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  • #38236

    hi all…

    Appreciate if somebody can brief explain, how MSU(in octet) is counted in MTP3,ISUP,MAP,BSSAP, and CAP.



    Hello Mohsin,

    MSU is a signaling unit which will have the following format.

    Flag: 8 bits
    FCS:16 bits
    SIF: (Signaling Info: MTP3 sent buffer)3 x 8 to 272 x 8 bits
    SIO: 8 bits
    pad:2 bits
    LI: (Length Indicator) 6 bits
    FIB:(Forward Indicator Bit)1 bit
    FSN:(Forward Sequence Number) 7 bits
    BIB:(Backward Indicator Bit) 1 bit
    BSN:7 (Back-ward sequence number) bits
    Flag:8 bits

    And this will be with MTP-2, only the SIF ( Signaling Information ) field is used by MTP-3. I mean the MTP-3 message embedded as SIF.

    And MTP-3 is take care of distributing to respective application ( ISUP, SCCP etc).

    Hope the above said was helpfull.


    Vijay Sharma

    In ANSI standard only one flag( at starting of MSU) is used and in European standard (ITU T) two flags ( at both ends) used.



    Hi Hari

    Thank you very much for the helpfull information.
    If we sum all the indacator (flag to flag) and take as the maximum SIF can carried 272*8=2176, it will get 2232 bits and divide by 8 = 279 bytes.
    For the application layer such a MAP, which will carried by SIF. Can we assume it was carried with the same load which is 2176/8=272 bytes??? or any reference i/we can used??


    Hi Moshin…

    Not alwyas C7-MAP Carrys 272 Octets.

    See the Range SIF = 3*8 TO 272*8 Bits.The SIF Octets value differes between different MAP/INAP Messages.

    You have calculate the average if you want to.



    Hi S.vijay

    So, how can compute the average of the octets.. any formula? some said.. i had to count from the message sending, for example for the message between VLR and HLR(to calculate the signalling bit and number of signalling between both NE). Start from UDT begin till end. Fuh!!! it can be blur at the end…:)



    Hello Moshin,

    There are lot of other Methodes.
    First Decide which things you want to calculate.


    ISUP-Just Need to Count OCTETS For a Call.At paek time take 10 Successful + 10 Unsuccessful Call and Count OCTETS and get average.

    MAP-SMS,LU,MSRN…There are Lot…Better analyze Avge of all.

    This is what I do…but not a perfect methode…still in search for a BEtter methode.

    PALs help us out.

    I have total BITs sent in one Hour how can I calculate Load.I know the basic Calculation but…I wnat to know is it ok…?

    ACCUMULATED/Actual Service.


    Vijay sharma

    Dear s.Vijay & Mohsin,

    To calculate the signalling load between two Point codes u need to know
    1) Total number of MSUs in an hour

    2) Total number of Octets in SIF in an hour

    3) Now each MSU = 8 + SIF Octets

    using 1 , 2 & 3 u can find total number of Octets in an hour.

    Now the signalling Traffic on a 64 kbps slot = (Total Number of Octets) * 8/64000/3600

    Now u use above formula for both Tx and Rx direction and Maximum of this will give u effective traffic on this link in Erlangs.

    Vijay Sharma


    Hello Vijay SHarma & Hari ,

    I feel theTotal Bits Transfered =[( MSU*6 Octets ) + ( SIFSIO Octets ) ]

    6 Octets in MSU used for MTP (BSN,FSN…) Puropse.Not 8 Octets.


    Vijay Sharma

    Hi Vijay,

    2 Flags = 2 Octets
    CRC = 2 Octets
    SIO = 1 Octet
    LI = 1 Octet
    FSN+FIB = 1 Octet
    BSN+BIB = 1 Octet

    Total = 8 Octet
    I think it will clear ur doubt.



    when SIOs, SIFs messages geting exchanged, I have tried to made the MTP3 link down and after some times made it up, but i could not get the SIOs and SIFs messages, Please any one can help me why i am not getting this 2 messages.

    Rajdeep De

    Please let me know how many MSU we can get in HLR at the time of freash LU hapenning in VLR. Please let me know also the calculation for the MSU for LU message.


    Hi all,

    When I monitor the linkset and find that amount of MSU in outing/incoming is same but the number of octet is differ. Should each MSU contain same no of octet (incoming and outing message)? Why have such different?


    How we can reduce MSU count

    Wallis Dudhnath

    MSU uses principles from HDLC.
    Layer 3 frames are conveyed by the MSU. Layer 2 uses FISU and LSSU.

    You will need start / stop flags (8 bits), BIB, FSN, FIB, LI, CK, SIO and the key SIF “envelope”

    Depending on the messages the SIF size can vary. The SIF is also related to call control,
    network management, or databases query/response. SIF varies from 16 to 2176 bits.

    Spent a few years with a K1198 decoding and testing SS7 (in partucular, NUP / BTNR_167)
    CO / NCR signalling systems.

Viewing 15 posts - 1 through 15 (of 16 total)
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