[Nsi-wg] [Nml-wg] NSI naming
jrv at internet2.edu
Wed May 13 10:36:14 CDT 2009
Jeroen - thanks for commenting - I think this is important to
understand. I am not sure there is a difference, depending on details
of how you define things.
I try again --
On May 13, 2009, at 4:56 AM, Jeroen van der Ham wrote:
> John Vollbrecht wrote:
>> I agree this is hard. I think levels and layers are different.
>> Layers apply to protocol layers. I may misuse the term. Levels for
>> me apply to what can be switched for a given topology. I.e. A given
>> topology allows VLANS to be created ete, by concatenating VLANS at
>> each edge point. The VLANS to be switched are carried on something
>> else - SONET trunks, GOLEs, Ethernet trunks, etc. Level in this case
>> refers to VLANs on one level and what carries them on the other.
> A node in a network operates on a certain layer in the network
> stack. The node switches, or routes based on (header)information from
> that layer, right?
Yes - assume that the node is an edgepoint in DCN. At the edgepoint
a VLAN from a Link is cross connected to a VLAN from a network.
> Using that definition, network encapsulated in VLANs are also in a
> on top of Ethernet (or other VLANs, or whatever you would want to
> encapsulate it in).
The network is the set of networks and links that are interconnected
in a way that they can create VLANs from edge to edge.
One level in this case is VLANs. That is what gets created. The
other level is whatever multiplexes VLANs. I am not sure what to
call that - it could be layer, but it is not a simple layer.
For example VLANs might be encoded in VCGs and carried in SONET. A
transport network might have multiple SONET trunks each of which are
carrying some VLANs encoded with GFP. The transport network switches
VLANs between trunks by switching VCGs. The network in this case
supports creating VLAN connections. Switching/ routing may be done by
SONET in one network and differently in other networks.
So the concept of level implies that switching is done on a specific
connection type. The type defines a level. A type might be VLAN or
timeslot or possibly TCP session for example. The upper level is
what carries the VLAN (for example) and presents it to the edgepoint
to be crossconnected with another VLAN.
> Perhaps it's me, but I still do not see a difference between layer and
> level so far.
I guess it depends on your definition of layer. Perhaps its me.
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