Call Delay Optimization_R1.0

Call Delay Optimization

R1.0

Call Delay Optimization Internal Use Only▲

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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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Follow-up document: After reading this document, you may need the following 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


ZTE Confidential Proprietary © 2014 ZTE CORPORATION. All rights reserved. 1

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.



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.



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.



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.



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


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



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



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


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


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


CHAN ACTIV ACK 0.023 0.095 0.0546

ASSIGNMENT CMD 0.001 0.000 0.0157

EIND 0.620 0.428 0.3188



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.



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


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




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


00:01.0



00:01.0



00:01.0



00:01.0




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


00:00.7



00:00.7



00:00.7



00:00.7


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


00:00.7



00:00.7



00:00.7


17:40.2 BSSAP The CIPHER MODE COMMAND message 00:00.7

17:40.9 BSSAP The CIPHER MODE



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


00:00.0



00:00.0



00:00.0



00:00.0


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



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




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




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.



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


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


16:09:14.6 BSSAP The PAGE RESPONSE Receive



Time Entity Type

Message Directio

n Remarks

6 message

16:09:14.67


16:09:14.67

BSSAP The SETUP message Send

16:09:14.90


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


message Receive

16:09:15.72


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


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.



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


23:49:14.18


23:49:14.18

BSSAP The CM SERVICE ACCEPT message

Send

23:49:14.41


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



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


23:49:16.02


23:49:17.38

BSSAP The PAGE RESPONSE

message Receive

23:49:17.39


23:49:17.39

BSSAP The SETUP message Send

23:49:17.66


message Receive

23:49:18.61

BSSAP The CALL CONFIRMED message

Receive

23:49:18.63


Send

23:49:18.70


message Receive

23:49:18.71


Send

23:49:18.80


message Receive

23:49:18.80


Send Assigning the originating call

23:49:19.49


Receive The assignment of originating call is completed.

23:49:19.49


Send Assigning the terminating call

23:49:20.17


Receive The assignment of terminating call is completed.

23:49:20.3 BSSAP The ALERTING message Receive



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.



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



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



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


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



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.



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


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.



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


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



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.



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

…



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

Call Delay Optimization_R1.0

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