GSM Part II
Transcript of GSM Part II
Presentation Outline:
Radio Resource ManagementMobility ManagementCall Control ManagementLayer 3 ProtocolsMobile Application Part protocolFlow chart of initial mobile acquisitionMobile originating call procedureStructure of a layer 3 messageWhy GSM?
Acronyms:
TMSI : Temporary Mobile Subscriber Identity IMSI : International Mobile Subscriber IdentityBCCH : Broadcast Control ChannelFCCH : Frequency Correction ChannelSCH : Synchronization ChannelRACH : Random Access ChannelAGCH :Access Grant ChannelSDCH : Stand-alone Dedicated Control ChannelSABM: Set Asynchronous Balanced Mode
Acronyms (cnt’d)
RIL3 : Radio Interface Layer 3MAP : Mobile Application PartUA : Unnumbered AcknowledgeTUP : Telephone User Part ISUP : ISDN User PartTCH : Tariff ChannelACCH: Associated Control ChannelBSSMAP : BSS Management PartSCCP : Signaling Connection Control Part
RIL3 - CC
RIL3 - MM
CCM
MM
RR
Air (Um)Interface
A-bisInterface
MAP/EMAP/G
MAP/D
DATP
RIL3 - RR RSM BSSMAP
Distribution Protocol TCAPComponent Sublayer
Transaction Sublayer
A B C,D HLR/AuC
MAP/C
PresentationLayer *Session Layer *TransportLayer *
NetworkLayer
Physical
Data Link LAP-D
Radio
LAP-D
64kbps ch
SCCP
MTP3
MTP2
MTP1
SCCP
MTP3
MTP2
MTP1
SCCP
MTP3
MTP2
MTP1
SCCP
MTP3
MTP2
MTP1
MTP3
MTP2
MTP1
TUP,ISUP
OSI
LAYERS
Radio Resource Management sublayer:
Tasks closely related to physical layermanagement of frequency spectrumeverything to do with maintaining a clear
channel between PLMN and MSHandles all procedures necessary to establish,
maintain and release dedicated radio channels
Procedures in RR layer:
Channel assignment Channel releaseChannel change and handoverChange of channel frequencies, hopping sequences
(algorithms) and frequency tablesMeasurement reports from the MSPower control and Time advanceModification of channel modes (speech and data)Cipher mode setting
Mobility Management sublayer:
Cope with all effects of handling a mobile user that are not directly related to radio functions. Support of user mobility, registration, and
management of mobility data checking user and equipment identity user allowed to use services ? Extra services
allowed ? Support user confidentiality ( register user under a
TMSI)
Provision of user security Provision of an MM connection, based on existing
RR connection, to the CM sublayer
Procedures in MM sublayer :
Location UpdatePeriodic updatingAuthentication procedure IMSI attach procedure (on power up a MS will present
its IMSI to network and get a TMSI) IMSI detach ( on power off of a MS, detach procedure to
tell network it is no longer in service.TMSI reallocation Identification
Call Control sublayer:
Manages all functions necessary for circuit-switched call control in GSM PLMN
includes several protocol entities e.g. CC itself, SS, and SMS.
CC entity includes control functions defined for ISDN network signaling, messages and procedures required for
call establishment,
call clearing
call information etc.
Procedures in CC sublayer:
Call establishment for mobile-originated callsCall establishment for mobile-terminated callsChanges of transmission mode during an
ongoing call ( incall modification)Call reestablishment after interruption of an
MM connectionDual-tone multifrequency (DTMF) control
procedure for DTMF transmission
RIL3 - CC
RIL3 - MM
CCM
MM
RR
Air (Um)Interface
A-bisInterface
MAP/EMAP/G
MAP/D
DATP
RIL3 - RR RSM BSSMAP
Distribution Protocol TCAPComponent Sublayer
Transaction Sublayer
A B C,D HLR/AuC
MAP/C
PresentationLayer *Session Layer *TransportLayer *
NetworkLayer
Physical
Data Link LAP-D
Radio
LAP-D
64kbps ch
SCCP
MTP3
MTP2
MTP1
SCCP
MTP3
MTP2
MTP1
SCCP
MTP3
MTP2
MTP1
SCCP
MTP3
MTP2
MTP1
MTP3
MTP2
MTP1
TUP,ISUP
OSI
LAYERS
Layer 3 Protocols:
RIL3-RR : establish and release radio connections between an
MS and various BSCs for the duration of a call despite user movements.
Provide system information broadcasting provide inter- and intracell change of channels provides ciphering mode setting
Radio Subsystem Management ( RSM ): provides RR functions between BTS and BSC
Direct Transfer Application Part ( DTAP ): provide RR messages between MS and MSC
BSSMAP : provides RR messages between BSC and MSC
Distribution Protocol : distinguishes between BSSMAP and DTAP
RIL3-MM : deals with MS location management
location updatingIMSI attachperiodic updating
security aspects of systemauthenticationTMSI reallocationidentification.
RIL3-CC : deals with mobile originating and terminating call
establishment SS SMS
All MM and CC functions reside in MSC. All CC and MM messages are not interpreted by either the BTS or BSC. An RR connection needs to be established before communication between MS and MSC can occur.
