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GSM Signaling System
ZTE University
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Objectives
At the end of this course, you will be able to: Know GSM system signaling model
State various types of GSM protocol messages
Understand GSM system basic signaling procedure
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Content
GSM System Signal ing Model
GSM protocol message
Basic Signaling Procedure
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GSM Interface
SGSN
AbisUm
BTS
BSC
TRAU
GGSN
MSC/VLR/GMSC
NSMU FSMU
Ater A
OMC
Qx
HLR/AUC
EIR SMC
PSTN / PLMN /
PSPDN / ISDN
BTS
BTS
BTS
Gb
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GSM System Signaling Model
GSM system signaling model adopts the lowest threelayer of OSI seven layer protocol model, from low to
high:
Application layer
Link layer/Network layer
Physical layer
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Physical Layer
The physical layer provides error protectiontransmission. It defines the electric parameters of
transmission.
In ZTE-GSM digital mobile communication
systems, The physical layer of Um interfacebetween 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.
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Data Link Layer
The data link layer major functions: frametransmissionerror-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).
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Application Layer
Application Layer
CM MM RR
CC SS SMS
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Application Layer
Radio Resources (RR) management handles theestablishment, 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 establish
maintenance and release the callShort Message Service
support (SMS) and Supplementary Service support (SS).
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Mobile
Switching
Centre
(MSC)
) ) )Base
Transceiver
Station
(BTS)
Base
Station
Controller
(BSC)
Equipment
ID
Register
(EIR)
Visitor
Location
Register
(VLR)
Home
Location
Register
(HLR)
Authenti-
cation
Centre
(AUC)
Mobile
Switching
Centre
(MSC)
Public Switched
Telephone Network
(PSTN)
MAP/TCAP + ISUP/TUP
To other VLR
ISUP/TUP
DTAP + BSSMAP
MAP/TCAP
MAP/TCAP MAP/TCAP
BTSM
A-bis interfaceA interface
GSM protocol
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DTAP
DTAP Direct Transfer Application PartBSSMAP BSS Management Application Part
CM Call Management
MM Mobile Management
RR Radio Resource Management
SCCP Signalling Connection Control PartMAP Mobile Application Part
TCAP Transaction Capability Application Part
ISUP ISDN User Part
MTP Message Transfer Part
CM
MM
RR
Sig. layer 2
Layer 1 (air)
Sig. layer 2
Sig. layer 1
MTP
SCCP
BSSMAPRR
(CM+MM)
MS BSC
MTP MTP
SCCP SCCP
CM
MM
BSSMAP TCAP
MAP
I
S
U
P
MSC
Sig. layer 2
Layer 1 (air)
BTS
(CM)
(MM)
(RR)
(CM)
(MM)
(RR)
(CM)
(MM)
(LAPDm) (LAPDm) (LAPD)
Sig. layer 2
Sig. layer 1
(LAPD)
BTSMBTSMRR'
BTSM BTS Management
Um Interface Abis Interface A Interface Inter-MSC
Interface
GSM Protocol Architecture
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Content
GSM System Signaling Model
GSM protocol message
Basic Signaling Procedure
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Um interface protocol stack
CM
MM
RR
LAPDm
Layer1 Layer1
LAPDm
RR
MSBTS
Um interface
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LAPDm frame format
The address field contains the service
access point identifier (SAPI).
SAPI = 0 represents the signaling link
SAPI = 3 represents the short message link
In 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)
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Operation mode
Acknowledged mode: Requires the confirmationfrom 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.
