GSM Signaling System

ObjectivesAt the end of this course, you will be able to:Know GSM system signaling model State various types of GSM protocol messagesUnderstand GSM system basic signaling procedure

ContentGSM System Signaling ModelGSM protocol message Basic Signaling Procedure

GSM Interface

GSM System Signaling ModelGSM system signaling model adopts the lowest three layer of OSI seven layer protocol model, from low to high:

Application layerLink layer/Network layerPhysical layer

Physical LayerThe physical layer provides error protection transmission. It defines the electric parameters of transmission. In ZTE-GSM digital mobile communication systems, The physical layer of Um interface between MS and BTS is Radio link. Abis interface physical layer adopts 75-ohm coaxial cable or 120-ohm symmetrical twisted pair whose rate is 2Mbit/s.

Data Link LayerThe data link layer major functions: frame transmissionerror-free transmission and realize end-to-end bits transfer between two connective entities. Open maintenance and close the connection of two connective entities. The link layer protocol used by the GSM system at the radio interface is the LAPDm protocol (Dm channel link access procedure). The data link layer of Abis interface between BTS and BSC is LAPD (D channel link access procedure).

Application Layer

Application LayerRadio Resources (RR) management handles the establishment, maintenance and release of physical channels. Its major functions are performed by BSC. Part of functions are performed by BTS.Mobility Management (MM) deals with the mobile stations register and the identify of the mobile subscriber, The function are performed by MSC.The CM Layer is composed of three functional entities: Call Control (CC), deals with the functions to establishmaintenance and release the callShort Message Service support (SMS) and Supplementary Service support (SS).

GSM protocolPublic SwitchedTelephone Network(PSTN)MAP/TCAP + ISUP/TUPTo other VLRISUP/TUPDTAP + BSSMAPMAP/TCAPMAP/TCAPMAP/TCAPBTSMA-bis interfaceA interface

GSM Protocol ArchitectureDTAPDTAP Direct Transfer Application PartBSSMAP BSS Management Application PartCM Call ManagementMM Mobile ManagementRR Radio Resource ManagementSCCP Signalling Connection Control PartMAP Mobile Application PartTCAP Transaction Capability Application PartISUP ISDN User PartMTP Message Transfer PartCMMMRRSig. layer 2Layer 1 (air)Sig. layer 2Sig. layer 1MTPSCCPBSSMAPRR(CM+MM)MSBSCMTPMTPSCCPSCCPCMMMBSSMAPTCAPMAPISUPMSCSig. layer 2Layer 1 (air)BTS(CM)(MM)(RR)(CM)(MM)(RR)(CM)(MM)(LAPDm)(LAPDm)(LAPD)Sig. layer 2Sig. layer 1(LAPD)BTSMBTSMRR'BTSM BTS ManagementUm InterfaceAbis InterfaceA InterfaceInter-MSCInterface

ContentGSM System Signaling ModelGSM protocol message Basic Signaling Procedure

Um interface protocol stack

CM

MM

RR

LAPDm

Layer1

Layer1

LAPDm

RR

MS

BTS

Um interface

LAPDm frame formatThe address field contains the service access point identifier (SAPI). SAPI = 0 represents the signaling linkSAPI = 3 represents the short message linkIn the control field, N (S) represents the sending serial number N (R) represents the receiving serial number

Address

Control

Information

SAPI

N(S)

N(R)

Operation modeAcknowledged mode: Requires the confirmation from the receiver. This mode provides a whole set of control mechanism for error recovering and flow control, the establishment mechanism and release mechanism for multi-frame operations. Unacknowledged mode: The receiver is not required to send a confirmation upon reception of a UI frame. This operation mode does not provide flow control or error recovering mechanism.

RR messages

TypeMessageChannel establishment messageImmediate assignmentImmediate assignment rejectCiphering messageCiphering mode commandCiphering mode complete

Handover messageHandover commandHandover completeHandover failureHandover accessChannel release messageChannel releasePaging messagePaging request Paging responseSystem infoSystem info:18

MM messages

TypeMessageRegistration messagesIMSI detach indicationLocation updating acceptLocation updating rejectLocation updating request

Security messagesAuthentication rejectAuthentication requestAuthentication responseIdentity requestIdentity responseTMSI reallocation commandTMSI reallocation completeConnection-management messagesCM service acceptCM service rejectCM service request

CC messages

TypeMessage

Call establishment messages

AlertingCall confirmedCall proceedingConnect

Call clearing messagesDisconnectReleaseRelease completeMiscellaneous messagesCongestion control notifyStart DTMFStop DTMF

