Re: Question on LMP.

[Michiel van Everdingen <MvanEverdingen@lucent.com>]

Hello Jonathan,

Could you please make clear in the LMP draft that
1. "control channels" are established *over* a "control network".
2. Not all signaling messages (example: the RSVP-TE notify
   message) are sent over "control channels".

If this could be added in the LMP draft, I would not have become
confused on the relation between "control channels" and
"control network".

Examples of text in the LMP draft that caused my confusion:

- Chapter 1: "To enable communication between nodes for routing,
     signaling, and link management, control channels must be
     established between the node pair ..."
  Why the "must" in this sentence ? I would think that
  communication is perfectly well possible over the "control
  network", not using "control channels" ?

- Chapter 2: "One or more active control channels may be grouped
     into a logical control channel for signaling, routing, and
     link property correlation purposes."
  This sentence seems to go in the direction of a kind of multi-
  link PPP protocol (L2). At least it made me believe that the
  control network is built on top of control channels - a thought
  that apparently is wrong.

- Chapter 2: "... the control channel MUST terminate on the same
     two nodes that the TE link spans"
  I could only understand this sentence assuming "control channels"
  are a kind of L2 technique. What does "terminate" in this
  sentence imply ? Is something more happening than the standard
  TCP/UDP termination to packets that are sent over control channels?

- Chapter 3: "The LMP Hello protocol is intended to be a lightweight 
     keep-alive mechanism that will react to control channel failures 
     rapidly so that IGP Hellos are not lost and the associated link-
     state adjacencies are not removed unnecessarily."
  Again, I could only understand this sentence assuming "control
  channels" are a kind of L2 technique. Is it possible to be more
  precise on what "IGP" is meant here (see also
  http://ops.ietf.org/lists/ccamp/ccamp.2002/msg00657.html).


Could you please also indicate that "control channel management" does
*not* need to be fast (O(mseconds)) ?
See http://ops.ietf.org/lists/ccamp/ccamp.2002/msg00700.html.


Looking back through this thread, I think at least the following
two questions are still open:

1. What does the control channel management achieve?
   a. IP reachability confirmation.
   b. Negotiation of Hello and Dead intervals.  
   http://ops.ietf.org/lists/ccamp/ccamp.2002/msg00653.html

2. Is there a mandatory need to distinguish between a failure of
   the RSVP-TE process and a failure of the LMP process ?
   http://ops.ietf.org/lists/ccamp/ccamp.2002/msg00670.html


You wrote:
> standard "ping" only tells you reachability. It does not tell you if the LMP
> component is functioning or not. This is similar to why Hellos are used in
> other protocols (e.g., RSVP Hello).

I'm not sure why we need *both* RSVP-TE Hellos as well as LMP hellos. See
also question 2 above.


Thanks,

Michiel

Jonathan Lang wrote:
> 
> Michiel,
> 
> <snip>
> >
> > If "control channels" are nothing more than the standard "ping" mechanism,
> > why not use this standard "ping" mechanism ?
> > If "control channels" does provide more than standard "ping", could you
> > please let me know what that would be (and why that would be mandatorily
> > needed) ?
> standard "ping" only tells you reachability. It does not tell you if the LMP
> component is functioning or not. This is similar to why Hellos are used in
> other protocols (e.g., RSVP Hello).
> 
> Thanks,
> Jonathan
> 
> >
> > I think I first need clarity on the relation between "control
> > network" and
> > "control channel" before being able to comment on your other points.
> >
> >
> > Thanks !
> >
> > Michiel

<snip>

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| Michiel van Everdingen                                           |
| Systems Engineer                                                 |
| Lucent Technologies - Optical Networking Group                   |
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