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A-INTERFACE

GENERAL INFORMATION

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Interfaces to MSC/VLR

MSC/VLR

MSC VLR

RNS

RNC

NodeB

MSC/VLR

MSCVLR

MSC/VLR

MSCVLR

HLR

SGSN

EIR

GMSC

A-I/fGs-I/f

G-I/f

D-I/fC-I/f

F-I/f

E-I/f

BSSAP

BSSAP+

MAP

MAPMAP MAP

MAP

BSS

BSC

BTS

Iur-I/f RANAP

RNC

NodeB

Iu-I/f

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TS GSM 48.001 General Aspects

48.002 Interface Principles48.004 Layer 1 - Specification48.006 Signaling Transport Mechanism48.008 Layer 3 Specification48.020 Rate Adaptation on the BSS-MSC Interface

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TS GSM 48.002 INTERFACE PRINCIPLES

Principles which 48.0x technical specification series are based, e.g.

– BSS (BSC+BTS) is considered as a whole– 1 or more 2048 kbit/s digital transmission– Layered signalling– Channel bit rate 64 kbit/s at MSC boundary, considering

net radio path traffic channel rate less than 16 kbit/s (transcoders)

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MSC Functions– Terrestrial channel allocation– Blocking of terrestrial channels– TCH channel release– DCCH channel release– Channel coding decoding– Interworking function (data calls)– Traffic measurements– Handover– Mobility management– Call control– Encryption

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Signaling protocol reference model

Distribution Function

DTAP BSSMAP

SCCP

MTP

Physical Layer

Applications e.g. call control

DTAP Direct Transfer Application Part+

BSSMAP BSS Management Application Part=

BSSAP BSS Application Part

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Network MS

MSC/VLR

BSS/RNS

BSSMAP

Initial MS/UE message

DTAP/NAS

SMS Message

Messages and logical difference

RANAP

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TS GSM 48.004 LAYER 1 SPECIFICATION

Defines structure of physical layer for supporting traffic channels

– 32 * 64 kbit/s time slots (E1)– 24 * 64 kbit/s time slots (T1)– Refers to CCITT recommendations and ANSI

specifications

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TS GSM 48.006 SIGNALLING TRANSPORT MECHANISM FOR MSC-BSC INTERFACEDefines the subsets of MTP, and SCCP and its use

– MTP provides a mechanism giving reliable transfer of signaling messages

– SCCP provides a referencing mechanism to identify a particular transaction relating to for instance a particular call. The SCCP can also be used to enhance the message routing

MTP– E1 links: CCITT Recommendations Q.701, Q.702, Q.703,

Q.704, and Q.707– T1 links: ANSI Specifications T1.111

with stated exceptions

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SCCP – E1 links: CCITT Recommendations Q.711, Q.712, Q.713,

and Q.714– T1 links: ANSI Specifications T1.112.1-4

with stated exceptions– Not used SCCP functions: error detection, receipt

confirmation, flow control

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Use of the SCCP– User function is BSSAP– One signaling connection per active mobile station

having one or more transactions for the transfer of layer 3 messages

– BSSMAP: Both connectionless and connection-oriented procedures

– DTAP: Connection-oriented procedures– Distribution Function

Distribution Data Unit: Discrimination Parameter, bit D

– D=0: BSSMAP message– D=1: DTAP message

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ADDRESSING

SSN + SPC or SSN onlyNo global title is used

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TS GSM 48.008

LAYER 3 SPECIFICATION

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GENERAL

Specifies Layer 3 procedures used on BSS-MSC interface for control of GSM services

Call control and mobility management messages and procedures (DTAP) are described in GSM TS 04.08/3GPP TS 24.008

BSSMAP

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MAIN PARTS

BSSMAP proceduresMessage formats and codingSignalling element codingSignalling diagrams

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BSSMAP PROCEDURES

General informationSuccessful/unsuccessful operationAbnormal conditions

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MESSAGE FORMATS AND CODING

Short descriptionInformation elementReferenceDirectionType (mandatory, optional)Length

