OMF010001 System Information ISSUE1.4

8/12/2019 OMF010001 System Information ISSUE1.4

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Wireless Curriculum Development SectionWireless Curriculum Development SectionWireless Curriculum Development Section

ISSUEISSUE

OMF010001System Information

OMF010001OMF010001System InformationSystem Information

1.41.4





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System information (SYS INFO) contains network parameters

sent to MS through air interface(Um), including network identity

parameters, cell selection parameters, system control

parameters and network function parameters. By reading system

information, MS can access the network, perform cell selection,

fully utilize various services provided by the network, and

achieve favorable cooperation with the network. SYS INFO can

be divided into two parts:

SYS INFO sent on BCCH, including SYS INFO 1, 2, 2BIS, 2TER,

3, and 4, which are used by MS in idle mode.

SYS INFO sent on SACCH, including system information 5, 5BIS,

5TER, and 6, which are used by MS in dedicated mode.

Additionally Huawei BSC supports the system information 7 and

13 to support GPRS.

System Information OverviewSystem Information Overview

BCCH system information belongs to common channel information. SACCH system

information basically belongs to TRX management information. Common channel

and TRX management information should be selected in order to observe all thesystem information when tracing on the layer 3 messages of radio interface.

Version G2BSC3203.0520B onwards, the system information 1, 2, 2TER, 3, 4, 5,

5TER, and 6 are default when system information is transmitted to cells. System

information 2BIS and 5BIS are conditionally transmitted on GSM1800 cells. It will be

explained in the following section.



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! SYS INFO 1! SYS INFO 1

"SYS INFO 1 - - Cell Channel Desc.

(cell channel description format)

- - RACH Control Parameter

(random access channel control parameter)

! Content! Content

SYS INFO 1SYS INFO 1

"It contains random access control information (RACH)

and cell frequency allocation table (i.e. CA table). It is

transmitted on BCCH.

The maximum number of cell frequencies configured in CA(Cell Allocation) is 64. Due

to the restriction of cell channel description format, the frequencies of a cell cannot be

configured unlimitedly.

The formats of cell channel description are determined respectively by Cell Channel

Description’s second byte Format ID (bit8, bit7, bit4, bit3, bit2).



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Bit8 Bit7 Bit4 Bit3 Bit2 Format TypeBit8 Bit7 Bit4 Bit3 Bit2 Format Type

0 0 X X X bit map 0

1 0 0 X X 1024 range

1 0 1 0 0 512 range

1 0 1 0 1 256 range

1 0 1 1 0 128 range

1 0 1 1 1 variable bit map

The above cell channel description formats correspond to different

requirements on the configured frequencies in a cell.

SYS INFO 1 - CA Description FormatSYS INFO 1 - CA Description Format

The CA ( channel allocation ) table frequency restriction is caused by different

description format; frequency here refers to M1800 frequency. M900 frequency is not

restricted, because it can always use the format “bit map 0”. Currently, Huawei BSCis able to select the formats automatically. The priority set for the formats are shown

as follow:

A. Bit map 0

B. Variable bit map

C. 1024 range

D. 512 range

E. 256 range

F. 128 range

Only when the previous bitmap format is not satisfied can the judgement of next

bitmap format goes on.

If none of the above formats is satisfied, format “1024 range” is used in the program

by default. This format can deliver up to 16 frequencies. No matter how the

frequencies are configured, they can be sent to BTS. But due to the restriction of

description format, some frequencies cannot be delivered to MS, this will cause

assignment failure.



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SYS INFO 1 - RACH Control ParameterSYS INFO 1 - RACH Control Parameter

! These control parameters include:

" Maximum re-transmitting times (MAX retrans)

" Extended transmission timeslots (Tx_interger)

" Cell Bar access (CBA, CELL_BAR_ACCESS)

" Common access control level(AC)

" Call reestablish permitted (RE)

" Emergency call permitted (EC)

These parameters will be explained in the following sections.



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SYS INFO 2

"It contains access control information (RACH), network color code

permitted (NCC Permitted), and neighbor cell frequency allocation list

(BA1 list). It is transmitted on BCCH. Generally speaking, SYS INFO

2, 2BIS, 2TER contains different parts of the neighbor cell BCCH

frequencies. Via reading and decoding BA1 list, MS can perform cell

reselection in idle mode. For a MS of GSM900 PHASE I, it only reads

the neighbor cell BCCH frequencies defined in SYS INFO 2, and

ignores those carried by 2BIS and 2TER.


! Content! Content

"SYS INFO 2 - - Neighbor Cell Desc.

- - NCC permitted


Neighbor cell description describes all the neighbor cells’ BCCH ARFCN. Currently,

Huawei supports 32 neighbor cells at most. Except the fifth bit (BA_IND) and sixth bit

(EXT_IND) of the second byte, the coding format of neighbor cell description is the

same as cell channel description.

Extended indication (EXT_IND) is transmitted in system information 2 and 5. It

indicates whether there are BCCH frequencies of neighbor cell transmitted in system

information 2BIS and 5BIS. It has one bit. If it is set to “0”, this indicates system

information 2 and 5 have carried all the BCCH frequencies (the same band as serving

cell’s )in the BA table. If it is “1”, it means system information 2 and 5 carries only part

of the content of BA table.

BA table indication (BA_IND) is transmitted in system information 2 and 5. It has one

bit and it is used to tell the MS to decide whether to use the data of BA1 or BA2 table.In other words, if the current neighbor cell relationship and BA2 table are modified

during the conversation of MS, BA_IND in system information 5 should be set to “1”

instead of “0”. It instructs MS to re-decode the neighbor cell frequency shown in the

system information to get the latest information.

Network Color Code Permitted (NCC Permitted) is transmitted on system information

2 and 6. It has eight bits.The eight bits are used to show if the particular NCC codes

are permitted for the MS to access. If bit N is set to “0” (0<=N<=7), the MS will not

measure the BCCH of the cell with NCC=N at all. Thus, the MS will not handover to

the cell with NCC=N.



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SYS INFO 2BIS

"2BIS contains RACH control data and neighbor cell BCCH

frequencies (part of BA1 list). It is optional and transmitted on

BCCH. As the number of frequencies in BA1 list carried by SYS

INFO 2 is limited; SYS INFO 2BIS carries the rest of the BCCH

frequencies in the BA1 list that are from the same band as in SYS

INFO 2.

! SYS INFO 2BIS! SYS INFO 2BIS

! Content! Content

SYS INFO 2BIS - - Neighbor Cell Desc.


(Same as that in SYS INFO 1.)

Note 1: Currently Huawei GSM BSS supports up to 32 neighbor cells. And for

GSM900 cells all these 32 neighbor cells’ BCCH can be transmitted via System

Information 2 while using bit map0. Therefor,BA1 table can be completely delivered tothe MS using system information 2. So, it is not necessary use System Information

2BIS.

Note 2: For GSM1800 cell, when the number of configured neighbor cells with the

same band is more than 16, it will send system message 2BIS.



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"2TER contains neighbor BCCH frequencies (part of BA1 list). It is

transmitted on BCCH. Only dual band MS can read this

information, and single band 900 or 1800 MS will ignore it. Since

this information carries BCCH frequencies that belong to different

band as those in SYS INFO 2, it is unnecessary for single band

MS to read.

"SYS INFO 2TER - - Neighbor Cell Desc. (extended)

! SYS INFO 2TER! SYS INFO 2TER

! Content! Content

SYS INFO 2TER SYS INFO 2TER

Except the fifth bit (BA_IND), sixth, and seventh bit (Multi-band reporting) of the

second byte, the coding of other information is the same with cell channel description.



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"It contains LAI, cell identity, RACH and parameters related to cell

selection. It is transmitted on BCCH. It is one of the most

important information in SYS INFO.

"SYS INFO 3 - - Cell Identity

- - LAI( location area identity)

- - Control Channel Desc

- - Cell Option BCCH

- - Cell Selection Parameter



! Content! Content




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Cell Identity and Location Area IdentityCell Identity and Location Area Identity

Cell Global Identity (CGI) consists of Location Area Identity (LAI) and

Cell Identity (CI). And LAI includes Mobile Country Code (MCC),

Mobile Network Code (MNC), and Location Area Code (LAC). SYS

INFO 3, 6, and 4 contain all or part of the information of CGI.

According to the received SYS INFO, MS decodes the CGI, and

decide whether it can register in the network based on the MCC and

MNC indicated by CGI. At the same time, it can judge whether the

current location area is changed, so as to decide whether it is

necessary to start the location updating process.

MCC is allocated globally. It consists of three decimal numbers. For example, China

is 460. MNC is allocated by the country. It consists of two decimal numbers. 00 is for

China Mobile, 01 is for China Unicom. LAC and CI are planned by each GSM networkoperator. They consist of two bytes. Please note that the value range of CI is 0X0001-

0XFFFE. 0X0000 and 0XFFFF are reserved for other use.



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Control Channel Description.Control Channel Description.

! Control channel description includes the following parameters

" IMSI Attach-Detach Allowed (ATT, Attach-Detach allowed)

" Common Control Channel Configuration (CCCH-CONF)

" Access Granted Blocks Reserved (BS_AG_BLKS_RES)

" Paging Channel Multi-frames (BS-PA-MFRAMS)

" Periodic Location Updating Timer (T3212)

They will be explained in details later.



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Cell OptionCell Option

! Cell option contains the following parameters:

" Power control indication (PWRC)

" Discontinuous transmission (DTX)

" Radio link timeout



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Cell Selection ParameterCell Selection Parameter

! Cell selection parameters indicate how the MS will behave

after the MS is powered on. It includes the following

parameters:

" Cell Selection Hysteresis

" Maximum power level of control channel

(MS_TXPWR_MAX_CCH)

" Minimum receiving level of MS permitted to access

(RXLEV_ACCESS_MIN)

" Additional reselection parameter indicator (ACS)

" Half-rate supported(NECI)



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! Content! Content

"SYS INFO 4 - - LAI

- - Cell Selection Parameter


- - CBCH Channel Desc. (optional)

- - CBCH Mobile Allocation(optional)

- - SI4 Rest Oct.(parameters related to cell reselection)


"It consists LAI, RACH, cell selection parameters and optional CBCH

channel information. It is transmitted on BCCH. When the system

supports cell broadcast function, CBCH together with the CBCH MA

describe the configuration of CBCH and the relevant frequency

information.

Among them, LAI, Cell Selection Parameter, and RACH Control Parameter have

been explained above.



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CBCH Channel Desc. and CBCH MACBCH Channel Desc. and CBCH MA

These two parameters are optional. When system supports

cell broadcast, CBCH Channel Desc. explains the CBCH

channel configuration situation. When CBCH Channel Desc.

is in frequency hopping mode, CBCH MA is also needed.

CBCH channel description includes: channel type and TDMA offset, Timeslot Number

(TN), Training Sequence Code (TSC), Hopping channel indication (H), Mobile

Assignment Indication Offset (MAIO), Hopping Sequence Number (HSN), AbsoluteRadio Frequency Channel Number (ARFCN). CBCH mobile configuration contains

sequence of frequency hopping channels and cell channel description.



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SI4 Rest Oct.SI4 Rest Oct.

! It contains the following parameters:

" Cell reselection parameter indicator (PI)

" Cell Bar Qualify (CBQ)

" Cell Bar Access (CBA)

" Cell_Reselect_Offset (CRO)

" Temporary_Offset (TO)

" Penalty_Time (PT)

Cell reselection is conducted on the basis of C2 value. C2 is obtained by the

calculation of a series of parameters. If Cell Selection Parameter “ACS” is set as “No”,

it means MS will use the relevant parameters in SI4 Reset Oct.to calculate CellReselection Parameter C2. If ACS is “Yes”, it means MS should extract cell

reselection related parameter PI and C2 calculation related parameters from the

residual bytes of system information 7 or 8.



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! Content! Content

"SYS INFO 5 - - Neighbor Cell Desc.


! SYS INFO 5

" It describes the neighbor cell BCCH frequencies(BA2 list). It is

mandatory and is transmitted on SACCH. Different from SYS

INFO 2, MS can read the frequency described in SYS INFO 5 in

dedicated mode, report the relevant information of neighbor cells

in measurement report, and use it as the basis for handover.

