lync's design for update request

Question

Hi,

I would like to know the way lync performs session refersh using the UPDATE method.

Is it always caller or callee performs refreshing or both?

Is it sticking to refresher=uac as per the standard.

I have observed logs between lync clients in which both uac and uas performs session refreshing.

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smitha

Answer 1

Smitha,

Thank you for this inquiry. One of our engineers will follow up with you soon.

Regards,

Edgar

Answer 2

Hi Edgar,

It would be great if i can get some inputs on my query.

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smitha

Answer 3

Hi smitha,

I am investigating this issue and will respond as soon as I have an update.

Regards,
Mark Miller
Escalation Engineer
US-CSS DSC PROTOCOL TEAM

Answer 4

Hi smitha,

As you probably know, Microsoft Office Communication Server (OCS) is a SIP server, and Microsoft Office Communicator 2007 (MOC) is a SIP client.  MS-TURN, STUN (rfc5389), MS-ICE, MS-ICE2 (extensions to rfcdraft ICE-19), etc, are used for NAT Traversal, whereas SIP is used, as the name implies, for controlling communication sessions over IP.  SIP is an Application Layer protocol and described broadly here though the specific reference sections in the RFC that detail session behavior for the UAC and UAS are rfc 3261 Section 14.1 and Section 14.2, respectively.  Microsoft extensions to SIP are described in MS-SIPAE, though there are no behavior notes that apply to your question since you are asking about standard SIP behavior.

J. Rosenberg has written several ietf drafts related to these protocols, and you may find a good overview in ietf draft Section 3 Overview of Operations and Section 4  Session-Expires Header Field Definition:

From the Session-Expires header field in the response, both UAs know that a session timer is active, they know when it will expire, and they know who is refreshing. At some point before the expiration, the currently active refresher generates a session refresh request, which is a re-INVITE or UPDATE [2]request.

You will also find specific SIP Session details in rfc 3261 Section 4 and Section 13, etc.

Q: I would like to know the way lync performs session refersh using the UPDATE method.

Is it always caller or callee performs or both?

A: In addition to the previous references, rfc 3261 Section 14 states: Either the caller or callee can modify an existing session.

I hope this answers your question.

Regards,
Mark Miller
Escalation Engineer
US-CSS DSC PROTOCOL TEAM