Subject: interface stacking of optical channels

From: [email-masked]
Date: Wed, 01 May 2002 21:05:26 -0400

This question is wrt to the Optical Interface MIB - draft 4

Statement in the MIB reads: (Section 3.1 Example 1)
"An OTN device connected with two adjacent nodes in a single
fiber ring that supports 10 wavelengths per fiber would have 2 opticalTransport ifEntries and 10 opticalChannel ifEntries, as depicted in Figure 2. Thus, the same 10 opticalChannel ifEntries are stacked above each of the opticalTransport ifEntries"

Question:
Given that one makes use of the concept that the combination of {shelf, slot, port, ...} is used to create an ifIndex for an optical channel, won't the ifIndexes of the optical channels stacked on top of otn1 opticalTransport ifEntry be different from the ifIndexes of optical channels
stacked on top of otn2 entry (this is because on the OTN device, the port in on which the light is received is different from the port out on which light is transmitted)

Thanks

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From: "C. M. Heard" <[email-masked]>
Date: Thu, 2 May 2002 08:34:49 -0700 (PDT)

On Wed, 1 May 2002 [email-masked] wrote:

> fiber ring that supports 10 wavelengths per fiber would have 2
> opticalTransport ifEntries and 10 opticalChannel ifEntries, as
> depicted in Figure 2. Thus, the same 10 opticalChannel ifEntries are
> stacked above each of the opticalTransport ifEntries"
> 
> Question:
> Given that one makes use of the concept that the combination of
> {shelf, slot, port, ...} is used to create an ifIndex for an optical
> channel, won't the ifIndexes of the optical channels stacked on top
> of otn1 opticalTransport ifEntry be different from the ifIndexes of
> optical channels stacked on top of otn2 entry (this is because on the
> OTN device, the port in on which the light is received is different
> from the port out on which light is transmitted)

Indeed, the usual procedure would be to associate an ifIndex with a
particular optical channel on a particular physical port, and typically
every interface would be bidirectional (i.e. has both source and sink
functions).  In that case one would need different ifIndex values
for the optical channels stacked on top of otn1 and otn2.  One would
also need some means (outside the scope of the present optical
interface MIB) to represent cross-connect information.

The example you cite, however, is a unidirectional 1-fiber ring, and
I think that the intention was that the two otn interfaces would be
modelled as unidirectional interfaces (otn 1 = sink, otn 2 = source).
The optical channels would still be modelled as bidirectional
interfaces;  however, the source would be associated with otn 1 and
the sink would be associated with otn 2.  If you had a bidirectional
ring then you would need two ifIndex values for each optical channel;
one ifIndex would model one direction around the ring, and the other
ifIndex would model the other direction around the ring.  This avoids
the need to have a separate table to represent cross-connect information,
but it requires twice as many otn ifIndex values.  I do not think that
this modelling technique is obligatory -- I think that the usual model
where a given optical channel ifIndex represents the source and sink
functions attached to a given physical otn port is also allowed.

I expect that there will be an -05 draft will be out soon, and I think
it will clarify these points.

Mike