Similarly, for 900 MS of PHASE 1, it only recognizes the

neighbor cell frequency information described by SYS INFO 5,

and ignores that carried by SYS INFO 5BIS and 5TER.

Corresponding to System Information 2(System Information 2 describes BA1),System

Information 5 is part of the BA2 table. It is used when MS is in the dedicated mode.

Generally, the contents of BA1 and BA2 are the same. In special cases,such as theyare modified for radio network optimization purpose, their contents can be different.



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SYS INFO 5BISSYS INFO 5BIS

! SYS INFO 5

" 5 BIS describes neighbor cells’ BCCH frequencies.These

frequencies are part of BA2 list. It is optional and is transmitted

on SACCH. Generally, as the number of frequencies which can

be described by SYS INFO 5 is limited, SYS INFO 5 BIS carries

the rest BCCH frequencies in the BA2 that are belong to the

same band as SYS INFO 5 for transmitting to MS.

! Content

" SYS INFO 5BIS - - Neighbor Cell Desc.

Corresponding to System Information 2BIS(2BIS is for BA1), the content of 5BIS is

part of the content of BA2 table. It is used when MS is in dedicated mode. The

neighbor cells’ frequencies which belong to the same band as the serving cell BCCHwill be put into 5BIS for transmitting to the MS while there is no room in System

Information 5.



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! Content! Content

"SYS INFO 5TER - - Neighbor Cell Desc.(Extended)

SYS INFO 5TER SYS INFO 5TER

"5 TER describes neighbor cells’ BCCH frequencies,these

frequencies are also part of the BA2 list. It is transmitted on

SACCH channel. Similarly, only dual band MS can read this

information, and single band GSM900 or GSM1800 MS will

ignore it. It carries the BCCH frequencies of neighbor cells

whose band are different from the serving cell’s.

Corresponding to System Information 2TER,(2TER is for BA1)the content of the

5TER is part of the content of BA2. It is used when MS is in the dedicated mode. The

neighbor cells’ frequencies which belong to the different band (900, 1800)from theserving cell in the BA2 will be put into 5TER for transmitting to the MS.



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! Content! Content

"SYS INFO 6 - - Cell Identity

- - LAI

- - Cell Option

- - NCC Permitted


"It describes LAI, cell identity, and some parameters

describing functions of the cell. It is transmitted on

SACCH. It is also one of the most important information

in system information.

Including part of the contents of SYS INFO 2 and 3. It is used for dedicated mode.



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Introduction to BSS Timers

System Information Overview

Parameters Introduction

Case Study

Course ContentsCourse Contents



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Introduction to SYS INFO ParametersIntroduction to SYS INFO Parameters

! Huawei GSM System Information Parameters:

" Network Identity Parameters

" System Control Parameters

" Cell Option Parameters

" Network Functional Parameters



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Network Identity Parameter — CGINetwork Identity Parameter — CGI

! Network identity parameters mainly include cell global identity

(CGI) and base station identity code (BSIC).

CGI=MCC+MNC+LAC+CI

" Once MS receives SYS INFO, it decodes the CGI information,

and decides whether it can stay in the cell according to the MCC

and MNC indicated by CGI. At the same time, it judges whether

the current location area is changed, so as to decide whether to

execute location updating. During the location updating process,MS will report the new LAI information to the network, so that

the network can know exactly the LA in which MS is currently

located.

As a global cellular mobile communication system, GSM conducts strict coding for

each GSM network in every country, and even every location area, BTS, and cell, so

as to ensure that each cell corresponds to a unique number all over the world. Theadoption of this coding scheme can achieve the following objectives:

1. Ensure that MS can correctly identify the current network, so that MS can

accurately select the network expected by subscribers and operators.

2. Ensure that the network can know the real-time position of MS, so that the network

can normally connect various service requests with the MS.

3. Ensure that the MS can report correct neighbor cells’ information to the network

during conversation, so that network can perform handover to keep continuous

conversation for the mobile subscribers when necessary.



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Network Identity Parameter — BSICNetwork Identity Parameter — BSIC

! BSIC=NCC+BCC

" In GSM system, each BTS is allocated with a color code, which

is called BSIC. MS can identify two cells with the same BCCH

by the help of BSIC, In network planning, effort should be made

to make sure that BCCH of neighbor cells different from the

serving cell’s BCCH to reduce the interference. Practically it is

still possible that a same BCCH is re-used in the surrounding

cells. For cells using the same BCCH in a relevant near distance,

their BSIC must be different so that MS can identify two

neighbor cells with same BCCH.

BSIC is transmitted on Synchronous Channel (SCH) of each cell. Its functions include:

1. If MS have read SCH, it is considered as being synchronous with that cell. But tocorrectly read the information on the downlink common signaling channel, MS must

get TSC adopted by common signaling channel. According to GSM specification,

TSC has eight fixed formats, which are represented by 0~7 respectively. TSC number

adopted by common signaling channel of each cell is the BCC of this cell. So one of

the functions of BSIC is to inform MS of the TSC adopted by the common signaling

channel of this cell.

2. Since BSIC attends the coding process of information bit of random access burst, it

can be used to avoid the case that BTS takes the RACH transmitted from MS in a

neighbor cell as the access signal of the MS from the serving cell.

3. When MS is in dedicated mode, it must measure the BCCH level of the neighbor

cell and report it to BTS according to BA2 on SACCH, including their respective BSIC.

In special circumstance, when there are two or more cells using the same BCCH in

the neighbor cells, BSC can rely on BSIC to distinguish these cells and avoid wrong

handover or even handover failure.

4. MS must measure the BCCH signals of neighbor cells in dedicated mode, and

report the result to the network. Since MS sends measurement report which contains

contents of maximum 6 neighbor cells each time, it is necessary to control MS to

merely report those cells that have neighbor relationships with the serving cell. The

higher three digits of BSIC are used for the above purpose. Network operators can

use parameter “ NCC Permitted” to control MS to report the neighbor cells with NCC

permitted in the serving cell only.



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Mobile Country Code MCCMobile Country Code MCC

" MCC is composed of 3 decimal numbers. The

coding range is decimal 000-999.

!Definition

" MCC consists of 3 decimal numbers. It

indicates the home country of the mobile

subscriber.

!Format

MCC is used in international mobile subscriber identity (IMSI) and location area

identity (LAI).

1. LAI. It is periodically transmitted in system information of each cell. MCC indicates

the home country of GSM PLMN. MS uses the received information as the important

basis for network selection.

2. IMSI of MS. MS IMSI also contains MCC. It shows the resident country of the

mobile subscriber. When MS logs on the network or applies for a certain service, it

must report IMSI to the network (When TMSI is unavailable.). The network uses the

MCC in IMSI to judge whether this subscriber is international roaming subscriber.

As the unique country identity standard, MCC source is allocated and managed by

International Telecommunication Union (ITU). ITU Recommendation E.212 (blue

book) regulates the MCC number for every country. MCC of China is 460 (decimal).

Due to the special meaning of MCC, modification is prohibited once it has been set in

the network.



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Mobile Network Code MNCMobile Network Code MNC

" MNC is composed of two decimal numbers. The

coding range is decimal 00-99.

" MNC is used to uniquely identify a specific GSM

PLMN network in a certain country (decided by

MCC).

!Definition

!Format

MNC is used in international mobile subscriber identity (IMSI) and location area

identity (LAI).

LAI. It is periodically transmitted in system information of each cell. Here, MNC

indicates the network number of GSM PLMN. MS uses the received information as

the important basis for network selection.

IMSI also contains MNC. It shows the home GSM PLMN network of the subscriber.

When MS logs on the network or applies for a certain service, it must report IMSI to

the network (When TMSI is unavailable.). The network judges whether this subscriber

is roaming subscriber according to MNC in IMSI, and uses it as one of the important

parameters for addressing subscriber HLR.

If a country has more than one GSM PLMN, different networks must have different

MNC. MNC is allocated by relevant telecommunication management department of

the country. One operator can have one or more MNC (which regard to the scale

provided by the service.). Different operators can share the same MNC. Currently,

China have two GSM networks, which are operated by China Mobile and China

Unicom. Their MNC are 00 and 01 respectively. Due to the special meaning of MNC,

modification is prohibited once it has been set in the network.



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Location Area Code LACLocation Area Code LAC

" LAI contains LAC, which is composed of two bytes. LAC

adopts hexadecimal coding. The available range is from

0001H to FFFEH. Code group 0000H and FFFFH

cannot be used (please refer to specification GSM0303,

0408, and 1111). One location area can contain one or

more cells.

" To locate the location of MS, the whole area covered

by each GSM PLMN is divided into different location

areas. LAC is used to identify different location areas.

!Definition

!Format

When MS is power-on or LAC of current cell is found to be different from its originally stored

contents, MS will inform network of the current location area via location update, and network

use it for paging. Generally the allocation and coding of LAC is set at the early stage ofnetwork construction, and seldom modified during the operation.

The size of location area (LA) is one of key factors in the system. If the LA coverage is too

small, the chances for MS to update location increase. It increases the signaling load in the

system. If the LA coverage is too large, when network conducts MS paging, the same paging

information will be transmitted in a lot of cells. This will lead to the strong load on CCCH. The

adjustment of LA size has no unified standard. Operating departments can decide whether to

adjust the size according to the currently running network. If the CCCH signaling load is heavy

because of too big LA coverage, then reduce the size of LA and vice versa. It is generally

recommended to set the LA as large as possible. The calculation of LA is related with the

paging strategies of different manufacturers. If Huawei equipment is employed, it is

recommended to set the TRX number to within 300 in one location area. In the early stage ofnetwork construction, the traffic is not heavy. So the TRX number in one LA can be larger than

this value. It is essential to monitor PCH load and the increase of traffic in a long term. PCH

capacity can be increased by adding one extended BCCH channel. But one traffic channel will

be reduced.

While making LA planning, try to make use of the geographical distribution and behaviors of

mobile subscribers to allocate the LA, so as to achieve the objective of reducing the times of

location update in boundary between location areas. Please note that LAC in cell parameters

must be in consistent with that in MSC. Otherwise, call setup failure will occurs.



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Cell Identity CICell Identity CI

" CI is composed of 16 bits, The available range is

from 0 to 65535.

" To uniquely identify each cell in the GSM PLMN, the

network operator needs to allocate one code for each

cell, which is the cell identity (CI). Cell identity, together

with LAI, is used for identity of each cell in the world.

(specification 0303).

!Definition

!Format

Cell Identity (CI) is one part of Cell Global Identity (CGI), transmitted in system

information of each cell.

There is generally no restriction for the allocation of CI. Value from 0 to 65535

(decimal) can be obtained. But it should be ensured that one location area cannot

have two cells with the same CI.

CI is usually determined in network system design. Except for some special cases, CI

value should not be changed during the operation of the system.

Please note that one location area is not permitted to have two or more cells using

the same CI. CI on MSC should be the same as that on BSC. Otherwise, MS cannot

make calls in this cell.



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Network Color Code NCCNetwork Color Code NCC

" NCC is composed of 3 bits, with

coding capacity of 8.

" NCC is part of BSIC. MS uses it to distinguish

adjacent BTS that belong to different GSM PLMN.

!Format

!Definition

NCC and BCC together constitute BTS identity code (BSIC),

transmitted on synchronous channel of each cell.

In many cases, different GSM PLMN employs the same frequency

resource. But their network planning are independent from each other.

To ensure that adjacent BTS with same frequency have different BSIC,

it is generally regulated that adjacent GSM PLMN select different NCC.

Adjacent or close cells with the same BCCH frequency must have

different BSIC. Special attention should be paid to the configuration of

cells in boundary areas.



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BS Color Code BCCBS Color Code BCC

" BCC is composed of 3 bits. The available

range is from 0 to 7.

" BCC is part of BSIC. For its function, please refer

to above sections.

!Format

!Definition

BSIC includes BCC and NCC which is transmitted on SCH. BCC is part of BSIC,used to

identify different cell with the same BCCH in the same GSM system. According to the

requirements of GSM specification, TSC of BCCH in each cell should be the same withBCC of the cell. Generally this consistency must be ensured by manufacturers. Adjacent or

close cells using the same BCCH must have different BSIC, otherwise, inter cell handover

might be failure.

BCC planning has three solutions. All of them have taken distance principle into

consideration to avoid collisions of adjacent cells with the same BCCH and same BSIC.

