Subject: [SIP] Few doubts

From: "rafi" <[email-masked]>
Date: Wed, 5 Jul 2000 14:56:42 +0530

Hi,

 (i)     What should be the action  of  a SIP entity  when it receives  a message
         in  which  one or more  mandatory parameters are missing ?

 (ii)     When  UAS ( section 4.2.1) receives another INVITE message before
         it has sent the final response to the first INVITE then it returns a 400
         response and includes  a Retry-After field with randomly chosen value.
         My question is if a random value is to be filled in Retry- After field then
         why this  header field is a MUST ? Why  can't UAC itself  choose
         random value  and resend  the  INVITE message ?

 (iii)    Many  Regular expressions does not prohibit the case of  repetition (it is a 
         limitation rather).  For eg,

              Authorization: pgp signature = "xxxx.." signature = "yyyyy...."

       is  valid according to the grammar.  In fact there are many places where these 
        things can happen.  What  should be  the  action  of  SIP entity  in such cases ?

Thank You  
Rafi Assadi H.M.
Silicon Automation Systems
Bangalore, INDIA

---

From: Rohan Mahy <[email-masked]>
Date: Wed, 05 Jul 2000 11:02:54 -0700

>          in  which  one or more  mandatory parameters are missing ?

Send an apropos error, ex: 400 Bad Request.

>          random value  and resend  the  INVITE message ?

This late in SIP's development, WHY questions are sort of futile.  The 
correct answer at this point is because a) lots of people implemented it 
that way, and b) it works.  I'm sure if you are curious you can dredge 
through the mailing list archives for the answer.  It could be a very good 
reason, or it could be arbitrary (I don't know), but as long as the 
mechanism works, who cares!

>        things can happen. What  should be  the  action  of SIP entity  in 

Unlike ASN.1 and DTDs, ANBF doesn't deal with repetition.  You have to use 
the semantics and common sense to tell you that only one signature (for 
example) makes sense in this case.  This makes parsers smaller and faster, 
and requires more work on the higher-level logic.

Generate an appropriate error message like 400 or 420, or if an extension 
if truly optional, maybe you can safely ignore it.  Use your best 
judgement, and bring your code to the bakeoffs and try it out.

thanks,
-rohan

>Silicon Automation Systems

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---

From: "Brett Tate" <[email-masked]>
Date: Wed, 5 Jul 2000 17:53:27 -0400

----- Original Message -----
From: Rohan Mahy <[email-masked]>
To: rafi <[email-masked]>
Cc: <[email-masked]>
Sent: Wednesday, July 05, 2000 2:02 PM
Subject: Re: [SIP] Few doubts

> >  (i)     What should be the action  of  a SIP entity  when it receives
a
> > message

In general, I agree that 400 Bad Request should be sent.

However since the Call-ID, CSeq, To, and From are all used to
match up a response to a request, I'd recommend not sending
back anything without at least these fields.  Also, where should
the response be sent when the Via is not present?

> >          My question is if a random value is to be filled in Retry-
After
> > field then
> >        things can happen. What  should be  the  action  of SIP entity
in
> > such cases ?