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traffic calc

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  • #21323 Reply
    Guillermo
    Guest

    Regarding the traffic Bandwidth calculaton, mosttakes into account only RTP traffic ( bandwidth is calculated based mainly on packet duration and coding algortithm being used), how does the RCTP traffic considered in the calculation.
    And if the links used share TCP traffic how can this be evaluated?

    thanks

    Guillermo

    #21324 Reply
    Dwayne P. Shrum
    Guest

    Good articles on the subject…,

    http://www.voip-calculator.com/protocols.html

    http://www.cisco.com/warp/public/788/pkt-voice-general/bwidth_consume.html

    RTP header not only refers to the RTP, but generally also refers to the IP/UPD part of the header also. Thus cRTP (compression of RTP – the whole header) can reduce the entire 40bytes (20-IP/8-UDP/12-RTP) into either 2 to 5 bytes.

    Here is a Cisco explaination of how cRTP works:

    http://www.cisco.com/warp/public/732/Tech/real/index.html

    In essence, it is shorthand. The whole header(s) are sent the first time. Both ends of the link remember the header, then each subsequent frame includes a shorthand reference to that header plus a small amount of info concerning what bits should be different for each time. The changes in the header propogate to the *remembered* header thus each change builds upon the previous.
    It is very CPU intensive and is link specific so both ends (routers) need to know about the other’s cRTP encoding.

    Sharing other IP/TCP/UDP traffic get tricky. Be more specific as to what you are looking for and I will try to give some pointers.

    Dwayne

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