Abis Interface Protocol stack

Abis

BTS

BTSM

LAPD

Layer1

BSC

interface

Layer1

LAPD

BTSM

RR

LAPD ProtocolSAPI = 0 represents the signaling link,SAPI = 62 represents the O&M link, and SAPI = 63 represents the management link of the LapD layer.

flag

Address

Control

Information

FCS

flag

SAPI

TEI

N(S)

N(R)

1

0-260

2

1

A interface protocol stack

Relationship between SCCP and OSI model

BSSAP

SCCP messageCRConnection requestCCConnection confirmCREFConnection refusedRLSDReleasedRLCRelease completeDT1Data form 1UDTUnit dataUDTSUnit data service

BSSMAP Message -1Assignment messages (setup of traffic channels)Assignment requestAssignment completeAssignment failureHandover messages Handover request(to BSC: request for handover to that BSC)Handover required(to MSC: inter BSC/MSC handover required)Handover request ack.(to MSC: acknowledge of handover request)Handover command(to BSC: contains new radio channel/BTS for the MS)Handover complete(to MSC: commanded handover successful)Handover failure(to MSC: commanded handover unsuccessful)Handover performed(to MSC: BSC has performed internal handover)Handover candidate enquiry(to BSC: MSC requests list of MS that could be handedover to another cell)Handover candidate response(to MSC: answer to handover candidate enquiry)Handover required reject(to BSC: required handover unsuccessful)Handover detect(to MSC: commanded handover successful)

BSSMAP Message -2Release messagesClear command (release of traffic channel)Clear completeClear requestSAPI n clear command (control of layer 2 SAPI n on the radio interface)SAPI n clear completeSAPI n reject

General messagesReset(initialisation of BSS or MSC due to failure)Reset acknowledgeOverload(processor or CCCH overload)Trace invocation(start production of trace recordReset circuit(initialisation of single circuit due to failure)Terrestrial resource messagesBlock (management of circuits/time slots between MSC and BTS)Blocking acknowledgeUnblockUnblocking acknowledge

BSSMAP Message -2Radio resource messagesResource request(available radio channels in BSS cells)Resource indicationPaging(paging of MS)Cipher mode command(start encryption)Classmark update(change of MS power class)Cipher mode completeQueuing indication(indicates delay in assignment of tch)

ContentGSM System Signaling ModelGSM protocol message Basic Signaling Procedure

Mobile Originating Call Establishment Procedure -1

MS

BTS

BSC

MSC

CH REQ(1)

CH RQD(2)

CH ACT(3)

IMM ASS(6)

CH ACT ACK(4)

IMM ASS CMD(5)

SABM(7)

UA(10)

EST IND(8)

CM SERV REQ(9)

AUTH REQ(11)

AUTH REQ(12)

AUTH RSP(13)

AUTH RSP(14)

CIPH MODE CMD(15)

CIPH MODE CMD(16)

CIPH MODE CMP(18)

CIPH MODE CMP(19)

CIPH MODE CMD(17)

Mobile Originating Call Establishment Procedure -2

MS

BTS

BSC

MSC

SETUP(24)

SETUP(25)

CALL PRO(26)

CALL PROCEEDING(27)

ASSIGN REQ(28)

ASSIGNMENT COMMAND(31)

CH ACT(29)

CH ACT ACK(30)

SABM(32)

UA(34)

TMSI REALL CMD(20)

TMSI REALL CMD(21)

TMSI REALL CMP(22)

TMSI REALL CMP(23)

EST IND(33)

ASSIGNMENT COMPLETE(35)

ASSIGN CMP(36)

RF CH REL(37)

RF CH REL ACK(38)

Mobile Originating Call Establishment Procedure -3

MS

BTS

BSC

MSC

CONNECT(41)

CONNECT(42)

MEAS REPORT(45)

MEAS REPORT(46)

DISCONNECT(47)

DISCONNECT(48)

RELEASE(50)

RELEASE COMPLETE(51)

RELEASE CMP(52)

CLEAR CMD(53)

ALERTING(39)

ALERTING(40)

CHANNEL RELEASE(54)

DISC(56)

DEACT SACCH(55)

CONNECT ACK(43)

CONNECT ACK(44)

UA(57)

RELEASE(49)

REL IND(58)

RF CH REL(59)

RF CH REL ACK(60)

CLEAR CMP(61)

SCCP REL(62)

SCCP REL ACK(63)

Mobile Terminating Call Establishment Procedure -1

MS

BTS

BSC

MSC

CH REQ(4)

