RE: [midcom] Identifying Intra realm calls

["Sanjoy Sen"<[e-mail]>]

Christian, Thanks for your comments. See inline.

> -----Original Message-----
> From: Christian Huitema [mailto:[e-mail]]
> Sent: Wednesday, March 06, 2002 10:23 AM
> To: Aoun, Cedric [QPD:MA01:EXCH]; Midcom IETF (E-mail)
> Cc: Sen, Sanjoy [NGC:B692:EXCH]
> Subject: RE: [midcom] Identifying Intra realm calls
> 
> 
> You are correct: many NATs will not "send back" the traffic. 
> The STUN statement is wrong: when two parties are behind the 
> same NAT, not only is the solution not very efficient; in 
> fact, it does not always work. 

I thought so too. Then this should be mentioned in the next version of STUN
document. 

> We should only use a solution 
> like STUN when we know that the two stations are "far apart". 

Not sure how would you determine if the stations are "wide apart".

> Even so, there are failure modes, e.g. in the cases of dual 
> NAT: an ISP allocate 10/8 addresses to its customers, who in 
> turn run a NAT.
> 
> A partial solution is to use multicast discovery to find out 
> whether the other party is local: from the UDP port that uses 
> STUN, send a multicast packet to a conventional IPv4 
> multicast address and port, documenting something like "I am 
> local and my STUN address is x.x.x.x:p"; the receiver of 
> these packet keeps a catalog; this is what is document in 
> version 04 of the shipworm/teredo draft. You may combine the 
> solution with a hint, e.g. the fact that the STUN mapped 
> addresses of the parties look alike. 

The problem, we noted, also occurs when there're multiple NAT's fronting a 
big network realm or in case of dual-homed NAT's, when this kind of hint
doesn't work. But, as you said, its a hint anyway:-)

Why can't we use a unicast ping-like message to determine connectivity
between private addresses behind NAT's? That's one of the possible solutions
discussed in the draft.

Sanjoy

> 
> -----Original Message-----
> From: Cedric Aoun [mailto:[e-mail]] 
> Sent: Wednesday, March 06, 2002 12:16 AM
> To: Midcom IETF (E-mail)
> Cc: Sanjoy Sen
> Subject: [midcom] Identifying Intra realm calls
> 
> Hello, 
> One of the open issues that had been briefly discussed in the 
> mailing list in the context of the pre-Midcom solutions - 
> STUN, PHANTOM and MINT - is how to effectively route 
> intra-realm calls (e.g. calls behind the same NAT), i.e., how 
> does the client or a signaling server determine that the 
> called party is in the same network realm and the media is 
> directly routable without going through the NAT or a relay 
> NAT (i.e. a Media Proxy). For example, the last para of Sec 
> 9.3 in STUN draft states: It is possible that both 
> participants in the multimedia session are behind the same 
> NAT. In that case, both will repeat this procedure
>    above, and both will obtain public address bindings. When 
> one sends 
>    media to the other, the media is routed to the nat, and then turns 
>    right back around to come back into the enterprise, where it is 
>    translated to the private address of the recipient. This is not 
>    particularly efficient, but it does work. 
> Note that, the above solution is not applicable to NATs all 
> vendors. Given that a significant percentage of Enterprise 
> calls are intra-realm, the issue, if resolved, will lead to 
> considerable saving of egress bandwidth at the NAT and will 
> lead to general improvement in service quality.
> Note that this is also an issue within the MIDCOM framework. 
> An ID was submitted to discuss this issue 
http://www.ietf.org/internet-drafts/draft-aoun-midcom-intrarealmcalls-00.txt

The intent of this ID is to initiate some discussions (perhaps, offline)
towards a solution for this issue. The intent is in no way to disrupt the
progress of the WG's chartered work items, so, if you're interested to work
on this problem, please send comments offline and we can move the
discussions to a private mailing list ([e-mail]).
Thanks 
Cedric 
Cedric Aoun 
Nortel Networks 
France 
mailto:[e-mail]