Subject: Re: Proposed way to move forward re ATM/MPLS

From: Eric Rosen <[email-masked]>
Date: Thu, 02 May 2002 16:40:39 -0400

Jim> How does  VC-based multiplexing require extra  VCs if the  only layer 3
Jim> protocol being widely used is IP? 

Traditionally  routers are  multiprotocol  systems which  expect to  receive
layer 2 frames, some  of which may be layer 2 control  packets of some sort,
some of  which contain layer  3 packets.  In  some of the latter  cases, the
packets are  to be  extracted and routed;  in others,  the frames are  to be
bridged.  I think  that's  why the  VC  multiplexing has  never proved  very
popular. 

It's only the very recent work  on IP L2 Interworking which suggests that we
can now  get away with  an IP-only L2  infrastructure, and much of  the work
there has  to do  with handling  the L2 frames  that contain  L3 information
(ARP, Inverse ARP, etc.).

---

From: Jim Harford <[email-masked]>
Date: Thu, 02 May 2002 17:23:45 -0400

Eric,
Your explanation is a very general one and it is relevant if the link 
between two routers is running some L2 protocol such as LLC or PPP.  But if 
we are  talking about an ATM VCC between two routers (and the only L3 
protocol of interest is IP), then I don't know why you would want to 
examine the frames for L2 control information.  In this case, the L2 
protocol is ATM and the SAR takes care of the L2 details.

Jim Harford