Subject: RE: GMPLS issues (was - GMPLS Last Calls)

From: [email-masked]
Date: Wed, 13 Jun 2001 14:08:47 +0100

> Where is the issue ? Why do we need NSAP addresses in GMPLS ?
> 
> Kind regards,
> 
> Eric
>
Eric, I understand your points on the 'management network'......that is, the
addressing of it's user-plane is a separate network to the user-plane
offered for cutsomer connections.  So let me concentrate on the 'external'
user-plane here in an attempt to answer your question.

Seems we have some choices in GMPLS at the moment:
Addressing - v4 or v6
Signalling - RSVP or CR-LDP
Routing - OSPF or IS-IS (but exterior is BGP only)

All these facets are, in principle, independent choices.  And, in
particular, since 'server layer trails = client layer links' then addressing
cannot be from the same space at a server and client layer.  The addressing
might have exactly the same format, but it comes from a different space, ie
address X at layer M is not = address X at layer M.

Given that the layers have to be decoupled in the general case (for
commercial as well as technical reasons - see the BT 'Freeland' requirements
draft to 12/00 mtg) then there seems to be no reason why an operator could
not use NSAPs for the access points of SDH or OTNs if he so wished.  And,
given this choice, that operator might also prefer to use PNNI as the
signalling/routing solution too.  So, the issue seems not one of
'necesssity' but simply choice......though there may be certain technical
benefits of choosing 1 solution over another.  I don't believe there is
anything technically wrong with saying this and giving operators/vendors a
choice here is there?.....if there is please point out the problems.

regards, Neil

---

From: Yakov Rekhter <[email-masked]>
Date: Wed, 13 Jun 2001 08:38:13 -0700

Neil,

> not use NSAPs for the access points of SDH or OTNs if he so wished.  

Please note that there is a way to carry NSAPs in IPv6 addresses,
although it does not support all types of NSAPs.  (see rfc1888 for
more details). Please also note that GMPLS supports IPv6 (as well
as IPv4). Finally, please note that a "perfect" solution (the one
that addresses all the requirements of everyone) is a *non* goal
for GMPLS.

> And,

Few points:

1. Providing multiple choices for performing essentially the same
thing, especially if these choices have similar characteristics,
doesn't help to develop multi-vendor interoperable solutions.

2. The fact that in the IETF there are not one, but two link-state
IGPs (OSPF and ISIS) is a bug, and not a feature. 

3. The same applies for MPLS signalling (CR-LDP vs RSVP).

4. Suggesting yet another routing/signalling protocol, in addition
to GMPLS, is adding yet another bug (not a feature).

5. I understand that BT submitted a contribution to the ITU
suggesting PNNI as (yet another) routing/signalling for optical 
cross connects.

Yakov.

---

From: Lloyd Wood <[email-masked]>
Date: Wed, 13 Jun 2001 17:50:56 +0100 (BST)

> 3. The same applies for MPLS signalling (CR-LDP vs RSVP).

Beg to differ. (and you mean RSVP-TE)

The IETF insists on at least two interoperable implementations of
anything to consider it for a standard. This allows the standard to be
proven, and to have a concept of the underlying standard that is
separate to any single implementation, while allowing choice of
competing implementations. Each implementation can be evaluated on its
merits; this exerts pressure on the implementations, and allows
debugging and improvement of the implementations with respect to the
underlying standard.

Similarly, going up a level of abstraction, having more than one
standard fulfil an implementation of a set of ideas increases
understanding of the underlying principles, independent of each
standard and its implementations, while allowing choice of competing
standards as expressed in their implementations. Each standard can be
evaluated on its merits; this exerts pressure on the standards, and
allows debugging and improvement of the standards with respect to the
underlying principles and algorithms.

If it wasn't for ISIS, OSPF would really suck. and vice versa.
Competition is Good.

L.

and I see just having BGP as a problem.

<[email-masked]>PGP<http://www.ee.surrey.ac.uk/Personal/L.Wood/>