Cisco SIP IP phone direct registration with Lync RRS feed

  • General discussion

  • I am trying to directly register a Cisco 7971G IP phone running the latest SIP firmware 9.2(1) with the Lync front end pool, but having a hard time configuring the phone to use SIP over TCP. Few questions related to this

    1) Has anyone successfully registered a Cisco SIP IP phone directly to Lync SIP registrar?

    2) Why does Lync only support SIP over TCP / TLS? According the SIP RFC 3261 Sec. 18 "All SIP elements MUST implement UDP and TCP."

    Friday, July 22, 2011 2:54 AM

All replies

  • Because...

    "...Making TCP mandatory for the UA is a substantial change from RFC 2543.  It has arisen out of the need to handle larger messages, which MUST use TCP, as discussed below.  Thus, even if an element never sends large messages, it may receive one and needs to be able to handle them..."

    Have you seen the size of UC messages. We are not talking INVITE, RINGING, ACK anymore.



    Friday, July 22, 2011 3:25 AM
  • Have you read my original post? I am not suggesting "don't use TCP". I am suggesting "also support UDP" so any standards-based SIP client can register and get dial tone. There are some who have invested heavily on non-Lync SIP clients and are moving to Lync and would like to use their existing SIP clients. They just want dial tone and voice mail and don't want to invest in new Lync compatible phones nor want to use a softphone tied to a headset

    Oh, and also, please adhere to RFCs. There is a reason why they use MUST, SHOULD, RECOMMENDED, etc.

    Friday, July 22, 2011 3:51 AM
  • Oh no. Not this TCP argument again. This is being around on the Net for years. I retract my statement, apologize and... let it go.



    Friday, July 22, 2011 4:01 AM
  • Got to agree with Drago on this one.

    You should probably take a look at this post by Russell Bennett. This will help explain the reason Lync doesn't support SIP UDP.


    There are lots of reason why companies dont follow RFC's to the letter at times. I could probably list about ten examples all from different companies off the top of my head.

    The decision to move to Lync should have taken into consideration the fact that your phones from Cisco won’t be able to directly register to Lync. There are however third party gateways out there that support what you are describing from NET and Audiocodes. Maybe not the perfect answer but then again its something that should have been considered before you decided to make the change as well.

    Coming back after the fact and complaining about RFC adherence really isn’t going to help you because you didn’t consider your requirements before selecting a system. The obvious one being that Cisco phones need to register to Lync. Not meaing to be harsh but good planning saves a lot of heart ache.

    Good luck.

    Friday, July 22, 2011 4:31 PM
  • Chris,

    Have you considered running for public office? Can’t be said better…

    I did not mean to get in confrontation. As I mentioned, this topic have been discussed many times before and every time someone asked “Why TCP only”, MS replied “Because. Period!” With the time, this fact was accepted and I was stricken it has been brought again.

    Subhan, hope you will understand.



    Friday, July 22, 2011 5:23 PM