VoIP and Packet Size

Discussion in 'Cisco' started by Bob Simon, Feb 6, 2007.

  1. Bob Simon

    Bob Simon Guest

    I've been asked to prioritize VoIP traffic for a customer that uses a
    private wireless network managed by another contractor for transport
    from the remote sites to headquarters. All VoIP traffic enters the
    network from 1711s at the remote sites (interface Fa2, VLAN 10). If I
    classify these packets, apparently the transport folks will offer
    expedited forwarding.

    Is the best way to accomplish this by setting diffserve to ef for
    these packets?

    Once these packets arrive at HQ, will all the Cisco routers and
    switches automatically prioritize these packets or do I need to
    configure PBR on every device in the path for expedited forwarding?

    Is it advisable to segment packets from competing streams to reduce
    latency? If so, can this be accomplished by simply setting MTU to
    something in, say, the 200 - 300 Byte range?
     
    Bob Simon, Feb 6, 2007
    #1
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  2. Bob Simon

    stephen Guest

    "Bob Simon" <> wrote in message
    news:...
    > I've been asked to prioritize VoIP traffic for a customer that uses a
    > private wireless network managed by another contractor for transport
    > from the remote sites to headquarters. All VoIP traffic enters the
    > network from 1711s at the remote sites (interface Fa2, VLAN 10). If I
    > classify these packets, apparently the transport folks will offer
    > expedited forwarding.
    >
    > Is the best way to accomplish this by setting diffserve to ef for
    > these packets?


    ask the WAN guys - but yes, EF is the normal way to do it.
    >
    > Once these packets arrive at HQ, will all the Cisco routers and
    > switches automatically prioritize these packets


    No.

    or do I need to
    > configure PBR on every device in the path for expedited forwarding?


    Use QoS setup instead.

    i suggest you look at some of the Cisco Voip / IPT / QoS best practice (even
    if the Voip traffic is from someone elses kit) - try here....
    http://www.cisco.com/en/US/netsol/ns656/networking_solutions_program_category_home.html

    >
    > Is it advisable to segment packets from competing streams to reduce
    > latency? If so, can this be accomplished by simply setting MTU to
    > something in, say, the 200 - 300 Byte range?


    No.

    And even if you do, the minimum IP MTU is 576.

    However, better to not break other things, and jitter from other packets is
    usually only an issue where the link speed is 1 Mbps or lower.

    in those cases you can use L2 fragment schemes on a link by link basis.

    --
    Regards

    - replace xyz with ntl
     
    stephen, Feb 7, 2007
    #2
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