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SIGNALLING ELEMENT CODING

Short descriptionStructure of the IE

– element identifier– length– value

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SIGNALLING DIAGRAMS

Sequence diagrams for the BSSMAP proceduresRelated to an unique procedure

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Block

Blocking Acknowledge

Circuit Group Block

Circuit Group Blocking Acknowledge

Circuit Group Unblock

Circuit Group Unblocking Acknowledge

Paging

Reset

Reset Acknowledge

Reset Circuit

Reset Circuit Acknowledge

Unblock

Unblocking Acknowledge

Unequipped Circuit

MSC

/VL

R

BSC

Connectionless BSSMAP messages between BSC and MSC/VLR

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Assignment Request

Cipher Mode Complete

Classmark Request

Classmark Update

Assignment Complete

Cipher Mode CommandM

SC/V

LR

BSC

Connection oriented BSSMAP messages between BSC and MSC/VLR

Assignment Failure

Cipher Mode Reject

Clear Command

Clear Complete

Clear Request

Complete Layer 3 Information

Queuing Indication

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Handover Command

Handover Detect

MSC

/VL

R

BSC

Connection oriented BSSMAP messages between BSC and MSC/VLR

Handover Complete

Handover Failure

Handover Performed

Handover Required

Handover Request

Handover Request Acknowledge

Handover Required Reject

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MSC Invoke Trace

MSC

/VL

R

BSC

Connection oriented BSSMAP messages between BSC and MSC/VLR

Connection Oriented Information

Connection Oriented Information

SAPI ‘n’ Reject

Trace Invocation

Perform Location Request

Perform Location Response

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BSC

MSC

/VL

R

MS

DTAP Messages for Mobility Management

Authentication Response

Authentication Request

Authentication Reject

CM Service Accept

CM Service Abort

CM Service Reject

CM Service Request

Identity Request

Identity Response

Location Updating Accept

Location Updating Reject

IMSI Detach Indication

TMSI Reallocation Command

TMSI Reallocation Complete

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/// BSSAP

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FS A-Interface Application Parts in MSC/VLR ServerMain A-Interface FS1/15517-1/APT 21026/2 Lists the sectionsThe use of SCCP

- Addressing- CO and CL services

BSSAP message and IE structure

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A-Interface, Section A: Location Updating, IMSI Attach and IMSI Detach Procedures

A-Interface, Section B: Basic Call Control ProceduresA-Interface, Section C: Call Related Supplementary

Service ProceduresA-Interface, Section D: Call Independent

Supplementary Service ProceduresA-Interface, Section E: Parallel Transaction

ProceduresA-Interface, Section F: Short Message Service

ProceduresA-Interface, Section G: Base Station System

Management Application Part ProceduresA-Interface, Section P: Location Services Procedures

FSs for Signalling Procedures

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A/Iu-Interface, Section R: UMTS to GSM Inter-

System Handover Procedures A/Iu-Interface, Section S: GSM to UMTS Inter-

System Handover Procedures

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FSs for Formats and Coding of Messages

A-Interface, Section H: Base Station System Management Application Part, BSSMAP, Message Formats and Coding

A/Iu-Interface, Section I: DTAP and RANAP/NAS, Message Formats and Coding for Mobility Management

A-Interface, Section J: Direct Transfer Application Part, DTAP, Message Formats and Coding for Short Message Service

A/Iu-Interface, Section K: DTAP and RANAP/NAS, Message Formats and Coding for Call Control and Call Related Supplementary Service Procedures

A-Interface, Section L: Direct Transfer Application Part, DTAP, Message Formats and Coding for Call Independent Supplementary Service Procedures

A-Interface, Section M: Supplementary Service ProtocolA-Interface, Section Q: Location Services Protocol Formats

and Coding

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FS A-interface, Section G: BSSMAP ProceduresSpecifies BSSMAP signalling sequences between

MSC/VLR Server and BSS/UEAll supported BSSMAP proceduresTime supervisions

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FS A-interface, Section H: BSSMAP Message Formats and CodingLists all supported messages, IEsDescribes Error handlingAdditionally compared with TS 48.008

– GSM phase information– notes about the use of IEs

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ERROR HANDLING

In case of inconsistent message length between delivered message length according to SCCP and BSSAP header message length, the BSSAP header message length has higher priority

Messages with faulty BSSAP header are ignored. Messages are ignored if they are not consistent

with the Signalling Type (CL, CO), with the direction, or with the recipient’s state

Not recognized or not implemented messages are ignored.

