Subject: [SIP] Detecting of retransmission in the first INVITE case

From: "Piotr S. Kossowski" <[email-masked]>
Date: Sat, 09 Dec 2000 21:58:06 +0100

Hello,

Section 11.5 of RFC2543bis-2 says:

"If the Call-ID exists, the request is for an existing call. If the To,
From, Call-ID, and CSeq values exactly match (including tags) those of any
requests received previously, the request is a retransmission."

I am not sure whether this statament applies when we processing the first
INVITE. The first INVITE does not include a tag. The tag is added when
response to this is created. According to 11.2:

"The UAS stores the values of the To and From field, including any tags. 
These become the local and remote addresses of the call leg,
respectively."

So, when we want to detect retransmission it will not be easy possible,
because UAS' To header has already tag, but retransmission of the INVITE
still does not include To's tag.

Could you correct my thinking or the spec. ?

Thanks in advance,
Piotr

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---

From: Jonathan Rosenberg <[email-masked]>
Date: Sun, 10 Dec 2000 18:39:47 -0500

> -----Original Message-----
> From: Piotr S. Kossowski [mailto:[email-masked]]
> Sent: Saturday, December 09, 2000 3:58 PM
> To: SIP discussion list
> Subject: [SIP] Detecting of retransmission in the first INVITE case
> 
> 
> Hello,
> 

The text should be updated to say (including tags, if present).

That is, the process is the same with or without tags.

> still does not include To's tag.

You are mixing two different things. A call leg is not the same as a
transaction. The call leg is idenfitied with a tag, but the transaction is
identified based on the To, From, Call-ID, CSeq, R-URI and top via. (the
latter two being new since rfc2543, to handle spirals and request merging,
respectively).

-Jonathan R.
---
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
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