Subject: [Sip] Few SIP Issues from rfc3261

From: Rohan Sen <[email-masked]>
Date: Mon, 24 Oct 2005 22:38:20 +0530

Issue # 1
------------------------------------------------------------------------------------------------
In rfc3261, Section 10.3 Page 65 'Processing REGISTER Requests',

"The registrar checks whether the request contains the Contact
header field..."

here, what I understood gives the following pseudo-code segment :

if (contact header field is present) {
  if (contact == '*') {
    if ((expires == '0') || (additional contact header field is present)) {
      Send 400 response
    }
    else {
      if (Call-Id != bound-call-id) {
        Remove binding
      }
      else if (Cseq < bound-cseq) {
        ERROR
      }
      else {
        Remove binding
      }
    }
  }
  else {
    /* General processing of contact field and update of binding */
  }
}
else {
  /* Fetching of binding */
}

Please let me know if my understanding is incorrect.

Issue # 2
------------------------------------------------------------------------------------------------
In rfc3261, Section 16.12 Page 117 'Summary of Proxy Route Processing'
"2.  The proxy will inspect the URI in the topmost Route header
       field value.  If it indicates this proxy,..."

My understanding of the purpose of route header field is to specify a 
next proxy server (can be a loose router)
for the SIP Message to the proxy server. I am unable to visualize any 
scenario where the 1st entry
of Router field can point to that of the receiving proxy, because at 
every step it gets removed and the
next value becomes the top most value (next poxy for the next proxy server).

Issue # 3
------------------------------------------------------------------------------------------------
In rfc3261, Section 10.3 Page 62 'Processing REGISTER Requests'
"Each REGISTER message MUST be processed independently of any
other registration or binding changes."

Does this imply that the registrar must not buffer register requests in 
attempt to answer
with 1 OK for several REGISTER messages for the same AOR ?
Ex: If a Registrar receives 2 consecutive REGISTER messages with same 
AOR but different contact fields,
       then should it send a single 200 containing 2 bindings or 2 
distinct OKs for each of the REGISTER messages ?
What exactly are the implications if REGISTER requests are not processed 
independently ?

Issue # 4
------------------------------------------------------------------------------------------------
In rfc3261, Section 10.3 Page 63 'Processing REGISTER Requests'
"If the address-of-record is not valid
for the domain in the Request-URI, the registrar MUST send a
404 (Not Found) response and skip the remaining steps."

What will be the response status code when a REGISTRAR responsible for 
domain
abc.def.com receives a REGISTER message
with :
i.    To field set to [email-masked] but Request-URI set to abc.def.com
ii.   To field set to [email-masked] and Request-URI set to abc.xyz.com

Any help with these issues will be very much appreciated.

thanks,
Rohan Sen

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