The MPLS WG Archive

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

Kappler Cornelia wrote:
> 
> My understanding is the following: Bandwidth for LSPs can be reserved
> using e.g. RSVP-TE. However, what does "reservation" mean? It means
> that at LSP establishment time, the LSR checks whether it has enough
> resources available. However, it only does a "book keeping" of its
> resources. It does not need to control their actual use. Admission
> control and policing must be performed by the LERs. If they don't do
> it, bandwidth is not guaranteed.

For the most part, this is correct.  Transit routers may or may not also
do policing.  It shouldn't be necessary if the ingress router is
properly policing traffic, but it may not be safe to assume that this
will always be true.

Also note that artifacts of packet queueing algorithms may cause
compliant traffic to become non-compliant (at least for short bursts) at
some point along the LSP.  This may require a transit router to perform
policing, in order to enforce any service guarantees.  Routers may also
perform traffic shaping to try and minimize this effect.

> I would expect to find something on the subject in the RSVP-TE draft,
> draft-ietf-mpls-rsvp-lsp-tunnel-07.txt. However, it only seems to talk
> about "reserving" bandwidth without defining what that is. It also
> says:

RSVP-TE, like RSVP, uses IntServ for its reservations.  Check out the
IntServ RFCs:
	RFC 2210
	RFC 2211
	RFC 2212
	RFC 2215

There are other possibly relevant RFCs that I haven't mentioned.  Search
for "Integrated Services" in the RFC index file to find them all.

-- David