Subject: RE: PPP question on draft-ietf-ccamp-lmp-test-sonet-sdh-02.txt

From: James Carlson <[email-masked]>
Date: Thu, 3 Apr 2003 11:32:29 -0500

Wijnen, Bert (Bert) writes:
> - LMP is a Link Management Protocol that runs on UDP and
>   all the control info goes over that path. In many cases
>   that control info goes out of band of the data path

Yep.

> - In the case where the LMP wants/needs to test that the
>   data path is indeed operational, that is where it sends
>   a test message. It does so over UDP if it is available
>   on the data path, via other methods if it is not available
>   on the data path (as is the case for sonet/sdh).

Understood.

> - This test message is only used for very short periods of
>   time.... so I wonder if it then makes sense to try and setup
>   a PPP connection first in order to be able to send a few
>   short test messages in order to just verify that the data
>   path is functioning.

That's the part that I don't fully understand.  Why wouldn't you just
negotiate up a PPP link over the DCC when the underlying link is
enabled, and then leave it in place at all times?

Switching back and forth is clumsy but makes (almost) some sense if
the data connection that we're talking about actually carried user
data.  Unlike the troubles with lambda switching, this channel doesn't
carry any user data -- it's an out-of-band management interface.

> Is a true statement, but the question is if it indeed makes sense to
> have to setup a PPP connection to send just a few UDP packets after
> which the connection (PPP) is to be removed again, cause there might 
> be otehr data (non IP even) traveling on the data path.

If you're actually switching back and forth between data and test mode
to send the messages, it probably also doesn't make sense to maintain
the overhead of UDP or IP either.  Unlike the LMP messages sent over
the control channel (which might be an internet), these messages
wouldn't be routable in any conventional sense.

As I said before, this proposal doesn't quite make sense to me, and,
in addition, reusing some elements of PPP but not others looks quite
odd.  There is however nothing that prohibits consenting peers from
doing strange things.

-- 
James Carlson, Solaris Networking         <[email-masked]>
Sun Microsystems / 1 Network Drive         71.234W   Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757   42.497N   Fax +1 781 442 1677