The MPLS WG Archive

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

Wayne wrote:
> 
> I think the RSVP hello is one of the enhancements from a vendor. Not a
> RFC as the moment. Is that true? Though the hello packet is small,
> 17.5ms seems a bit aggressive for a large network with a lot of RSVP
> enabled routers/links.

It's not part of the RSVP working group at all.  It's not
vendor-specific, either, however.  It's part of the RSVP-TE draft, and
is part of the MPLS working group.

As for 17.5ms, where do you get that number?  I didn't see it in the
draft anywhere.  I found a 5ms interval, but that's not a requirement -
it's a recommended default value for a user-configurable parameter.

That aside, 17.5ms isn't that terrible.  It's a worst-case of sending 57
hellos per second.  This is substantially less overhead than not using
hellos.

A link with 500 inbound and 500 outbound LSPs, configured with a 30s
refresh interval will generate 34 refresh messages per second (17 Path
refresh, and 17 Resv refresh).  Given that refresh messages are around
100-150 bytes long, and hello messages are 12 bytes long, we're talking
about generating 3400-5100 bytes per second for refreshes, vs. 684 bytes
per second for hellos.  Even with the recommended a 5ms interval
(worst-case of 200 messages per second), hellos would still only
generate 2400 bytes per second worth of control traffic.

And, of course, the amount of bandwidth consumed by hello traffic won't
increse as the number of LSPs increases.

-- David