Subject: [L2tpext] Queries with respect to the LAC-LAC and LNS-LNS Reference Models

From: "Nagendra B.S" <[email-masked]>
Date: Mon, 18 Mar 2002 10:49:16 +0530

Hi,

I have few queries with respect to the LAC-LAC and LNS-LNS Reference
Models.

>From the "draft-ietf-l2tpext-l2tp-base-02.txt",

                     Figure 2.0: L2TP Reference Models

INTERNET DRAFT                   L2TPv3                       March 2002

   (b) LAC-LAC Reference Model: In this model, both LCCEs are LACs.
   Each LAC forwards circuit traffic from the remote system to the peer
   LAC using L2TP, and vice versa.  A LAC does not perform any native
   handling of the tunneled L2 frame, and thus, does not utilize a
   virtual L2 interface.  Rather, a LAC acts as a simple cross-connect
   between a circuit and an L2TP session.  This model typically involves
   symmetric establishment; that is, either side of the connection may
   initiate a session at any time (or perhaps simultaneously).

   +-----+  L2  +-----+                      +-----+  L2  +-----+
   |     |------| LAC |...[packet network]...| LAC |------|     |
   +-----+      +-----+                      +-----+      +-----+
   remote                                                 remote
   system                                                 system
                      |<- emulated service ->|
         |<----------------- L2 service ----------------->|

   (c) LNS-LNS Reference Model: This model has two LNSs as the LCCEs.
   Each LNS logically terminates the L2TP session locally, requiring
   virtual L2 interfaces for each L2TP session on each side of the L2TP
   session.  A user-level or traffic-generated event typically drives
   session establishment from one side of the control connection.  Also
   known as "voluntary tunneling" [RFC2809].

                    +-----+                      +-----+
   [home network]...| LNS |...[packet network]...| LNS |...[home
network]
                    +-----+                      +-----+
                          |<- emulated service ->|
                          |<---- L2 service ---->|

   Note: If an LNS initiates session establishment due to an event
   (generally user-driven), the LNS is sometimes referred to as a "LAC
   Client" as defined in [RFC2661].

1)Where can this kind of systems be deployed and what are the
advantages/disadvantages of the above two models against the regular
LAC-LNS model ?

2)How exactly is the tunneling of packets taking place in the above
models? 

Can somebody please clarify ?

Thanks,
Nagendra

-- 
------------------------------------------------------------------------
Nagendra B.S                    [email-masked]
Infosys - India                 Phone Office : 91-80-8520261  xtn : 6566
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