CH RQD(5)

CH ACT(6)

IMM ASS(9)

CH ACT ACK(7)

IMM ASS CMD(8)

SABM(10)

UA(13)

EST IND(11)

PAGE RSP(12)

AUTH REQ(14)

AUTH REQ(15)

AUTH RSP(16)

AUTH RSP(17)

CIPH MODE CMD(19)

CIPH MODE CMP(21)

CIPH MODE CMP(22)

CIPH MODE CMD(20)

CIPH MODE CMD(18)

PAGING CMD(1)

PAGING CMD(2)

PAGING RQT(3)

Mobile Terminating Call Establishment Procedure -2

MS

BTS

BSC

MSC

TMSI REALL CMD(23)

TMSI REALL CMD(24)

TMSI REALL CMP(25)

TMSI REALL CMP(26)

SETUP(27)

SETUP(28)

CALL CONFIRMED(29)

CALL CONF(30)

ASSIGN REQ(31)

CH ACT(32)

CH ACT ACK(33)

ASSIGNMENT COMMAND(34)

SABM(35)

UA(37)

EST IND(36)

ASSIGNMENT COMPLETE(38)

ASSIGN CMP(39)

RF CH REL(40)

RF CH REL ACK(41)

Mobile Terminating Call Establishment Procedure -3

MS

BTS

BSC

MSC

ALERTING(42)

ALERTING(43)

DEACT SACCH(58)

CONNECT(44)

CONNECT(45)

RELEASE(52)

CONNECT ACK(46)

CONNECT ACK(47)

MEAS REPORT(48)

MEAS REPORT(49)

DISCONNECT(50)

DISCONNECT(51)

RELEASE(53)

RELEASE COMPLETE(54)

RELEASE CMP(55)

CLEAR CMD(56)

CHANNEL RELEASE(57)

DISC(59)

UA(60)

REL IND(61)

RF CH REL(62)

RF CH REL ACK(63)

CLEAR CMP(64)

SCCP REL(65)

SCCP REL ACK(66)

Location Update Procedure -1

MS

BTS

BSC

MSC

CH REQ(1)

CH RQD(2)

CH ACT(3)

IMM ASS(6)

CH ACT ACK(4)

IMM ASS CMD(5)

SABM(7)

UA(10)

EST IND(8)

LOC UPDATE REQ(9)

AUTH REQ(15)

AUTH REQ(16)

AUTH RSP(17)

AUTH RSP(18)

IDENTITY REQ(12)

IDENTITY RSP(13)

IDENTITY REQ(11)

IDENTITY RSP(14)

CIPH MODE CMD(20)

CIPH MODE CMP(22)

CIPH MODE CMP(23)

CIPH MODE CMD(21)

CIPH MODE CMD(19)

Location Update Procedure -2

MS

BTS

BSC

MSC

LOC UPDATE ACC(24)

LOC UPDATE ACCEPT(25)

TMSI REALL CMP(26)

TMSI REALL CMP(27)

DEACT SACCH(30)

CLEAR CMD(28)

CHANNEL RELEASE(29)

DISC(31)

UA(32)

REL IND(33)

RF CH REL(34)

RF CH REL ACK(35)

CLEAR CMP(36)

SCCP REL(37)

SCCP REL ACK(38)

Intra Cell Handover Procedure

MS

BTS

BSC

MSC

MEASURE REPORT(1)

MEASURE REPORT(2)

CH ACT(3)

CH ACT ACK(4)

SABM(6)

UA(8)

EST IND(7)

RECEIVE READY(10)

ASSIGNMENT COMMAND(5)

ASSIGNMENT COMPLETE(9)

HO PERFORMED(11)

RF CH REL ACK(13)

RF CH REL(12)

Intra BSC Handover Procedure

MS

BTS1

BSC

MSC

MEAS REPORT(1)

MEAS REPORT(2)

CH ACT ACK(4)

CH ACT(3)

HO DETECT(8)

PHYSICAL INFO(9)

SABM(10)

RF CH REL ACK(18)

HO CMD(5)

HO ACCESS(7)

RF CH REL(17)

HO PERFORMED(16)

HO CMP(15

BTS2

HO CMD(6)

EST IND(11)

UA(12)

HO CMP(13)

RECEIVER READY(14)

Inter BSC Handover Procedure

MS

BTS1

BSC1

BSC2

MEAS REPORT(1)

MEAS REPORT(2)

CH ACT(5)

CH ACT ACK(6)

HO CMD(8)

HO REQUIRED(3)

HO CMP(17)

