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Erlang tables

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    Joseph Brew

    The Erlang tables uses the offered traffic to calulate the number of circuts and also the loss probability. since we can only measure the carried traffic how do we find the offred traffic?

    Richard Arcadi

    Joseph:May be it can help. For more than a decade I’ve been using the following relationship for peak hour traffic calculations.
    It’s been certified by ITU and also by tons of real data provided by many telcos around the globe.
    The simple equation goes as:
    BHC = ASR * BHCA where
    BHC: Busy Hour Calls :Switch OUTPUT
    BHCA: BHC Attempts:INPUT at switch
    ASR: Attempting Seizure Ratio (or the probability of getting al call through the switch).
    Tipically ASR is between 60% to 80%. I use tipically 70%.
    The calls stopped at the switch are grouped on 2/3 major factors:
    1- B User Busy (about 8%-10%)
    2- B User doesn’t answwer (same)
    3- Network Congestion (the rest)
    At Europe, Japan and USA ASR is above 80% for long distance and 85% for local calls.
    The remaining countries average a 65%. This can be used with PABX.


    Sorry, I remember that ASR is Answer seizure ratio and not Attempt seizure ratio.


    Richard Arcodi

    Regarding ASR%
    You mentioned you used 70%and user busy (about 8%-10%) is it the standards ?
    What about:
    – ASR 35% ?
    – user busy 30% ?
    – user not answer 35% ?

    as we know the subscriber behaviou it can not be controlled .

    for user busy can be solved by waiting call?

    Gary Schultz


    Interesting discussions.

    Offered traffic is a measurement that is normally obtained directly from the trunk group or line being examined.

    In the DMS, offered traffic is called “incoming attempts” for trunks and “origination attempts” for lines.

    These figures are referred to as “peg counts” – in actuality they are software registers peged by the call processing software whenever such an event occurs.

    In the DMS, these registers are available from OM’s – Operational Measurements.

    Every switch, whether it be Nortels DMS or Lucent’s 4/5e track the same information.


    Gary Schultz

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