On May 12, 2009, at 9:24 AM, Martin Swany wrote:
Hi Jeroen,
I'm (re-?) adding Jason to the cc list as he's right in the middle of this discussion as well.
I would add that I think that we are all very close on the way in which things are related, which gives rise to layers/levels of the network. I think that the "Relation" element that we're using in UNIS (perfSONAR/DCN) land really makes the expressions there start to look like the RDF 3-tuples in a way. While that problem is hard, I think that we've been inching closer to having a common solution framework.
I think the relation might work for this if it is defined -- but still it is complicated and important to agree on. See comment below.
best, martin
On May 12, 2009, at 4:13 AM, Jeroen van der Ham wrote:
Hi,
I think Martin's analysis of your description is correct. I only want to add that you seem to be contradicting yourself regarding layering, and I think it is very important that we clear that up.
Before I begin, I want to clear something up: Networks transport data by encapsulating it in different layers. I think we can all agree on that analysis, and we all know what layers are in general. Therefore I don't want to complicate this (already complex) discussion by introducing yet another term (i.e. "level").
Then on to your analysis: in the beginning you say that NSI wants to describe links at a certain layer going over links at a lower layer. Then later on you say that NSI operates at a single layer for a particular request.
Current networks operate at multiple layers (Ethernet, SONET, Lambda, etc.). Therefore, if the NSI wants to be able to provision services across these networks, then it will have to handle multiple layers.
Please realise that the NML is currently describing a layer-less model. Layers are not part of the model and we are only describing the general things that are part of every layer. So NML is currently not able to describe that links at one layer run over a link at a lower layer.
As Martin said, describing layers, and the adaptations between them is a very very hard problem. One that the NML group will be taking on soon though. 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.
Jeroen.
John Vollbrecht Senior Network Engineer, Internet2 office 734 352 4960 cell 734 395 7890
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 protocol stack. The node switches, or routes based on (header)information from that layer, right? Using that definition, network encapsulated in VLANs are also in a layer on top of Ethernet (or other VLANs, or whatever you would want to encapsulate it in). Perhaps it's me, but I still do not see a difference between layer and level so far. Jeroen.
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 protocol 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 layer 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.
John
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John Vollbrecht Senior Network Engineer, Internet2 office 734 352 4960 cell 734 395 7890
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