Softphone QoS

Discussion in 'VOIP' started by Arnold Ligtvoet, Oct 9, 2003.

  1. Hi,
    I'm working on a project to implement Cisco CM in a corporate network.
    The network itself is fine (100Mbit, switched) and based on Cisco
    switches. The problem is that the customer wants to use only softphones
    and does not have a CAT6500.

    I'm having trouble separating 'normal' data traffic from VoIP traffic,
    since the softphone does not set TOS fields or any other unique

    I was wondering if I could use a linux machine to insert the TOS into
    packets based on content (ie. VoIP or any other data) or if there are
    any other solutions that I can use.

    The network uses a CAT2950-24 switch in conjunction with 2 clustered
    MCS7825 CM servers.

    Arnold Ligtvoet, Oct 9, 2003
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  2. Arnold Ligtvoet

    Plato Guest

    you can prioritize traffic to the call manager via the destination IP
    address. Unfortunately, no method that I'm aware of will allow you to
    mark IP QoS for the call data traffic.
    Plato, Oct 9, 2003
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  3. Yup, I thought of that option, also prioritized traffic to the gateway.
    However the problem still remains on internal calls.

    If was looking at solutions like a packetclassifier
    (, but I can't see a way to implement
    this on a switched network.

    Arnold Ligtvoet, Oct 9, 2003
  4. Arnold Ligtvoet

    Steve Blair Guest


    Some NIC cards include utilities that allow you to set
    802.1p COS bits for specific applications. I realize
    this may not fit your requirements but it is an option.
    I know 3Com has such a utility for their NICs.

    This an area I'm also interested in. We've been
    pressuring softphone vendors to implement settable
    802.1p COS within the soft client GUI, or it's
    configuration file. Do Cisco have plans for such a

    Steve Blair, Oct 9, 2003
  5. Arnold Ligtvoet

    Pete Harris Guest

    Are you sure your voice packets NEED to be handled differently? It
    sounds like this network will rarely if ever saturate. On an
    unsaturated network, QoS priority makes no difference, as all packets
    are immediately forwarded.

    Also, are you sure that the Cisco softphones don't set the ToS fields?
    Why would they not set them? Is this a FUD tactic to get you to buy
    more hard phones and extra routers?

    In my experience, VoIP over LAN always works perfectly. VoIP over WAN,
    especially VPN, is where the challenges are. If anybody has other
    expeiences, I'd like to hear them.

    - Pete
    Pete Harris, Oct 9, 2003
  6. Arnold Ligtvoet

    shope Guest

    Cant you use IP / UDP and socket numbers to identify the RTP packets for

    I read some Cisco stuff on their IP Tel docs about IDing voice packets in
    that way when they were showing suggested firewall filters for voice- try
    the CM 3.x design guide info at

    Not sure if you will be able to filter at that level with a 2950 though -
    3550 needed?
    shope, Oct 9, 2003
  7. Yep I'm pretty sure. I did another project a couple of months ago where
    I ran into the exact same problem. Came in after the solution was sold
    and the problem was there. Since the customer refused to invest in a
    'better' switch I ended up installing hardphones. It would seem to me
    that cisco could set ToS/CoS bits from an app, but they don't.
    I did some troubleshooting at a customer the other day. Setup was CM 3.3
    with 2950 switches. Prioritized all traffic coming to and from the VG200
    (voice to pstn was ok now). Internal voice calls were still very bad.
    This customer was using 10 access databases which were opened from a
    server and kept open all day :-(
    Arnold Ligtvoet, Oct 9, 2003
  8. IP is not that important (since all clients could potentially talk to
    one another), UDP ports are negotiated in H.323 call setup or skinny in
    Cisco's case. I could of course prioritize *all* UDP traffic, but I'm
    not sure what implications that has.
    Yep you need a CAT3550 or CAT6000 to these kind of things. Both are a
    *bit* more expensive than the 2950.

