Skype for Business 2015 Conferencing Attendant Application

Through many years of delivering training on Microsoft Unified Communications products such as Office Communication Server (OCS), Lync Server 2010 and 2013 and now Skype Business server 2015.  I can count on a single hand how many times that I have run into an issue with the conference attendant application.  However, I feel the need to explain how knowing what it is will greatly benefit you going forward.  Why you ask?  That is because I recently ran into an issue that relied on me knowing what it does and how it works and what I have relayed too many who have ever attended one of my training classes through the years.  The core components of the conference attendant haven’t changed that much through the revisions of the Microsoft product we know now as Skype for Business server.  Yes there are some subtle features that have been added along the way, but what the Unified Communication Application Services (UCAS) do are basically still the same.  Two of those services that fit under the UCAS umbrella are Conference Attendant Application service (CAA) and Conference Announcement Application service (CAS).  I will talk about them both, but focus on the CAA service in more detail.

Unified Communication Application Services (UCAS)

The Application service provides a platform for deploying, hosting, and managing unified communications (UC) applications. Conferencing uses two UC applications that require Application services: Conferencing Attendant and Conferencing Announcement. Application service is installed and activated by default on every Front End Server in a Front End pool and on every Standard Edition server when you deploy a Conferencing workload, which includes dial in conferencing. 

Conferencing Attendant application is a UC application that accepts public switched telephone network (PSTN) calls, plays prompts, and joins the calls to an A/V conference. Conferencing Attendant application is installed and activated by default when you deploy a Conferencing workload and select the dial-in conferencing option.

Conferencing Announcement application is a UC application that plays tones and prompts to PSTN participants on certain actions, such as when participants join or leave a conference, participants are muted or unmuted, someone enters the conference lobby, or the conference is locked or unlocked. Conferencing Announcement application also supports dual-tone multifrequency (DTMF) commands from the phone keypad. Conferencing Announcement application is automatically installed and activated by default when you deploy a Conferencing workload and select the dial-in conferencing option.

Figure 1: Audio Conferencing Architecture 

Conferencing Announcement application 

Now brings me to my statement earlier of teaching Lync Skype through the years. I would emphasize something that is not widely documented with regards to the importance of the CAA service. So when we see by definition what the CAA accomplishes:

Conferencing Attendant application is a UC application that accepts public switched telephone network (PSTN) calls, plays prompts, and joins the calls to an A/V conference. Conferencing Attendant application is installed and activated by default when you deploy a Conferencing workload and select the dial-in conferencing option.

I would to emphasize part of the definition “Joins the calls to an A/V conference…”, When a user calls into a conference and gets the greeting, “Welcome to the audio conferencing center, please enter a conference ID followed by pound (#). 

The CAA service is what is providing the message to be played.  So hypothetically if I were to stop that service that is running on the front end server, I would not be able to get into any Lync Skype conferences for that particular pool.  This is what lead to me writing this article, for I recently ran into this issue again, recall I stated I can count on a single hand how many times I’ve run into something like this; but the important thing is I had an idea of what to look for immediately.

The conferencing related issue

I recently made changes to dial in conferencing in an environment and when I tried to test the new conferencing phone number I was not able to join the call from Lync client on the inside or outside of the network. After capturing the client side logs from my Lync client and then analyzing them with the help of snooper I was able to get closer to the root cause.  Figure 2 below is the actual snooper capture from the incident.  The area in red gives a more detailed view of the issue in the view panel to the right which is included the log information in figure 3.

