Omf001006 Gsm Signaling System-bssap(Bss)

OMF001006 GSM Signaling System-BSSAP(BSS)

OMF001006 GSM Signaling System-BSSAP(BSS)

Huawei Wireless Training Department

ContentsContents

• 1 BSSAP Functional Structure

• 2 Distribution Sub-layer Functional Structure

• 3 DTAP Functional Structure

• 4 BSSMAP Functional Structure

• 5 Message Example

• 6 Means of BSC Signaling and Interface Tracing

• 7 Relevant GSM Specifications

1 BSSAP Functional Structure1 BSSAP Functional Structure

BSSAP Functional Structure

BSSAP Functional Structure

BSS

BSSAP

SCCP

DTAP BSSMAP

Distribution Function

BSSAP

SCCP

DTAP BSSMAP

A-Interface

MSC

MTP MTP

Transmission Equipments for Air Interface

Corresponding BSC Processing Modules

Distribution Function

Corresponding MSC Application and Control Modules

BSSAP Functional StructureBSSAP Functional Structure

• BSSAP ： BSS Application Part

• BSSMAP ： BSS Management Application Part

• DTAP ： Direct Transfer Part

• SCCP ： Signaling Connection Control Part

• MTP ： Message Transfer Part

SCCPSCCP

Distribution FunctionDistribution Function

DTAP BSSMAP

2 Distribution Sub-layer Functional Structure

2 Distribution Sub-layer Functional Structure

• To converge the DTAP messages received from radio link L2 to A-interface signaling link

Functions of BSSAP’s Distribution Sub-layer Functions of BSSAP’s Distribution Sub-layer

To discriminate DTAP and BSSMAP messages

To distribute the DTAP messages to radio link L2 joint

Components of Distribution Sub-layerComponents of Distribution Sub-layer

Components of Distribution Sub-layer

Components of Distribution Sub-layer

Octet 1

Octet L

Octet 3

Octet 2

Octet 1

Octet 2

Octet 3

Octet 4

Octet L

DTAP BSSMAP

Identifier Identifier

DLCI

LI LI Length Indicator

L3 L3

Message Message

……

..

L3 Messages

Distribution Data Unit

……

..

3 DTAP3 DTAP

• DTAP takes charge of transferring transparent L3

messages from MS to MSC or from MSC to MS. BSS

will not analyze it. It is transferred between BSS and

MSC by using SCCP service class 2 (basic connection-

oriented class).

III Detailed L3 Message

User data

I Distribution Data Unit

II Length Indication

DTAP Distribution Data UnitDTAP Distribution Data Unit

• Distribution Data Unit has two parameters: Discriminator : 00000000 Data Link Connection Identity （ DLCI ） :

• To indicate the data link type that should be used on the radio interface for the messages sent from MSC to BSS

• To indicate the data link type on the radio interface that reports the message which is sent bye BSS to MSC.

Discriminator:

Bits: 8 7 6 5 4 3 2 1

0 0 0 0 0 0 0 D D=0 stands for non-transparent transmission

4 BSSMAP4 BSSMAP

The transmission of BSSMAP messages upon SCCP

is for the BSSMAP functional entities of both MSC and

BSS to exchange information.

The distribution data unit of BSSMAP messages only

has the discriminator. ‘D’ should equal to 0 which

stands for non-transparent transmission.

Discriminator:

Bits: 8 7 6 5 4 3 2 1

0 0 0 0 0 0 0 D D=0, non-transparent transmission.

5 Message Example5 Message Example

• For better understanding of BSSAP message,

there are two examples for BSSMAP and

DTAP respectively.

BSSMAP message

DTAP message

Example of BSSMAP MessageExample of BSSMAP Message

• The following is a real message traced with MA10 on A-interface.

000 ： FB 0B 3B C3 B2 40 30 E0 01 01 00 41 02 02 06 04 43 B2 00 FE

020 ： 04 04 43 C1 00 FE 0F 21 00 1F 57 05 08 00 64 F0 00 25 00 00

040 ： 01 17 12 05 08 20 64 F0 00 25 00 01 08 49 06 20 72 90 00 00

060 ： 60 00


MTP and SCCP message disassemble


Network Indicator11??????NI??XXXXXX

Spare??00??????XX???? 0xC3

Service Indicator????0011SI????XXXX

Spare00??????XX??????

0x3BLength Indicator??111011LI??XXXXXX

Forward Indication Bit1???????FIBX???????

0x0BForward SN?0001011FSN?XXXXXXX

Backward Indication Bit1???????BIBX???????0xFB

Backward SN

?1111010BSN?XXXXXXX

According Bytes

According ContentsStandard Message Format




Spare0000????XXXX????0x02

Class 2 Service????0010Protoco

lClass

????XXXX

0x010x000x41

010041hSource Local

Reference3 Bytes

0x01CR message00000001Message TypeXXXXXXXX

SLS 0E1110????SLSXXXX????

OPC 00C101??????00110000????0000

OPCXX??????

XXXXXXXX????XXXX

0xB20x400x300xE0

DSP 00B210100010??000000

DPCXXXXXXXX??XXXXXX

According Bytes

According ContentsStandard Message Format

Source LocalReference




Domestic Standby0???????X???????

