GSM_II
Transcript of GSM_II
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GSM : The Network Layer
Rasha Morsi
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Presentation Outline:
Radio Resource Management
Mobility Management
Call Control Management
Layer 3 Protocols
Mobile Application Part protocol
Flow chart of initial mobile acquisition Mobile originating call procedure
Structure of a layer 3 message
Why GSM?
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Acronyms:
TMSI : Temporary Mobile Subscriber Identity
IMSI : International Mobile Subscriber Identity
BCCH : Broadcast Control Channel
FCCH : Frequency Correction Channel
SCH : Synchronization Channel
RACH : Random Access Channel AGCH :Access Grant Channel
SDCH : Stand-alone Dedicated Control Channel
SABM: Set Asynchronous Balanced Mode
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Acronyms (cntd)
RIL3 : Radio Interface Layer 3
MAP : Mobile Application Part
UA : Unnumbered Acknowledge
TUP : Telephone UserPart
ISUP : ISDN UserPart
TCH : Tariff Channel ACCH: Associated Control Channel
BSSMAP : BSS Management Part
SCCP : Signaling Connection Control Part
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RIL3 - CC
RIL3 - MM
CCM
MM
RR
Air (Um)
Interface
A-bis
Interface
MAP/EMAP/G
MAP/D
DATP
RIL3 - RR RSM BSSMAP
Distribution ProtocolTCAP
Component Sublayer
Transaction Sublayer
A B C,D HLR /AuC
MAP/C
Presentation
Layer *
Session
Layer *
Transport
Layer *
Network
Layer
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
O
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Radio Resource Management sublayer:
Tasks closely related to physical layer
management of frequency spectrum
everything to do with maintaining a clear
channel between PLMN and MS
Handles all procedures necessary to establish,
maintain and release dedicated radio channels
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Procedures in RR layer:
Channel assignment
Channel release
Channel change and handover
Change of channel frequencies, hopping sequences
(algorithms) and frequency tables
Measurement reports from the MS
Power control and Time advance
Modification of channel modes (speech and data)
Cipher mode setting
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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 servicesallowed ?
Support user confidentiality ( register user under a
TMSI)
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Provision of user security
Provision of an MM connection, based on existing
RR connection, to the CM sublayer
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Procedures in MM sublayer :
Location Update
Periodic updating
Authentication 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
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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.
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Procedures in CC sublayer:
Call establishment for mobile-originated calls
Call establishment for mobile-terminated calls
Changes of transmission mode during an
ongoing call ( incall modification)
Call reestablishment after interruption of an
MM connection
Dual-tone multifrequency (DTMF) control
procedure for DTMF transmission
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RIL3 - CC
RIL3 - MM
CCM
MM
RR
Air (Um)
Interface
A-bis
Interface
MAP/E
MAP/G
MAP/D
DATP
RIL3 - RR RSM BSSMAP
Distribution ProtocolTCAP
Component Sublayer
Transaction Sublayer
A B C,D HLR /AuC
MAP/C
Presentation
Layer *
Session
Layer *
Transport
Layer *
Network
Layer
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
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Layer 3 Protocols:
RIL3-RR :
establish and release radio connections between an
MS and various BSCs for the duration of a calldespite user movements.
Provide system information broadcasting
provide inter- and intracell change of channels
provides ciphering mode setting
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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
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RIL3-MM :
deals with MS location management
location updating
IMSI attach
periodic updating
security aspects of system
authentication
TMSI reallocation
identification.
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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.
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RIL3 - CC
RIL3 - MM
CCM
MM
RR
Air (Um)
Interface
A-bis
Interface
MAP/E
MAP/G
MAP/D
DATP
RIL3 - RR RSM BSSMAP
Distribution ProtocolTCAP
Component Sublayer
Transaction Sublayer
A B C,D HLR /AuC
MAP/C
Presentation
Layer *
Session
Layer *
Transport
Layer *
Network
Layer
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
O
S
I
L
A
Y
E
R
S
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Transaction Capabilities Application Part
(TCAP) :
provides correlation between individual operationsand 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.
