Subject: interdomain LSP setup

From: "Taner OKUMUS" <[email-masked]>
Date: Sun, 26 Nov 2000 22:32:41 -0500

I have a general question.
I understand that LSP setup in an autonomous domain is well-defined. Owner
of the domain can setup end-to-end ( ingress to egress) LSPs inside the
domain.
How does interdomain transfers handled? Suppose I want to setup an LSP
passing through 2 different ASs and ends up in some subnets in the second
domain. Each domain uses LDP or RSVP to distribute the label between ingress
and egress of that domain. Then each domain can setup LSPs in their domain.
What happens between the egress of the first domain and the ingress of the
second domain? To put inanother way, does LSPs end-to-end in an AS or are
they end-to-end in the system ( meaning from one ingress of a domain to
egress of another domain) ?

Taner

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From: [email-masked]
Date: Mon, 27 Nov 2000 09:57:15 -0000

Taner....you are referring to the architectural concept of 'layered
networks', which is one facet of the larger discipline of functional
modelling of networks.  That is, a link connection of a client trail (which
is 1 hop in the client trail) = a server layer trail.  LSPs create layered
networks (of theoretically arbitrary nested depth), and it is something the
IETF are going to have to get to grips with if MPLS is going to progress
beyond an intra-domain 'IP accessory' and have any properly engineered
future.  This does not seem well understood by many it seems, and it has
some very important consequences that cannot be ignored....especially wrt
the functionality that must be applied at trail termination points and the
server->client adaptation mappings.  Getting to grips with these concepts is
critical as one moves the focus from intra-domain to inter-domain.

You may have seen some mails from me in the past that gave some warnings on
the need for more architectural rigour in this area....such as:
-	since client layer links = server layer trail terminations,
addressing across nested layer networks cannot be congruent (this is an
important issue for the Optical Transport Network and its many
clients....here the concept is generalised MPLS);
-	PHP......makes the trail termination point of an LSP ill-defined for
server->client functional handling, eg this has several OAM consequences;
-	EXP codepoints......if one is carrying a higher layer LSP between 2
private MPLS networks say and using one or more public MPLS networks for
transit (ie on lower layer LSPs) than one cannot assume some consistent EXP
relationships across all the layer networks;  In particular, one must have
the ability to convey the private domain's client LSP EXP codepoints
transparently and independently of any use of EXP codepoints in lower layer
server LSPs;
-	TTL....similar to above, and again TTL is only relevant to layer it
is generated in.  In particular one should never guess a latent number of
server layer hops (for example, one consequence is that on server layer LSP
restoration the number of server layer hops will generally change, and this
should be of no consequence to the client layer LSP....since from its
perspective, its still just 1 client layer hop, ie a link connection).

For further information see ITU Rec G.805.  There are also some good text
references on functional modelling, in particular this one that was
co-authored by a BT colleague of mine Andy Reid and Mike Sexton (of
Alcatel):
Broadband Networking, Artech House; ISBN: 0890065780.

Until we all accept and get a better understanding of the architectural
nature of layered networks, MPLS will flounder as soon as its moves its
focus to inter-domain....and without such a move it offers very little real
benefit since it becomes architecturally non-scalable.

Neil
> -----Original Message-----
> From:	Taner OKUMUS [SMTP:[email-masked]]
> Sent:	Monday, November 27, 2000 3:33 AM
> To:	mpls
> Subject:	interdomain LSP setup 
>

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From: Sandeep Sharma <[email-masked]>
Date: Mon, 27 Nov 2000 17:25:03 -0600

I think the initial question was geared more towards signaling protocols
that need to come into play if a LSP is needed between routers in two ASs.
For example, can you progress an RSVP message between AS boundaries?

While modeling layered networks helps in the network management of these
networks, it does not help in real-time signaling problems in the network.

- Sandeep

Sandeep Sharma
  Iris Labs

> From: [email-masked] [mailto:[email-masked]]
> Sent: Monday, November 27, 2000 3:57 AM
> To: [email-masked]; [email-masked]
> Cc: [email-masked]; [email-masked]
> Subject: RE: interdomain LSP setup 
> 
>

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From: [email-masked]
Date: Tue, 28 Nov 2000 08:48:22 -0000

Hi Sandeep,
<snipped>
> networks, it does not help in real-time signaling problems in the network.
	NH=> I understand the sentiments of the initial question.  But
unless one also has a clear functional model of both the user and the
control planes and also understands the 'service' requirements (a very
important issue for the development of the OTN), then one cannot relate
their required behaviour in an unambiguous manner.  MPLS creates layer
networks, and whilst we can pretend this is not true it does not help us
take MPLS forward.  It is not the same as a simpler IP-only connectionless
mode.  We don't have that recognition yet and I believe we need it.
	<snipped>