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GSM Call FLOW - The Network Layer

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					GSM : The Network Layer




         www.XpressKnowledge.com
Presentation Outline:

zRadio Resource Management
zMobility Management
zCall Control Management
zLayer 3 Protocols
zMobile Application Part protocol
zFlow chart of initial mobile acquisition
zMobile originating call procedure
zStructure of a layer 3 message
zWhy GSM?
Acronyms:

zTMSI : Temporary Mobile Subscriber Identity
zIMSI : International Mobile Subscriber Identity
zBCCH : Broadcast Control Channel
zFCCH : Frequency Correction Channel
zSCH : Synchronization Channel
zRACH : Random Access Channel
zAGCH :Access Grant Channel
zSDCH : Stand-alone Dedicated Control Channel
zSABM: Set Asynchronous Balanced Mode
Acronyms (cnt’d)

zRIL3 : Radio Interface Layer 3
zMAP : Mobile Application Part
zUA : Unnumbered Acknowledge
zTUP : Telephone User Part
zISUP : ISDN User Part
zTCH : Tariff Channel
zACCH: Associated Control Channel
zBSSMAP : BSS Management Part
zSCCP : Signaling Connection Control Part
                Air (Um)      A-bis        A              B                    C,D HLR/AuC
                Interface     Interface
CCM                     RIL3 - CC
                                                                     MAP/D             MAP/C
MM                      RIL3 - MM
RR                             DATP                     MAP/E                                   TUP,
               RIL3 - RR        RSM         BSSMAP      MAP/G                                   ISUP

                                                        Component Sublayer                             O
                               Distribution Protocol                                                   S
                                                               TCAP
                                                        Transaction Sublayer                           I


                                                                                                       L
                                                                                                       A
Presentation                                                                                           Y
Layer *                                                                                                E
Session                                                                                                R
Layer *                                                                                                S
Transport
Layer *
 Network
 Layer




                                           SCCP        SCCP          SCCP             SCCP

                                                                                               MTP3
                                           MTP3        MTP3          MTP3             MTP3
                                                                                               MTP2
 Data Link      LAP-D         LAP-D        MTP2        MTP2          MTP2             MTP2
 Physical                                                                                      MTP1
                Radio        64kbps ch     MTP1                      MTP1             MTP1
                                                       MTP1
Radio Resource Management sublayer:

zTasks closely related to physical layer
zmanagement of frequency spectrum
zeverything to do with maintaining a clear
 channel between PLMN and MS
zHandles all procedures necessary to establish,
 maintain and release dedicated radio channels
Procedures in RR layer:

zChannel assignment
zChannel release
zChannel change and handover
zChange of channel frequencies, hopping sequences
 (algorithms) and frequency tables
zMeasurement reports from the MS
zPower control and Time advance
zModification of channel modes (speech and data)
zCipher mode setting
Mobility Management sublayer:

zCope with all effects of handling a mobile user
 that are not directly related to radio functions.
  ySupport of user mobility, registration, and
   management of mobility data
  ychecking user and equipment identity
  yuser allowed to use services ? Extra services
   allowed ?
  ySupport user confidentiality ( register user under a
   TMSI)
yProvision of user security
yProvision of an MM connection, based on
 existing RR connection, to the CM sublayer
Procedures in MM sublayer :

zLocation Update
zPeriodic updating
zAuthentication procedure
zIMSI attach procedure (on power up a MS will
 present its IMSI to network and get a TMSI)
zIMSI detach ( on power off of a MS, detach
 procedure to tell network it is no longer in service.
zTMSI reallocation
zIdentification
Call Control sublayer:

zManages all functions necessary for circuit-switched
 call control in GSM PLMN
zincludes several protocol entities e.g. CC itself, SS,
 and SMS.
zCC entity includes
   ycontrol functions defined for ISDN network signaling,
   ymessages and procedures required for
    call establishment,
    call clearing
    call information etc.
Procedures in CC sublayer:

zCall establishment for mobile-originated calls
zCall establishment for mobile-terminated calls
zChanges of transmission mode during an
 ongoing call ( incall modification)
zCall reestablishment after interruption of an
 MM connection
zDual-tone multifrequency (DTMF) control
 procedure for DTMF transmission
                Air (Um)      A-bis        A              B                    C,D HLR/AuC
                Interface     Interface
CCM                     RIL3 - CC
                                                                     MAP/D             MAP/C
MM                      RIL3 - MM
RR                             DATP                     MAP/E                                   TUP,
               RIL3 - RR        RSM         BSSMAP      MAP/G                                   ISUP