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RR messages
Type Message
Channel establishment message Immediate assignment
Immediate assignment reject
Ciphering message Ciphering mode command
Ciphering mode complete
Handover message
Handover command
Handover complete
Handover failure
Handover access
Channel release message Channel releasePaging message Paging request
Paging response
System info System info:18
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MM messages
Type Message
Registration messages
IMSI detach indication
Location updating accept
Location updating reject
Location updating request
Security messages
Authentication reject
Authentication request
Authentication response
Identity request
Identity response
TMSI reallocation commandTMSI reallocation complete
Connection-management messages
CM service accept
CM service reject
CM service request
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CC messages
Type Message
Call establishment messages
Alerting
Call confirmed
Call proceeding
Connect
Call clearing messages
Disconnect
Release
Release complete
Miscellaneous messages
Congestion control notify
Start DTMF
Stop DTMF
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Abis Interface Protocol stack
Abis
BTS
BTSM
LAPD
Layer1
BSC
interface
Layer1
LAPD
BTSM
RR
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LAPD Protocol
SAPI = 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
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A interface protocol stack
BSC
MTP3
MTP2
Layer1
MSC
A interface
Layer1
MTP2
MTP3
RR
SCCP SCCP
BSSAP BSSAP
MM
CM
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Relationship between SCCP and OSI model
MTP-1
MTP-2
MTP-3
SCCP
ISP
TCAP
INAP OMAP MAP BSSAP ISUP TUP
HLR VLR
Layer1
Layer2
Layer3
46
Layer 7
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BSSAP
MTP
SCCP
Distribution
BSSMAP DTAP
BSSAP
RR
MM
CC
MTP
SCCP
Distribution
BSSMAP DTAP
BSSAP
L1
LAPDm
RR
CC
MM
RR
LAPDm
L1
MSCBSS
MS
DTAP
BSSMAP DTAP
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SCCP message
CR Connection request CC Connection confirm
CREF Connection refused
RLSD Released RLC Release complete
DT1 Data form 1
UDT Unit data
UDTS Unit data service
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BSSMAP Message -1
Assignment messages (setup of traffic channels) Assignment request Assignment complete
Assignment failure
Handover 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
handed over 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)
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BSSMAP Message -2
Release messages Clear command (release of traffic channel) Clear complete
Clear request
SAPI n clear command (control of layer 2 SAPI n on the radio interface)
SAPI n clear complete
SAPI n reject
General messages Reset (initialisation of BSS or MSC due to failure)
Reset acknowledge
Overload (processor or CCCH overload)
Trace invocation (start production of trace record
Reset circuit (initialisation of single circuit due to failure)
Terrestrial resource messages Block (management of circuits/time slots between MSC and
BTS)
Blocking acknowledge
Unblock
Unblocking acknowledge
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BSSMAP Message -2
Radio resource messages Resource request (available radio channels in
BSS cells)
Resource indication
Paging (paging of MS) Cipher mode command (start encryption)
Classmark update (change of MS power class)
Cipher mode complete
Queuing indication (indicates delay in
assignment of tch)
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Content
GSM System Signaling Model GSM protocol message
Basic Signaling Procedu re
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Mobile Originating Call Establishment Procedure -1
MS BTS BSC MSCCH 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(16)
CIPH MODE CMP(18)CIPH MODE CMP(19)
CIPH MODE CMD(17)
CIPH MODE CMD(15)
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Mobile Originating Call Establishment Procedure -2
MS BTS BSC MSC
TMSI REALL CMD(20)TMSI REALL CMD(21)
TMSI REALL CMP(22)TMSI REALL CMP(23)
SETUP(24)SETUP(25)
CALL PRO(26)CALL PROCEEDING(27)
ASSIGN REQ(28)CH ACT(29)
CH ACT ACK(30)
ASSIGNMENT COMMAND(31)
