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why 0.2 Erlang is assumed for link load?

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  • #65222 Reply

    I reviewed specs as ITU-T E.733 ,ETSI q.706/709/ 300 008 and other, it is not clear to me why 0.2 Erlang as normal link load is assumed for all planning calculations.
    why not 0.25 Erlang?
    thank you.

    #65223 Reply

    Hi Asaf,

    ITU E.733

    the topic of this document is to describe what is the max load of a SS7 link. I didn’t go much in the details, but it looks to me that “pmax” is chosen between 0.2 and 0.4 (chapter 7), and that all explanations are written in the previous chapters.

    But it is not 0.2 erlang, it is just a factor = 0.2.

    “7.1 Signalling link dimensioning objectives
    Signalling links should be dimensioned so that the link utilization, ρ, does not exceed a maximum
    utilization, ρmax, when there are no failures in the network. To handle failures, the link should be able
    to support a utilization of 2ρmax. The signalling load that determines the link utilization, ρ, is
    determined as described in clause 6.”


    #65224 Reply
    Wallis Dudhnath

    The bandwidth of a SS7 signalling link is normally 64 kbit/sec. If a larger bandwidth is
    necessary up to 16 links between two signaling points can be used. These links between
    two SPs are called a linkset.

    The loadsharing in SS7-networks is based on the signaling link selection field (SLS),
    a 4-bit integer provided by the userpart in the MTP-TRANSFER primitive.

    The point codes of the destination (DPC) and of the origin (OPC) are also provided
    by the userpart and the triple consisting of the SLS, OPC and DPC is called routing label
    and is part of each MTP-3 protocol data unit, called message signal unit (MSU).

    By effectively extending the 4-bit SLS field individual linksets
    consisting of up to 16 links each can be fully utilized in a combined linkset.
    Due to the 4 bit SLS field the maximum number of links in a linkset (or route) is 16.

    To help with load balancing each link should handle a maximum of 40% utilisation. Once exceeded
    the SLS bit field will ensure another link is used. This ensures an even distribution of traffic (load) within a defined linkset.

    VBR/ Wallis Dudhnath

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