                                                        Component Sublayer                             O
                               Distribution Protocol                                                   S
                                                               TCAP
                                                        Transaction Sublayer                           I


                                                                                                       L
                                                                                                       A
Presentation                                                                                           Y
Layer *                                                                                                E
Session                                                                                                R
Layer *                                                                                                S
Transport
Layer *
 Network
 Layer




                                           SCCP        SCCP          SCCP             SCCP

                                                                                               MTP3
                                           MTP3        MTP3          MTP3             MTP3
                                                                                               MTP2
 Data Link      LAP-D         LAP-D        MTP2        MTP2          MTP2             MTP2
 Physical                                                                                      MTP1
                Radio        64kbps ch     MTP1                      MTP1             MTP1
                                                       MTP1
Layer 3 Protocols:

zRIL3-RR :
  yestablish and release radio connections between
   an MS and various BSCs for the duration of a call
   despite user movements.
  yProvide system information broadcasting
  yprovide inter- and intracell change of channels
  yprovides ciphering mode setting
zRadio Subsystem Management ( RSM ):
  yprovides RR functions between BTS and BSC
zDirect Transfer Application Part ( DTAP ):
  yprovide RR messages between MS and MSC
zBSSMAP :
  yprovides RR messages between BSC and MSC
zDistribution Protocol : distinguishes between
 BSSMAP and DTAP
zRIL3-MM :
 ydeals with MS location management
    xlocation updating
    xIMSI attach
    xperiodic updating
 ysecurity aspects of system
    xauthentication
    xTMSI reallocation
    xidentification.
zRIL3-CC :
  ydeals with mobile originating and terminating call
   establishment
  ySS
  ySMS
zAll 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.
                Air (Um)      A-bis        A              B                    C,D HLR/AuC
                Interface     Interface
CCM                     RIL3 - CC
                                                                     MAP/D             MAP/C
MM                      RIL3 - MM
RR                             DATP                     MAP/E                                   TUP,
               RIL3 - RR        RSM         BSSMAP      MAP/G                                   ISUP

                                                        Component Sublayer                             O
                               Distribution Protocol                                                   S
                                                               TCAP
                                                        Transaction Sublayer                           I


                                                                                                       L
                                                                                                       A
Presentation                                                                                           Y
Layer *                                                                                                E
Session                                                                                                R
Layer *                                                                                                S
Transport
Layer *
 Network
 Layer




                                           SCCP        SCCP          SCCP             SCCP

                                                                                               MTP3
                                           MTP3        MTP3          MTP3             MTP3
                                                                                               MTP2
 Data Link      LAP-D         LAP-D        MTP2        MTP2          MTP2             MTP2
 Physical                                                                                      MTP1
                Radio        64kbps ch     MTP1                      MTP1             MTP1
                                                       MTP1
zTransaction Capabilities Application Part
 (TCAP) :
  yprovides correlation between individual
   operations and structured exchanges building up a
   complete transaction.
  yTransaction sublayer : manages transactions on an
   end-to-end basis.
  yComponent sublayer : correlates commands and
   responses within a dialog.
MAP Protocol :

zHandles non-call related signaling between
 different network parts
zdesigned to interact with MSC, VLR/HLR, AUC,
 and GMSC so they can communicate with each
 other.
zQuery - response
zcontains a number of Application System Elements
 (ASE)
zall messages contain either mandatory or optional
 application parameters.
zFunctions can be grouped into two categories:
   yMM and
   y basic service support.
MAP Protocol Connections :
RIL3         BSSMAP                           MAP/F
                          MSC                                   EIR
                                  MAP/B

                                VLR            MAP/I
                                                                HLR
                                               MAP/D


                                                       MAP/C
       BSS        MAP/E
                                      MAP/G
                                                                   MAP/C



                                                 GMSC

                                 VLR


                          MSC         MAP/B                    SMS
                                                               Gateway
                                                 MAP/H
MAP Communication between peer-
to-peer nodes :

              ASE 1                 ASE1
                                                   MAP
 MAP

              ASE n                 ASE n




       TCAP                                 TCAP




              Physical Connection
Flow Chart of Initial Mobile Acquisition:
                       Scan channels,             Select channel with highest
 Power on              monitor RF                 RF level among control ch.s
                       levels
                                                  Scan ch. For frequency
                                                  correction burst (FCCH)

                                                            Is
      Select ch. With next highest           NO
      RF level from control list                        FCCH detected?