The information elements are classified into conditional, essential, non-essential, and transparent types:

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Messages containing an unrecognisable or unexpected IE before the last essential IEs are rejected with the cause 'Invalid message' if a reject message exists. If no reject message exists the message is ignored

Messages containing an unrecognisable IE or unexpected IE, after the last essential IEs have been received, are accepted

Messages with a missing essential information element are rejected with the cause 'Invalid message' if a reject message exists. If no reject message exists the message is ignored

Messages with a missing non-essential IE are accepted

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If the MSC/VLR receives a message and diagnoses a missing conditional IE or an unexpected conditional IE or when it receives a message containing at least one syntactically incorrect conditional and non-transparent IE which is required to be present, then the message will be rejected with the cause 'Invalid Message' if a reject message exists. If no reject message exists the message is ignored

Messages that have an essential and non-transparent IE with field having an incorrect value are rejected if applied with the cause 'Invalid message'. If no reject message exists, the message is ignored

Messages that have a non-essential IE with fields having incorrect value are accepted. IE is ignored

Transparent IEs are not checked

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MMS FUNCTION SPECIFICATIONS

Administration and Handling of A-Interface Lines in MSC/VLR

– The purpose of this function is to give the operation and maintenance staff the ability to define and supervise A-interface lines

– The A-interface lines are the channels on the trunk between the MSC/VLR Server and the BSC

– The A-interface line can be configured according to ITU-T specifications or ANSI specifications.

Administration of BSC Data in MSC/VLR– This function allows the operation and maintenance

staff to administer BSC data by means of exchange commands

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– The administration of BSC data includes the following commands

Definition of BSCChange of BSC capabilities Connection of alternative route to a BSCDisconnection of alternative route from a BSCRemoval of BSC Printing of BSC data

Administration of Cell Data in MSC/VLR Server– For this function, two function specifications exist. The

function specification to be ordered depends on the ordering information. Either administration of cell data is supported or administration of both location area data and cell data is supported.

Assignment of Radio Channels in MSC/VLR Server– The Function Specification describes the radio channel

assignment and release procedures for signaling channel assignment and traffic channel assignment over A-interface

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Circuit Pools for A-interface in MSC/VLR– This function groups, by means of commands, circuits

supporting the same channel type characteristics into circuit pools in the MSC/VLR server.

– It enables the MSC/VLR Server to interwork with BSC which control different transcoder and rate adaptor units (TRAU) connected to different A-interface lines

– This function selects a circuit in an adequate circuit pool at channel assignment or handover when it is ordered by the MSC/VLR Server or when it is requested by the BSC due to circuit pool handling reasons.

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FUNCTION DESCRIPTIONS

A-Interface Line Terminal Functions– The A-interface line terminal functions allow the seizure

and release of an A-interface line (device) towards a BSS. The function also takes care of the administration of A-interface lines

– The A-interface line terminal functions handle BSSAP messages, concerning A-interface lines (block, unblock, circuit group block, circuit group unblock, reset circuit, unequipped circuit)

– The type of signaling used for the A-interface is ITU-T or ANSI signaling for the SCCP and Message Transfer Part (MTP)layers

– The A-interface line terminal functions take care of the handling of transmission concerning A-interface lines (A-law or U-law idle pattern sending, 24-channel(T1) or 32-channel(E1) Pulse Code Modulation (PCM) Interface or SDH/STM-1 interface)

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Administration of BSCs– Administration of BSCs is a part of the administration of

Base Station subsystem data in MSC/VLR ServerAdministration of Cells

– The administration of the cells is performed by means of seven commands, if the Location Area (LA) administration is supported, and four commands, if the LA administration is not supported. The LA administration involves the definition of a LA before the definition of the cells to be connected to it, and removal of a LA after all cells are removed from this LA

Administration of Circuit Pools for A-Interface– This function is responsible for the administration of the

circuit pools for A-interfaceAssignment of Radio Channels in MSC/VLR

– This function handles the assignment request, and possible repetition assignment request due to circuit pool handling, of a traffic channel or a dedicated signalling channel, when requested by other functions

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MM Transaction Establishment in MSC/VLR– The MM transaction establishment function establishes the

transaction of internal AXE links between the upper layer (CM) and the lower layer (RR). It distributes messages and signals coming from the link in both directions, to the proper user function

MM Connection Management– The MM connection management function establishes,

maintains and releases internal links between the upper layer (CM) and the lower layer (RR), after a first transaction has been established. It distributes messages and signals coming from the link in both directions, to the proper user function

MM Traffic– Takes part for instance packing and unpacking of MM

messagesMonitoring of Mobile Subscribers, A-interface Lines

and Iu Connections in MSC/VLR– This function describes the implementation of monitoring in

the MMS subsystem.

