Re: draft-ietf-ccamp-lmp-10 comments

["Adrian Farrel" <adrian@olddog.co.uk>]

Hi Marco,

I think the first quote comes from a paragraph that begins "A unique
characteristic of transparent devices" making clear that this text applies
specifically to transparent devices, while the second quote comes from the
subsequent paragraph and is more general, applying to opaque and
transparent devices (as the text later in that paragraph makes clear).
Thus there is no contradiction.

The question may be phrased another way. In the case that you have a
transparent switch, how will you send a test signal on a link? The answer
is usually: I will turn off all signals except for the one I am testing.
That means two things...
1. You need to turn off all other signals at the sender
2. You must not transparently forward signals at the receiver
    (because a. you would not notice the signal and b. the next
     downstream node would receive the signal)

Cheers,
Adrian


----- Original Message ----- 
From: "Marco Ruffini" <ruffinim@tcd.ie>
To: <ccamp@ops.ietf.org>
Sent: Tuesday, October 25, 2005 5:59 PM
Subject: draft-ietf-ccamp-lmp-10 comments


Hi all,

I was reading the draft-ietf-ccamp-lmp-10 document and in the paragraph 5
I
found a part which is not completely clear to me.



Suppose I want to verify the link connectivity between two transparent
switches, A and B, where A is the node that initiates the procedure.

-          One part of the text asserts that "to ensure proper
verification
of data link connectivity, it is required that until the data links are
allocated for user traffic, they must be opaque (i.e., lose their
transparency).": from here I understand that node B has to terminate all
the
ports that are not currently transmitting data (i.e. all the ports that
have
not been already verified).

-          On another part I found: "There is no requirement that all data
links be terminated simultaneously, but at a minimum, the data links MUST
be
able to be terminated one at a time": here it looks like B does not have
to
terminate all the not-yet-verified ports at the same time. However in this
case B may not receive a message sent from node A over a certain link even
if that link is actually connecting node A to B (in fact the port of B
relative to that link may be not terminated in that occasion).



Which one is the correct interpretation? Should node B have all the
not-yet-verified ports terminated at the same time when node A starts the
link verification?





This is the text of paragraph 5 I referred to:

"A unique characteristic of transparent devices is that the data is

   not modified or examined in normal operation. This characteristic

   poses a challenge for validating the connectivity of the data links

   and establish the label mappings. Therefore, to ensure proper

   verification of data link connectivity, it is required that until

   the data links are allocated for user traffic, they must be opaque

   (i.e., lose their transparency). To support various degrees of

   opaqueness (e.g., examining overhead bytes, terminating the IP

   payload, etc.), and hence different mechanisms to transport the Test

   messages, a Verify Transport Mechanism field is included in the

   BeginVerify and BeginVerifyAck messages.



   There is no requirement that all data links be terminated

   simultaneously, but at a minimum, the data links MUST be able to be

   terminated one at a time. Furthermore, for the link verification

   procedure it is assumed that the nodal architecture is designed so

   that messages can be sent and received over any data link. Note that

   this requirement is trivial for opaque devices since each data link

   is electrically terminated and processed before being forwarded to

   the next opaque device, but that in transparent devices this is an

   additional requirement."







Best Regards,

Marco Ruffini.



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Dublin 2,

Ireland.

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