Subject: [Sipping] Question on draft-ietf-sipping-v6-transition

From: "Livio Torrero" <[email-masked]>
Date: Tue, 26 Sep 2006 16:46:35 +0200

I have a question on this draft concerning the behaviour of a dual-stack UA.
Consider the configuration shown here: 

UA A------Proxy A------------------Proxy B-------UA B.

 Assume that UA A, Proxy A and Proxy B are dual-stack, while UA B is IPv4
only. Suppose that UA A wants to send an INVITE request to UA B: since the
next hop (Proxy A) is dual-stack, it sends the request through IPv6; for
this reason UA A has chosen its IPv6 address and has placed it in the
Contact header of the INVITE request. Since proxy B is dual-stack too, proxy
A forwards the request using IPv6. Then the request reaches Proxy B that can
reach UA B only using IPv4: this means that Proxy B adds a record-route
header to the INVITE and delivers it to UA B using IPv4 (and proxy B will
forward all the future SIP requests belonging to the INVITE dialog). Is this
the expected behaviour of this infrastructure? Is it possible to assume that
UA B (IPv4 only) will place correctly the URI of UA A in the request-URI of
the mid-dialog SIP requests sent to UA A, even though such URI contains an
IPv6 address (I know it is supposed to be true for Record-routing entries)?

Best regards, Livio Torrero.

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