Subject: [SIP] Interacting with CAs that dont support CANCEL

From: "Sharath Rajasekar" <[email-masked]>
Date: Wed, 28 Feb 2001 15:50:39 -0800

Hi,

An interesting call flow resulted when interacting with a 
Call Agent that does not support CANCELs.

Lets say we have two CAs, one (A)supporting CANCEL and the 
other (B) that does not support CANCEL and uses BYE instead.
(Support for CANCELs is a "should" not "must" as per bis02)

Do you treat the CANCEL as a "CANCEL" or as a "BYE" ?
	A                       B
      |				|
      |<-----INVITE-----------|
      |-----180-------------->|
      |<-----BYE--------------|
      |------200------------->|
      |				|

Is this legal ?

If we treat it as a BYE, as per bis-02, the INVITE must
be completed with a final response and an ACK ? So will 
the previous flow, result in another 200OK and an ACK for 
that. 

In the other case, when we send the CANCEL, since the 
other CA does not support CANCELs, they drop the CANCELs
and continue to ring the phone after the A has disconnected.

	A                       B
      |				|
      |------INVITE---------->|
      |<-----180--------------|
      |------CANCEL---------->|
      |<-----180--------------|
      |<-----180--------------|
      |				|      				

In this case, should B, send back a 405 Not supported in 
response to a CANCEL ? And should we follow that with a 
BYE and wait for a 200OK. 

Regards
Sharath

_______________________________________________
This list is for continuing development of the SIP protocol.
The sip-implementor's list is the place to discuss implementation,
and to receive advice on understanding existing sip.
To subscribe to it, send mail to 
[email-masked] with "subscribe" in the body.