Signalling Prot

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    Tik-109/110.300 Fall 2000 Hannu H. Kari Page 1

    Tik-109/110.300

    Telecommunications architectures:Protocols

    Hannu H. KARI/Helsinki University of Technology (HUT)

    TML-laboratory/CS/HUT

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    Agenda

    Protocol designMultivendor interfaces

    Handling protocol error

    Handling lost packets

    Handling corrupted data

    Handling failed network elements

    Fault tolerant system design

    Protocol examples

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    Protocol design

    Example protocol stack

    Um GbMS BSS SGSN

    SNDC SMSGMM

    LLC

    RLC

    MAC

    GSM RF

    Relay

    RLC

    MAC

    GSM RF

    BSSGP

    Network

    Service

    L1

    SNDC SMSGMM

    LLC

    BSSGP

    Network

    Service

    L1

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    Protocol design

    Basic operation model

    4. Confirm1. Request 3. Response 2. Indication

    Level - N+1

    Level - N

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    Multivendor interfaces

    Proprietary interfaces Implementations of different manufacturers wont

    necessarily interwork

    Possible manufacturer extensions, interpretations,

    solutions, combined equipments, ...

    Multivendor interfaces

    Well defined protocols

    Strong interoperability requirements Interoperability testing (type approvals)

    Support for multiple versions

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    Handling protocol errors

    E.g., in GTP protocol (GPRS Tunneling Protocol), theprotocol layer handles:

    Protocol has version numbers

    Handling too short packets

    Unknown and erroneous headers Unexpected message

    Missing or invalid mandatory elements

    Unknown information element

    Out of sequence information elements

    Repeated information elements

    Incorrect optional information elements

    TLV, TV, V formatting (T=Type, L=Length, V=Value)

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    Handling lost packets

    In principle, data packets at any protocol layer may belost

    Methods to cope lost packets

    Acknowledges

    Timers Retries

    State machines

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    Handling corrupted data

    Methods to cope corrupted data CRC checks (RLC, LLC, L2 under IP, ) Sanity checks of data

    State machines

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    Handling failed network

    elements

    Network elements with permanent data (HLR failure) After restart, inform all MSC/VLRs and SGSNs that have MSs ofthat HLR

    Network elements with non-permanent data (SGSN

    failure) Inform associated neigboring element

    VLRs

    Inform MS next time when it next time sends uplink message

    Inform GGSN next time when GGSN sends MT data. MS may bepaged

    MT SMSs are rejected

    CS page is sent to entire MSC/VLR area or to MSC/VLR specifiedarea

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    Handling failed network

    elements

    Simpler network elements (GGSN failure)

    Inform SGSN when SGSN sends MO data

    Reject data packets MT packets

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    Fault tolerant systems

    Fault models

    Only knows faults can be handled (i.e., if you are not preparedto handle the faults, you cant survive those faults)

    Fault prevention

    Fault detection Fault isolation

    Reduced/Degraded service

    Fault recovery

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    Example:

    Simple procedure, Attach

    MS etwork

    ATTACH REQUEST

    ATTACH ACCEPT

    ATTACH COMPLETE

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    Example:

    Signaling chart

    7d. Cancel Location Ack

    7c. Cancel Location

    7b. Update Location

    7g. Update Location Ack

    7e. Insert Subscriber Data

    7f. Insert Subscriber Data Ack

    6d. Insert Subscriber Data

    6c. Cancel Location Ack

    6b. Cancel Location

    3. Identity Response

    2. Identification Response

    2. Identification Request

    1. Attach Request

    5. IMEI Check

    3. Identity Request

    4. Authentication

    6a. Update Location

    7a. Location Updating Request

    7h. Location Updating Accept

    6f. Update Location Ack

    6e. Insert Subscriber Data Ack

    MS BSS new SGSN old SGSN GGSN HLR EIR

    old

    MSC/VLR

    new

    MSC/VLR

    9. Attach Complete

    8. Attach Accept

    10. TMSI Reallocation Complete

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    Example:

    Signaling chart

    1) The MS initiates the attach procedure by the transmission of an

    Attach Request (IMSI or P TMSI and old RAI, Classmark, CKSN, AttachType, DRX Parameters, old P TMSI Signature) message to the SGSN.IMSI shall be included if the MS does not have a valid P TMSI available. Ifthe MS has a valid P TMSI, then P TMSI and the old RAI associated withP TMSI shall be included. Classmark contains the MS's GPRS multislot

    capabilities and supported GPRS ciphering algorithms in addition to theexisting classmark parameters defined in GSM 04.08. Attach Type indicateswhich type of attach that is to be performed, i.e., GPRS attach only, GPRSAttach while already IMSI attached, or combined GPRS / IMSI attach. DRXParameters indicates whether the MS uses discontinuous reception or not.

