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Mapping between SCCP and BSSMAP

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  • #54486 Reply
    Sachin
    Guest

    Hi All,

    I have a query. Does SCCP provides any connection identifier (SCCP connection to peer entity) to BSSMAP? The aim is to uniquley map the downlink messages to BTS/MS, for which there is no identifier in RSL messages.

    Please respond or let me know if my query is not well understood.

    #54487 Reply
    fedem
    Guest

    Hello Sachin,

    to establish a SCCP connection you have an exchange of initial messages:
    1) SCCP ConnectionRequest (it contains a local connection identifier, let’s say for example 0x01)
    2) SCCP ConnectionConfirm (it contains both its own local connection identifier, let’s say 0x02, and the destination one, 0x01)

    Then each following messages will contain the destination conn id, 0x01 or 0x02.

    Hope this can help you,
    Federico

    #54488 Reply
    Sachin
    Guest

    Hey Federico,

    Thanks for the information. I also have seen this “Source Local Reference” and “Destination Local Reference” identifiers. However, I couldnt find how SCCP will communicate this to BSSMAP?
    This “Id” needs to be communictated to BSSMAP so that it is able to map, to which BTS an downlink message has to be forwarded to.

    #54489 Reply
    fedem
    Guest

    Hi Sachin,

    as far as I understand you are talking about something internal to the protocol stack. So this is an implementation-dependent matter.
    Anyway I agree with you that BSSMA has to know how to map the SCCP connection with the mobile id.

    #54490 Reply
    Sachin
    Guest

    Hi Federico,

    Thanks for the reply. I understood this. I think may be this mapping can be done through SAPI value. If BSSMAP opens a new SAP for every SCCP connection, then this mapping can be done through SAPI. AS I have seeb, SCCP can support upto 255 SAPI.

    What’s ur opinion on this?

    Sachin

    #54491 Reply
    fedem
    Guest

    Hi,

    ok now I understand your point of view.
    In my opinion always there is a single SCCP connection for each mobile, except in the special case of an external handover.

    And so you have a strict relation between SLR/DLR (sccp local references) and the mobile id.
    But inside this SCCP cobbection you can establish more “application” (BSSAP) connections and they are identified by the field DLCI (=Data Link Connection Identifier).
    These BSSAP connections have a relation with the radio links (LAPDm).

    For instance you can have a connection for the current call and another one for the SMS exchange, because the LAPDm links are independent. Indeed they have different SAPIs (0 and 3).

    In the A interface this is something redundant because the L3 message contains the protocol discrimnator, and so we dont need strictly the presence of DLCI to deliver the message correctly.
    Anyway I agree with you that there can be a “distribution function” based on SAPI also.

    More infos about this subject are present in 3GPP 48.006 par. 9.3.1

    ciao,
    Federico

    #54492 Reply
    pix
    Guest

    fedem,

    finally, now i understand what are the SAPI for! thanks a lot for the explanations 🙂

    #54493 Reply
    Pan
    Guest

    Dear, Sachin!
    SCCP does not provide any connection identifiers to BSSAP. On the contrary the application part (i.e. BSSAP)must provide Source Local Reference to SCCP by means of SCCP-primitives (e.g. N-CONNECT_request primitive) on interface between BSSAP and SCCP. You can see more details about SCCP and its primitives in 711 Recommendation of ITU-T.
    With best Regard, Pan

    #54494 Reply
    fedem
    Guest

    You’re welcome Pix.

    About SAPI, of course this is important in LAPDm protocol because the priority and other stuff about its links are based on.
    But outside of radio interface this information is not relevant, I guess, and we usually dont care about.
    For example, as we said in previous posts, when it is present in DLCI field of BSSAP.
    ciao
    Federico

    #54495 Reply
    Sachin
    Guest

    Thanks Pan,

    Thanks alot. It solves my problem.
    To summarize, BSSMAP must generate SLR and provide to SCCP. SCCP should now keep a mapping of SLR/DLR and provide the same to BSSMAP. Isnt it?

    Regards
    Sachin

    #54496 Reply
    Pan
    Guest

    Dear Sachin,
    Yes you are right. Interface between Application Part and SCCP is not implementation-dependent, as Fedem said. It is specified in SCCP ITU-T Rec’s (Q.711-719).

    #54497 Reply
    fedem
    Guest

    Sorry,
    you’re rigth. the local reference is passed by BSSAP or other client of SCCP.

    #54498 Reply
    Sachin
    Guest

    Thanks Pan and Fedem
    Sachin

    #54499 Reply
    Pan
    Guest

    …And about SAPI 🙂 In SCCP context SAPI is SubSystem Number (i.e. MAP, BSSAP, CAP etc.)/

    #54500 Reply
    Sachin
    Guest

    Ya… Its given in 3GPP 48.006…

    Hey Pan, do you know what’s Circuit Identifier Code (CIC) is for?
    As per my understanding, there is a static mapping on A-interface E1 card which TRX (and which TS) would be mapped to which E1 TS (and which channel).

    But if in Assignment Request message, MSC sends CIC then we have to use that mapping??? Then TRX/TS mapping on E1 is not static anymore!!!!!!!!!!

    Sachin

Viewing 15 posts - 1 through 15 (of 24 total)
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