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Re: [Sipping] About changing sending address during session:

Hi Christer,

As you can see, I have the same point.

But did you notice that I put the defintion of media flow and IP flow from 3GPP. It would be a interworking problem while IMS interworking with UE/Softphone from other IP networks.



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Christer Holmberg <christer.holmberg@xxxxxxxxxxxx>

2010-05-04 19:46

"'gao.yang2@xxxxxxxxxx'" <gao.yang2@xxxxxxxxxx>, "sipping@xxxxxxxx" <sipping@xxxxxxxx>
Paul Kyzivat <pkyzivat@xxxxxxxxx>
RE: [Sipping] About changing sending address during session:

From pure SIP/SDP perspective, I think it's allowed to change source port. Of course, if you use the source attribute to explicitly indicate your source port, you will have to update that also.
Whether it will work is another question... In many NAT/SBC cases it won't even work unless the media is symmetrical.

From: sipping-bounces@xxxxxxxx [mailto:sipping-bounces@xxxxxxxx] On Behalf Of gao.yang2@xxxxxxxxxx
4. toukokuuta 2010 9:30
Paul Kyzivat
[Sipping] About changing sending address during session:

As we know, if one side's UA want change it's receiving address, it needs a new O/A procedure. Not considering symmetrical RTP, can UA change it's sending address during session?

IETF level:

By current RFC3264, it seems that there's no normative text to forbid such behavior.

3GPP(definition of media flow):

IP Flow: Unidirectional flow of IP packets with the following properties:

-        same source IP address and port number;

-        same destination IP address and port number;

-        same transport protocol (port numbers are only applicable if used by the transport protocol).

Media Flow: One or more IP flows carrying a single media instance, e.g., an audio stream or a video stream. In the context of this specification the term Media Flow is used instead of IP Flow regardless of whether the actual IP packet corresponds to media plane information (e.g. audio RTP flow) or control signalling (e.g. RTCP or SIP Signalling).

[Inference] By 3GPP's definition, 3GPP's usage seems UE can not change it's sending address(the media flow should has same source IP address and port number).

And informative:
I heard lots of NAT/SBC equipment developers/providers said that the media might be blocked by their equipment if UE changing sending address during session.    

Today, someone asked me the problem again. But I am not sure about the answer, so I'd like to hear people's points here.



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