DPC+SSN Addressing?1??????RouteIndicator?X??????

Have not GT??0000??GT Indicator??XXXX??

Including SSN??????1?SSN Indicator??????X?

0x43

Including SPC???????1SPC Indicator???????X

0x04Called AddressLength

04hLength Indicator1 Byte

0x06Calling AddressPointer000001101 Byte

0x02Called AddressPointer

00000010Mandatory variablelength parameter pointer

1 Byte

According BytesAccording ContentsStandard Message Format

Mandatory variablelength parameter pointer




0x21SCCP user data length)

0x21Optional ParameterLength1 byte

0x0FSCCP user data0x0FOptional ParameterName

1 byte

04 43 C1 00 FEh

Same format to called address

04 43 C1 00FEh

Optional ParameterContents5 bytes

0x04OPC0x04Optional ParameterName

1 byte

0xFEA-interface SSN0xfeSSN1 byte

0xB200DPC00B2hSPC2 bytes

According BytesAccording ContentsStandard Message

Format


• 0x00 ； BSSMAP indicator• 0x1f ； BSSMAP message length = 31• 0x57 ； Complete L3 information• 0x05 ； Cell ID IEI• 0x08 ； Cell ID length• 0x00 ； Cell ID discriminator• 0x64 0xf0 ； MCC dig.• 0x20 ； MNC dig.• 0x25 0x00 ； LAC• 0x00 0x01 ； CI

BSSMAP Message Disassemble BSSMAP Message Disassemble


• 0x17 ； L3 information IEI

• 0x12 ； L3 information length = 18

• 0x05 ； Skip Indicator = 0 ， PD =5(Mobile Manager)

• 0x08 ； message type ： Locate Update request

• 0x20 ； LocUpdate type = 0 ， Normal Location Updating

• ； Ciphering key sequence = 2



• 0x64 0xf0 ； MCC dig.

• 0x20 ； MNC dig.• 0x25 0x00 ； LAC• 0x01 ； Classmark1

• 0x08 ； Mobile ID length

• 0x49 ； Mobile ID type = 9 ： IMSI,length is odd number

• 0x06 0x20 0x72 0x90 0x00 0x00 0x60 ； IMSI number


Example for DTAP MessageExample for DTAP Message

• The following is a real message traced with MA10 on A-interface.

000 ： 0C FF 22 C3 C1 80 2C 30 06 03 00 41

00 01 16 01 00 13 05 12

020 ： 03 11 11 11 11 11 11 11 11 11 11 11

11 11 11 11 11




Network Indicator11??????NI??XXXXXX

Spare??00??????XX???? 0xC3

Service Indicator????0011SI????XXXX

Spare00??????XX??????

0x22Length Indicator??100010LI??XXXXXX

1???????FIBX???????

0xFF?1111111FSN?XXXXXXX

Backward Indication Bit0???????BIBX???????

0x0CBackward SN?0001100BSN?XXXXXXX

CorrespondingBytes

CorrespondingMessage Content

Standard Message format

Forward SN

Forward Indication Bit




SLS03

0011????SLSXXXX????

OPC00B2

10??????00101100????0000

OPCXX??????

XXXXXXXX????XXXX

0xC10x800x2C0x30

DSP00C1

11000001??000000DPC

XXXXXXXX??XXXXXX

CorrespondingBytesCorresponding Message ContentStandard Message format




0x16User data length

00010110Parameter length1 Byte

0x01User data pointer00000001Mandatory variable length parameter pointer

1 Byte

0x00No more data00000000Segmentation/Reassembly

1 Byte

0x030x000x41

030041hSource Local

Reference3 Bytes

0x06DATA FORM 100000110Message TypeXXXXXXXX

CorrespondingBytesCorresponding Message ContentStandard Message format

Source LocalReference


• 0x01 ； DTAP message type

• 0x00 ； Spare ， DLCI

• 0x13 ； DTAP message length

• 0x05 ； Protocol Discrimination (PD)=5(MM),

Skip Indicator=0 （ effective ）

DTAP message disassemble DTAP message disassemble


• 0x12 ； Authentication Request

• 0x03 ； Ciphering key sequence number(CKSN ，Kc SN)= 3

• Authentication parameter rand IEI

• 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01

• 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01

DTAP message disassemble DTAP message disassemble

6 Means of BSC Signaling and Interface tracing6 Means of BSC Signaling and Interface tracing

• Signaling analyzer

MA10 KC1297

BSC Maintenance Console

GSM Interface Tracing

GSM Interface Tracing

Review

NO7 Message Tracing

NO7 Message Tracing

Review

Comparison of different meansComparison of different means

• Signaling Analyzer Expensive. Need additional investment Can trace all the signaling of A-interface and Abis-interface from the ph

ysical layer.

• GSM Interface Trace Need no additional equipment and investment. A-interface Trace: Trace BSSAP and SCCP in BSC. A-bis Interface Trace: A-bis interface L3 messages. Um Interface: Um interface L3 messages.

7 Relevant GSM Specifications7 Relevant GSM Specifications

GM 0808 ： A interface

GM 0858 ： A-bis interface

GM 0408 ： Um interface

Documents

Omf001006 Gsm Signaling System-bssap(Bss)