Re: Internal WG Review: Recharter of IP Telephony (iptel)

[Jonathan Rosenberg <jdrosen@dynamicsoft.com>]

Harald Tveit Alvestrand wrote:
> relationship to ENUM?
When you look up a phone number in enum, one of the things that can
happen is that there is no match. More than likely this means that the
number is just a plain old telephone number, and has no relationship
to any Internet resource. In such a case, the phone number is really
an address, pointing to a specific line in the telephone network. If
you need to get there from a SIP proxy, there are a large number of
routes one can use - via different VoIP gateways. TRIP and the gateway
registration protocol (which we call tgrep) fit in here, allowing you
to figure out which one is best to route a call. So, they are 
orthogonal, and when routing a call to a phone number, you would 
generally do enum first and then possibly trip/tgrep if enum didnt pop 
out a SIP URI, for example.

and Patrick writes:
> I would like to have words on how the TRIP model fits with the DNS
> based mechanism for routing used in SIP, and the DNS based
> announcement of E.164->SIP URI mappings (which is followed by DNS
> based routing for SIP.
>
> To a certain degree these mechanisms overlap, where the TRIP model
> (from my point of view) very much is a way for (for example) a set
> of gateways to PSTN announce to SIP outbound proxies what gateways
> exists, and what the cost is.
The distinction here is similar to the enum/trip distinction. The SIP 
DNS mechanisms would be used to take a SIP URI and route the call to a 
proxy in that domain. Once in that domain, a proxy would examine the 
user part of the URI. It can then make a call routing decision based 
on any policy it likes. If the user part is a phone number, one valid 
choice is to use the database populated by trip/tgrep to determine the 
next proxy or gateway to which the call should be routed.


I think the following text, added to the charter, would address both 
issues:

TRIP and the gateway registration protocol are orthogonal to the 
DNS-based mechanisms specified in ENUM and RFC 3264. Those mechanisms 
are used to translate a URI, representing a name, to an address. If 
that address is a phone number in the telephone network, trip and 
tgrep can be used to assist in determining the right route (through 
various gateways) to that number.


Is that satisfactory? If so, I will add the text in the appropriate place.

Thanks,
Jonathan R.

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