CUCM 11.5 and Skype for Business Conference Fast Busy

[bwolf]

Skype for Business 2016

CUCM System version: 11.5.1.14900-11

We're working on integrating CUCM and Skype For Business 2016.  We currently have a trunk set up between the two, it is fully up and working.  We can use the Skype for Business client installed on my Windows machine to make calls out. We can call any internal extension, or any external number just fine. 

What isn't working fine is being able to call a Skype for Business conference from a desk phone.  We have extension 7779 set up for the conferencing line.  If we dial it from the Skype client, it connects to the conference as expected.  But if we dial from a desk phone, we get a fast busy.

I worked on this with a TAC agent for a few days.  He believes the issue will be resolved if I change the servers in CUCM from IP addresses to FQDNs.  One of the guys here worked at another company who had this integration successfully set up, but he said they did not use FQDNs for their CUCM servers, they used IP addresses just like we are here.

So, I'm wondering, is there anyone out there who has a successful Skype for Business integration using IP addresses.  I don't want to set up an after hours change window to change the server names if it is not 100% necessary.  I just don't see how it would make a difference if we're using FQDN or the IP address since DNS is just going to resolve the IP address. 

When we look at the trace, it's attempting to dial out with <extension #>@<CUCM server IP> where we would expect to see the URI: <extension>@<company name>.com. or <username>@<company name>.com.

Has anyone out there had a similar experience with this?  Should I just go through with changing to FQDN for my CUCM server list?  Should I ask for a different TAC agent?

thanks

[Gregory Brunn]

You have a SIP trunk pointing to your skype for business correct?

Have you confirmed that the trunk pointing to your device has a sip profile that states use fully qualified domain name in SIP request and that you have your organization top level domain set in enterprise parameters?

[bwolf]

Hey Gregory,

Thanks for your response. 

Yes, correct, we have a SIP trunk in full service that points to Skype For Business.

I can confirm that the sip profile the trunk is using does NOT have "Use Fully Qualified Domain Name in SIP Requests" checked.  I assume I would want this box checked if I was using FQDN for my CUCM servers, whereas now, my CUCM servers are the IP addresses.  I can also confirm that Organization Top Level Domain does have our organization's domain.

I may be wrong in my thinking that I'd only need to check the "Use FQDN in SIP Requests" if I wasn't using server IP addresses (CUCM System -> Server).  I can check that box and give it a go.  The TAC guy got me a little confused saying that we needed to use FQDNs for the CUCM server addresses under System -> Server in CUCM.  Seems to me I should be able to use IP addresses or FQDNs for those and it would work the same.

[Gregory Brunn]

My understanding of this is that what will happen is your top level domain will be added to the SIP request.  It is always a best practice starting since 9.X to do FQDNs as server names but I have done deployments of course were we don't do this because DNS is not stable for customers. 

There was a bug if I am tracking correctly that states the using the fully qualified domain in sip request didn't solve it and the name was needed.  I would give the Check box a go first before going through the problem of changing the server names.

If you do change the server names to fqdn, remember phones will need the DNS server information handed out to them via DHCP is not already, also your MGCP gateways will need dns added as the names change.

Let me know how it goes.