The MPLS WG Archive

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

Mareline Sheldon wrote:
> 
> I am a newbie and i am not sure as to what exactly is the
> difference between Upstream and Downstream binding ?
> Please can anyone of you explain ?

You definitely must read the MPLS architecture RFC (at the very least):

	RFC 3031 - Multiprotocol Label Switching Architecture

RFCs may be retrieved from http://www.ietf.org/, and other places around
the net.

As for your specific question, the difference is in terms of which
router assigns labels over a given link.

Upstream and downstream are relative to the direction that the data will
be flowing through the LSP, once it is set up.  Signaling protocols send
control packets in both directions when they set up the LSPs.

With downstream label binding, the downstream router (for a given link)
picks the label and informs the upstream router about the choice.  With
upstream label binding, the upstream router chooses the label and
informs the downstream router about the choice.

RSVP-TE, LDP and CR-LDP all use downstream label binding.  I think the
GMPLS versions of these protocols may also have provisions for upstream
binding.

-- David