Sorry - NBMA L2 networks are really L3 networks. There is not theoretical difference between FR network with OSPF routing and IP CORE network with OSPF routing. Fixed-sized ATM cells make switching easier but I do not think it's of any importance for the modern hardware developers, and the announcement CISCO did about developing AIC's for the CEF (L3) switching just prove it. You are talking abouth the wrong things. The real MLPS and L2/L3 idea was to divide core and customer's routing into 2 independent levels - core routing should work with N nodes (where N is the number if your routers/switches) and should be mono-vemdor, mono-protocol system, and the customer's routing should work with the unstable, multi-vendor and multi-protocol Internet (and private networking) world. Just this is the real reason for this L2/L3 playing. MLPS just realise this idea and mixture this idea with _classify and mark QoS parameters_ idea - just both great ideas. But when people add AMT QoS there, with a lot of _pvc bundles, svs's , etc etc_ they fraud themself - it's possible to build this, but it's not easiest way to do it. For example, if you built some kind of 2 level IP-like (circuit-less) network, and translate QoS parameters into some kind of IP TOS and precedence, and avoid complex and huge BGP tables inside the core network - you can achieve QoS just by existing tools (preferences, RSVP if you want it, WFQ, etc etc) and you can avoid useless QoS calculations over the huge network while you have not congested links in it (if you use queue-based QoS control it work only when it's nessesary, if you use circuit-based QoS you should calculate QoS everywhere and forever even if you have not congestions at all). But it's offtopic for this thread, sorry - a lot of people are tired of this discussions and ATM/MLPS/QoS words... The most important idea in L2/L3 division some theoretics are doing now is to divide CORE/CUSTOMRE's switching into the 2 independent levels, and use the simplicity of the core backbones (plain, single-vendor usially) to make the packet switching more stable and effective. Alex. On Wed, 11 Aug 1999, Martin Cooper wrote:

Date: Wed, 11 Aug 1999 15:35:52 +0100 From: Martin Cooper <mjc@cooper.org.uk> To: Joel Halpern <joel@mcquillan.com> Cc: nanog@merit.edu Subject: RE: What frame relay switch is causing MCI/Worldcom such grief?

Joel Halpern <joel@mcquillan.com> wrote:

...

Martin Cooper said something similar to:

...

But the reason ISPs adopted NBMA L2 networks in the first place is because the telcos convinced them that L2/L3 integration was going to happen.

Actually, that turns out not to be the case. The adoption of layer 2 switching technology into the internet core set of tools predates any of the ATM hype. It was done with frame relay.

Oh absolutely - I wasn't just referring to ATM in the context of NBMA L2 switching.

...

It was not done on the basis of L2/L3 integration, but because it gave the ISPs something more useful than just a fixed size (DS3) set of pipes between places.

Well ok, but if you follow that marketing pitch (making nailed up L2 links more useful to extremely popular overlayed L3 networks like the Internet) to its logical conclusion, it ends up there, because the motivation behind it is to be seen to add value to the product (shifting unspecified data from A to B) to stave off commoditisation.

M.

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