Subject: [IPTEL] TRIP for gateways

From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 21 Nov 2000 02:42:48 -0500

Folks,

At the last two meetings, Hussein and I have presented a draft on the usage
of TRIP for gateways. The problem that the draft is trying to address comes
up more and more, and it is becoming urgent that the group come to some kind
of decision regarding this work. We can discuss this at the meeting, of
course, but I'd much prefer to start a list discussion first so we can
identify what the problems are.

As I recall from the last meeting, one of the concerns raised was that BGP
is bad for intra-domain route propagation. Since this is an intra-domain
issue (intra-ITAD in our terminology), TRIP, being a bGP4 equivalent, is ill
suited. I thought about this, and came to the conclusion that intra-domain
route propagation for VoIP is different from IP. I would expect ITADs to
have many LSs, and which routes an LS uses for a particular call is still
very much a policy issue. IP layer intra-domain protocols like OSPF are
simply topology flooding mechanisms. Policy doesn't play a role. You are
always looking to take the least cost route. Not so here; the direction a
call is routed within a domain still depends on administrative policy. So,
it seems that it would be useful to still run TRIP between LS's within an
ITAD.

Another issue raised was that SLP appeared more appropriate than TRIP, as
this was a service advertisement issue (specifically, the gateway would send
out SLP service advertisement messages to the LS). I don't think SLP is
really quite right here. For example, in SLP, service advertisements need to
be refreshed by resending the service template. This would mean that a
gateway would need to periodically resend its entire routing table. Seems
inefficient compared to the much smaller keepalive in TRIP. The smaller
keepalive means that it can be sent more often, resulting in a much more
rapid failure detection.

Comments?

THanks,
Jonathan R.

---
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.cs.columbia.edu/~jdrosen         PHONE: (973) 952-5000
http://www.dynamicsoft.com

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From: "Hussein F. Salama" <[email-masked]>
Date: Mon, 27 Nov 2000 15:45:44 -0800

> identify what the problems are.

Before going into the details of SLP and TRIP, we need to agree on the
requirements. Here are a few questions to get started:
- Is multi-hop call routing a requirement for intra-domain calls? Or is
a single-hop sufficient?
- Is aggregation within a domain required?
- Is it required to advertise the services (e.g. voice or fax) and
capabilities (e.g. which codecs) a specific route supports?
- Dynamic attributes, e.g. residual capacity of GW?
- What's the required convergence time when a route changes?
- Gateway registration vs. intra-domain call routing, are they different
problems?

Thanks.

Hussein

-- 
Hussein F. Salama
Cisco Systems
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