SABM(32)
UA(34)EST IND(33)
ASSIGNMENT COMPLETE(35)ASSIGN CMP(36)
RF CH REL(37)
RF CH REL ACK(38)
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Mobile Originating Call Establishment Procedure -3
MS BTS BSC MSC
ALERTING(39)ALERTING(40)
DEACT SACCH(55)
CONNECT ACK(43)CONNECT ACK(44)
RELEASE(49)
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)CHANNEL RELEASE(54)
DISC(56)
UA(57)REL IND(58)
RF CH REL(59)
RF CH REL ACK(60)CLEAR CMP(61)
SCCP REL(62)
SCCP REL ACK(63)
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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)
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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)
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)
SETUP(27)SETUP(28)
CALL CONFIRMED(29)
CALL CONF(30)
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Mobile Terminating Call Establishment Procedure -3
MS BTS BSC MSC
DEACT SACCH(58)
RELEASE(52)
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)
ALERTING(42)ALERTING(43)
CONNECT(44)CONNECT(45)
CONNECT ACK(46)CONNECT ACK(47)
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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(11)IDENTITY REQ(12)
IDENTITY RSP(13)IDENTITY RSP(14)
CIPH MODE CMD(20)
CIPH MODE CMP(22)CIPH MODE CMP(23)
CIPH MODE CMD(21)
CIPH MODE CMD(19)
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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)
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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)
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Intra BSC Handover Procedure
MS BTS1 BSC MSCMEAS REPORT(1)
MEAS REPORT(2)
CH ACT ACK(4)
CH ACT(3)
PHYSICAL INFO(9)
HO ACCESS(7)
HO PERFORMED(16)
HO CMP(15
BTS2
HO CMD(5)HO CMD(6)
HO DETECT(8)
SABM(10)
EST IND(11)
UA(12)
HO CMP(13)
RECEIVERREADY(14)
RF CH REL ACK(18)
RF CH REL(17)
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Inter BSC Handover ProcedureMS BTS1 BSC1 BSC2
MEAS REPORT(1)MEAS REPORT(2)
CH ACT(5)
CH ACT ACK(6)
HO CMD(8)
HO REQUIRED(3)
BTS2
HO REQ(4)
HO CMD(9)
HO ACCESS(10)
MSC
HO REQ ACK(7)
HO DETECT(11)
HO DETECT(12)
PHYSICAL INFO(13)
SABM(14)
EST IND(15)
UA(16)
HO CMP(17)
RECEIVER READY(18)
HO CMP(19)
HO CMP(20)
CLEAR COMMAND(21)
RF CH REL(22)
RF CH REL ACK(23)
CLEAR COMPLETE(24)
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Call Re-establishment Procedure
MS BTS BSC MSC
CONN FAIL IND(1)
CLEAR CMD(3)
CLEAR REQ(2)
CHANNEL REQ(5)
CM RE-EST REQ(6)
CIPH MODE CMD(7)CIPH MODE CMP(8)
STATUS(12)
STATUS ENQUIRY(11)
CLEAR CMP(4)
ASS REQ(9)
ASS CMP(10)
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Directed Retry Procedure
MS BTS1 BSC MSC BTS2 MSCH REQ(1)
CH RQD(2)
CH ACT(3)
CH ACT ACK(4)
IMM ASS CMD(5)
SABM(6)
UA(7)EST IND(8)
CR(9)
CC(10)
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)
S O S CC S
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Short Message Procedure On SDCCH When MS Is
Calling -1
MS BTS BSCMSC
CH REQ(1)CH RQD(2)
CH ACT(3)
CH ACT ACK(4)
IMM ASS CMD(5)
SABM(6)UA(7)
EST IND(8)CM SERV REQ(9)
AUTH REQ(11)
AUTH RSP(12)
CC(10)
SABM(SAPI3)(13)
UA(14)EST IND(SAPI3)(15)
CIPH MODE CMD(16)
CIPH MODE CMP(17)
CP DATA(18)
CP ACK(19)
Sh t M P d O SDCCH Wh MS I
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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)
Sh t M P d O SDCCH Wh MS I
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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)
PAGING CMD(1)PAGING CMD(2)
CP DATA(17)EST REQ(SAPI3)(18)
SABM(19)
UA(20)EST CMP(SAPI3)(21)
Sh t M P d O SDCCH Wh MS I
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Short Message Procedure On SDCCH When MS Is
Called -2
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)
CP DATA(24)
CP ACK(25)
MS BTS BSC MSC
Short Message Procedure On SACCH When
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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
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Short Message Procedure On SACCH When
MS Is Called
MS BTS BSC MSC
SABM(3)
UA(4)EST CNF(SAPI3)(5)
CP DATA(8)
CP ACK(9)
CP DATA(6)
CP ACK(7)
ACTIVE CALL
ACTIVE CALL
CP DATA(1)EST REQ(SAPI3)(2)
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