Re: 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.

Thanks,

Gao

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Christer Holmberg <[email protected]> 
2010-05-04 19:46

收件人
"'[email protected]'" <[email protected]>, "[email protected]" 
<[email protected]>
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Paul Kyzivat <[email protected]>
主题
RE: [Sipping] About changing sending address during session:






Hi,
 
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.
 
Regards,
 
Christer

From: [email protected] [mailto:[email protected]] On Behalf 
Of [email protected]
Sent: 4. toukokuuta 2010 9:30
To: [email protected]
Cc: Paul Kyzivat
Subject: [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. 

Thanks, 

Gao 

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