Figure 2: Snooper capture of dial in conferncing phone number not connecting to the CAA service

02/26/2016|00:09:52.884 1C18:2694 INFO  :: Data Received -10.113.51.37:5061 (To Local Address: 10.10.10.10:61940) 1122 bytes:02/26/2016|00:09:52.884 1C18:2694 INFO  :: SIP/2.0 404 Not FoundAuthentication-Info: TLS-DSK qop="auth", opaque="6AED208E", srand="CCE588F0", snum="49", rspauth="6e4710c42d48d5d2c71d3ab4cc57346d26d3f5a9", targetname="LYNCFE01.contoso.com", realm="SIP Communications Service", version=4Via: SIP/2.0/TLS 10.10.10.10:61940;ms-received-port=61940;ms-received-cid=6208C00CONTENT-LENGTH: 0From: "Spurlock,Byron O";tag=acfa88f59a;epid=c96d6da198To: "CAAPrivateContactObject-43b72ebd-7dc6-438e-b87b-d3354272ba59";epid=F892E5E005;tag=d37c67d0CSeq: 1 INVITECall-ID: 81398bb59f2a448ea657e903529c49e5Priority: NormalSupported: ReplacesP-Asserted-Identity: "CAAPrivateContactObject-43b72ebd-7dc6-438e-b87b-d3354272ba59"Server: RTCC/5.0.0.0 Conferencing_Attendant_1.0ms-diagnostics: 33034;source="LYNCFE02.contoso.com";reason="Ms-Application-Aor header is not valid.";component="urn:application:Caa";AOR="sip:[email protected]"Ms-Conversation-ID: AdFwXE4bwKFcC8bSSvKO1Y73+v4wxA== ====================   02/26/2016|00:26:21.562 1C18:2694 INFO  :: Data Received -10.20.30.5:5061 (To Local Address: 10.10.10.10:62192) 1373 bytes:02/26/2016|00:26:21.562 1C18:2694 INFO  :: SIP/2.0 180 RingingAuthentication-Info: TLS-DSK qop="auth", opaque="14266B60", srand="55F254E8", snum="43", rspauth="f883914dfb121a6309350e10e36021bca36c4ca3", targetname="LYNCFE01.contoso.com", realm="SIP Communications Service", version=4Via: SIP/2.0/TLS 10.10.10.10:62192;ms-received-port=62192;ms-received-cid=623FF00FROM: "Spurlock,Byron O";tag=05324feca2;epid=c96d6da198TO: "Byron Conference Bridge (Toll Free)";tag=80d6825c75;epid=B33E4A66F6CSEQ: 1 INVITECALL-ID: bc4600b1807b49379d3c0f09e80d43d8RECORD-ROUTE: ,CONTACT: ;automata;actor="attendant";audioCONTENT-LENGTH: 0SUPPORTED: gruu-10ALLOW: CANCELALLOW: BYEALLOW: UPDATEALLOW: PRACKP-ASSERTED-IDENTITY: "Byron Conference Bridge (Toll Free)",SERVER: RTCC/5.0.0.0 Conferencing_Attendant_1.0 02/26/2016|00:26:21.562 1C18:2694 INFO  :: End of Data Received -10.113.51.37:5061 (To Local Address: 10.10.10.10:62192) 1373 bytes

I took a small section of figure 3 to highlight the portion of the client log that calls out the conferencing attendant.  Now recall what the conferencing attendant does and that is it allows people into a conference.  

P-Asserted-Identity: "CAAPrivateContactObject-43b72ebd-7dc6-438e-b87b-d3354272ba59"Server: RTCC/5.0.0.0 Conferencing_Attendant_1.0

So what I ended up doing was restarting the service seen in figure 3 on each of the Front End servers. 

Figure 4: Skype Business server services

Once each CAA service was restarted I was able to call in to the new conferencing number again and I was able to get into the conference with no issues and heard the sweet sounds, “Welcome to the audio conferencing center, please enter a conference ID followed by pound (#).”

Don’t take UCAS services lightly

At the end of the day I have always had a soft spot for teaching and knowledge transferring to others.  I figure I have run across many deployments in the field and wanted to share some first-hand experience into some challenges that I have faced as well. In the classroom I’m glad that I’ve always drilled deep down into the conferencing areas and talked about the Conferencing Auto Attendant and the Conferencing Announcement service and the importance of what these relatively under the radar application services bring to the table for Lync Skype Server functionality.  Yes the Front End, Backup Service, File Transfer Agent services and others get a lot of the notoriety, but let’s not underestimate the friendly UCAS services.