Hi Guang,
One key difference between a dialog or no dialog is that if there's a
dialog, the callee (UAS, or server) can send requests to the caller (UAC)
using the same dialog. Otherwise, there's no dialog. Because Registrar never
send requests to the client, there's no dialog created for REGISTER.
But you still can create a Register client object to hold the existing
header information as required by the RFC to keep the Call-ID same for each
REGISTER request.
"
[quote] Call-ID: All registrations from a UAC SHOULD use the same
Call-ID
header field value for registrations sent to a particular
registrar.
If the same client were to use different Call-ID values, a
registrar could not detect whether a delayed REGISTER request
might have arrived out of order.
"
Jerry
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] Behalf Of Paul
> Kyzivat
> Sent: Wednesday, March 21, 2007 5:26 AM
> To: [EMAIL PROTECTED]
> Cc: [email protected]
> Subject: Re: [Sip-implementors] doubt about dialog in RFC 3261
>
>
> This is widely confusing. Once upon a time the dialog concept wasn't
> very well defined. REGISTER and INVITE use some of the same elements, so
> it looks a bit like REGISTER establishes a dialog. Since then the
> fundamentals of dialogs have been clarified, and new uses of dialogs
> (e.g. SUBSCRIBE) have been defined. While REGISTER uses some of the
> elements of a dialog, it doesn't use them all, and just doesn't qualify
> as a dialog establishing request.
>
> You should just view REGISTER as following its own set of rules, without
> regard for the rules defined for dialog establishment.
>
> Paul
>
> [EMAIL PROTECTED] wrote:
> > Hi
> >
> > I have a doubt about the dialog concept in RFC 3261.
> >
> > In Section 4 Overview of Operation, it says that the
> combination of the To
> > tag, From tag, and Call-ID completely defines a peer-to-peer SIP
> > relationship between two user agent (Alice and Bob) and is
> referred to as
> > a dialog.
> >
> > In section 12, it says that a dialog is identified at each UA with a
> > dialog ID, which consists of a Call-ID value, a local tag and a remote
> > tag.
> >
> > In section 10.2 Constructing the REGISTER Request, it says that
> a REGISTER
> > request does not establish a dialog.
> >
> > A REGISTER request contains From tag and a Call-ID. The 200 response to
> > the REGISTER typically contains To tag. As a result, a registration
> > transaction when completed has Call-ID, From tag and To tag to define a
> > peer-to-peer SIP relationship between a SIP endpoint and the Registrar.
> > Why this peer-to-peer relationship is not considered as a dialog?
> >
> > Thanks
> >
> > Guang
> >
> >
> > _______________________________________________
> > Sip-implementors mailing list
> > [email protected]
> > https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
> >
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