1. Based on the existing BCC set, select one of the BCC that has been used by other cell,

ensure at the same time that BCC selected will not cause BSIC/BCCH collision with

adjacent cell. The advantage of this solution is that it can ensure BCC be even distributedin the whole network. However, if done manually, this solution is time-consuming and

troublesome, we can use automatic distribution tools.

2. When defining BCC, try to assign the value from 0. When causes BSIC/BCCH collision,

expand the value range. The advantage is that the number of BCC used is kept to the

smallest. So when adding a new BTS, in order to avoid the BSIC/BCCH collision, a new

BCC can be selected without modifying the BCC of original cells around.

3. Allocate BCC according to its reuse model. That is to use the same BCC within one

cluster. It means that adjacent cells cannot use the same BCCH with the service cell. This

solution is frequently used, and also the simplest one.



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" ATT

"CCCH-CONF

"BS-AG-BLKS-RES

"BS-PA-MFRAMS

"T3212

"Cell Channel Description format

"Radio Link Timeout

"Neighbor Cell Desc.

"NCC Permitted

"MS MAX re-trans

"Tx-integer

"CBA

"Common Access Control Class

"Wait-for-indication (T3122)

"MBR

"ECSC

"Power Deviation Indication

"Power Deviation

"CBCH Channel Description

"CBCH Mobile Allocation

System Control ParametersSystem Control Parameters

There are a lot of parameters in GSM system,they are usually transmitted to MS from

BTS via Um interface. It aims to maintain favorable cooperation between MS and

BTS. On the other hand, the values of these parameters directly affect the traffic loadand signaling flow of each part of the system. Therefore, proper configuration of these

parameters is important to the favorable and stable operation of the system. The

following will elaborate on the definitions, value ranges, and effects on the system of

these system control parameters.



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ATTATT

! Value range: Yes, No

! Content It is “Attach-Detach allowed” (ATT) in Huawei data

management system. It is used to inform MS whether IMSI

attach-detach is allowed in this cell. If it is set to “Yes”, the

network will not process the connection to the subscriber called

when MS is power-off. Thus network processing time and

resource are saved. Otherwise the network will process the

connection even though the MS has been powered off.

! Recommendation Yes

Detach process (IMSI) refers to the process that MS informs the network that it is

shifting from working state to non-working state (usually a power-off process), or the

SIM card is being taken out from MS, upon receiving the notice from MS, the networkwill indicate that the IMSI subscriber is in non-working state. Therefore, if the MS is

called, the call connection will be rejected.

IMSI attach process is opposite to detach process. It is the process that MS informs

the network that it has entered the service area (usually a power-on process) or SIM

card has been inserted into MS. After entering service state again, MS will test

whether the current location area (LAI) is the same with the latest LAI recorded in MS.

If yes, MS will start IMSI attach process. Otherwise MS will start location update

process (replacing IMSI attach process), upon receiving the location update or IMSI

attach process, the network will indicate that this IMSI subscriber is in working state.

Note that ATT configuration of different cells in the same LAI must be the same. It is

because IMSI detach process will be started when MS is power-off in the cell with

ATT as 1. The network will record that this subscriber is in non-working state and

reject all the called connection requests of this subscriber. When MS is power-on

again, if it is in the same LAI when it was power-off (thus the LAI update process will

not be started) but in different cells, and ATT of this cell is set as 0, MS will not start

IMSI attach process. In this case, this subscriber will not be called normally until MS

starts the location update process.



34

CCCH-CONFCCCH-CONF

! Value range: 1 non-combined CCCH, 1 combined CCCH, 2 non-

combined CCCH, 3 non-combined CCCH, 4 non-combined CCCH.

! Content: It is “Common Control Channel Configuration”.The number of

CCCH message blocks in one corresponding BCCH multi-frame are 9,

3, 18, 27, and 36 respectively. CCCH configuration determines the

capacity of PCH, AGCH and RACH.

! Unit: None

!

Recommendation: When there is one TRX in the cell, one combinedCCCH is recommended (in a system with few paging messages in

location area). For others, it is configured according to the number of

TRX in the cell.

In GSM system, the common control channel mainly include Access Granted Channel

(AGCH) and Paging Channel (PCH). It serves to send the access granted (immediate

assignment) and paging message. CCCH is shared. According to the configuration oftraffic channel and traffic model, CCCH can be carried by either one or multiple

physical channels. Moreover, CCCH and SDCCH can share one physical channel.

Which combination mode to be adopted in the cell depends on CCCH_CONF.

When CCCH is a physical channel which combined with SDCCH, the capacity of

CCCH is the lowest. When CCCH is a physical channel which does not combined with

SDCCH, the capacity is higher. For other cases, the more the physical channels used

as CCCH, the higher the capacity.

Configuration of CCCH_CONF is specified according to the traffic model. This modelis closely related to the cell location and environment. According to experiences, when

TRX quantity in the cell is 1 or 2, it is recommended to use a combined CCCH as the

common control channel. When TRX quantity in the cell is 3 or 4, it is recommended to

use a non-combined CCCH as the common control channel.

Currently CCCH can be configured according to actual traffic load. If the paging load is

very heavy, the paging traffic of cell can be distributed via multiple CCCH physical

channels or other ways. Special attention should be paid to PCH in CCCH. Generally

PCH capacities of various cells under one LAC must be the same.



35

BS-AG-BLKS-RESBS-AG-BLKS-RES

! Value range: 0~2 (1 combined CCCH), 0~7 (others)

! Unit: Block

! Content: It is also called Access Granted Blocks Reserved.

It is the number of CCCH channel message blocks that are

reserved for access granted channels(AGCH).

! Recommendation: 2

As downlink CCCH includes both AGCH and PCH, it is necessary to set the number

of blocks, among CCCH message blocks, which are reserved for AGCH. To let MS

know such configuration information, the system information of each cell includes aconfiguration parameter, which is the number of access granted blocks reserved

(BS_AG_BLKS_RES). After CCCH configuration complete, this parameter actually

assigns the proportion of AGCH and PCH on CCCH. it affects the time of MS’s

response to the paging.

The network operator can adjust this parameter to balance the traffic of AGCH and

PCH by referring to the following principles:

1. Principle for BS_AG_BLKS_RES: make this parameter as small as possible

without causing overload of AGCH, so as to increase the capability of paging andimprove the system performance.

2. Generally it is recommended to select 1 (when CCCH_CONF is 001), 2 or 3 (when

CCCH_CONF is one of other values) for BS_AG_BLKS_RES.

3. During operation, observe the statistics of AGCH overload and adjust

BS_AG_BLKS_RES properly.

Note: In Huawei system, when AGCH has been occupied, PCH can be used to send

the immediate assignment command if it is free. If AGCH blocks reserved is set as 0,

then the immediate assignment would be sent only when there is an idle CCCHdownlink channel. Therefore, a fixed capacity reserved for AGCH is necessary.



36

BS-PA-MFRMSBS-PA-MFRMS

! Value range: 2 9

! Unit: Multi-frame period (51 frames)

! Content: It is Paging Channel Multi-frames. It defines the

number of multi-frames used as a loop of paging sub-

channels.

! Recommendation: 2

This parameter specifies how many paging sub-channels are assigned in a cell. In

the network, MS only monitors the paging sub-channel it belongs to while ignoring

contents of others. When it becomes larger, there will be more paging sub-channelsin the cell and accordingly there will be less MS in each paging sub-channel.

Therefore, the bearing capability of PCH will be much more(theoretically the capacity

of PCH does not increase, but the buffer that buffers paging message in each BTS is

increased, which makes the sending of paging messages more even in the time and

space), and the lifetime of MS battery will be longer. The value of this parameter

should be as smallest as possible as long as it will not cause overload on PCH. In the

operation, the PCH load should be measured regularly and the value of it should be

adjusted properly according to the load. In same location area, any paging must be

sent in all cells within this location area. Therefore, all cells in the same location area

should have the same or nearly the same PCH capacity (number of paging sub-

channels). In the area where the PCH bears a medium or large load, it is set as 6 or 7

(6 or 7 multi-frames are used as a loop of paging group). For the area with a small

load, it is set as 4 or 5. Besides, it is often set as 2.

Note:

1. One paging block (four consecutive CCCH timeslots) can bear two IMSI pagings or

four TMSI pagings or one AGCH immediate assignment message.

2. In idle mode, When MS camps on a cell, DSC initialized to be close to 90/N (N is

BS_PA_MFRMS, with the value range: 2~9). when MS decodes the message on

paging sub-channel, DSC will increase by 1 for one successfully decoding, but will

not exceed initially value. If decoding fails, DSC will decrease by 4. If DSC<=0, the

downlink signaling link will be announced failure, resulting in cell reselection.



37

T3212T3212

! Value range: 0~255

! Unit: 6 minutes

! Content: It is Periodic Location Update Timer. It defines

the period length of location updating.

! Recommendation: 30 (for urban area), 20 (for suburban

area)

MS will make location update when detecting the change of location, besides, MS will

make periodic location update controlled by parameter T3212. Once MS read T3212 from

system info., it will store it in SIM card. When the time exceeds T3212 value, the locationupdate process will be triggered. The shorter the period the better the performance, but it

will bring more signaling load for system. On setting of this parameter, the processing

capabilities of MSC and BSC should be considered, also the flows of A interface, Abis

interface, Um interface as well as those of HLR and VLR. Generally larger value for

continuous covered urban area while smaller in the suburb, countryside or the place with

poor coverage.

Large T3212( 16 hours 20 hours) is recommended for the area with much traffic, and

small T3212 (3 hours, 2 hours) for the area with a little traffic. For the area where the

traffic exceeds the system capacity, it is recommended to set T3212 as 0 (no periodiclocation update). To set the value of T3212 properly, it’s necessary to conduct long-term

measurement on the processing capability and flow of each entity in the system. If any

overload occurs, increase the value T3212. Note that this value should be smaller than

the period by which the network queries the IMSI attached subscriber. Otherwise, the

following situation occurs: When MS has not done any operation in a certain time, and it

is not yet the time for periodic location update, the network will set IMSI flag of MS as

detach, because its query result shows that MS has not done any operation. Thus, the

network will not process the paging of this MS. So, before MS initiates another round of

periodic location update, once there is a call for the MS, the network will voice the calling

subscriber that the called MS is out of service area or has been powered off. When MS

reselects a different location area, MS will make a non-periodic location update and reset

T3212 in the new cell. If it reselects in the same location area, then the timer value will be

remainder of the original one divided by the new T3212.



38

Application of T3212Application of T3212

Even if T3212 setting is less than the system(MSC)

query time, The system will still sometimes voice “The

subscriber you dialed is powered off”.

A B

T3212=4 T3212=8

LAC

“Ping-pong Reselect”

The system query time is set to 1 hour, T3212 value of cell A is set to 4 (0.4 hour),

and T3212 value of the adjacent cell B is set to 8 (0.8 hour), and they are in the same

location area. MS reselects B when the periodic location update status in A is 3/4,and the MS periodic location update status in B changes to 3/8. If MS stays in B for

some time and the location update status reaches 7/8, then MS reselects A. At this

time, it can be seen that in cell A, MS reselection status changes to “7/4”, i.e. 3/4. If

MS reselects to B at this time, the status will change to 3/8, instead of 7/8. The above

analysis shows that if the above case occurs (the probability is high), though T3212

values of both cells are smaller than the system query time, MS reselects so

frequently that the final equivalent time is greater than system query time. Thus the

subscriber will be considered as a power-off subscriber within certain time even it is

in normal idle mode.



39

Cell Channel Description FormatCell Channel Description Format

! Value range: Bitmap, 1024, 512, 256, 128,

variable length

! Content: That is CA table. Presently, the parameter

has been automatically selected by the program

according to actual CA configurations.

Message element is actually the available absolute frequency number list of a serving

cell, i.e. CA table, with 17 bytes. Specifically, there are altogether 124 bits from D3 bit

of the 2nd byte to D0 bit of the 17th byte, which are respectively marked as carriers124, 123, 122......3, 2, 1. If No. N is 1, then No. N carrier belongs to this cell.



40

Application of CA TableApplication of CA Table

Module ID Cell ID Effective

frequency 0

Effective

frequency 1

Effective

frequency 2

Effective

frequency 3

Effective

frequency 5

...

2 51 45 59 68 77 86 ...