    Arnold Ligtvoet, Oct 9, 2003
  9. Ok, I'll check the NIC's at this customer and see what the possibilities
    are in this area.
    I worked at a software company previously where we implemented a 'Cisco'
    softpone on the basis of TAPI and wave redirect. The cisco wave drivers
    take care of creating the packets and as far as we could determine there
    is no way to set QoS parameters. The wavedrivers are also used by the
    real Cisco softphone so my best guess would be that there is no support
    for this.

    I'm not aware of any plans that Cisco has in this area and never heard
    it in any of there release schedules.

    Arnold Ligtvoet, Oct 9, 2003
  10. Arnold Ligtvoet

    Pete Harris Guest

    What was wrong with the internal voice calls? Voice quality: Dropouts?
    Latency? Distortion? ... or something else ?

    How can the Access DBs cause enough traffic to saturate the network?
    Are they serving up images or video? Is this or maybe something else
    producing large numbers of high priority packets?

    Is the backbone (that is, whatever's interconnecting the 2950s)
    perhaps undersized ?

    And how do you think the phones could talk to the PSTN gateway OK, but
    not to each other? I suppose you must be doing some sort of
    prioritization beyond TOS fields, and which is able to somehow favor
    phone-to-gateway connections compared to phone-to-phone connections.

    Something doesn't add up would be great if you could fill in
    some of the blanks.

    - Pete
    Pete Harris, Oct 10, 2003
  11. Echo and delay. I did not notice any dropouts. At first I thought it was
    related to el cheapo headsets in use, but after replacing these the
    problem was still there.
    50 meg databases, +/- 10 per agent, +/- 30 agents. When I came into the
    situation there was no QoS whatsoever implemented on the client/switch side.
    I'm not a cabling expert but the problem seemed to be in some part
    related to 'bad' cables and connections (wires stripped on patch panel),
    as far as I understand.
    What I did is to prioritize *all* traffic on the switch to gateway. The
    problem in phone-to-phone is that there is IMO no method to filter out
    the VoIP traffic unless you are using a 3550 or 6000
    Hope this helps. This puzzeled everybody I have seen in this project.
    Everybody, including Cisco and the reseller, saw no problems in setting
    up a CM on 100 mbit network with 40 softphones. In reality it proved a
    little bit more work than everybody expected. In this case we ended up
    replacing the softphones with hardphones (7960) and everything worked fine.

    My original question comes from the fact that I'm going into a simular
    project now, except for the databases (phew!) and I want to make sure
    that I won't run into the same probs again.

    Arnold Ligtvoet, Oct 10, 2003
  12. Arnold Ligtvoet

    Pete Harris Guest

    Sounds like one of those projects from hell. I guess you'll never find
    the smoking gun. But I wouldn't condemn all softphone on the basis of
    this one experience. Maybe a strike against Cisco's--I did confirm
    from their Best Practices literature that they don't set the QoS/ToS
    field in their current softphones.

    More likely, the problems were caused by your headsets and handsets,
    which have to be carefully selected and set up to match your sound
    card or you WILL get echo and distortion. In my experience USB devices
    are the way to go.

    So with respect to your original question, I don't think you will need
    to add a box to to insert ToS settings to your packets. But if you
    don't want to get burned twice, you might look at softphones from
    IPBlue. They're Cisco compatible, almost certainly do the correct
    QoX/ToS stuff, and support multiple USB devices. I haven't used them
    myself, but they look impressive.

    - Pete
    Pete Harris, Oct 14, 2003
  13. Thanks for the info. I'll look into the IPBlue phones.

    BTW. The headsets used in the project from hell were USB..
    Arnold Ligtvoet, Oct 14, 2003
  14. Arnold Ligtvoet

    shido Guest

    You may want to look into an asterisk based solution.

    Greg Merriweather
    The NuFone Network

    519-251-8225 x 3000
    shido, Oct 15, 2003
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