 s longer.
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Table 3-11 Late Assignment Flow (The Function Against Missing Call Being Enabled)
Time Entity Type
Message Directio
n Remarks
23:49:14.17
BSSAP The CM SERVICE REQUEST
message Receive
Receiving the first message from the radio side
23:49:14.18
BSSAP The COMMON ID message Send
23:49:14.18
BSSAP The CM SERVICE ACCEPT message
Send
23:49:14.41
BSSAP The CLASSMARK UPDATE
message Receive
23:49:15.11
BSSAP The SETUP message Receive Starting the internal flow
23:49:15.12
GSMSSF
The CAP OPEN REQUEST message
Send
23:49:15.12
BSSAP The CALL PROCEEDING
message Send
23:49:15.12
GSMSSF
The CAP INITIAL DP message
Send
23:49:15.12
GSMSSF
The CAP DELIMITER REQUEST message
Send
23:49:15.54
GSMSSF
The CAP OPEN CONFIRM
message Receive
23:49:15.54
GSMSSF
The CAP REQUEST REPORT BCSM EVENT
message Receive
23:49:15.55
GSMSSF
The CAP APPLY CHARGING
message Receive
23:49:15.56
GSMSSF
The CAP FURNISH CHARGING INFORMATION
message Receive
23:49:15.58
GSMSSF
The CAP CONTINUE message
Receive
23:49:15.58
MSCMAP
The MAP OPEN REQUEST
message Send
23:49:15.58
MSCMAP
The SEND ROUTING INFO REQUEST message
Send
23:49:15.58
MSCMAP
The MAP DELIMITER REQUEST message
Send
23:49:15.83
VLRMAP The MAP OPEN INDICATION
message Receive
23:49:15.83
VLRMAP The MAP OPEN RESPONSE message
Send
23:49:15.83
VLRMAP The PROVIDE ROAM NUMBER REQUEST
Receive
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Time Entity Type
Message Directio
n Remarks
message
23:49:15.83
VLRMAP
The PROVIDE ROAM NUMBER RESPONSE
message Send
23:49:15.83
VLRMAP The MAP CLOSE REQUEST message
Send
23:49:16.00
MSCMAP
The MAP OPEN CONFIRM
message Receive
23:49:16.00
MSCMAP
The SEND ROUTING INFO RESPONSE message
Receive
23:49:16.02
BSSAP The PAGING message Send Terminating paging
23:49:16.02
BSSAP The PAGING message Send
23:49:16.02
BSSAP The PAGING message Send
23:49:17.38
BSSAP The PAGE RESPONSE
message Receive
23:49:17.39
BSSAP The COMMON ID message Send
23:49:17.39
BSSAP The SETUP message Send
23:49:17.66
BSSAP The CLASSMARK UPDATE
message Receive
23:49:18.61
BSSAP The CALL CONFIRMED message
Receive
23:49:18.63
H248 The EVT_H248S_ADD_REQ message
Send
23:49:18.70
H248 The EVT_H248S_ADD_RPL
message Receive
23:49:18.71
H248 The EVT_H248S_ADD_REQ message
Send
23:49:18.80
H248 The EVT_H248S_ADD_RPL
message Receive
23:49:18.80
BSSAP The ASSIGNMENT REQUEST message
Send Assigning the originating call
23:49:19.49
BSSAP The ASSIGNMENT COMPLETE message
Receive The assignment of originating call is completed.
23:49:19.49
BSSAP The ASSIGNMENT REQUEST message
Send Assigning the terminating call
23:49:20.17
BSSAP The ASSIGNMENT COMPLETE message
Receive The assignment of terminating call is completed.
23:49:20.3 BSSAP The ALERTING message Receive
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Time Entity Type
Message Directio
n Remarks
1
23:49:20.32
H248 The EVT_H248S_MODIFY_REQ
message Send
23:49:20.39
H248 The EVT_H248S_MOD_RPL message
Receive
23:49:20.39
BSSAP The ALERTING message Send Originating call alerting
3.3 Parameter Optimization
3.3.1 Number of Paging Multi-Frames
According to the GSM protocol, each mobile user (corresponding to each IMSI) belongs
to one paging group. In each cell, every group corresponds to one sub paging channel.