2 52 49 62 71 80 89 ...

2 53 53 65 74 83 92 ...

This table describes all the effective frequencies configured in a cell.

Each cell has a record, i.e. CA table.

CA table indicates effective (available) frequencies for the specified cell and maxi. 64frequencies can be configured. The actual domain is configured according to the TRX

frequency configuration and no vacant is allowed amidst. BSC sends the cell CA to

MS via system message. To obtain a standard data configuration, it is recommended

to set the effective frequency 0 in CA as BCCH.

CA table is sent in certain description format. Different formats has different extra

requirements on the CA table. It is determined by the cell channel description format.



41

Radio Link TimeoutRadio Link Timeout

! Value range: 4~64, the step size is 4

! Unit: SACCH period (480ms)

! Content: This parameter is used for MS to decide down-link

disconnection in case of SACCH decoding failures.

! Recommendation: 20~56

•

Once assigned with a dedicated channel, MS will start counter S. From then on, S will

decrease by 1 when a SACCH message fails to be decoded, and will increase by 2

when decoded correctly. When S decreases to 0, there will be a radio link failure.This allows either re-establishment or release of the connection. If the value of this

parameter is too small, the radio link will easily get failed which will result in call drops.

If it is too large, MS will not release for a long time which will lower the availability of

resources (this parameter functions for the downlink).

For area with little traffic (remote area), it is recommended to be between 52~62.

For area with light traffic and large coverage(suburb or countryside), it is

recommended to be between 36~48.

For area with heavy traffic (urban), it is recommended to be between 20~32.

For the area with very heavy traffic (area covered by microcell), it is recommended to

be between 4~16.

For the cell with obvious coverage hole or the area where the call drops is serious

during movement, this parameter can be increased appropriately in order to increase

the possibility to resume the conversation.

Note: Radio link timeout is the parameter used to judge the downlink failure. Likewise,

the uplink will be monitored at BTS, either based on the uplink SACCH error or based

on the receiving level and quality of the uplink.



42

Application of Radio Link TimeoutApplication of Radio Link Timeout

Impact of radio link timeout

A B

P Q

Poor coverage

If cell A and B are adjacent to each other, assume that one MS moves from point P to

point Q during a conversation, usually an outgoing cell handover will occur. If the

value of parameter “radio link timeout” is too small and the quality of signal at theedge of cells A and B is poor, it is likely that the radio link will be timeout before the

handover starts, thus resulting in call drops.

If it is too large, when MS stays near point P and makes a conversation, though the

voice quality is unacceptable, the network still has to wait for a long time before the

related resources can be released, thus the resources utilization rate is lowed.



43

Neighbor Cell DescriptionNeighbor Cell Description

! I.e. Huawei BA tables. There are table BA1 and table BA2.

! Table BA1 describes BCCH frequencies of the adjacent cells

to be measured when the MS is in idle mode.

! Table BA2 describes BCCH frequencies of the adjacent cells

to be measured when the MS is in dedicated mode.

MS keeps on measuring the BCCH signal levels of the serving cell as well as the

neighbor cells. In order to know the adjacent cells, neighbor cell description information

will be broadcast periodically in system information of each cell. This information lists theBCCH of all neighbor cells. MS extracts the information from system information and use

it as basis for neighbor cell measurement.

For GSM network, the neighbor relationship between cells is finalized when designing the

network topology. During the network construction, the neighbor cell relationship must be

configured in accordance with the topology design that has been planned. Moreover, after

the commission of network, neighbor relationship should be modified according to the

data of driver test and traffic measurement. When network’s architecture is changed (e.g.

Adding BTS or changing the network frequency configuration.), network operator must

strictly follow the changed cell neighbor relationship, reset and verify it. Improperneighbor cell description is usually one of the important reasons of call drop. Besides,

since the actual network topology structure is often greatly different from the theoretical

calculation result, and network is in the ever-changing environment, network operator

must modify the neighbor cell description information according to the real situation.



44

Application of Neighbor Cell Description

Theoretical Neighbor Cells Actual Neighbor Cells

B

CA

D

B

CA

D

In theoretical calculated neighbor cell relationship, cell A and cell C are not adjacent

cells. Assume that one MS moves from cell A to cell C during the conversation,

theoretically, MS needs twice of cross-cell handovers. Assume that the interference incell D is rather serious, call drop is likely to occur during this period. But in fact, the

coverage of A, B, C, and D is not the case as the theory. A and C have overlapping

coverage. If A and C are regarded as adjacent cells here, that is to add BCCH of C

and A respectively to the neighbor cell description of A and C, then when MS passes

from A to C, only one handover happens. What’s more, call drop could be avoided

because of the good quality of cell C signals.



45

B

C

A

Application of Neighbor Cell Description

A

Part of the signals from cell A leaks out and covers some areas far away from this cell.

It is over shooting. If MS is in dedicated mode in the shady area and moves from this

area towards B and C, since there are no BCCH of cell B and C in cell A’s neighborcell description, call drop is unavoidable. If the antenna of BTS is located too high, or

the transmitting power is too large, over shooting phenomenon will occur. BTS built at

the early stage of GSM construction usually have this problem, because coverage is

the major problem at that time and the antenna height is very high. The best solution

for this phenomenon is to adjust the location and downtilt of the antenna, and adjust

the transmitting power of the BTS to eliminate the BTS covering the shady area. In

real situation, it is hard or even impossible to change the location of antenna. So one

more simple and applicable method is to add BCCH of B and C to the neighbor cell

description of cell A (no need to add A’s BCCH to B and C). But it must be ensured

that there are no cells, which are neighbor cells of cell A, using the same frequency

and same BSIC with cell B and C. Generally, this method is not recommended.



46

NCC PermittedNCC Permitted

! Value range: Check box, including options 0~7.

! Content: Network Color Code, to be sent in system messages

2 and 6. It lists NCC that need be measured by MS. If a

neighbor cell with NCC permitted, MS will report M.R. Of the

neighbor cell to the network.

! Recommendation: Subject to the concrete conditions.

In working status, MS needs to measure adjacent cells BCCH signals

and report them to network. But each report can only include max. six

adjacent cells. Thus it is necessary to make MS only report the

potential target cells for handover, instead of reporting all according to

the signal level (usually MS does not report the signals of cells from

other GSM PLMN). The above function can be implemented by making

MS only measure the cells whose NCC are selected. Parameter “NCC

Permitted” lists the NCC of the cells that MS needs to measure.

BSIC is transmitted continuously on SCH of each cell and the higher

three bits of BSIC are NCC, therefore, MS only needs to compare themeasured NCC of the adjacent cell with parameter NCC Permitted. If it

is in this set, MS will report it to BTS; otherwise it will discard the

measurement result.

Note: Improper setting of this parameter will lead to lots of call drops.



47

MS MAX Re-transMS MAX Re-trans

! Value range: 1, 2, 4, 7

! Unit: Times

! Content: One of the parameters of random access control

information. i.e. MS MAX. Re-trans Times. It is the upper limit of

times that MS is allowed to send “Channel Request” in one

immediate assignment procedure.

! Recommendation: Set to 7:For areas with low traffic (suburban or

rural area) and the cell radius more than 3 km.Set to 4: For areas

with ordinary traffic (non-busy area in the city) and the cell radius

less than 3km. Set to 2: For micro-cellular Set to 1: For micro-

cellular with heavy traffic or with obvious congestion. And 4 or more

is recommended to set for satellite transmission BTS.

After initiating immediate assignment process, MS keeps monitoring messages on BCCH

and CCCH group it belongs to. If the network does not send Immediate Assignment or

Immediate Assignment Extend message, MS will resend the channel request message ata certain time interval. The larger this value, the higher the call setup success rate, but

the heavier the loads of RACH and SDCCH.

When MS initiates immediate assignment, it will send the “channel request” message to

the network via RACH. As RACH is an ALOHA channel, the network is incapable of

controlling the access time of MS. Thus in heavy traffic spot, it is unavoidable that several

MS may simultaneously make an access request and cause collision which will lead to

two results: one is when one request signal level is obviously higher than those of other

access signals, the access request with higher level will be handled; the other is the

network can recognize none of them due to mutual-interference. As the traffic increasing,access request loss due to collision will increase too. To make sure that the system can

correctly receive the access request and increase the access success rate, the network

allows MS to send several channel requests before receiving an immediate assignment

message so as to have a higher access probability. MS will return to idle mode if it fails to

receive an immediate assignment command after the max. retrans times. After MS sends

channel request, it will start timer T3120 and wait on the downlink CCCH and BCCH.

When timer is timeout while RACH resend times is not more than “MAX re-trans.”, MS

will resend channel request message (contains one new random reference), and restart

T3120 with a random value. When timer is timeout and “MAX re-trans” is reached, MS

will start T3126. If MS still fails to receive a response from the network after T3126 is

timeout, it will give up the access. If MS receives the access rejection, it will stop T3120

and start T3122. Within T3122, no new access attempt will be allowed.



48

Tx-integerTx-integer

! Value range: 3~12, 14, 16, 20, 25, 32, 50

! Unit: Number of RACH timeslots (equivalent to one timeslot,

0.577ms)

! Content: Extended Transmission Timeslots(T), used to calculate the

number of timeslots in the interval between two channel requests

sent by MS.

! Recommendation: 25 (If the cell immediate assignment success

rate is low, set the S with a larger value. Select 32 for satellite

transmission, so as to reduce satellite transmission delay).

It is set to reduce the collisions on RACH. It mainly affects the execution efficiency of

the immediate assignment process. The value of this parameter is related to CCCH

configuration mode, both work together to determine parameter S. The number oftimeslots (excluding the timeslot from where the message is sent) from MS starts the

immediate assignment process to the first channel request message sent is a random

value in the set {0, 1, …, MAX(T, 8)--1}. And the number of timeslots between any

two adjacent channel request messages is a random value in the set {S, S+1, …,

S+T-1}.

Generally, parameter S should be as small as possible (in order to shorten the

access time of MS) when parameter T is fixed, but AGCH and SDCCH must not be

overloaded. During the operation, a random value can be selected for parameter T for

the cell with unknown traffic to ensure the minimum value of S. If AGCH or SDCCH ofthe cell is overloaded, then parameter T can be changed to make parameter S larger,

until AGCH or SDCCH of the cell is not overloaded.

The range of value T can be specified according to the above principles (multiple

values can be selected for parameter T corresponding to various values of parameter

S). When the RACH collisions is serious, value T should be large. When the number

of RACH collisions is small, value T should be as small as possible.



49

Calculation of SCalculation of S

ST

Combined

CCCH

Non-combined

CCCH

3, 8, 14, 50 55 41

4, 9, 16 76 52

5, 10, 20 109 58

6, 11, 25 163 86

7, 12, 32 217 115

When T becomes larger, the interval range between channel request messages sent

by MS will increase and RACH collisions will be reduced. When value S becomes

larger, the interval between channel request messages sent by MS will increase,collisions on RACH will be reduced and the availability of AGCH and SDCCH will

increase. But the increase of both will prolong the access duration of MS, resulting in

deterioration of access performance of the entire network. Generally, value T should

be selected to make S as small as possible (in order to shorten MS access time), but

AGCH and SDCCH must not be overloaded.



50

CBACBA

! Value range: Yes (0), No (1)

! Unit: None

! Content: Cell Bar Access, worked together with CBQ to set

the priority status of the cell in idle mode for cell selection and

reselection.

! Recommendation: Yes

Cell access permitted is the parameter that the network operator can set. Usually all

cells allow MS to access, thus it is set as “Yes”. But in the special cases, the operator

may want a cell to be used for handover service only, which can be realized bysetting the parameter as “No” (CBQ should be “No”).



51

Application of CBAApplication of CBA

CBQ(A)= “NO”

CBA(A)= “NO”

A

C

B

D

Assume that area D in the diagram is a hot spot. Usually micro cell is adopted in

order to have a better access performance with the limited frequency resources. And

usually dual-layer network is adopted in order to reduce the handover times when MSmoves at a high speed, that is, site A is established to cover the entire area A.

