The MPLS WG Archive

[George Swallow <swallow@cisco.com>]

Shahram -

> 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.

> 2) You could use the first 2 octets, and encode the 2-byte RSVP-TE
> LSP-ID in the first 2 octets of Y.1711 LSP-ID and encode the 2-byte
> RSVP-TE Tunnel-ID in the last 2 octets of Y.1711 LSP-ID.

Not enough space to be future proof.  We already have requests to
support thousands of tunnels.  If I give just 4 bits to LSP-ID that
only leaves 4k tunnels.

> Just a question, isn't it possible to change the LSP by changing the
> Tunnel-ID, rather than LSP-ID?

You cannot share bandwidth between different RSVP sessions only
between different senders.  The tunnel ID is in the session ID to say
"the various LSPs with this identification all belong to the same
tunnel".

The LSP-ID is in the sender template so that they can be
distingueshed, yet associated via the session and thus can share
bandwidth.

...George

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