The MS calculates the paging group that it belongs to according to the IMSI and then
calculates the location of the sub-paging channel of this paging group. In the actual
network, the MS only 'listens" to the sub-paging channel that it belongs to and ignores the
contents of other sub-paging channels.
The number of the multi-frames of the paging channel means how many multi-frames are
considered to be one loop of the sub-paging channel. Because the number of
multi-frames is larger, the interval between the sub-paging channels is large. That is to
say, the time from the paging being delivered by the CN to the MS receiving the paging is
quite long. Therefore, the call delay can be reduced if the engineers set the number of
paging multi-frames properly.
The following figure shows one comparison test made in the experimental environment.
Judging from this figure, the paging responding time differs. Generally speaking, the
larger the number of the paging multi-frames is, the longer the paging responding time is.
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Figure 3-1 Paging Responding Time
The default number of multi-frames of the network is 5. In some fields, such as the fields
of Ericsson, the number is set to 2.Judging from the field test result, after the number of
multi-frames is changed from 5 to 2, the average call time can be 0.6 s shorter.
In the condition of the maximum CS paging traffic being 150000 each day, after the
number of paging multi-frames is changed from 5 to 2, the paging success rate keeps
stable.
Figure 3-2 Paging Success Rate
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Figure 3-3 Paging Success Rate Min Value Per Day
3.3.2 Number of Reserved AGCH Blocks
Number of reserved AGCH blocks means the blocks used for the AGCH in 51
multi-frames. After the CCCH structure is fixed, this parameter is actually used to allocate
proportions occupied by the AGCH and PCH on the CCCH. The engineers can balance
the AGCH and PCH bearing conditions through adjusting this parameter. Usually, the
engineers can reduce the value of this parameter to shorten the paging responding time
of the MS, with the prerequisite of no overloading on the AGCH.
Right now, the preemption mechanism is adopted for the BTS. The messages needing to
be delivered on the AGCH will preempt the PCH and be delivered. Therefore, it is
suggested to set the number of the reserved AG blocks to be 0.
3.3.3 Interval Between Two Paging Times of the CN
The two paging mechanism is adopted for the CN. If the paging response is not received
after N s of the first paging being delivered, the second paging will be delivered. The flow
is shown in the following figure.
78.00%
80.00%
82.00%
84.00%
86.00%
88.00%
90.00%
92.00%
94.00%
96.00%
Paging Success Rate Min value per day
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Figure 3-4 Flow of Two-Paging Mechanism
MS BTS BSC MSC
PAGING
PAGING CMDPAGING REQ
PAGINGPAGING CMD
PAGING REQ
No Paging Response
In the test, sometimes, the response appears after the second paging. Then one paging
interval is added to the delay and the whole call delay is affected. Therefore, it is
necessary to check whether the interval between the two paging times is reasonable.
Usually, it is required that the interval should be longer than the maximum access
attempting time at the radio side and it should be no longer than 6 s.
3.3.4 Assignment Queuing
During the cell congestion, if the function of allowing the assignment queuing is enabled,
the MS will perform the queuing and wait for the TCH resource allocation. The flow is
shown in the following figure.
Figure 3-5 Flow of Assignment Queuing
MS BTS BSC MSC
SABM
UA
ASSIGNMENT REQ
CHANNEL ACT
CHANNEL ACT ACK
ASSIGNMENT CMD
EST IND
ASSIGNMENT CMPASSIGNMENT CMP
No radio resource, queuing
The waiting time of queuing is about 0 ~ 5 s. After the queuing is completed successfully,
the call duration is much longer. Therefore, if the call that is abnormally long appears, it is
necessary to check whether the assignment queuing exists in the assignment
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measurement. If the queuing exists, it is suggested to increase the radio resources
through capacity expansion and HR activating, so as to reduce the chance of queuing
during the call.
3.4 System Version Optimization
3.4.1 Optimization of Immediate Assignment Flow
In the immediate assignment flow, the immediate assignment message can be sent at
the time of sending the channel activation message to the BTS. For the immediate
assignment process, the connection process at the Abis interface is unnecessary.
The flow before the optimization is shown in the following figure.