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MAPProtocol :
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 - response
contains a number of Application System Elements
(ASE)
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all messages contain either mandatory or optional
application parameters.
Functions can be grouped into two categories: MM and
basic service support.
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MAPProtocol Connections :RIL3
BSS
BSSMAP
MAP/B
VLR
MSCEIR
HLR
GMSC
SMS
Gateway
MAP/C
MAP/C
MAP/I
MAP/D
MAP/F
VLR
MSC
MAP/H
MAP/B
MAP/EMAP/G
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MAP Communication between peer-
to-peer nodes :
ASE1
ASE n
ASE1
ASE n
MAPMAP
TCAP TCAP
Physical Connection
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Flow Chart of Initial Mobile Acquisition:
Power onScan channels,
monitor RF
levels
Select channel with highest
RF level among control ch.s
Scan ch. For frequency
correction burst (FCCH)
Is
FCCH detected?
NO
YES
Scan ch. For timing sync.
Burst ( SCH )
Select ch. With next highest
RF level from control list
isSCH detected ?
NO
YES
Read data from BCCH ch and determine ifthe ch is a control ch ( BCCH )
isthe current
BCCH incl.
YES
NOFrom the ch data update the
control ch list
Camp on BCCH and start
decoding
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Mobile Originating Call Procedure:MS BSS MSC VLR HLR /EIR/AUC PSTN/ISDN
Press send RIL3-RR Ch. Request
RACH
RIL3-RR IMM SABM
AGCH
< 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
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MS BSS MSC VLR HLR /EIR/AUC PSTN/ISDN
RIL3-CC Setup ( Call Information ) MAP/B Send Call
setup information
Call complete MAP/B
RIL3-CC
Assignment cmd
RIL3-CC assign.
complete
SDCH (Up.Lk.)
RIL3-CC assign
complete
TUP/ISUP Initial Address Message ( IAM )
TUP/ISUP
Answer
Signal
TUP/ISUPAddress Complete Message ( ACM )RIL3-CC alerting
Answer MessageRIL3-CC connectTCH/ACCH
RIL3-CC Connect Ack.
Conversation Starts
RIL3-CC call Proceeding
SubscriberPhone
Rings
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Structure of a layer 3 message:
CRC
Address field
Control field
Length indicator field
Information field
1
2
3
4
.
.
.
10
11
12
Layer2 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
TI
flagTI Protocol
Discriminator
Structure of a GSM layer 3 message
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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
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Protocol Discriminator ( PD )
Links layer 3 protocol to the entity the
message is addressed to.
Identifies 6 protocolsProtocol PD Binary
RRM 0110
MM 0101
CC 0011SMS 1001
SS 1011
Test procedure 1111
All other values reserved
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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 protocol
Bit 8 = 0 ( reserved )
Bit 7 = send sequence variable and may be
used for MM and CC messages.
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Information Elements (IE):
Depending on MT, may
or may not have one or
more IE
Types of IE :
Mandatory fixed length
( MF )
Mandatory variablelength ( MV)
Optional Fixed Length
(OF)
OV
Information Elements
mandatory
Information Elements
optional
0 Message Type
TI
flagTI Protocol
Discriminator
Structure of a GSM layer 3 message
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Why GSM ?
Digital
High audio quality and link integrity
High spectral efficiency
Identical system in all countries
Intersystem Roaming
High degree of flexibility ( open architecture
that will allow new services to be introduced
in the future.
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Economy in both sparsely and heavily
populated areas
Integration with ISDN
Other security features
SMS and use of facsimile features
Easy to introduce the system
Low-cost infrastructure
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References:
GSM System Engineering, Asha Mehrotra,
Artech House Publishers, 1997
An Introduction To GSM, Redl, Weber,
Oliphant, Artech House Publishers, 1995