Resolves A/V call issue that can only be IM chat between Lync Federation users

First, problem Phenomenon

After a company's local Lync 2013 is configured with a foreign SFB Server 2015 Federation, local Lync Users and federated users are able to make IM text communication, but the video and voice are never built up, and the A/V video voice connection rings after the 10s automatically interrupts.

The environmental architecture diagram is as follows:

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Second, the problem analysis

1. First I determined that the ports used by Lync Federation and A/V publishing between two organizations are no problem.

2. When a A/V call is made, the Lync Debug Tool is used to crawl the packet.

First we need to understand the process of establishing a complete SIP protocol session. A complete SIP protocol session is established as follows:

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Terminal A first sends a invite (invitation) to the terminal b,invite that contains the IP Path list information that is required to connect to terminal A (the Lync server will attempt to connect to it based on the IP address information in the Cadidate list after receiving invite information). When terminal B receives invite, a reply to terminal A will be given to a trying to tell Terminal A to be trying to establish and to attempt to ring on terminal B. Next, terminal B will restore a ringing ringing request to terminal A. Next, terminal B will reply to terminal A with a confirmation reply to the invite invitation, which contains the IP path address information that terminal a connects to Terminal B needs to include.

When the information is confirmed, terminal A responds with an ACK, and then starts a media (A/V) session until the session ends.

3, according to the data packet Capture analysis:

We were able to see that at 08:29:13 Point in time Beijing Lync Server sent a invite invitation to Lync Server in South Africa, the list of IP addresses that the Lync server connecting to Beijing needs to pass through is included in the Cadidate list, but the list uses internal server IP ( Lync Server in South Africa receives the invite information and tries to connect to each other according to the IP address information in the Cadidate list, and the IP in the Cadidate list is the internal private IP, which cannot be successfully connected. Next South Africa Lync Server to Beijing Lync Server reply to the Tring, ringing and 183 Session Progress.

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The candidate in a normal invite invitation packet is as follows:

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At Point 08:29:19, the Lync Server in South Africa replies to the 1 INVITE of the Lync Server in Beijing, and the list of IP paths that the Lync server that connects to South Africa needs to pass through is included in the candidate list. This includes the public IP x.x.x.x.

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The 08:29:30,a/v connection is automatically interrupted at a point in time. (Because the Lync Server in South Africa tried all the IP addresses in the candidate list to successfully connect to the Lync Server in Beijing), an error message was generated:ms-client-diagnostics: 25; Reason= "A Federated call failed to establish due to A media connectivity failure where both endpoints is internal"; Usertype= "Callee"; Mediatype= "Audio" incorrectly indicates that Lync server cannot determine that the current connection is an external connection and is not considered an internal connection (due to the internal IP in the candidate list). This situation is typically caused by a "A/V Edge Server enabled NAT" setting that is not configured on the Lync Edge server.

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Third, the solution

1, based on the above analysis, we need to adjust the current Lync Edge server settings, the following:

1), enable the "A/V Edge Server enabled Nat" setting for Lync Edge Server.

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2), configure the public network address after NAT for each edge server

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3), publish the Lync topology.

4), restart the A/V service on each edge server. (It's a good idea to rerun the Lync Deployment Wizard on each edge server)

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Resolves A/V call issue that can only be IM chat between Lync Federation users