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Packing and Unpacking of Messages on RR Level– The function packs and unpacks all BSSAP messages

related to the radio resources levelRR & SCCP Connection Management

– This function is responsible for the following actions:Establishment and release of SCCP and

RrconnectionsDistribution of BSSMAP messages received from

SCCP to the appropriate user functionForwarding of Direct Transfer Application Part

(DTAP) messages received from SCCP to the 'MM connection management' function

Sending of BSSMAP messages from user functions or DTAP messages from function 'MM-connection management'to SCCP

Sending, reception and distribution of connectionless messages

Handling of process at reception of a RESET message from a BSC

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BLOCKS

DIPST (Digital Path Supervision and Test)– The Function block DIPST contains functions for Digital Path

(DIP) administration and maintenance, as well as hardware and clock reference administration

DIPHID (Digital Path Historical Data)– The function block contains functions for historical data

administrationET (Exchange Terminal function)

– Function block ET handles the hardware supervision of Exchange Terminal Circuit (ETC) and takes part in the supervision of DIP. It also handles the connection/disconnection of the Exchange Module (EM) and Switching Network Terminal (SNT)

ETDIF (Exchange Terminal - Device InterFace)– ETDIF is an interface block between a Device Owner, in this

case MALT, and SNT owner ET. This function is needed for ET155

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MALT (Mobile Telephony A-interface Line Terminal)– MALT owns the A-Interface lines, it handles the selection and

the release of devices, performs actions as blocking, deblocking and reset of the devices according to the reception of messages from the BSS. The block can send BSSAP messages to acknowledge or initiate actions. For remote A-interface MRALT and MRALTM are the corresponding blocks.

MALTC (Mobile Telephony A-interface Line Terminal Co-ordinator)

– MALTC co-ordinates together with MBSCA the administration of alternative routes (of different device types) to a BSC. The block is also involved in traffic handling by co-ordinating the selection of alternative routes at seizure of A-interface line, when the main route is congested.

MLABT (Mobile Telephony Line Terminal Label Translation)

– MLABT handles the translation of the BSS pointer and Circuit Identity Code (CIC) into a device number and a device block.

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MMMMH (Mobile Telephony Mobility Management Message Handler)

– MMMMH performs the packing and unpacking of all BSSAP messages related to the mobility management level

MMMSAMH (Mobile Telephony Mobility Management Satellite Application Message Handler)

– The function block MMMSAMH performs analysis,packing and unpacking of Global Satellite System specific MM IEs

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MRRM complex (Mobile Telephony Radio Resources Management, /MRRM, MRRMASG, MRRMHO/)

– MRRM supervises the establishment and the release of the signaling connections between the MSC/VLR server and the BSC, and handles the messages

– At the reception of the messages, MRRM checks and distributes the different messages to the appropriate user function. The transparent messages (DTAP) are forwarded to the block MMM. The BSSMAP messages, received from MSCCO in connection-oriented mode or from MSCCL in connectionless mode are distributed to the appropriate function on RR level which will initiate the unpacking of the message and take the appropriate action

– In the connection oriented mode, MRRM receives the sending signals from the upper layer for DTAP messages or from MRRMH for BSSMAP messages and forwards them to MSCCO.

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-In the connectionless mode at message sending stage, MRRM does not act-The block is also involved in several BSSMAP procedures during the assignment of a terrestrial line, the BSC recording initiation process, the ciphering process, the handover and the global reset.

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MRRMH (Mobile Telephony Radio Resources Message Handler)

– MRRMH is used for unpacking of incoming BSSMAP messages at message reception and for packing of outgoing BSSMAP messages at message sending

MRRRSMH (Mobile Telephony Radio Resources Regional Satellite Application Message Handler)

– The function block MRRRSMH is responsible for the analysis, packing and unpacking of Regional Satellite application specific Ies included in RR layer messages

MRRSAMH (Mobile Telephony Radio Resources Satellite Application Message Handler)

– The function block MRRSAMH is responsible for the analysis, unpacking and packing of Global Satellite System Specific RR IEs

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MSCCL (Mobile Telephony SCCP Connectionless Signaling)

– MSCCL is used to provide the connectionless message service between the MSC/VLR server and the BSC. It handles the interface between MMS and CCS (SCCP) subsystems

MSCCO (Mobile Telephony SCCP Connection Oriented Signaling)

– MSCCO transfers connection oriented messages between the MSC/VLR server and a BSC.

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Remote A-interfaceIntroduced in MSC R10

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TSC/GMSCServer

Site

MSCServer

Site

BSCBTSTDM: BSS A

MAPMAPBICC CS2

GCP GCP

HLR

ATM or IPConnectivityNetwork

MGWSGW

MGWSGW

What is the aim of this function?

Simply said: to use stand alone (Cello) media gateway for GSM

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MLABT MALTC

ET MALT ETDIF

DIPST DIPHID

Local BSC TrunkInt.

MLABT

MRALT TAF

Remote BSC TrunkInt.

MMS blocks for local and remote BSC connection