[SIPForum-discussion] rport and received parameter in Via header

[Thomas Lentz]

Dear Gnana,
let me answer you inline...

What is the purpose of rport and received parameter in sip via header? 
The purpose of the rport parameter is to convey the fact that your SIP UAC 
(VoIP-Phone) isn't able to detect its external signalling port (e.g. 
because it is behind a Firewall or NAT/PAT) and consequently the port 
information in the Contact header mitght be wrong.
The received parameter is populated by the UAS (SIP Server / VoIP 
platform). The UAS puts in the received parameter the source port from the 
IP packet which was sent from the UAC, that carried your SIP message.

Will it be needed if sip client is behind NAT router? 
It is needed in cases where the VoIP phone isn't able to determine its 
communication parameters (IP/Port in Contact), normally it doesn't harm, 
when rport is sent although the Contact header carries correct 
information.

If so, how router can process this sip header as router only handle the IP 
header but cannot application layer header?
Your local router isn't responsible to populate the received parameter, 
since (as you already correctly stated) this is an application layer 
header. It is the responsibility of the SIP platfrom.

Ideally the  SIP UAC / VoIP phone learnse its external port and 
re-register and/or sends it subsequent SIP Messages with the updated 
external port.
If you didn't stumble across it yet:

https://www.ietf.org/rfc/rfc3581.txt

Greetings
 Thomas


Mit freundlichen Grüßen / Kind regards

Thomas Lentz

Senior IT Architect
Global Business Services
NGN Competence Center (www.ngn-factory.com)


Phone:
+49-69-90551-137
 IBM Deutschland

Mobile:
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E-Mail:
lentz at de.ibm.com
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 Germany


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From:   Gnana Guru Natarajan <gnanaguru3012 at gmail.com>
To:     discussion at sipforum.org
Date:   27.09.2017 18:41
Subject:        [SIPForum-discussion] rport and received parameter in Via 
header
Sent by:        discussion-bounces at sipforum.org



Hi,

       What is the purpose of rport and received parameter in sip via 
header? Will it be needed if sip client is behind NAT router? If so, how 
router can process this sip header as router only handle the IP header but 
cannot application layer header?

Thanks,
Gnana Guru N._______________________________________________
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