[Nml-wg] [Nsi-wg] Conversation about ITU concepts with Ciena folks
victor.reijs at heanet.ie
Tue Sep 8 12:27:48 CDT 2009
Hello all of you,
John Vollbrecht wrote:
>> The approach that must be taken for collapsing is:
>> - have a path find agent find multiple paths
>> - let the stitching framework try each path in order till a valid path
>> is found.
>> The consequence is that in rare situations no valid path may be found,
>> even though one might be available.
> How is it possible to try every path and not find a valid one, if a
> valid one exists?
Would be interested why indeed it would not find it. I am more concerned
that a certain path is not found.
If a path is found and the technology in principle is able to make a
working path, the SF should also agree with that (otherwise there is
something wrong with (the implementation of) SF.
>> If these situations are sufficiently rare, the simplification that this
>> approach brings may outweigh the disadvantage of false negatives.
>> So I think this may be a viable approach, even though it is different
>> than what I have pursued so far.
I think this approach stays a valid approach. Always good to reduce to
complexity (and I think we will need to do that when abstracting a
topology for pathfinding).
>> This is not to say I have no concerns about topology collapsing and
>> stitching approaches. I have two concerns about the stitching framework,
>> and one about topology collapsing.
>> For stitching, I like to make sure there is no implicit assumption of
>> order in network layers, or worse, that the number of network layers is
>> fixed (e.g. as in layer 1-7 in the OSI model), or that a layer may only
>> occur once in an adaptation stack.
> I don't think this is a problem, but I leave that for Victor. I am not
> sure what an adaptation stack is. Is it something you see over a
> complete path? I don't think it happens in a single device does it?
The SF knows no layers, it knows the concept of 'Parameter'; at what
layer this is, is not defined. Can be at any level as defined by the two
parties that need to negotiate it (the two peering domains). So a
Parameter can be 'Available time', 'AAI information', 'Policy for
access', 'Connector', 'a secret human handshake', etc.
<remember: beside defining the parameter name string, the two peering
domains also need to agree on the meta data as defined in SF. This thus
all allows new technology to negotiate parameters [like 'inband'
wavelength choice in Adva equipment and other PON stuff] over the
I normally don't use OSI layers, but I still use the layered concept (as
I think that is the best part of the OSI model).
All the best,
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