Generally MS works in the micro cell (this can be realized by setting the priority and

proper reselection parameters of the cell). When MS moves at a high speed during

the conversation, the network will force MS to hand over to cell A. If MS stays close

to cell A and at the edge of micro cell when the conversation ends, as the signal

quality of cell A is much better than that of micro cell, MS will not initiate the cell

reselection process according to GSM specification. As cell A usually have a small

capacity, it will be congested in the above case. The solution is to set the cell bar

access of cell A as “No”, certainly CBQ should also be set as “No” to prohibit MS from

accessing cell A directly and only permit MS to enter the coverage area of cell A by

HO. In this way, MS will reselect the micro cell when the conversation ends.





53

Special Access Control ClassSpecial Access Control Class

! Value range: Check box, including level 11 forbidden,level12

forbidden,…till level 15 forbidden

! Content: I.e. 11~15 bits of “AC”. It is used for load control,

permitting or forbidding the network access of some special level

users. “1” stands for forbidden and “0” for permitted.

! Recommendation: 00000

For some special subscribers, GSM specifications have reserved five special access

levels 11-15, which usually have higher access priority. A special subscriber can have

one or multiple access levels (between 11 and 15) at the same time, which are alsostored in the SIM card of the subscriber.

For subscribers with the access levels 0-9, their access right is also applicable to the

home PLMN and visit PLMN. For subscribers with the access levels 11-15, their

access right is only applicable to the home PLMN. For subscribers with the access

levels 12, 13 and 14, their access right is applicable to the area of the country to

which the PLMN belongs.

Subscribers with the access level 11-15 have a higher access priority than those with

the access levels 0-9.

The access level control parameter consists of 16 bits: C0-C15, which respectively

corresponds to 15 access levels in bit mapping mode (C10 is used for permitting

emergency call). When a bit is 1, it indicates not to allow MS with the corresponding

level to access then cell. Otherwise it indicates to allow the access.



54

" When the network receives “channel request” message sent by MS,

if there is no appropriate channel assigned to MS, the network will

send immediate assignment rejection message to MS. To avoid the

congestion of radio channel which is caused by MS’s frequently

sending of “channel request”, immediate assignment rejection

message contains the timer T3122 (the wait-indication). After MS

receives immediate assignment rejection message, only after T3122

is timeout MS can send a new channel request.

T3122T3122

!Definition

!Format

" T3122 is 8-bit binary. It indicates the time that MS has to wait before

sending the second request.Its timing length is 0-255 seconds.

T3122 is contained in “immediate assignment rejection”. When MS sends channel

request to BTS, if system temporarily has no idle radio channel, radio resource

management entity of the system will send this information to MS.

When there is shortage of radio resource in the network,MS is forced to wait for a time

to originate a new call attempt after its first call attempt fails. That time is T3122. So it

value has great impact on network performance. If the value of T3122 is too short, it is

likely to cause another congestion of the channel when the load of radio channel is

heavy.However, if T3122 is too large, the average network access time will increase,

which cause the decrease of the average performance of network.

The principle for T3122 setting is: So long the network CCCH is not overload,try to set

T3122 as small as possible. It is generally recommended to set to 10-15 seconds, and15-25 seconds in area with heavy traffic .

Each cell may have different setting because of the different traffic. Even for the same

cell, the traffic may be different in different period of time. So T3122 can be dynamically

set in a cell.

Note: Currently in Huawei BSS system, this parameter is f ixed and set by the program.



55

MBR MBR

! Value range: 0~3

! Unit: None

! Content: Multi-band Reporting. It is used to inform MS to

report the adjacent cells in a controllable way. It is sent in

the System Information 2ter and 5ter.

When the value is “0”, MS will report measurement results of six strongest adjacent

cells no matter which band it’s in. When it is “X(X<=3)”, MS will report measurement

results of X adjacent cells with the strongest signals from the same band as theserving cell and X adjacent cells from the different band. If there is still spare

locations, it will report adjacent cells from the same band. After this, if there is still

space for MR,then, MS will report the other adjacent cells. If there are no special

requirements on different bands and the traffics on various bands are basically the

same, “0” is recommended. When the traffics on various bands are obviously

different from each other and MS is expected to enter a band preferably, “3” is

preferred. When traffics on various bands are slightly different from each other, “1” or

“2” is recommended.

In the initial stage of dual-band network, the traffic of GSM1800 system is very l ight,usually dual-band MS are expected to work on this band preferably. Therefore, the

priority of GSM1800 cells for HO should be higher than these of GSM900 cells and

“3” is recommended for MBR.

Note: In the single-band system, system messages 2ter and 5ter should not be used.

Therefore, the “multi-band indication” parameter does not exist.



56

Application of MBR Application of MBR

-92dBm-82dBm A

B

C -68dBm

D -90dBm

E -78dBm

F -88dBm

G -96dBm

H -84dBm

GSM1800

GSM900S

S is a GSM900 cell, cells A~H are adjacent to cell S. Of them, A and B are GSM1800

cells and others are GSM900 cells. The above diagram shows the influences of

different MBR parameters as follows:

1)When MBR = 0, MS will report six adjacent cells with strongest signals without

considering the bands, the report result is: C, E, B, H, F, D.

2)When MBR = 1, the result is: C, B, E, H, F, D.

3)When MBR = 2, the result is: C, E, B, A, H, F.

4)When MBR = 3, the result is: C, E, H, B, A, F (3 GSM1800 cells should be reported.

But there are only 2 currently, so 2 GSM1800 cells are reported. In the rest, GSM900

cells will be reported).



57

ECSCECSC


! Unit: None

! Content: Early Classmark Sending Control. It informs MS in a

cell whether class-mark 3 should be sent in advance actively or

not.

! Recommendation: No.

Upon receiving information classmark change, MS sends the additional classmark

information to the network as soon as possible. CM3 (classmark 3) information

consists of information about the powers of various bands of multi-band MS. In thehandover between various bands, the power level must be described correctly. CM3

message must be known when paging is conducted and BA2 table is sent in different

bands. ECSC is valid mainly for dual-band MS only. For dual-band MS, when ECSC

is not used, MSC will still send the CLASSMARK REQUEST message after MS

reports ESTIND. When MS reports the CLASSMARK UPDATE message, other

functions will not be affected.



58

Power Deviation IndicationPower Deviation Indication


! Unit: None

! Content: Determine whether to adjust the output the power for

class 3 MS of GSM1800.

! Recommendation: None



59

Power DeviationPower Deviation

! Value range: 0~3, corresponding value: 0dB, 2dB, 4dB, 6dB

! Unit: None

! Content: After random access, when the initial power command is

not received, the power used by GSM1800 Class 3 MS is MS max.

transmitting power plus the value of power offset.

! Recommendation: 1



60

Cell Selection ParameterCell Selection Parameter

! MS_TXPWR_MAX_CCH

! RXLEV_ACCESS_MIN

! ACS(Additional Reselect Parameter

Indication)

! PI(Cell Reselect Parameters Indication)

! CBQ(Cell Bar Qualify)

!

CRO(Cell Reselection Offset)

! TO(Temporary Offset)

! PT(Penalty Time)

! CRH( Cell Reselection Hysteresis)

When MS is powered on, it will try to find a GSM PLMN. MS will select an appropriate

cell and read system information. This process is called cell selection. The appropriate

cell is restricted by many factors. For example, whether this cell belongs to the selectednetwork (under manual network selection mode), whether the cell is barred, the priority

level of the cell, whether the access level of MS is prohibited by the cell, whether the

quality of radio channel meets the requirement of communication, etc. Among them, the

quality of radio channel is one important factor of cell selection. GSM specification

stipulates one parameter called path loss principle C1. The appropriate cell must ensure

the C1>0. C1 is obtained by the calculation of cell selection parameters.

After MS selects cell, MS will settle in the selected cell. At the same time it begins to

measure the signal level of BCCH of neighbor cells. It records six neighbor cells with the

strongest signals (refresh at least every 60s), extracts various system information andcontrol information of each neighbor cell from it. (MS must conduct data block decoding

for six strongest BCCH of neighbor cells within 5 minutes, including parameters

affecting cell reselection. When MS regards a new neighbor BCCH as one of the six

strongest BCCH, it will conduct data block decoding for this new BCCH at least within

30s). Moreover, MS must check one of the six strongest at least within 30s. If BSIC has

any changes, it is regarded as a new BCCH and data decoding will be conducted again.

During this process, MS will not stop monitoring PCH. when a certain condition is

satisfied, MS will move from current cell to anther cell. This process is called cell

reselection. The condition includes many factors which integrate to measure the quality

of radio channel. When neighbor cell’s quality of radio channel is better than current cell,

cell reselection occurs. The channel quality standard for cell reselection is C2. C2 is

obtained by calculation of a set of parameters.



61

Cell Selection ProcessCell Selection Process

! There are two kinds of cell selection.

! Normal cell selection

! Stored list cell selection

! In fact, the process might be different for different MSs

If SIM card of MS does not store any BCCH, it will search all the 124 RF channels and

374 more GSM1800 channels for dual-band MS, measure the receiving signal level of

each. The whole process lasts about 3s to 5s. During this, MS obtains at least 5

measurement samples from each channel. Then MS tunes to the carrier with strongestreceiving level, and judge whether it is BCCH(by searching for FCCH). If yes, MS tries

to decode SCH and enable it synchronous with that BCCH, and reads system

information on it. If MS can correctly read the system information and verify this cell

belongs to the selected PLMN and C1 is larger than 0 and cell priority is normal, then

MS conducts location update. After passing, MS resides in that cell. Otherwise, MS will

tune to second BCCH and go on with the same procedure. After trying the strongest 30

(single-band) or 40 (dual-band) carriers, if it is impossible to access, MS will try to

access the cell with low cell selection priority level. If still unsuccessful, MS will use

PLMN allowed on SIM card to try on. If fail again, MS will go on monitoring all RF

channels and find out a cell(Signal is the strongest. C1 is larger than 0. Access is not

prohibited.) without considering the PLMN , and MS enters emergency call mode

(service bar mode).

Note:1. When MS access level is prohibited by this cell, cell selection algorithm is not

affected. If the condition is fulfilled, MS will still reside in this cell.

2. MS belongs to the PLMN selected, but is prohibited from access, or C1<0. Then MS

obtains BA table from this cell and search BCCH according to this BA.

When MS is powered off, it will store some BCCH carrier information. When powered on,

it will first search the BCCH carrier that have been stored. If MS can decode the BCCH

data of this cell but cannot reside, it will check the BCCH in BA table of this cell. If it still

cannot pass, MS will start the cell selection process without BCCH table.



62

Cell Reselection ProcessCell Reselection Process

! Cell reselection for cells in same location area

" If the C2 value of the target cell is higher than that of the serving cell and

last for longer than 5 seconds, a cell reselection process will be

performed and the MS tunes to the new cell.

! Cell reselection for cells in different location areas

" If the C2 value of the target cell is higher than that of the serving cell by

at least the value of CRH and last for longer than 5 seconds, a location

updating process and the cell reselection process will be performed.

! Cell reselections caused by C2 have a time interval of 15 seconds

! If current serving cell is prohibited, or down link fails, or C1 is less

than 0 continuously for 5s, cell reselection will also be triggered.

! MS starts a cell reselection if the access times exceed the MAX

retrans .

C2=C1+CRO-TO*H(PT-T)

When PT is not equal to 31:

C2=C1-CRO

When PT is equal to 31.

Wherein:

1. Function H(x)=0, when x<0; H(x)=1, when x>0.

2. T is a timer with initial value 0. When a certain cell becomes of one of the six

neighbor cells with highest signal level, T corresponding to this cell begins to count

with accuracy of one TDMA frame (about 4.62ms). When it is out of the six strongest

neighbor cells, the corresponding timer is reset.

3. CRO is used for manually correct the cell reselection parameter C2.

4. The function of TO is to reduce the value of C2 from the time when timer begins to

count to the time when the value of timer reaches the stipulated PENALTY_TIME.

5. PT is the time TO acts on C2. But PT=31 is reserved as the symbol to change the

CRO’s effect on C2.



63

MS_TXPWR_MAX_CCHMS_TXPWR_MAX_CCH

! Value range: 0~31

! Unit: level

! Content: This parameter determines the max. allowed output

power of the MS when it begins to access a cell and has not

yet received power command.

! Recommendation: 5(900MHz), 0(1800MHz)

During MS’s communication with BTS, its transmitting power is controlled by the

network via power command. This command is transmit in SACCH (There are two

head bytes. One is power control byte, the other is time advance). MS must get the

power control head from the downlink SACCH, and use its stipulated transmitting

power as the output power. If power level of the MS cannot output that power, the

transmitting power will use the nearest value.

