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"are you still there" temporary workaround on UM and Windows Server 2008

  • Article
  • This blog helps in understanding a specific UM scenario where the UM is not able to recognize any DTMF or RTP from the User when leaving a voicemail
  • It happens mainly in scenarios where the UM IPGW has a media card on a separate device (for eg: - in case of Nortel where the signaling server and media GW are on 2 separate devices)
  • Before following the below blog make sure the UM IP GW is indeed sending the RTP/DTMF. You can confirm this from wireshark using RTP stream player

 Below is the call flow for such a scenario. Microsoft UM receives 3 ICMP Port Unreachable messages from the Media GW, an indication of media device not being ready to exchange RTP packets.

 As per the RFC3264, section 5.1 on page 7, it states:

Once the offerer has sent the offer, it MUST be prepared to receive media for any recvonly streams described by that offer. It MUST be prepared to send and receive media for any sendrecv streams in the offer, and send media for any sendonly streams in the offer (of course, it cannot actually send until the peer provides an answer with the needed address and port information). In the case of RTP, even though it may receive media before the answer arrives, it will not be able to send RTCP receiver reports until the answer arrives.

If there is no immediate fix available to address this from the GW end, then the admin can use "Windows Firewall with Advanced Security" from "Administrative Tools" to block the ICMP port unreachables from reaching the application. Below are the screenshots to configure this.

 

 

 

 

 

Give it a friendly name and the firewall should now block the specific ICMPs from going to the application.