The MPLS WG Archive

[George Swallow <swallow@cisco.com>]

Shahram -

Just realized that I mis-spoke when I said:

> > The LSP-ID defined in Y.1711 is essentially a combination of LSP-ID + Tunnel-ID
> > as defined in RSVP-TE.  
> > 
> > In the current version of Y.1711, 4 bytes are assigned to
> > this. However the current version of Y.1711 sets the first 2 octets of
> > this field to zero for future use. Therefore two methods are possible:
> > 
> > 1) Compress the LSP-ID + Tunnel-ID in to 2 bytes 
> 
> This uses up all the space.  If RSVP-TE is the only application for
> Y.1711 then this would be acceptable.  But since it's called MPLS OAM,
> I assume there were other apps in mind as well.

This is not even sufficient for RSVP-TE.  When I set up backup paths,
the means of identification is to keep the same Session_Object, and the
same LSP-ID.  The source_IP address is set to the router setting up
the backup tunnel.  Thats the only change.  

So suppose (a most common situation)

router A has tunnel number 1, LSP number 1.
  this tunnel passes through some other router B

router B has its own tunnel number 1, LSP number 1.

router B sets up a backup to protect tunnel A,1,1.

it would like to ping (i.e. verify connectivity) the backup tunnel
after it is set up to make certain that it is working

It can't set the TTSI to B,1,1 - since that is the ID for his own
tunnel.  He can't set it to A,1,1 because that is the working path and
he wants to check the protect path.

So the TTSI does not seem to be sufficient even for RSVP-TE!

...George

==================================================================
George Swallow       Cisco Systems                  (978) 497-8143
                     250 Apollo Drive
                     Chelmsford, Ma 01824