RIL3 - CC
RIL3 - MM
CCM
MM
RR
Air (Um)Interface
A-bisInterface
MAP/EMAP/G
MAP/D
DATP
RIL3 - RR RSM BSSMAP
Distribution Protocol TCAPComponent Sublayer
Transaction Sublayer
A B C,D HLR/AuC
MAP/C
PresentationLayer *Session Layer *TransportLayer *
NetworkLayer
Physical
Data Link LAP-D
Radio
LAP-D
64kbps ch
SCCP
MTP3
MTP2
MTP1
SCCP
MTP3
MTP2
MTP1
SCCP
MTP3
MTP2
MTP1
SCCP
MTP3
MTP2
MTP1
MTP3
MTP2
MTP1
TUP,ISUP
OSI
LAYERS
Transaction Capabilities Application Part (TCAP) : provides correlation between individual operations
and structured exchanges building up a complete transaction.
Transaction sublayer : manages transactions on an end-to-end basis.
Component sublayer : correlates commands and responses within a dialog.
MAP Protocol :
Handles non-call related signaling between different network parts
designed to interact with MSC, VLR/HLR, AUC, and GMSC so they can communicate with each other.
Query - responsecontains a number of Application System Elements
(ASE)
all messages contain either mandatory or optional application parameters.
Functions can be grouped into two categories: MM and
basic service support.
MAP Protocol Connections :RIL3
BSS
BSSMAP
MAP/B
VLR
MSC EIR
HLR
GMSC
SMSGateway
MAP/C
MAP/C
MAP/I
MAP/D
MAP/F
VLR
MSC
MAP/H
MAP/B
MAP/EMAP/G
MAP Communication between peer-to-peer nodes :
ASE1
ASE n
ASE 1
ASE n
MAP
MAP
TCAP TCAP
Physical Connection
Flow Chart of Initial Mobile Acquisition:
Power onScan channels,monitor RFlevels
Select channel with highestRF level among control ch.s
Scan ch. For frequency correction burst (FCCH)
IsFCCH detected?
NO
YES
Scan ch. For timing sync.Burst ( SCH )
Select ch. With next highestRF level from control list
isSCH detected ?
NO
YES
Read data from BCCH ch and determine if the ch is a control ch ( BCCH )
isthe currentBCCH incl.
YES
NOFrom the ch data update thecontrol ch list
Camp on BCCH and start decoding
Mobile Originating Call Procedure:MS BSS MSC VLR HLR/EIR/AUC PSTN/ISDN
Press send RIL3-RR Ch. RequestRACH
RIL3-RR IMM SABMAGCH
< identity of message >SDCH (Up.Lk)
UASDCH (Dn. Lk.)
Service Request
TMSI, Call Setup
SDCH (Up. Lk.)
Service Request
TMSI, Call Setup
MAP/B Service Request, TMSI,Call Setup
Authentication, Ciphering, and TMSI assignment
MS BSS MSC VLR HLR/EIR/AUC PSTN/ISDN
RIL3-CC Setup ( Call Information ) MAP/B Send Callsetup information
Call complete MAP/B
RIL3-CCAssignment cmd
RIL3-CC assign.
complete
SDCH (Up.Lk.)
RIL3-CC assigncomplete
TUP/ISUP Initial Address Message ( IAM )
“ TUP/ISUPAnswer Signal”
TUP/ISUP Address Complete Message ( ACM )RIL3-CC alerting
Answer MessageRIL3-CC connectTCH/ACCH
RIL3-CC Connect Ack.
Conversation Starts
RIL3-CC call ProceedingSubscriberPhone Rings
Structure of a layer 3 message:
CRC
Address field
Control field
Length indicator field
Information field
1
2
3
4
.
.
.
101112
Layer 2 Format type B
8 7 6 5 4 3 2 1 Octet Bit 8 7 6 5 4 3 2 1 Octet
Information Elements “ mandatory ”
Information Elements “ optional ”
0 Message Type
TIflag
TI Protocol Discriminator
Structure of a GSM layer 3 message
Transaction Identifier ( TI ) :
Used to distinguish between possible (multiple) parallel CC connections and between various transactions taking place over these simultaneous CC connections.
TI not relevant for RR and MM connections ( coded “ 0000” )
TI flag : indicates originator of a CC message ‘0’ by originator and coded ‘1’ by its peer entity
originator fills in TI value. Kept and serves as a label during transaction
Protocol Discriminator ( PD )
Links layer 3 protocol to the entity the message is addressed to.
Identifies 6 protocolsProtocol PD Binary
RRM 0110MM 0101CC 0011SMS 1001SS 1011Test procedure 1111All other values reserved
Message Type :
MT indicates the function of layer 3 message.Uses lower 6 bits ( 64 possible message types)
for a protocol type indicated by PD.MT is part of a set of messages in a protocolBit 8 = 0 ( reserved )Bit 7 = send sequence variable and may be
used for MM and CC messages.
Information Elements (IE):
Depending on MT, may or may not have one or more IE
Types of IE : Mandatory fixed length
( MF ) Mandatory variable length
( MV) Optional Fixed Length (OF) OV
Information Elements “ mandatory ”
Information Elements “ optional ”
0 Message Type
TIflag
TI Protocol Discriminator
Structure of a GSM layer 3 message
Why GSM ?
DigitalHigh audio quality and link integrityHigh spectral efficiencyIdentical system in all countriesIntersystem RoamingHigh degree of flexibility ( open architecture
that will allow new services to be introduced in the future.
Economy in both sparsely and heavily populated areas
Integration with ISDNOther security featuresSMS and use of facsimile featuresEasy to introduce the systemLow-cost infrastructure