Problem sending faxes through VoIP

Discussion in 'Cisco' started by mramos, Sep 21, 2006.

  1. mramos

    mramos Guest

    Hello every one!

    I have a problem sending faxes through VoIP

    This is what we have:
    PBX with VoIP Card --- Cisco --- E1 --- (Internet VPN) --- T1--- Cisco
    --- PBX

    The cisco router has activate the QoS, to priority the communication
    saving 512 kbps of bandwidth, for the matching VoIP ports.

    The voice and faxes work fine, but when the bandwidth is over use, the
    voice is not affected but the faxes can not communicate even when the
    QoS is saving bandwidth for them. I been trying with traffic-shape, fax
    passthrough , fax relay and other options, but no one fix the problem.

    I figure out that the cisco router is working only as data gateway not
    as voice gateway, because the VoIP card in the PBX is making job, so
    may I?m look to solve the problem in the wrong place.

    The VoIP card is configured by a provider, but I try changing the
    communication options between G.729, G723 and G.711, when use G.711 the
    voice is better, but the same happen with the faxes.

    The question is:

    Do I have to correct the fax problem in the VoIP card configuration or
    is possible to fixed in the cisco Router?

    If it can be in the Cisco router, I will appreciate any suggestion.

    Thank you very much, regards.
    mramos, Sep 21, 2006
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  2. mramos

    Dana Guest

    Voice more than likely is taking priority in this situation.

    I been trying with traffic-shape, fax
    What is your actual bandwidth??
    Yes of course G711 offers better quality.
    You may want to see if you can change your sample rate to a value such that
    voice quality does not suffer, but you send less traffic per VOIP call.
    Dana, Sep 21, 2006
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  3. mramos

    Thrill5 Guest

    QoS is not a substitute for bandwidth. If you have 512k, line and you have
    400k of priority traffic, and 120k of regular traffic, you have a problem.
    QoS only gives PRIORITY to traffic, it does NOT guarantee that the traffic
    is going to be delivered. The only solution is to increase the bandwidth,
    or decrease the VoIP traffic.

    Thrill5, Sep 26, 2006
  4. mramos

    t Guest

    What I tried with success and read in many places is to reduce the baud
    rate to 9600 on the fax.


    See review at
    t, Sep 28, 2006
  5. mramos

    Fer Mtz Guest

    When you use G729 what kind of codec are you using?
    What kind of ports are you using, E&M, FXS or FXO ?

    try to send me info about config in your router and QoS and if posible
    for your ISP QoS
    send me:
    sh run
    sh voice port sum
    sh call active voice brief
    sh call active voice

    send me all info from A-->B i mean source and destination.

    Maybe the problem is with codecs, some PBX tell cisco not to change the
    codec and when is compresed on cisco faxes has so many problems.

    When you use G711 REMEMBER!!! you are using 64K for every voice call,
    also for faxes!
    So i am sure that if you doesnt have any voice call on place, faxes
    pass OK.

    Send me all the info please.

    stay in touch.
    Fer Mtz, Sep 29, 2006
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