fresh field mtc 001 section 4

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    GSM SystemOverviewSection Four

    Simple GSM Call Sequences

    and Ladder Diagrams

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    2001 Freshfield Communications Limited.Company Confidential Slide 2

    Layer 3 MessagesLayer 3 Messages Call SequencesCall Sequences

    Service Request and IMSI attach

    Location Area Update

    Authentication and Encryption

    Mobile Terminated Calls

    Mobile Originated Calls

    Channel Release

    Handover

    SummarySummary

    Presentation OutlinePresentation Outline

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    2001 Freshfield Communications Limited.Company Confidential Slide 3

    At the end of this course, attendees will:At the end of this course, attendees will: Have an appreciation of call sequences in GSM

    Have an appreciation of different types of handover

    ObjectivesObjectives

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    2001 Freshfield Communications Limited.Company Confidential Slide 4

    BSS MSCVLR

    HLR

    Call Control (CC)

    Mobility Management (MM)

    Radio Resource (RR)

    BSS MSCVLR

    HLR

    BSS MSCVLR

    HLR

    Layer 3 MessagesLayer 3 Messages

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    2001 Freshfield Communications Limited.Company Confidential Slide 5

    Grouped into three categoriesGrouped into three categories Call Control

    Mobility Management

    Radio Resource

    To understand these categories, think of a mobile phoneTo understand these categories, think of a mobile phone

    as being:as being:

    A telephone

    A mobile device A radio

    Layer 3 MessagesLayer 3 Messages

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    2001 Freshfield Communications Limited.Company Confidential Slide 6

    Call ControlCall Control Messages to and from the telephone part of phone

    Responsible for setting up and clearing down calls

    Messages pass between phone and MSC and are transparent

    to the BSS

    Mobility ManagementMobility Management

    Concerned with mobility aspect of phone

    Messages pass between phone and VLR and HLR

    Messages are transparent to the BSS and MSC

    Layer 3 MessagesLayer 3 Messages

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    2001 Freshfield Communications Limited.Company Confidential Slide 7

    Radio ResourcesRadio Resources Messages are concerned with establishment, maintenance and

    clearing down of radio links

    Messages are exchanged between the phone and the BSS

    In some equipment, messages may be transparent to the BTSand are instead all routed to the BSC.

    In other equipment, some messages may stop at the BTS

    Layer 3 MessagesLayer 3 Messages

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 8

    Service Request and IMSI AttachService Request and IMSI Attach

    MS MSC

    SCCP Connection Request

    BSSMAP Complete Layer 3 Information

    SCCP Connection Confirm

    (SDCCH) SABM Establishes the signalling link

    (SDCCH) UA

    (RACH) RIL3-RR Channel request

    (AGCH - CCCH) RIL3-RR IMM Assignment - Move MS to SDCCH

    BSS

    BSS Transparent to MS

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 9

    Service Request and IMSI Attach (contd)Service Request and IMSI Attach (contd)MS

    (SDCCH)

    (SDCCH)

    (SDCCH)

    (SDCCH)

    (SDCCH) UA

    RIL3 - RR DISC

    BSSMAP Clear Complete

    IMSI Attach Ack

    RIL3 -RR IMSI Attach Ack

    BSSMAP Clear Cmd

    RIL3 - RR Channel Release

    UA

    RIL3 -MM IMSI Attach

    MAP/B Attach IMSI

    MAP/B IMSI Attach Ack

    BSS

    (RACH)

    (AGCH - CCCH)

    (SDCCH)

    (SDCCH)

    RIL3 - RR Channel Request

    RIL3 - RR IMM Assignment - Move MS to SDCCH

    SABM Establishes the signalling link

    MSC VLR

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 10

    Location Area UpdateLocation Area Update

    MS BSS MSC VLR HLR

    (RACH)

    (AGCH - CCCH)

    (SDCCH)

    (SDCCH)

    (SDCCH)

    (SDCCH)

    (SDCCH)

    RIL3 - RR Channel Request

    RIL3 - RR IMM Assignment - Move MS to SDCCH

    SABM Establishes the signalling link

    UA

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 11

    Location Area Update (contd)Location Area Update (contd)

    MS BSS MSC VLR HLR

    MAP/D Location

    Update Result

    MAP/B Location

    Update Ack

    RIL3-MM Location Update Accepted

    RIL3-MM Location Update Reject

    Unnumbered Acknowledgement

    (SDCCH)

    (SDCCH)

    (SDCCH)

    BSSMAP Clear Command

    Channel release

    Disconnect

    BSSMAP Clear Complete

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 12

    Authentication and EncryptionAuthentication and Encryption

    MS BSS MSC VLR HLR AUC

    MAP/D Send Parameters

    MAP/D Send Parameters Result - RAND, SRES, Kc

    MAP/D Authenticate

    RAND + CKSN RIL3 - MM Authentication Request

    (SDCCH)

    SRES + CKSN RIL3 - MM Authentication Response

    (SDCCH) MAP/B Authentication Complete

    (SDCCH) RIL3 - MM Service Accept

    (SDCCH) RIL3 - MM Service Reject (if SRES's do not equal)

    MAP/D Authentication Complete

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 13

    Authentication and Encryption (contd)Authentication and Encryption (contd)

