Subject: [Sip] Timer C, Timer B, and Spiraling

From: "Vijay K. Gurbani" <[email-masked]>
Date: Mon, 29 Apr 2002 10:46:02 -0500

Some comments on -09bis on Timers C, B, and spiraling:

1) In SIP, proxies can fork either in serial or in parallel.  Consider
    serial forking for this discussion.  Normally, in the presence of
    multiple Contact headers to an address-of-record, a proxy will sort
    the Contacts based on their q value and fork serially to each
    Contact.  If Contact 1 did not elicit a final response within a
    certain time, Contact 2 will be tried, and so on.  Problem is,
    what exactly is the time for a proxy to give up on the current
    Contact and try the next one?

    Reading -09bis, it appears that timer C can serve this function.
    But the initial value of timer C is too high (3 minutes, and it is
    a MUST to set it to at least 3 mins), so that will not work.  Another
    possible candidate is the transaction timeout; if a proxy allows a
    client transaction to continue (T1*64 seconds = 32 seconds) until it
    times out, the time between trying the next Contact (32 seconds) is
    too large for the caller to keep holding.  So, this does not work
    either.

    Should -09bis provide some guidance on timers to use in proxy cores
    if serial forking is being used and > 1 Contact header is present,
    or should this be left upto the implementer?

2) Timer B controls transaction timeouts in INVITE client trans-
    actions.  The state diagram in Figure 5 is silent on what to
    do if Timer B fires while control is in "Proceeding" state; i.e.
    received a 180, but no final response.  The correct behavior
    should be to sent a CANCEL and enter "Terminated" state.

3) Regarding finding the spiraled R-R on responses in order to
    modify it (section 16.7, step 8), won't it be the case that
    the first R-R in a response corresponds to the inner-most
    spiral?  Since the inner-most spiral will generate the first
    response, can't we just get the first R-R header on a response
    in order to modify it?

If I mis-represented something and the solution is in -09bis, please
let me know.

Thanks,

- vijay
-- 
Vijay K. Gurbani  vkg@{lucent.com,research.bell-labs.com,acm.org}
Wireless Networks Group/Internet Software and eServices
Lucent Technologies/Bell Labs Innovations, 2000 Lucent Lane, Rm 6G-440
Naperville, Illinois 60566     Voice: +1 630 224 0216

_______________________________________________
Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use [email-masked] for questions on current sip
Use [email-masked] for new developments on the application of sip