Figure 3-6 Immediate Assignment Flow Before Optimization
MS BTS BSC
Channel Request
Channel Activation
Channel Active Ack
100ms
Channel Required
Imm Assign
SABM
UAEstablish Indication
280msImm Assign
MSC
Immediate Assignment Flow at the Abis Interface
The flow after the optimization is shown in the following figure.
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Figure 3-7 Immediate Assignment Flow After Optimization
Immediate Assignment Optimization
Flow at the Abis Interface
MS BTS BSC MSC
Channel Request
Channel Activation
Channel Active Ack
100ms
Channel Required
Imm Assign
SABM
UAEstablish Indication
280ms
Imm Assign
Judging from the above figure, if the assignment process at the Abis interface is to be
optimized, make the optimization at the same time of the channel activation. Then the call
delay will be 100 ms shorter.
The above analysis is based on the condition of the Abis interface being the E1
transmission. If the Abis interface is IP transmission, the delay will not be compressed,
because the message interaction process at the Abis interface is quite short in the IP
mode (20 ms for a round). For the satellite site, the delay is much shorter and the SD
assignment success rate can be enhanced.
In iBSCV6.20.200fp10 and later versions, this function is realized. In iBSCV6.20.61, the
OMC system control parameters can be modified directly.
3.4.2 Optimization of Connection Flow at the Abis Interface
For the BTS of iBSC + E1, it is necessary to make the Abis connection before the TCH
activation.
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The Figure 3-8 Connection Flow at the Abis Interface Before Optimization
MS BTS BSC MSC
CMM Connection ResponseChannel Activation
Channel Active Ack100ms
Assign Cmd
SABM
UAEstablish Indication
320ms
CMM Connection
Command
Assignment Request
90ms
Connection Flow at the Abis Interface
Assign Cmd
Because the packing delay of the LAPD is quite long, the delay of the message exchange
at the Abis interface is long. The interaction of one message needs the time longer than
70 ms. What is more, the connection at the Abis interface is not closely related to the
channel activation, so it is unnecessary to make the two operations in a serial mode.
What is more, the Abis connection is always successful. From the aspect of delay
reduction, the two operations can be made at the same time.
The delay at the Abis interface after the change is shown in the following figure.
Figure 3-9 Connection Flow at the Abis Interface After Optimization
Optimization of the Connection at
the Abis Interface
MS BTS BSC MSC
CMM Connection Response
Channel Activation
Channel Active Ack
100ms
Assign Cmd
SABM
UA Establish Indication
320ms
CMM Connection Command
Assignment Request
90ms
Assign Cmd
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Judging from the above figure, if the assignment process at the Abis interface is to be
optimized, make the optimization at the same time of the channel activation. Then the call
delay will be 90 ms shorter.
The above analysis is based on the condition of the Abis interface being the E1
transmission. If the Abis interface is IP transmission, the delay will not be compressed,
because the message interaction process at the Abis interface is quite short in the IP
mode (One round is 20 ms at most.).
In iBSCV6.20.61 and later versions, this function is realized. If the V2 BTS exists, the
version later than iBSCV6.20.614cp006 is needed. In iBSCV6.20.61, the OMC system
control parameters can be modified directly.
The comparison of the test effects before and after the two flows of immediate
assignment and connection are enabled at the same time.
Table 3-12 Test Effects Comparison
Before the Switch Is Turned on After the Switch Is Turned on
CM Service Request
Alerting Delay CM Service Request
Alerting Delay
09:01:21.613 09:01:27.392 00:05.8 08:00:38.500 08:00:42.680 00:04.2
09:04:55.921 09:04:59.968 00:04.0 08:04:10.700 08:04:15.304 00:04.6
09:08:27.596 09:08:32.620 00:05.0 08:07:43.735 08:07:48.168 00:04.4
09:15:39.663 09:15:44.714 00:05.1 08:11:15.783 08:11:19.831 00:04.0
09:19:12.598 09:19:17.526 00:04.9 08:14:47.643 08:14:52.202 00:04.6
09:22:45.706 09:22:50.030 00:04.3 08:18:20.731 08:18:24.943 00:04.2
09:26:17.658 09:26:22.597 00:04.9 08:21:52.871 08:21:57.711 00:04.8
09:29:50.721 09:29:55.529 00:04.8 08:25:25.658 08:25:30.223 00:04.6
09:33:23.613 09:33:28.428 00:04.8 08:28:57.818 08:29:03.126 00:05.3
09:36:56.657 09:37:02.812 00:06.2 08:32:30.686 08:32:35.338 00:04.7
09:40:30.720 09:40:35.771 00:05.1 08:36:03.678 08:36:07.998 00:04.3
09:44:03.788 09:44:08.099 00:04.3 08:39:35.638 08:39:40.366 00:04.7
09:47:35.668 09:47:39.827 00:04.2 08:43:08.738 08:43:15.790 00:07.1
09:51:07.671 09:51:12.423 00:04.8 08:46:43.711 08:46:49.170 00:05.5
09:54:40.679 09:54:45.834 00:05.2 08:50:16.761 08:50:20.422 00:03.7
09:58:13.907 09:58:18.709 00:04.8 08:53:48.693 08:53:53.086 00:04.4
Average Delay
00:04.9
00:04.7
Judging from the above table, the average delay is 200 ms shorter.
