[SIPForum-discussion] Can A call to B party without proxy?

[Eric Burger]

You already stated the solution, and it was the whole point of SIP  
from the beginning: end-to-end communications without the need for  
service providers or network equipment in the network.

Proxies have always been for route discovery when the calling party  
does not know the actual address of the called party. The initial idea  
was the email model, where you might know that Foo works at Example,  
so you would try sip:foo at example.com. It is up to example.com's proxy  
to expand that to foos-phone-at-home at phone.example.net.  If you know  
the address directly, there is nothing to stop you in the Internet  
from sending a message directly to that address. HOWEVER, many folks  
break the Internet model by putting in firewalls, NATs, and SBC's. By  
definition, to gain access to those poor people cut-off from the  
Internet, you will have to go through their B2BUA's. Then again, the  
address of the B2BUA is the endpont from your perspective, so if you  
know that address (which would be something like sip:user at sbc.example.net) 
  then you still do not need a proxy.

On Jul 31, 2009, at 7:51 AM, arvind shukla wrote:

> Hi All,
> I have one confusion plz help me in that. In sip protocol when A  
> call first time to B party it don't have B's address so, in this  
> case proxy should be there in between A and B. But once A party will  
> know the B's party address then can it be possible for the second  
> time when A call to B, A directly can reach to B without proxy or  
> for the second time also it needs a proxy in between to call B from A.
> Please give the solution for this.
>
>
> Thanks in advance,
> Arvind
>
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