Since SACCH is associated with signaling, it must be used after combining with other

channels, such as SDCCH, TCH. Therefore, the network’s control of MS power

begins after MS receives SACCH.While the power used by MS before it receives

SACCH (power used when RACH is sent) is determined by the maximum power level

of control channel.

List is the corresponding dBm values related to the 32 maximum transmitting power

control levels for GSM900:

{39, 39, 39, 37, 35, 33, 31, 29, 27, 25, 23, 21, 19, 17, 15, 13, 11, 9, 7, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5}

For GSM1800:

{30, 28, 26, 24, 22, 20, 18, 16, 14, 12, 10, 8, 6, 4, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 36, 34, 32}.

This parameter will affect cell selection and cell reselection.

C1 = RLA_C - RXLEV_ACCESS_MIN- MAX((MS_TXPWR_MAX_CCH- P), 0)

RLA_C: mean receiving level of MS

RXLEV_ACCESS_MIN: minimum receiving level of MS permitted to access

P: maximum physical transmitting power level of MS.



64

RXLEV_ACCESS_MINRXLEV_ACCESS_MIN

! Value range: 0~63

! Unit: Level

! Content: It means the minimum received signal level

required for MS to access a cell.

! Recommendation: 8

To prevent MS from accessing the system when the receiving signal level is very low

that makes the satisfying communication quality unavailable and wastes the radio

resources of the network, GSM specifications require that when MS needs to register inthe network, its receiving level must be greater than a threshold, i.e. the minimum

receiving level of MS permitted to access; otherwise MS will fail to access.

For some cells with high traffic, this parameter can be increased appropriately to lower

the values of C1 and C2 of this cell. Accordingly the effective coverage range of the cell

will be reduced. But the value of RXLEV_ACCESS_MIN should not be too large,

otherwise coverage hole (with regard to idle mode MS) will be created at the edge of

the cell. When this method is used to balance the traffic, the value of

RXLEV_ACCESS_MIN is recommended to be no more than 20.

Except for the areas with densely distributed BTS and good coverage, generally it is not

recommended to use RXLEV_ACCESS_MIN to adjust the traffic of the cell. For isolated

BTS or BTS with poor coverage, this value can be increased properly; otherwise the call

drop rate will increase and QoS will be affected.



65

ACSACS

! Value range:Yes, No.

! Unit:None

! Content: Additional Reselect Parameter Indication. It is

used to inform MS of the location of reselection parameter in

the cell.


According to the definition of GSM specification, cell selection and reselection rely on

parameter C1 and C2.Additional reselect parameters indication (ACS) is used to

inform MS the location of parameters which are used to calculate C2 in the process ofcell reselection.

In SYS INFO 4, ACS=0(NO) means MS should extract cell reselection related

parameter PI and C2 calculation related parameters from the residual bytes of SYS

INFO 4. ACS=1 (Yes) means MS should extract cell reselection related parameter PI

and C2 calculation related parameters from the residual bytes of SYS INFO 8.

Since SYS INFO 7 and SYS INFO 8 (They are optional.) are seldom adopted in the

configuration of ordinary cells, ACS is generally set as 0. If SYS INFO 7 and SYS

INFO 8 are adopted in the cell, and the cell reselection uses parameter C2, ACSshould be set to 1.



66

PIPI

! Value range: Yes (1), No (0).

! Unit: None

! Content: Cell Reselect Parameters Indication, sent on the

broadcast channel of the cell. It is an indication of existence

of “Cell Reselect Offset(CRO)”, “Temporary Offset(TO)”

and “Penalty Time(PT)”.

! Recommendation: Yes.

This parameter is to inform MS whether C2 is used as the standard for cell

reselection. The minimum interval between cell reselections caused by C2 parameter

is 15s to avoid too frequent cell reselection.

If PI=1. C2 is used for cell reselection standard; if PI=0, C1 is used for cell reselection.

For example, cells A and B are adjacent to each other. It is given that cell A CRO=10

and cell B CRO=10. And cell A is the serving cell of a MS which measures to obtain

that cell A C1=40 and cell B C1=35.

Case 1: If PI parameters of both cell A and cell B are set as 1, then C2 parameters of

cell A and cell B are respectively 50 and 45 and cell reselection will not take place.

Case 2: If cell A PI = 1 and cell B PI = 0, then C2 parameters of cell A and cell B arerespectively 50 and 35 and reselection will not take place.

Case 3: If cell A PI=0 and cell B PI=1, then C2 parameters of cell A and cell B are

respectively 40 and 45 and this MS in cell A will reselect to cell B.



67

CBQCBQ

! Value range: Yes(1) , No(0)

! Unit: None

! Content: Cell Bar Qualify. CBQ only affects the

selection of cells but is not related to cell reselection. It

works with CBA to define the access priorities of cells.


For the area overlapped by cells, the operator often wants MS to preferably select

certain cell during cell selection according to the cell capacity, traffic and cell

functions, i.e. setting the cell priority. This function can be implemented by settingparameter “cell bar quality”. It works with parameters “cell bar access” to determine

the priority of the cell.

CBQ CBA Cell selection priority Cell reselection priority

No Yes Normal Normal

No No Disabled Disabled

Yes Yes Low Normal

Yes No Low Normal

Usually the priorities of all cells should be set as “Normal”. But in some special cases

such as micro-cell and dual-band network, the operator may expect MS to preferably

enter the cell of a certain type. In this case, the network operator can set the priority

of this type of cell as “Normal” while setting the other cells as “Low”. MS will select

the cell with lower priority only when there is no appropriate cell with the priority as

“Normal During the network optimization by means of cell priority, it is necessary to

note that CBQ only influences the cell selection. Therefore, in order to achieve the

target, C2 (cell reselection parameter) must be taken into consideration.



68

Application of CBQApplication of CBQ

The traffic of cell A and B is heavy. Set these two cells with

CBA=“No”, CBQ=“No”.

A B

Each circle in the diagram indicates a cell. For some causes, the traffic in cell A and

that of cell B are obviously higher than those of the adjacent cells. To make the traffic

of the entire area distributed on average, set the priorities of cell A and cell B as “Low”and those of other cells as “Normal”. In this way, the services in the shadow areas in

the diagram will be shared by the adjacent cells. It must be pointed out that this

setting will reduce the actual coverage areas of cell A and cell B, which is different

from decreasing the transmitting powers of cell A and cell B.



69

Application of CBAApplication of CBA

B is a micro cell. Set B to “Normal” and A to “Low”.

B

A

Assume that micro-cell B and macro-cell A together cover an area. In order to make

micro-cell B share more traffic of macro-cell A, the priority of cell B can be set as

“Normal” and that of cell A as “Low”. Thus in the coverage area of cell B, MS willselect cell B as long as the level of cell B reaches the cell selection threshold, no

matter whether cell B has a lower signal level than cell A’s. And then reselection

parameters can be set appropriately to make MS not to reselect cell A.



70

CROCRO

! Value range: 0~63, the corresponding level value: 0~126dB,

stepped every 2dB.

! Unit: None

! Content: Cell Reselect Offset. It is a parameter in C2

calculation to give a manual modification in MS cell reselection.

! Recommendation: 0

After cell selection, MS will reselect another better cell in idle mode. It is C2

parameter that determines cell reselection. The principle for MS reselection is: select

the cell with the maximum C2 as the serving cell. C2 is determined by the followingfactors:

C2=C1+CRO-TO*H(PT-T)(PT <31)

C2=C1-CRO (PT = 31)

H(x)=0 if PT-T<0

H(x)=1 if PT-T>0

As shown above, C1 indicates the quality of radio channel. The larger C1 is, thebetter the channel is. C2 value is based on C1, through CRO, C2 of various cells can

be adjusted. Thus C2 value can be calculated according to CRO, TO and PT in order

to prefer selecting the cell in reselection process. That is, in dual-band

network,several parameters that influence C2 value can be set to make C2 value of

GSM1800 larger than that of GSM900. Therefore, even though the signal strength of

GSM1800 cell is weaker than that of GSM900 cell, MS can still reside in GSM1800 by

the aid of these parameters. Besides CRO, there are another two parameters

influencing C2:TEMPORARY_OFFSET(TO) and PENALTY_TIME(PT).

CRO is a manual modification on C2. Reasonable setting of this parameter canreduce handover times and realize assignment to a better cell. Usually it is not set as

larger than 25dB. Generally the cells with the same priority in the network have

basically the same CRO. Setting of this parameter only affects MS of GSM Phase II.



71

TOTO

! Value range: 0~7 , the corresponding value is 0~60dB, 7

corresponds to “Infinite”

! Unit: None

! Content: Cell Reselect Temporary Offset. It is a parameter in

C2 criterion to give a temporary modification within PT time.

! Recommendation: 0

TO indicates the temporary modification on C2. Temporary means that it functions for

C2 only within a duration which is determined by PT parameter. Setting of this

parameter only affects MS of GSM Phase II.



72

PTPT

! Value range: 0~31, the corresponding time is 20~620s.

31 is to change the function direction of CRO on C2.

! Unit: None

! Content: Cell Reselect Penalty Time.

! Recommendation: 0

If the communication in a cell is affected due to very heavy traffic or some other reasons,

this cell should be the last where MS works in (there is a repulse for this cell). In this

case, PT can be set as 31, which causes TO invalid. C2 value is the difference of C1and CRO, therefore, C2 value of this cell is decreased manually. MS will reselect this

cell with little possibility. Besides, the network operator can set CRO according to the

repulse degree to this cell. The higher the repulse degree, the larger CRO.

For the cell with very low traffic, MS should prefer to work in this cell. In this case, CRO

is recommended to be between 0-20dB. It can be set according to the preference

degree to this cell. The higher the preference degree and the larger CRO. Generally TO

is recommended to be the same or a little more than CRO. PT is mainly used to prevent

MS’s too frequent cell reselections. Generally it is recommended to be 0 (20s) or 1 (40s).

For the cell with medium traffic, generally CRO is recommended to be 0 and PT be 31

as a result of C2=C1, that is, no manual modification on the cell.

Setting of PT can effectively prevent the fast moving MS from accessing the micro-cell.

This parameter can be set according to the size of micro-cell. And it is recommended to

be 20s for the ordinary micro-cells. When PT is set as 31, it is used to change the

direction of action to CRO.



73

CRHCRH

! Value range: 0~14 , the step size is 2

! Unit: dB

! Content: Cell Reselection Hysteresis. It is the parameter

used when cell reselection happens between two location

areas.

! Recommendation: 4

This parameter aims to prevent the frequent location update that may increase the

network signaling flow and to reduce the possibility of paging message loss. If the value

of this parameter is too small, the location update will have “ping-pong” effect and thesignaling load on SDCCH will increase. Moreover, the call setup successful rate of the

system will become lower because MS fails to be paged during location update. When it

is too large, the cell where MS resides for a long time may not be the best when MS

enters a new location area.When MS reselects a cell from a different location, MS will

start a location update process following the cell reselection. Due to the fading of radio

channel, C2 values of two cells measured at the edge will fluctuate, which causes MS to

reselect frequently. To reduce the influence, GSM specifications define a parameter

called cell reselection hysteresis. It is required that MS start cell reselection only when

C2 value of the adjacent cell (in a different location area) is greater than that of serving

cell and their difference is greater than the value of reselection hysteresis.

Appropriate cell reselection hysteresis is important for network optimization. Usually it is

recommended to be 8~10dB and can be adjusted in the following cases:

When the traffic of an area is very heavy and the signaling flow overload often occurs, it

is recommended to increase the value of cell reselection hysteresis of the adjacent cells

belonging to different LAC.

When the overlap coverage of the adjacent cells belonging to different LAC are wide, it

is recommended to increase the value of cell reselection hysteresis.



74

Network Function ParameterNetwork Function Parameter

! PWRC (Power Control Permitted)

! UL DTX(Uplink Discontinuous Transmission)

! NECI(New-Establishment Cause Indication)

! Call Re-establish Allowed(RE)

! EC Allowed(Emergency Call Allowed)

! Frequency Hopping



75

PWRCPWRC

! Value range: Yes, No.

