The MPLS WG Archive

[David Charlap <david.charlap@marconi.com>]

Lyndon Ong wrote:
> 
> ... how is the logical topology (ATM or MPLS) created?  Is this
> through some offline tools and configuration, or done directly
> by switches?

There are two common ways:

1: Each switch can have its forwarding tables hand-configured (or via
   an external network management package).  In the ATM world, this is
   how PVC's (permenant virtual circuits) are created.

2: The network can be given a list of endpoints for the virtual circuits
   and let the switches set up the actual circuits via a routing and
   signalling protocol.  In the ATM world, this is the SPVC (signalled
   PVC), using PNNI for a routing protocol and UNI/NNI as a signalling
   protocol.  In the MPLS world, it would use an IGP (like OSPF or ISIS)
   as the routing protocol and an IP signalling protocol (like RSVP or
   LDP.)

There are other ways as well.  For instance, ATM supports SVCs
(signalled VC) which are created on-demand by edge hosts/routers and are
torn down by those hosts/routers when no longer needed.  This would not
be a good idea in an ISP's core, but is often used in enterprise
networks.

-- David