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3.4.3 BSC Packing Delay Optimization
According to the communication overhead feature of the signaling transmission on the
control plane of iBSC and the 20-bite payload mode of common signaling, the overhead
of the IP head is large, which affects the throughput capability and capacity handling of
the CMP control plane greatly. Therefore, it is necessary to pack the signaling of the Abis
control plan, so as to reduce the impact of the overhead of the IP head. According to the
maximum bite number (260 bites) of the LAPD frame, the packing threshold is set to be
255 bites and the packing delay is also set. The principle is shown in the following figure.
Figure 3-10 BSC Packing Principle
The O&M messages should not be packed. The signaling messages and packing
messages are packed with the unit being rack. The SPB board creates independent
buffer areas for different racks and the organized data packages on the CMP will be put
into different buffer areas according to different targets. The paging messages are sent
only to the main rack of the BTS and the main rack CMM sends the paging messages to
the BCCH carriers of the racks.
Because the LAPD packing will make the call delay longer, the engineers optimize the
LAPD packing delay in iBSCV6.20.200fp005, so as to shorten the delay. The delay of the
signaling packing is changed to 10 ms to 30 ms and the delay of the paging packing is
changed to 50 ms to 30 ms. The engineers make the statistics of the traffic in the sending
direction of each site for every 2 s. If the traffic is lower than 2 KB/s, the signaling and
paging messages will not be packed. If the traffic is higher than 2 KB/s, the signaling and
paging messages will be packed.
The LAPD packing delay optimization can reduce the call delay for about 200 ms.
Protocol
identifier
Message
Type
Message
Length
Packing message body
Message
head
Message
body
… Message
head
Message
body
Message
Head 消
息
体
Message
Head
Message
body
Signaling or
paging message
信令或寻呼消息
Message
length
Maximum bite number of packing: 255
Packing
message
Making packing before the delay
Ethernet
Sending the message
during the delay
…
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3.4.4 BTS Packing Delay Optimization
There are three kinds of LAPD UL signaling: OAM message, measurement report, and
signaling message. The OAM messages are sent in the non-packing mode and have a
low priority; the measurement reports and signaling messages are sent in the packing
mode and the priority level of the signaling message is higher than that of the
measurement report.
One sending buffer queue is created for the measurement reports and signaling
messages. The request data sent by the Abis interface of upper level is put in the buffer
queue and the packing is made in the queue. Then the engineers use the regular
scanning task to put the packing data of the buffer queue in the corresponding priority
queue. The signaling message is put in the high-priority level sending queue and the
measurement report message is put in the low-priority level sending queue. The packing
mode is not used for the UL OAM messages and the UL OAM messages are not put in
the buffer queue but are directly put in the low-level priority sending queue and sent with
the measurement report messages.
Some changes of the packing flow are made in the BTS version (BTSV6.20.243n), so as
to shorten the call delay.
The test environments include V3 8018 site, iBSC, and AMR.
The call delay test comparison result is shown in the following table.
Table 3-13 Call Delay Test Comparision Result
Originating Call to 10010 (ms)
Originating Call to the MS (ms)
The LAPD packing switch being turned on
3434.59 6564.03
The LAPD packing switch being turned off
3522.26 6704.92
Delay at the Um interface being reduced
87.67 140.89