! Unit: None

! Content: It is used to indicate MS weather to reduce

received level value obtained from the timeslots of BCCH

when MS measures receiving level during base band

hopping mode. When it is set to “No”, it means the

influence of receiving level on BCCH is not in

consideration. If it is set to “Yes”, process it in the waymentioned above.


In order to monitor the communication quality of radio link and conduct power control,

both MS and BTS must have measurement function. But the measurement will

encounter some problems when several independent functions of GSM specificationare combined for use. First, GSM specification allows BCCH carrier to attend

frequency hopping (except the BCCH timeslot); secondly, GSM specification allows to

conduct downlink power control for the frequency hopping channel; finally, the power

of BCCH is not allow to be changed because MS needs to measure the signal level of

the adjacent cell. In the above conditions, the downlink power control can actually be

used in the channels except the channel from BCCH carrier, that is, the channel from

BCCH carrier during the frequency hopping process cannot be included. If MS

measures the downlink channel level in ordinary mode, the measurement result will

be inaccurate for the power control, because this average value involves the downlink

receiving level of BCCH carrier whose power cannot be changed. To reduce the

influence of this problem upon power control, MS is required to deduct the receiving

level value obtained from the timeslot from BCCH carrier when calculating the

average value of receiving level during frequency hopping. To make MS execute the

above operation, this parameter should be set in the system. This value actually

depends upon the setting of other parameters, such as whether the frequency

hopping is adopted, whether the frequency hopping frequency includes BCCH carrier,

and whether the system adopts the downlink power control. If BCCH attends

frequency hopping, and downlink power control is enabled, the setting should be

“Yes”. Otherwise, inaccurate power control will be resulted, which in turn brings about

abnormal situations.



76

UL DTXUL DTX

! Value range: May use, Must use, Can not use.

! Unit: None

! Content: It is used to indicate whether MS uses DTX

function. In System Information 3, it is 2 bits coding. In

System Information 6, 3 bits coding. It shows the DTX

state of the MS in the previous measurement period.

! Recommendation: Must use.

DTX has very limited influence on the conversation quality. But its application has two

advantages: one is that the interference on radio channel is effectively reduced and a

better average conversation quality can be achieved, the other is that DTX canconsiderably reduce the power consumption of MS. Therefore DTX is recommended

on the network.

According to the protocol, MS reports BTS with two kinds of measurement report, One

is called full measurement report. It will average the levels and qualities of 100

timeslots in the whole measurement cycle (one measurement cycle involves 4 TCH’s

26 multi-frames except idle frames). The other is called sub measurement. It averages

the levels and qualities of 12 timeslots, including eight “consecutive” TCH bursts and

four SACCH bursts.

According to GSM specification, both BTS and MS should conduct this two kind of

measurement(FULL and SUB) no matter whether the uplink/downlink DTX of the

system is activated or not. Each measurement report of SACCH indicates whether

DTX is active or not. According to this indication, BTS can make the right selection,

FULL or SUB.



77

NECINECI

! Value range: Yes, No.

! Unit: None

! Content: Informing MS whether half-rate service are

supported in the cell.

! Recommendation: No

According to the GSM specification, traffic channel in GSM system can be divided

into full-rate channel and half-rate channel. Common GSM systems support full-rate

channel. Whether the network supports half-rate service is decided by the networkoperators. New-establishment cause indication (NECI) is used to inform MS whether

half-rate service are available in this area or not.

NECI is composed of one bit with the meaning as follows:

NECI=0, indicates this cell does not support half-rate service.

NECI=1, indicates this cell supports half-rate service.

NECI is contained in information unit “cell option parameters”, and sent on the system

information of cell broadcast.

In half-rate mode, one physical timeslot is equivalent to two channels.



78

Call Re-establishment AllowedCall Re-establishment Allowed


! Unit: None

! Content: RE, Informing MS whether call reestablishment is

supported or not.

! Recommendation: No

Burst interference or high buildings cause “coverage hole ”, which in turn causes the

failure of radio link. For call drops resulted from this kind of failure, MS can start call

re-establish process to recover the conversation. The network has the right to decidewhether to re-establish or not. This function is achieved by setting “Call Re-

establishment Permitted”.

Call Re-establishment Permitted (RE) is contained in “RACH control parameters”,

and sent on system information of each cell.

In some special cases (e.g. This area has fixed coverage hole .), call drop will occur if

MS passes by coverage hole during the conversation. If call re-establishment is

permitted, the average call drop rate can be reduced. However, re-establish of the

call takes relatively long time. Most of the subscribers have already releasedmanually before the re-establish is completed. Therefore, the re-establish of call not

only fails to achieve the target, but also wastes a lot of radio resource. So it is

recommended that except for some special cells, it is not permitted to re-establish the

call on the network.



79

EC AllowedEC Allowed


! Unit: None

! Content: Emergence Call Allowed . When EC is set to

“Yes”, it means emergency call is permitted.

Otherwise it is prohibited.

! Recommendation: Yes.

For MS with common access control class 0~9, when EC is “Yes”, it indicates to allow

emergency call. For MS with access levels 11~15, the emergency call will not be

allowed only when the corresponding access control bit and EC are set as 0 at thesame time.



80

Others in Data Management systemOthers in Data Management system

! System Information Used

! Regular Transmission

! Regular Transmission Interval



81

System Information UsedSystem Information Used

! Value Range: It is a check box, including system information

1~12, 2bis, 2ter, 5bis, 5ter, 10bis.

! Unit: None

! Content: It is used to determine whether a type of system

information should be sent. A selected box means support,

! Recommendation: Select system information: 1~6, 2bis, 2ter,

5bis, 5ter

It informs all MS in its located area of the information about related location area, cell,

available carrier, available hopping sequence, channel allocation and random access

control, helping MS to locate network resources quickly and accurately.

In the pull-down check box, select the system information type supported by the BSC

system.



82

Regular TransmissionRegular Transmission


! Unit: None

! Content: It shows whether BSC chooses to perform timing

update of system information contents transmitted by BTS. If it

is “Yes”, BSC will send system information to BTS at a certain

interval (it is decided by timing updating interval.). Otherwise, it

must be transmitted through operating the BSC.




83

Regular Transmission IntervalRegular Transmission Interval

! Value range: 0~255

! Unit: Minute

! Content: It stipulates the time interval that BSC

sends system information to BTS.

! Recommendation: 10 minutes

BSC needs to periodically refresh the system information in BTS to avoid the change

or dead-lock of the system information.

Note: If this value is too small, it is likely to increase the signaling flow of A-bis

interface. So it is recommended to set it between 10 to 40 minutes.



84




Case Study




85

Case StudyCase Study

"Case Description

# During the process of optimization in a certain area, it is found out that the signal

is poor in a certain section of suburban highway. The signal strength measured

is less than -95dBm.

" Handling Procedure

# Modify the data in BSC BA1 table. Cell A-3 and B-3 add adjacent data for each

other. The coverage problem is thus solved.

" Summary and Suggestions

# There is a lot of signals received in this area, it is difficult to solve the coverage

problem if we check data independently. Try to conduct frequency scanning in

highway sections where the signal is poor, find out the receiving frequency with

the highest signal level, check BA1 table, BA2 table, and the neighbor cell

relationship, and modify the data. In this way, problem can be solved quickly.

! Case 1: Incorrect Configuration of BA Table! Case 1: Incorrect Configuration of BA Table

Procedure analysis:

The place is located in a highway section in suburb and is about three kilometers

away from downtown. The terrain structure does not fluctuate seriously. Theoretically,

the signal strength should be about -80dBm, which is very different from the actual

value measured. After conducting frequency scanning here, and it is found that the

Frequency A(Fa) signal strength is about -95dBm, Frequency B(Fb) signal strength is

about -80dBm. There are two urban cells (cell A-3 and B-3) and one suburban cell

(C-1)simultaneously cover this highway section (BCCH frequency for A-3, B-3 and C-

1 are Fa ,Fb and Fc). In suburban, After checking the data, it is found that Fb does

not exist in neighbor cell frequency configuration of A-3 cell in BA1 table. When a MS

reside on Cell A-3 in urban area, it cannot reselect to Cell B-3 because Fb is not in

Cell A-3’s BA1 table.In cell relation table, A-3 and B-3 are not set as neighbor cells.

Fb is not configured in neighbor frequency configuration of Cell A-3 cell in BA2. So indedicated mode, MS make a call in Cell A-3. When it reaches this highway section, it

can not handover to B-3 cell. Thus the signal and the quality of the conversation are

poor.



86


" Case description

# The subscriber complains that MS cannot register to the network, or

it is difficult to register to the network between BTS A and B, or no

network mark is displayed on the MS, but MS indicates that the

signal is very good. Some subscribers also complain that MS can

make MTC but cannot make MOC.

" Cause analysis

# CGI of the cell is modified. So the network register flow is not

normal. Although the signal is very good, MS cannot get registeredin the network.

" Recommendation and summary

# CGI is a very important parameter and should be configured

correctly, thus to ensured that the CGI data in BSC and MSC are

same.

! Case 2: Incorrect CGI causes MS unable to register on the network.! Case 2: Incorrect CGI causes MS unable to register on the network.

Procedure analysis:

This BTS site originally works normally. The problem arises recently. Since the

subscriber complains that the problem are most serious near BTS A and B, we decide

to check these two BTS first. First we check the alarms on BTS A and B, they are

normal. Then we check the traffic statistics data and find out: the times of SDCCH

request in cell 2 of BTS A rises from about 3000 in 17th May to about 6000 in 18th May.

Obvious change begins from 7:00AM on 18th May. At the same time, times of SDCCH

attempt failure rises suddenly to more than 3000. It is obviously abnormal. And SDCCH

congestion rate in cell 3 of BTS A is about 30%, but viewed from traffic, congestion rate,

and call drop rate, TCH traffic measurement of BTS A is normal. No abnormal situation

is found in BTS B’s traffic measurement. After checking the SDCCH traffic

measurement of all the adjacent cell of BTS A, we found a cell in which times of SDCCHattempt decreases dramatically. The SDCCH statistics result shows the problem should

exist in cell2 and 3 of BTS A.

Where do the 3000 times of SDCCH requests come from? Analyzed from the failure, we

suspect that the data is modified, so we check the BSC data operation log. Use MA10 to

trace the network access flow of MS, and find out a lot of LOCATION UPDATE

REJECTED information. Since there is no record of modification of BSC data, we check

MSC related cell parameters, and find that CGI of cell 2 and 3 of BTS A are modified. All

the three cells in BTS A have exactly the same CGI. After correct the CGI of cell 2 and 3

and make a dial test. Everything is back to normal.



87

" Case description

# SDCCH congestion rate is as high as 4.91% in 2 cells of an urban BTS. The

configuration of this BTS is S1/1/1. And the busy hour TCH traffic of each

cell does not exceed 3 Erl.

" Handling procedure

# Modify the LAC of this BTS into 0520, which is the same as the surrounding

cells. And the problem is solved.


# LAC configurations of all the cells in the same location area must be the

same. Different cells must have different CGI. When there is modification on

BSS side, corresponding modification should be made on MSC.

! Case 3: Incorrect LAC configuration causes high SDCCH congestion rate.! Case 3: Incorrect LAC configuration causes high SDCCH congestion rate.


Procedure analysis:

1. Check TCH and SDCCH performance indices. It is found that TCH traffic is not

heavy, and busy hour traffic of each cell does not exceed 3 Erl. But times of SDCCH

attempt is very high. In busy hour, it is up to 3032, traffic is1.86 Erl, and congestion

rate 4.91%.

2. SDCCH congestion rate = times of attempted seizures meeting an SDCCH blocked state

/ attempted SDCCH seizures (all). The main approaches to SDDCH attempt are:

a. Signaling before call is set up.

b. Signaling during SDCCH handover.

c. Signaling of location updating in idle mode.

3. In this case, TCH traffic is 2.79 Erl (number of available TCH is 6), times of TCH

attempt (including handover) is 318, and times of handover is 146. Since all of them

are normal, it predicted that it is the frequent location updating causes the heavy

attempt of SDCCH.

4. Check LAC of this BTS, which is 0500. The LAC of other cells around the BTS are

all 0520. After LAC of these three cells is modified into 0520, times of busy hour

SDCCH attempt is 298, congestion rate is 0, and traffic is 0.27 Erl. No congestion

occurs.