                                                                    YES
                                                    Scan ch. For timing sync.
                                                    Burst ( SCH )

                                        NO                      is
                                                           SCH detected ?
                                                                       YES
                                             Read data from BCCH ch and determine if
                                             the ch is a control ch ( BCCH )

                                        NO                     is
      From the ch data update the                          the current
      control ch list                                      BCCH incl.
                                                                      YES
                                                    Camp on BCCH and start
                                                    decoding
      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)

                     UA
                                       SDCH (Dn. Lk.)


             Service Request
                                       SDCH (Up. Lk.)      MAP/B Service
             TMSI, Call Setup          Service Request     Request, TMSI,
                                                           Call Setup
                                       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 Call
                                            setup information

       RIL3-CC call Proceeding              Call complete MAP/B
                                                                                            Subscriber
                                                                                            Phone
                         RIL3-CC                                                            Rings
                         Assignment cmd


     RIL3-CC assign.     SDCH (Up.Lk.)                                                      “ TUP/ISUP
                                                                                            Answer
     complete            RIL3-CC assign         TUP/ISUP Initial Address Message ( IAM )    Signal”
                         complete
                                                TUP/ISUP Address Complete Message ( ACM )
                         RIL3-CC alerting

      TCH/ACCH           RIL3-CC connect
                                                    Answer Message
     RIL3-CC Connect Ack.


                                  Conversation Starts
    Structure of a layer 3 message:
8    7     6      5   4    3   2   1   Octet    Bit   8      7        6     5    4      3     2       1   Octet


               Address field                1         TI         TI                   Protocol
                                                      flag                            Discriminator
               Control field                2
         Length indicator field             3         0                Message Type
                                        4
           Information field
                                        .
                                        .                             Information Elements
                                        .                                 “ mandatory ”

                                        10                            Information Elements
                                                                          “ optional ”
                   CRC                  11
                                        12
         Layer 2 Format type B                                   Structure of a GSM layer 3 message
Transaction Identifier ( TI ) :

zUsed to distinguish between possible (multiple) parallel
 CC connections and between various transactions taking
 place over these simultaneous CC connections.
zTI not relevant for RR and MM connections ( coded “
 0000” )
zTI flag : indicates originator of a CC message ‘0’ by
 originator and coded ‘1’ by its peer entity
zoriginator fills in TI value. Kept and serves as a label
 during transaction
Protocol Discriminator ( PD )
zLinks layer 3 protocol to the entity the
 message is addressed to.
zIdentifies 6 protocols
   Protocol                     PD Binary
 RRM                                0110
 MM                                 0101
 CC                                 0011
 SMS                                1001
 SS                                 1011
 Test procedure                     1111
 All other values reserved
Message Type :

zMT indicates the function of layer 3 message.
zUses lower 6 bits ( 64 possible message types)
 for a protocol type indicated by PD.
zMT is part of a set of messages in a protocol
zBit 8 = 0 ( reserved )
zBit 7 = send sequence variable and may be
 used for MM and CC messages.
Information Elements (IE):

zDepending on MT, may        TI     TI                   Protocol
                             flag                        Discriminator
 or may not have one or
 more IE                     0            Message Type

zTypes of IE :
  y Mandatory fixed length
   ( MF )                                Information Elements
                                             “ mandatory ”
  yMandatory variable
   length ( MV)                          Information Elements
                                             “ optional ”
  yOptional Fixed Length
   (OF)                             Structure of a GSM layer 3 message

  yOV
Why GSM ?

zDigital
zHigh audio quality and link integrity
zHigh spectral efficiency
zIdentical system in all countries
zIntersystem Roaming
zHigh degree of flexibility ( open architecture
 that will allow new services to be introduced
 in the future.
zEconomy in both sparsely and heavily
 populated areas
zIntegration with ISDN
zOther security features
zSMS and use of facsimile features
zEasy to introduce the system
zLow-cost infrastructure
References:

zGSM System Engineering, Asha Mehrotra,
  Artech House Publishers, 1997
zAn Introduction To GSM, Redl, Weber,
 Oliphant, Artech House Publishers, 1995
THANK YOU

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DOCUMENT INFO
Description: GSM Call FLOW - The Network Layer. * 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?