    MS BSS MSC VLR

    MAP/B Set Cipher Mode

    MAP/B Cipher Mode Command

    (SDCCH) RIL3 - RR Cipher Mode Command

    (SDCCH) RIL3 - RR Cipher Mode Complete - Encrypted

    BSSMAP Cipher Mode Complete

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 14

    Optional

    Mobile Terminated CallsMobile Terminated Calls

    MS

    UA

    Encryption Process

    (RACH)

    (PCH - CCCH)

    RIL3 - RR IMM Assignment(AGCH - CCCH)

    RIL3 - RR Paging Response

    (SDCCH)

    (SDCCH)

    RIL3 - RR Paging Request

    BSS MSC VLR

    MAP/B Send Info

    LAI & TMSI

    MAP/B Complete Call

    LAI & TMSI

    Request - TMSI

    BSSMAP - Page TMSI

    RIL3 - RR Channel Request

    Paging Response

    MAP/B - Process Access

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 15

    Mobile Terminated Calls (contd)Mobile Terminated Calls (contd)

    MS BSS MSC VLR

    (SDCCH) RIL3 - CC Call Setup

    (SDCCH) RIL3 - CC Call Confirmation

    (SDCCH) RIL3 - CC Alerting

    Channel Assign Comd

    (SDCCH)

    (SDCCH) Channel Assign Complete

    (FACCH - TCH) RIL3 - RR Alert

    MS Rings

    (FACCH - TCH) RIL3 - RR Connect

    MS Answers

    RIL3 - CC Connect Acknowledge

    Channel Assign Comd

    Conversation Starts

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 16

    Mobile Originated CallsMobile Originated Calls

    MS BSS MSC VLR

    Service Request - TMSI, Call Setup

    MAP/B Service Request - TMSI, Call Setup

    MAP/B - Fwd new TMSI

    (SDCCH) RIL3-MM Reallocate New TMSI

    (SDCCH) RIL3-MM Reallocation complete

    MAP/B - TMSI Ack

    (SDCCH) UA

    (SDCCH) Service Request - TMSI, Call Setup

    (SDCCH) SABM

    (RACH) RIL3 - RR Channel Request

    (AGCH - CCCH) RIL3 - RR IMM Assignment

    Press Send

    Encryption

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 17

    Mobile Originated Calls (contd 1)Mobile Originated Calls (contd 1)

    MS BSS MSC VLR

    (TCH) Conversation Starts

    (TCH - FACCH)

    (TCH - FACCH)

    RIL3-CC Connect

    RIL3-CC Connect Ack

    (SDCCH) RIL3-CC Assign Complete

    (TCH - FACCH) RIL3-CC Alerting

    MAP/B Call complete

    (SDCCH) RIL3-CC Call Proceeding

    (SDCCH)

    (SDCCH) RIL3 - CC Setup (Call Info)

    MAP/B - Send Call Setup Info

    RIL3-CC Channel Assign Comd

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 18

    Mobile Originated Calls (contd 2)Mobile Originated Calls (contd 2)

    MS BTS 1 BSC BTS 2 MS

    UA Frame

    RIL3-RR Handover Complete

    Resume Communication on New Channel

    RSM RF Channel Release

    RSM RF Channel Release Ack

    RIL3-RR Handover Command

    RIL3-RR Handover Access

    RIL3-RR Physical Information

    SABM Frame

    Call in Progress

    RSM Channel Activation

    RSM Channel Activation Ack

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 19

    Channel ReleaseChannel Release

    MS BSS MSC PSTN

    Release (REL)

    BSSMAP Release Complete

    Conversation

    BSSMAP Disconnect

    Release Confirmed (REL CONF)

    (FACCH) DTAP - Release

    (FACCH) RIL3-RR Disconnect

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 20

    There are 3 purposes for handover:There are 3 purposes for handover: The first purpose is to rescue a call. If the call is not transferred

    immediately, it will be lost.

    The second purpose may be to reduce the interference that a

    call in one cell may cause to calls in another cell. The third purpose is to ease traffic congestion by moving some

    calls from a highly congested cell to a cell that is not so

    congested.

    HandoverHandover

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 21

    There are 3 types of handover:There are 3 types of handover: First, there is a handover from one radio to another of the same

    or different BTS but same BSC

    Second, there is a handover between channels of different

    BSCs under the control of the same MSC Third there is a handover between channels under the control of

    different MSCs in the same PLMN

    Handover (Contd 1)Handover (Contd 1)

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 22

    MSC (a) MSC (b) MSC (c)

    BSC (1) BSC (2)

    Cell 1

    Cell 2

    Cell 3

    Cell 4

    Cell 5

    Cell 6

    Cell 7

    Cell 8BTS BTS

    BTS BTS

    BSC (3) BSC (4)

    4

    3

    3 41 2

    1a 1b 2a 2b3a

    3b4a

    4b

    PSTN

    Handover (Contd 2)Handover (Contd 2)

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    2001 Freshfield Communications Limited.Company Confidential

    Slide 23

    Layer 3 messages are essential for the control ofLayer 3 messages are essential for the control ofresources and for mobility managementresources and for mobility management

    Simple call sequences highlight component parts of GSMSimple call sequences highlight component parts of GSM

    architecture usedarchitecture used

    Different types of handovers are supportedDifferent types of handovers are supported

    SummarySummary