Subject: l2vpn framework issue

From: Eric Rosen <[email-masked]>
Date: Tue, 29 Jul 2003 13:08:43 -0400

Awhile back  we had a  discussion of  the VPLS model  in this doc,  but that
discussion is not reflected in draft-ietf-l2vpn-l2-framework-00.txt which is
now being last called. 

My proposal  is to add the  following text at  the end of section  2.2 (just
before  section  2.2.1).  I  think  this  text does  the  proper  job for  a
framework document,  i.e., places the  controversial issue in  context while
leaving the resolution of the controversy to the solutions work. 
-------------------------------------------------------------------------------

   This framework specifies that each "bridge module" has a single
   "Emulated LAN interface".  It does not specify the number of bridge
   modules that a VPLS-PE may contain, nor does it specify the number of
   VPLS instances which may attach to a bridge module over a single
   "Emulated LAN interface".

   Thus the framework is compatible with at least the following three
   models:

     - Model 1

       A VPLS-PE contains a single bridge module, and supports a single
       VPLS instance.  The VPLS instance is an Emulated LAN; if that
       Emulated LAN contains VLANs, 802.1Q tagging must be used to
       indicate which packets are in which VLANs.

     - Model 2

       A VPLS-PE contains a single bridge module, but supports multiple
       VPLS instances.  Each VPLS instance is thought of as a VLAN (in
       effect, an "Emulated VLAN"), and the set of VPLS instances are
       treated as a set of VLANs on a common LAN.

     - Model 3

       A VPLS-PE contains an arbitrary number of bridge modules, each of
       which attaches to a single VPLS instance.

   There may be other models as well, some of which are combinations of
   the 3 models above.  Different models may have different
   characteristics, and different scopes of applicability.

   Each VPLS solution should specify the model or models that it is
   supporting.

   This framework does not specify the way in which bridge control
   protocols are used on the Emulated LANs.

---

From: Ali Sajassi <[email-masked]>
Date: Thu, 31 Jul 2003 12:14:48 -0700

Hi Eric,

By defining the three models for VPLS-PE, it makes it more clear than what 
it was before. However, it seems you use the term VPLS instance to refer to 
a group of PWs as their associated forwarders, right ? Previously, the term 
VPLS instance was used to refer to a service instance (uni-to-uni) 
including the portion over IP/MPLS. The figure 2 in framework includes a CE 
connected to a VPLS-PE over an access network (e.g., QinQ) and the CE is 
marked to be included in that service instance. And that is consistent with 
my understanding. In other words, I consider a VPLS instance as a service 
instance that is between uni to uni and spans across access networks as 
wells as core MPLS/IP network.

We can call, the group of PWs and their associated forwarder an emulated 
LAN that can correspond to one or more VPLS instances. If it corresponds to 
a single VPLS instance, then we also refer to it as emulated VLAN because 
it looks like a VLAN to a bridge module.

Besides indicating which of these models a given solution uses, it should 
also indicated if the bridged module that it uses, is the standard IEEE 
802.1 bridged module or not.

-Ali