RECEIVER READY(18)

BTS2

HO REQ(4)

HO CMP(19)

HO CMP(20)

CLEAR COMMAND(21)

HO CMD(9)

RF CH REL(22)

HO ACCESS(10)

RF CH REL ACK(23)

CLEAR COMPLETE(24)

MSC

HO REQ ACK(7)

HO DETECT(11)

HO DETECT(12)

PHYSICAL INFO(13)

SABM(14)

EST IND(15)

UA(16)

Call Re-establishment Procedure

MS

BTS

BSC

MSC

CLEAR CMP(4)

CONN FAIL IND(1)

CLEAR CMD(3)

ASS REQ(9)

CLEAR REQ(2)

ASS CMP(10)

CHANNEL REQ(5)

CM RE-EST REQ(6)

CIPH MODE CMD(7)

CIPH MODE CMP(8)

STATUS(12)

STATUS ENQUIRY(11)

Directed Retry Procedure

MS

BTS1

BSC

MSC

BTS2

MS

CH REQ(1)

CH RQD(2)

CH ACT(3)

CC(10)

CH ACT ACK(4)

IMM ASS CMD(5)

SABM(6)

UA(7)

EST IND(8)

CR(9)

CM SERVICE ACCEPTED(11)

SETUP(12)

CALL PROCEEDING(13)

ASS REQ(14)

CHANNEL ACT(15)

CHANNEL ACT ACK(16)

HANDOVER COMMAND(17)

HO ACCESS(18)

HO DETECT(19)

PHY INFO(20)

SABM(21)

UA(23)

EST IND(22)

HO CMP(24)

ASS CMP(25)

Short Message Procedure On SDCCH When MS Is Calling -1

MS

BTS

BSC

MSC

CH REQ(1)

CH RQD(2)

CH ACT(3)

CC(10)

CH ACT ACK(4)

IMM ASS CMD(5)

SABM(6)

UA(7)

EST IND(8)

CM SERV REQ(9)

SABM(SAPI3)(13)

AUTH REQ(11)

AUTH RSP(12)

UA(14)

CIPH MODE CMD(16)

CIPH MODE CMP(17)

CP DATA(18)

CP ACK(19)

EST IND(SAPI3)(15)

Short Message Procedure On SDCCH When MS Is Calling -2

MS

BTS

BSC

MSC

CP DATA(20)

CP ACK(21)

DEACT SACCH(24)

CLEAR CMD(22)

CHANNEL RELEASE(23)

DISC(25)

UA(26)

REL IND(27)

RF CH REL(28)

RF CH REL ACK(29)

CLEAR CMP(30)

SCCP REL(31)

SCCP REL ACK(32)

Short Message Procedure On SDCCH When MS Is Called -1

MS

BTS

BSC

MSC

CH REQ(3)

CH RQD(4)

CH ACT(5)

CH ACT ACK(6)

IMM ASS CMD(7)

SABM(8)

UA(10)

EST IND(9)

CM SERV REQ(11)

AUTH REQ(13)

AUTH RSP(14)

CC(12)

CIPH MODE CMD(15)

CIPH MODE CMP(16)

SABM(19)

UA(20)

PAGING CMD(1)

PAGING CMD(2)

CP DATA(17)

EST REQ(SAPI3)(18)

EST CMP(SAPI3)(21)

Short Message Procedure On SDCCH When MS Is Called -2

CP DATA(24)

CP ACK(25)

CP DATA(22)

CP ACK(23)

DEACT SACCH(28)

CLEAR CMD(26)

CHANNEL RELEASE(27)

DISC(29)

UA(31)

REL IND(30)

RF CH REL(32)

RF CH REL ACK(33)

CLEAR CMP(34)

SCCP REL(35)

SCCP REL ACK(36)

MS

BTS

BSC

MSC

Short Message Procedure On SACCH When MS Is Calling

MS

BTS

BSC

MSC

CM SERVICE REQ1

CM SERVICE ACC(2)

SABM(SAPI3)(3)

UA(4)

EST IND(SAPI3)(5)

CP DATA(6)

CP ACK(7)

CP DATA(8)

CP ACK(9)

ACTIVE CALL

ACTIVE CALL

Short Message Procedure On SACCH When MS Is Called

MS

BTS

BSC

MSC

CP DATA(1)

EST REQ(SAPI3)(2)

SABM(3)

UA(4)

EST CNF(SAPI3)(5)

CP DATA(8)

CP ACK(9)

CP DATA(6)

CP ACK(7)

ACTIVE CALL

ACTIVE CALL