Re: [Sip] Reg. session timer+earlyupdate

[Brett Tate <[e-mail]>]

Similar to many other of SIP RFCs, RFC4028 has race condition issues.  Thus the UAC, UAS, and proxies might not be in agreement concerning session-expires value, activation, and/or refresher.

Based upon RFC4028, it is basically the latest negotiated 2xx sent/received.  Within the call flow provided, the INVITE 2xx's Session-Expires value is latest.  However since there can be race conditions associated within UPDATE, UPDATE 2xx, and INVITE 2xx, the UAC, UAS, and proxies might not all be in agreement concerning which 2xx was the latest.

From: Harbhanu [mailto:[e-mail]]
Sent: Tuesday, May 18, 2010 9:44 AM
To: Brett Tate; [e-mail]
Subject: RE: [Sip] Reg. session timer+earlyupdate

May be your expectation is correct, but here the issue is in defining the behavior of UA for the following scenario.
I will rephrase the issue...Which value should the UAC and UAS take for SE and interval timer, when either of them is acting as refresher ? i.e.


 1.  UAC refresher, then SE and refresh time for UAC and SE value at UAS?
 2.  UAS refresher, then SE and refresh time for UAS and SE value at UAC?

Please consider the consistency of behavior incase there is a crossover of 2xx of UPDATE and that of INVITE.

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From: Brett Tate [mailto:[e-mail]]
Sent: Tuesday, May 18, 2010 6:10 PM
To: Harbhanu; [e-mail]
Subject: RE: [Sip] Reg. session timer+earlyupdate

The UAS is compliant; thus sending BYE (because think UAS is acting incorrectly) is not correct behavior.  If the following is the section 9 snippet in question, notice that the dialog's previously negotiated session-expires value has no relevance; the "MUST NOT" is associated the header received within the request.  If you are referring to another "MUST NOT" (within this section or another), please send the paragraph.


"  If the UAS wishes to accept the request, it copies the value of the
   Session-Expires header field from the request into the 2xx response.

   The UAS response MAY reduce its value but MUST NOT set it to a

   duration lower than the value in the Min-SE header field in the

   request, if it is present; otherwise the UAS MAY reduce its value but

   MUST NOT set it to a duration lower than 90 seconds.  The UAS MUST

   NOT increase the value of the Session-Expires header field.
"

From: [e-mail] [mailto:[e-mail]] On Behalf Of Harbhanu
Sent: Tuesday, May 18, 2010 4:35 AM
To: [e-mail]
Subject: [Sip] Reg. session timer+earlyupdate

Hi,
We were unable to locate the specific behavior of session timer handling in UA, for the following scenario:

1. UE1 --- INVITE SE-1800 --> UE2
2. UE1 <--- 183 ------------------ UE2

3. UE1 --- UPDATE SE-600 --> UE2
4. UE1 <--- 200 UPDATE -SE600 -- UE2

5. UE1 <--- 200 INVITE SE-1800 -- UE2

6. UE1 -------------------------  BYE --> UE2
7. UE1 <--- BYE 200 ------------------ UE2


Here, UE1 sends a BYE since UE2(UAS) has increased the value of session expires, which it MUST NOT (4028-Section-9, Page-16).

Please let me know whether this behaviour is correct or not.

Thanks in advance.

Regards,
Harbhanu

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