    If the MS uses discontinuous reception, then DRX Parameters also indicatewhen the MS is in a non-sleep mode able to receive paging requests andchannel assignments. If the MS uses P TMSI for identifying itself and if ithas also stored its old P TMSI Signature, then the MS shall include the oldP TMSI Signature in the Attach Request message.

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    Example:

    Signaling chart

    8) The SGSN sends an Attach Accept (P TMSI, VLR TMSI, P TMSI

    Signature) to the MS. P TMSI is included if the SGSN allocates a newP TMSI.

    9) If P TMSI or VLR TMSI was changed, the MS acknowledges thereceived TMSI(s) with Attach Complete (P TMSI, VLR TMSI).

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    Example:

    Time critical approach

    MS Network

    ATTACH REQUESTStart T3310

    ATTACH ACCEPT

    Stop T3310

    ATTACH COMPLETEStop T3350

    If P-TMSI and/or

    TMSI allocatedStart T3350

    If P-TMSI and/or

    TMSI allocated

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    Sequence diagramC.1 ATTACH, GPRS only, MS unknown in the network

    GMMREG-ATTACH- REQ

    [Attach type,

    READY-timer,STANDBY-timer ]

    START TattachLL-UNITDATA-REQ

    [PDU=Attach Req (

    IMSI or TLLIplusRAI),

    oldTLLI,Cipher=off ]

    GRR-DATA-REQ

    [LLC-UI,

    SAPI=signalling]

    GRR-DATA-IND

    [LLC-UI, TLLI,

    RAI,CI]

    LL-UNITDATA-IND

    [PDU=Attach Req (

    IMSI or TLLIplusRAI),

    oldTLLI, CI]

    LLGMM-ASSIGN-REQ

    [Kc, Algorithm]

    START Tauth

    LL-UNITDATA-REQGRR-DATA--REQ

    STOP Tauth

    [ PDU=Auth-Cipher-

    Req (Alg, RAND,..),

    oldTLLI, Cipher=off ]

    [LLC-UI,

    DRX, CLM,

    SAPI=signalling]

    GRR-DATA-IND

    [LLC-UI]

    LL-UNITDATA-IND

    [PDU=Auth-Cipher-

    Req (Alg., RAND,)]

    LL-UNITDATA-REQ

    [PDU=Auth-Cipher-

    Resp (SRES),

    oldTLLI,Cipher=off ]

    GRR-DATA-REQ

    [LLC-UI,

    SAPI=signalling]

    GRR-DATA-IND

    [LLC-UI, oldTLLI]

    LL-UNITDATA-IND

    [PDU=Auth-Cipher-

    Resp (SRES),

    oldTLLI ]

    [Kc, Algorithm]

    MS NET

    GMMSNDCP LLC RR SM SNDCPLLCRR BSSGPSM GMM

    LLGMM-ASSIGN-REQ

    START Tident

    LL-UNITDATA-REQ

    [ PDU=

    Identification Req,

    oldTLLI, Cipher=off ]

    GRR-DATA--REQ

    [LLC-UI,

    DRX, CLM,

    SAPI=signalling]

    GRR-DATA-IND

    [LLC-UI]

    LL-UNITDATA-IND

    [PDU=

    Identification Req]

    STOP Tident

    LL-UNITDATA-REQ

    [PDU=Identification-

    Resp (IMSI),

    oldTLLI,Cipher=off ]

    GRR-DATA-REQ

    [LLC-UI,

    SAPI=signalling]

    GRR-DATA-IND

    [LLC-UI, TLLI]

    LL-UNITDATA-IND

    [PDU=Identification-

    Resp (IMSI),

    oldTLLI ]

    The oldTLLI may be a

    Local TLLI, or a

    Foreign TLLI, or a

    Random TLLI

    IMSI fetched if

    - No GPRS MM Context exists, and- Attach Request without IMSI

    The network starts theauthentication together with setting

    the ciphering mode.

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    Example:

    Ser