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Delayed ringing for Incoming PSTN calls - waiting for PRACK RRS feed

  • Question

  • I have an OCS 2007 R2 front end server. The Mediation server has direct SIP trunking. I have enabled QoS on both the servers. We can make outgoing and receive incoming PSTN calls. The only problem is there is a delay for all incoming PSTN calls.

     

    This delay doesn’t happen with outgoing calls or pc-pc (internal) calls.

    All incoming PSTN calls are taking at least 15 seconds or 6 rings to show up on CPE or MOC.

    ·         Ping time from mediation to front end server and vice versa is < 1ms

    ·         Ping time from mediation to CPE or MOC is < 1ms

    ·         Ping time from front end server to CPE or MOC is < 1ms

     

    The windows firewall service is disabled on both front end and mediation server.  We don’t have A/V edge server.

    When I configured QoE for OCS, I had to install QoS Packet Scheduler which is not enabled on Windows Server 2003 by default. Will this introduce a delay?

    I have run packet trace with wireshark on the mediation server for an incoming call. When I dial one of the phone numbers from my mobile, the call immediately shows on the mediation server. I can hear the ringing tone as soon as I dialled. It is taking 15 seconds for the call to transfer from mediation server to end user clients. After 15 seconds/6 rings, my communicator is showing the incoming call. My communicator starts ringing only when the OCS receives PRACK from the SIP provider. The following is the packet trace. Please see the time difference on the first column.

    Time         Source                      Destination          Protocol       Info

    11:10:47  10.254.255.125        10.1.3.201            SIP/SDP        Request: INVITE sip:EMAIL REMOVED:5060;transport=tcp;lr, with session description

    11:10:47  10.1.3.201            10.254.255.125        SIP                Status: 100 Trying

    11:10:47  10.1.3.201            10.254.255.125        SIP/SDP        Status: 183 Session Progress, with session description

    11:11:03  10.254.255.125        10.1.3.201            SIP                Request: PRACK sip:ocstest.domain.local:5060;maddr=10.1.3.201;transport=TCP

    11:11:03  10.1.3.201            10.254.255.125        SIP                Status: 200 OK

    11:11:03  10.1.3.201            10.254.255.125        SIP                Status: 183 Session Progress

    11:11:03  10.1.3.201            10.254.255.125        SIP                Status: 180 Ringing

    11:11:04  10.1.3.201            10.254.255.125        SIP                Status: 183 Session Progress

    11:11:11  10.254.255.125        10.1.3.201            SIP                Request: CANCEL sip:EMAIL REMOVED:5060;transport=tcp;lr

    11:11:11  10.1.3.201            10.254.255.125        SIP                Status: 487 Request Terminated

    11:11:11  10.1.3.201            10.254.255.125        SIP                Status: 200 OK

    11:11:11  10.254.255.125        10.1.3.201            SIP                Request: ACK sip:EMAIL REMOVED:5060;transport=tcp;lr

     

    Later, I have uninstalled QoS Packet Scheduler from both mediation and front end servers. Now when I call the number from my mobile, I don’t hear the initial ringing tones. I hear the first ringing tone after 15 seconds and that is when my communicator also shows the incoming call notification. But the delay is still present.

    Any help is much appreciated.

    Wednesday, October 7, 2009 10:37 AM

Answers

  • Hi there,

    Which SIP trunking provider are you using, and is it on the approved list?  http://technet.microsoft.com/ucoip

    In R2, the mediation server now supports early media which prevents any audio packets from getting lost in the the first couple seconds of a call and enabling the provider to send a custom in-band ring tone.  The 183/PRACK is the signaling mechanism for enabling early media, but it appears the SIP trunking provider is not behaving according to specifications.  The PRACK should come right after the 183 SESSION PROGRESS, similar to how an ACK comes right after receiving a 200OK.

    If your provider is on the approved list, then I would ask whether there is some sort of session border controller or other gateway device between the mediation server and the SIP trunking provider.  If your provider is not on the approved list (and you don't have border device), then I suspect the issue lies in the SIP trunking provider's implementation of early media.  You'll need to either work with the SIP Trunking provider to correct their implementation or move to a provider that is on the approved list.  There is no mechanism to disable early media on the mediation server.

    thanks,
    Alan
    • Marked as answer by Sujeeth.J Thursday, October 15, 2009 11:43 AM
    Wednesday, October 7, 2009 3:09 PM

All replies

  • Hi there,

    Which SIP trunking provider are you using, and is it on the approved list?  http://technet.microsoft.com/ucoip

    In R2, the mediation server now supports early media which prevents any audio packets from getting lost in the the first couple seconds of a call and enabling the provider to send a custom in-band ring tone.  The 183/PRACK is the signaling mechanism for enabling early media, but it appears the SIP trunking provider is not behaving according to specifications.  The PRACK should come right after the 183 SESSION PROGRESS, similar to how an ACK comes right after receiving a 200OK.

    If your provider is on the approved list, then I would ask whether there is some sort of session border controller or other gateway device between the mediation server and the SIP trunking provider.  If your provider is not on the approved list (and you don't have border device), then I suspect the issue lies in the SIP trunking provider's implementation of early media.  You'll need to either work with the SIP Trunking provider to correct their implementation or move to a provider that is on the approved list.  There is no mechanism to disable early media on the mediation server.

    thanks,
    Alan
    • Marked as answer by Sujeeth.J Thursday, October 15, 2009 11:43 AM
    Wednesday, October 7, 2009 3:09 PM
  • Hi
    Any update for your issue?


    Regards!
    Wednesday, October 14, 2009 10:42 AM
    Moderator
  • Thank you Alan for your suggestion.

    We are not using an approved SIP trunking provider. I have informed our service provider about the 183/PRACK mechanism. Hopefully they will fix it.
    Thursday, October 15, 2009 11:45 AM