[SIPForum-discussion] What is the significance of "a:nortpproxy:yes" attribute in SIP SDP message.

[Jiri Kuthan]

just a minor clarification -- this is SER-specific hack, no-rtp-proxy is
by no means a standard.

-jiri

At 13:57 19/02/2007, samuel wrote:
>SIP Proxy detects that both client are behind the same IP and the
>associated NAT transversal solution (RTPProxy) is not needed, that is
>why there is such attribute in the SDP. (no rtp proxy = yes).
>
>It is expected that the router takes care of the media of the clients
>connected in the same LAN but some of them does not do it properly.
>The "technical" term for this behaviour is that the router must
>support hairpining (if I recall properly).
>
>You've got 2 options:
>1)either does not check wether SIP proxy clients are behind the same
>public IP and  use RTPproxy also in these situations.
>2)Configure/Change the NAT Router for one supporting hairpining.
>
>If you go for option 1 you'll provide a more reliable solution (you
>will avoid more similar cases) at the expenses of increasing RTP proxy
>use and therefore costs...it's up to you.
>
>Hope it helps,
>Samuel.
>
>2007/2/19, Naveen Gujje <gujjenaveen at gmail.com>:
>> Hi All, go through the problem below and suggest me your view.
>>
>>
>> The setup is as follows.
>>
>>                     |                           |
>>      H1 ----------|                           |-------{ SIP Proxy }
>>                     |---- NAT Router ----|         ( Iptel )
>>                     |                           |
>>      H2 ----------|
>>                     |
>>
>>  Private Network                         Public Network [internet]
>>
>>
>>
>> H1 & H2 are registering with external SIP Proxy server.
>>
>> When H1 is calling H2, it is sending INVITE request which contains
>> H1's Private IP in the connection information part of SDP message to
>> SIP Proxy. Before sending it out, NAT router replaces this ip with Nat
>> Ip. And before SIP Proxy forwarding this INVITE to H2, it is replacing
>> the Nat Ip in connection information part of SDP message with some
>> server ip and also adding a new media attribute "a:nortpproxy:yes".
>>
>> This behaviour of SIP Proxy is also observed in case of 200 OK message
>> which is sent by H2 as a response to INVITE of H1.
>>
>> And in this case, the IP in the connection information part of SDP
>> message, which is replaced by SIP Proxy, is same in INVITE & 200 OK.
>>
>> Due to this, both H1 & H2 are sending RTP traffic to the new ip which
>> is replaced by SIP Proxy and the SIP Proxy itself is not doing any
>> kind of proxying. With this voice flow is failing.
>>
>> So, can anyone explain me the reason for this type of behaviour by SIP
>> Proxy. And also, what is the purpose of media attribute
>> a:nortpproxy:yes ?
>>
>> The SIP Proxy is IPTEL and Clients are SJPhones.
>>
>> Looking forward for your responses,
>> Naveen G.
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--
Jiri Kuthan            http://iptel.org/~jiri/