Satya,
Please see RFC3261 section 8.1.1.7 (covering Via header). It states that:
********************************
When the UAC creates a request, it MUST insert a Via into that
request. The protocol name and protocol version in the header field
MUST be SIP and 2.0, respectively. The Via header field value MUST
contain a branch parameter. This parameter is used to identify the
transaction created by that request. This parameter is used by both
the client and the server.
The branch parameter value MUST be unique across space and time for
all requests sent by the UA. The exceptions to this rule are CANCEL
and ACK for non-2xx responses. As discussed below, a CANCEL request
will have the same value of the branch parameter as the request it
cancels. As discussed in Section 17.1.1.3, an ACK for a non-2xx
response will also have the same branch ID as the INVITE whose
response it acknowledges.
The uniqueness property of the branch ID parameter, to facilitate
its use as a transaction ID, was not part of RFC 2543.
The branch ID inserted by an element compliant with this
specification MUST always begin with the characters "z9hG4bK". These
7 characters are used as a magic cookie (7 is deemed sufficient to
ensure that an older RFC 2543 implementation would not pick such a
value), so that servers receiving the request can determine that the
branch ID was constructed in the fashion described by this
specification (that is, globally unique). Beyond this requirement,
the precise format of the branch token is implementation-defined.
********************************
Thus, the server is able to distinguish between older and newer clients.
Regards,
Kirill
---
Kirill Bolshakov
SoftJoys Labs
[EMAIL PROTECTED]
Yadavalli, Satyamurthy wrote:
> Am I missing something here?
>
> I thought the RFC3261 SHOULD have assigned a different SIP version number...
> that's what a version number is meant for!
>
> - Satya
>
>
>>-----Original Message-----
>>From: Yadavalli, Satyamurthy [mailto:[EMAIL PROTECTED]]
>>Sent: Thursday, August 15, 2002 12:18 PM
>>To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
>>Subject: [Sip-implementors] sip version
>>
>>
>>The new SIP RFC-3261 specifies the SIP protocol version to be
>>used as SIP/2.0. So was it with the obsoleted RFC 2543.
>>How do SIP entities distinguish between these implementations?
>>
>>Thanks,
>>Satya
>>_______________________________________________
>>Sip-implementors mailing list
>>[EMAIL PROTECTED]
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>>
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