Subject: [SIP] Clarification of CSeq

From: "Velibor Cakarevic (ECS)" <[email-masked]>
Date: Mon, 22 May 2000 10:10:09 +0200

In the document draft-ietf-sip-call-flows-00.txt there is an example of a successful SIP to SIP session establishment (chapter 3.1.1).

I wonder if the CSeq should not increase its value by one when a session is terminated with the BYE signal? In the draft example the Invite signal has the value CSeq: 1 INVITE and the bye signal CSeq: 1 BYE. Should it not be CSeq: 2 BYE?  

Assume that a User A sends 'INVITE' to a User B (CSeq: 1 INVITE). User B replies with '486 busy here' (CSeq: 1 INVITE). What should the value of CSeq be in 'ACK' from User A to User B? I think it should be CSeq: 2 ACK.

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Velibor Cakarevic <[email-masked]>

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From: [email-masked]
Date: Mon, 22 May 2000 16:00:16 +0530

vc > I wonder if the CSeq should not increase its value by one when a
session is terminated
vc > with the BYE signal? In the draft example the Invite signal has the
value CSeq: 1
vc > INVITE and the bye signal CSeq: 1 BYE. Should it not be CSeq: 2 BYE?

CSeq numbering is maintained separately in each direction.
The sequence nos. from A - B does not relate to the sequence nos. from B-A.

so, A had sent an INVITE - and its seq no is 1
B sends a BYE, and hence its seq no can also be 1 (or whatever else). There
is no relation b/w the two seq nos.
If A sent BYE, then sequence would be 2.

vc >Assume that a User A sends 'INVITE' to a User B (CSeq: 1 INVITE). User
B replies with
vc >'486 busy here' (CSeq: 1 INVITE). What should the value of CSeq be in
'ACK' from User A
vc >to User B? I think it should be CSeq: 2 ACK.

The value should be the same as the INVITE. ie 1, so as to match the
original INVITE-OK transaction to the ACK. (ACK is a new request and its
CSeq method param is changed to ACK, the CSeq helps to associate it to the
OK response)

Regds
Arjun

--
Arjun Roychowdhury @ Hughes Software Systems

"Velibor Cakarevic (ECS)" <[email-masked]> on 05/22/2000
01:40:09 PM

To:   [email-masked]
cc:

Subject:  [SIP] Clarification of CSeq

In the document draft-ietf-sip-call-flows-00.txt there is an example of a
successful SIP to SIP session establishment (chapter 3.1.1).

I wonder if the CSeq should not increase its value by one when a session is
terminated with the BYE signal? In the draft example the Invite signal has
the value CSeq: 1 INVITE and the bye signal CSeq: 1 BYE. Should it not be
CSeq: 2 BYE?

Assume that a User A sends 'INVITE' to a User B (CSeq: 1 INVITE). User B
replies with '486 busy here' (CSeq: 1 INVITE). What should the value of
CSeq be in 'ACK' from User A to User B? I think it should be CSeq: 2 ACK.