88


" Case description

# After Huawei BSC has been running successfully in a network. Some subscribers

complain that they cannot be called. The system announcement that the subscriber

called is powered off. After they make a call, this phenomenon disappears.


# 1. When analyzing the distribution of the complaining subscribers, it’ found the

distribution are very dispersed. So this should not be caused by poor coverage.

# 2. Use the complaining subscribers’ mobile for dial test, And the result shows tested

mobiles are okay.

# 3. Trace the cause from MSC. After checking location update time of MSC with the

operator, we reduce T3212 of BSC to 30 minutes.


# T3212 in BSC must be less than that in MSC.

! Case 4: MSC T3212 is too small caused part of MS cannot be called.! Case 4: MSC T3212 is too small caused part of MS cannot be called.

Cause analysis:

Huawei BSC is connected to Nortel MSC. And the T3212 of the BSC is set to 3 hoursaccording to the local situation. It is latter confirmed that T3212 of Nortel MSC is 48

minutes, greatly shorter than that of BSC. VLR will query the state of the subscriber in

database every 48 minutes. If MS maintains in power-on state and makes no calls, no

location update and state reporting will be conducted, because the BSC T3212 is not

timeout yet. After one VLR query cycle has passed, VLR will mark this subscriber as

IMSI detach in the database because this subscriber makes no report. If you call for

this MS at this moment, you will hear the voice announcement indicating that the

subscriber is powered off.



89


! Case description

" Subscribers complain that the signal fluctuates in a certain area. On-site

tests shows that this phenomenon does exist. From the testing mobile,

we can see that there are a lot of cells’ signals in this area. Some

frequencies are the suburb BTS signals far away from this area. The cell

reselection of MS is rather frequent.

! Handling procedure

" Modify parameter “RXLEV_ACCESS_MIN” of all cells in urban area and

make them consistent with each other. The problem of signal fluctuationis solved.

! Recommendation and summary

" In area with complicated coverage, the “RXLEV_ACCESS_MIN” of each

cell should be kept same.

! Case 5: MS Min-access Level causes the fluctuation of MS signal.! Case 5: MS Min-access Level causes the fluctuation of MS signal.

Cause analysis

1. The fluctuation in this area is not caused by hardware problems (e.g. Unstableoutput power of TRX, clock error, etc.). It is caused by MS’s frequent cell reselection.

Check CRO and TO of the cells whose signals can be received in this area. It is

found that their data configuration are basically consistent. Parameter C1 is the basis

for cell selection. According to the formula of C1 and C2, if the configurations of

“RXLEV_ACCESS_MIN” of cells in data management system are not consistent, and

the actual signal levels that MS receives from two cells are the same, MS will surely

select the cell with smaller “RXLEV_ACCESS_MIN”. If the actual levels that MS

receives from cell 1 and cell 2 are respectively A1 and A2 (assume A1>A2), and

“RXLEV_ACCESS_MIN” of these two cells are set to B1 and B2 (assume B1>B2),

when A1-A2 B1-B2, MS will actually reselect to the cell 2 with poor signals.

2. We check the parameter “RXLEV_ACCESS_MIN” in data management system,

and find out that “RXLEV_ACCESS_MIN” of correlative cells are not consistent, and

some even have great differences. Then in this area, MS is quite likely to reselect the

cell with poor signals. And subscribers will feel the obvious fluctuation of signals.

3. The signals in this area are various and complicated. It is also one of the causes of

the problem. After on-site observation, we find that the over shooting problem exists

in this BTS area.



90


" Case description

# A network operator finds that the SDCCH call drop rate is about 2% after

BSC cutover. This is far away from the acceptable standard.


# 1. Modify relevant parameters in system information and cell attribute

tables. The modification helps to avoid the radio link failure which will

cause call drop, and to adjust the balance between uplink and downlink.

# 2. Check the situation of other indices, especially handover successful rate

and TCH related indices. Analyze hardware and parameters and see if

they are in compliance with the actual running situation of the network.

# 3.Check the performance of the hardware on-site. Analyze the drive test

result. Check and make proper adjustment to the azimuth and downtilt of

the antenna system. Check whether the connectors are loosened.

! Case 6: High SDCCH call drop rate! Case 6: High SDCCH call drop rate

The equipment is provide by vender A and Huawei. Huawei provides only one BSC.

Right before the cutover of Huawei equipment, A has just finished the cutover of

MSC-B. After that, two BSC of A and one Huawei BSC are connected to MSC-B.

Huawei engineers cut over the Huawei BSC from MSC-A to MSC-B after having

updated the BSC expansion data. The new data keeps the original data of Huawei

BTS and add the data of newly BTSs’. But after the cutover, SDCCH call drop rate

stays on about 2%. Analyze traffic measurement of “BSC measurement function“ and

“cell measurement function”, and find that SDCCH call drop mainly occurs in ten BTS.

After conduct on-site drive test on some of these BTS, we find these BTS are located

in high mountains and have the wide coverage. And the mountain is cragged and

have many blind bends. This causes the sudden call drop, which is the main cause of

call drop. So the following parameters were modified:

RACH min. access level: changed from 5 to 10

RELEV_ACCESS_MIN: changed from 10 to 15Radio link timeout counter: changed from 56 to 64

After the modification, SDCCH call drop rate drops from 2% to 0.8%.



91

" Case description

# In a dual-band network, performing GSM1800 single network drive test, during

the driver test, MS often lost connection with the network. But when MS

reconnects with the network, the signal level is very strong.


# After analyzing the actual traffic in each cell of GSM900 network in details, MS

minimum access level and cell reselection offset (CRO) of GSM1800 are

adjusted to make C2 of cells in GSM1800 close to one another when received

signal levels are the same. At the same time, the traffic carried by equipment of

other network is not reduced. After several times of adjustment, CRO of most

1800 cells are 30dB, MS minimum access level is -90dBm. For GSM900 cells,

CRO is 0, MS minimum access level is -100dBm. The cross-cell coverage

phenomenon is basically eliminated.

! Case 7: Cell reselection caused fluctuation of signals.! Case 7: Cell reselection caused fluctuation of signals.


Cause analysis:

Analysis on driver test data shows: Signal level of MS in problem area suddenlydrops to none. After it re-accesses the network, the signal is very strong. The

phenomena is quite similar in several areas. They are not the so-called coverage hole.

The reason for network drop might be the interference. To approve the above

prediction, driver test is re-conducted. And it is found out that DSC timer is often

invalid when MS is in these areas. After timer is invalid, receiving level will suddenly

drop to 0, and cell reselection is conducted. After cell reselection, the signal level of

MS is very strong. To find out the source of interference, background analysis

function of optimization software is used to display the cell coverage range. It shows

serving cell of problem area is the cell with the strongest signal. In fact, to absorb the

traffic in GSM900, CRO configurations of GSM1800 cells are different from that ofGSM900. GSM1800 cell with high CRO value absorbs not only the traffic of GSM900

cells but also that of GSM1800 cells. It causes over shooting,and causes interference.



92

" Case description

# A local GSM network has more than 6000 subscribers. There are four BTS. The

network has been working properly. But from sometime on, some MS often lost

connection with network suddenly. The complaint from subscribers in urban

area increased.


# Modify the time of BSC periodic location update (T3212) to 10, i.e. 60 minutes.

Modify the corresponding time of MSC to 180 minutes. Two days’ observationshows no subscriber complains and the problem is solved.

! Case 8 Too small T3212 causes MS lose connection with network.! Case 8 Too small T3212 causes MS lose connection with network.


Cause analysis:

First, check the hardware. Check from OMC, TRX are working normally. All of TCHand SDCCH channels have records of being seized successfully by subscribers.

Then check BSC hardware. Indicators of MPU, LAPD, 32BIE and CK3 boards are all

working normally. The above checking result shows that hardware on BTS side has

no problem.

Recently, no modification is conducted on the BSC. The current network only differs

from original network in that the number of subscriber increases a lot. In VLR, there

are more than 4000 local subscribers and 5000 roaming subscribers. Therefore, the

problem might be caused by the sudden increase of subscribers.

The pressure brought by subscriber increase on network is mainly shown in two

aspects: (1) TCH (traffic channel) congestion rate increases; (2) SDCCH (signaling

channel) congestion rate increases. MS maybe cannot make MOC or MTC, and at

the same time cannot conduct location updating successfully. The direct result of

location updating failure is MS loses connection with network. Check BSC system

information data table. It is found that T3212 is set to 2 (unit: 6 minutes), i.e. 12

minutes, and MSC corresponding time is set to 30 minuets. This kind of configuration

will cause the result that all activated MS will originate a periodic location update

every 12 minutes via SDCCH. When the number of subscriber reaches a certain limit,

SDCCH will be fully seized. If at this time other MS originates periodic location update,the update will fail because there is no spare SDCCH available. Thus MS is out of

network service.



93




Case Study




94

Some of the BSC Timers -T3101Some of the BSC Timers -T3101

! Definition

" It is used in the immediate assignment process. During the

process of immediate assignment, T3101 is activated when

BSC sends CHANNEL-ACTIVE to BTS, and reset when it

receives ESTABLISH INDICATION sent from BTS.

! Value range

" 0~255s

Guard time for Immediate Assign. Started as 'IMM_ASS_CMD' is sent to

BTS and stopped by reception of 'EST_IND' from BTS. The allocated

channel will be released at timer expiry.

Note that the value should be larger than the maximum time of data link layer

establishment attempt. This timer is timeout usually because of the repeating

assignment or interference in up or down links. Experience shows that averagely 30%

signaling resource of the system is seized by second RACH information sent by MS.

When there is no overload, the maximum time from BSC originating CHANNEL

ACTIVATE to receiving ESTABLISH INDICATION is 1.8s.

these timer parameters are fixed by the program and are not changeable for data

configuration.



95


! Definition

" T3103 defines the time that BSC reserves the TCH of both the

target cell and the original cell simultaneously during the

handover process. T3103 starts when BSC originates handover

command and resets when handover complete (intra BSC

handover) or clear command is received (inter-BSC handover).

! Value range

" 0~255s

The purpose of T3103 is to reserve the original channel for enough long time so that

MS can return to it when handover fails. If MS lost connection, it is used to release

the original channel. The maximum inter-MSC handover time is about 5s.



96


! Definition

" It is used in the TCH assignment process. BSC starts T3107.

when TCH assignment command is sent to BTS, and stop

after receiving “assignment complete” from BTS.

! Value range

" 0~255s

Note that T3107 must be larger than maximum transmission time of assignment

command + T3124 + maximum time of data link multi-frame mode establishment

attempt. It is timeout normally because of the poor coverage of radio links. After thistimer timeout, it is considered that MS has lost its access to the network. The system

will release the resource assigned for this call. Experience shows channel

assignment process can generally complete within 2s. Otherwise, the assignment

process will fails. But if the network quality is bad, this value can be prolonged to 5s. If

cells are relatively of low load, it can even be set to 10s.



97


! Definition

" SACCH release time allowed is indicated by this timer.

! Value range

" 0~255s

Guard timer for channel release indication when clearing mobile station.

Started by sending DEACT_SACCH to BTS and stopped by reception of

'REL_IND' from BTS. It is controlled by RLINKT.T3109=a + RLINKT

T100 x 0.480s Where a = 1s or 2s unit=s=seconds

Before executing RF program, T3109 is started when network checks out low layer

failure. T3109 can also be used for channel releasing process. It is to release channel

when communication is lost.

Once BSC receives SACCH release command, radio link algorithm will reduce the

value of radio link timeout. Note that the summation of T3111 and T3109 must be

larger than the value of the radio link timeout, and larger than the value of BTS radiolink timeout algorithm (number of SACCH multi-frames).

If T3109 is too small, then before radio link timeout (i.e. Radio channel has not been

released yet), radio resource has been re-assigned. If it is too big, It will greatly waste

the system resource.



98


! Definition

" According to timer T3111, BSC delays the channel release

at BTS side. After BSC receives information of BTS

channel releasing, it start T3111. BSC will not send

channel release command to BTS until T3111 is timeout.

! Value range

" 0~255s

After the main signaling link is released, this timer is used to postpone the releasing

of channel. It allows BTS to re-send channel release command to MS during the

delayed period. After BTS sends release command, channel resource will bereserved for the time defined by T3111. The value is generally 2s. If it is too large, it

will waste the system resource.



Documents

OMF010001 System Information ISSUE1.4