QoS - Traffic Shaping

Discussion in 'Cisco' started by Mike, May 26, 2005.

  1. Mike

    Mike Guest

    I need some guru help on this one.

    I am dealing with several Wide Area Networks which have or are
    implementing VoIP. Here is an example of a network:

    Host Site = 1.5MB
    Remote Site A = 512K
    Remote Site B = 768K
    Remote Site C = 512K
    Remote Site D = 768K
    Remote Site E = 960K

    These are private circuits all brought back to a VLAN on the carrier’s
    network (Layer 2).

    The ones that have implemented QoS, are either incomplete or not setup
    properly. They are having Voice Quality issues, such as, when someone
    downloads a large file from the internet, from a remote site to the host
    site, any calls going across those circuits get crushed and the quality
    stinks. This, to me, is a sign that the QoS is not working properly.

    I have recommended some traffic shaping policies, basically determining
    how much bandwidth is needed for voice at each location, then putting a
    policy in place that allows data (all but voice), to have X amount of
    bandwidth on the circuits, and leaving the rest for Voice.

    The big question that I have is:

    How, with the Cisco IOS, would you handle the fact that a remote site
    could be flooded with data? Meaning the aggregate of the bandwidth of
    sites C,D, and E could flood site A. Is there a concept/technique that
    addresses this possibility? I made some suggestions about redesigning
    the network, and keeping all servers central, and minimizing data
    traffic between remote sites. I have to think there is something in
    Cisco’s QoS options that would address this, so Voice always has
    priority and NEVER takes a hit.

    I hope I explained this well enough. I appreciate any help. Please
    yell at me if I am missing something important!


    Mike, May 26, 2005
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  2. Hello Mike,

    traffic-shaping, for voice, is not a good solution. You have to
    implement LLC (Low Latency Queueing), so voice will be priority queued.
    Additionally you have to make sure that your voice traffic is marked
    with the right TOS/DSCP Parameters. For more information look at the
    IOS configuration guides at CCO
    (http://www.cisco.com/univercd/home/home.htm) They are listed under the
    IOS Menue.

    bastardnetworkerfromhell, May 27, 2005
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  3. Mike

    Mike Guest


    Anybody else?
    Mike, May 28, 2005
  4. Mike

    stephen Guest

    this shows that there is some contention in the carrier network - if each
    remote sends data to the centre, some packets are going to be dropped.

    so - unless the carrier understands drop precedence so that your Voip
    traffic gets through preferentially under congestion, you are going to have
    voice quality issues.
    you need to check if this happens between sites as well. time for some
    there are 2 basic approaches.

    1 limit the flow so that drops dont happen (i.e. limit the data rates from
    the remote sites).
    2 mark the traffic so that high priority stuff gets better treatment inside
    the telco network.

    I made some suggestions about redesigning
    cisoc QoS on your routers cant influence what happens elsewhere in the
    stephen, May 29, 2005
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