Re: [Detnet] L2/L3 model?

Hi Erik,

One of the L2/L3 use cases is in industrial networks. 

In a typical industrial use case, there would be: 
Dedicated control networks (i.e. the network for machine or a group of machines with an L2 network connecting the controllers, sensors and actuators connected to
A supervisory control network (a L2 network or mixed L2 and L3 depending on the size of the plant)  by L3 forwarding devices connected to
An Enterprise network (e.g. a data center - probably multiple L3 subnets with L2 forwarding within the subnets)

The tightest timing requirements would be in the dedicated control networks, but time synchronization and some scheduled traffic would extend up the to the supervisory control network and perhaps the Enterprise network.

You might look at slides 11 and 12 of this IEEE 802 tutorial for a couple of figures relevant to this use case. 
http://www.ieee802.org/802_tutorials/2013-07/Winkel_00_0713_DMLT_SG_Tutorial_v04.pdf

The type of path in the arbitrary use case would fit here. 

If one has an L3 PCE that sees the L3 topology, it would need an accurate view of the L2 cost (i.e. latency) of the L3 hops to choose a good path and an interface to something in L2 (perhaps the L2 PCE) to create a reservation for scheduled traffic through the L2 forwarders for an L3 hop.

Regards,
Pat

-----Original Message-----
From: detnet [mailto:detnet-bounces@ietf.org] On Behalf Of Erik Nordmark
Sent: Monday, November 17, 2014 10:11 AM
To: detnet@ietf.org
Subject: [Detnet] L2/L3 model?

After the BoF I realized there was one thing we didn't talk about which 
is what combined L2 and L3 topologies that folks have in mind.
It is true that from a packet forwarding perspective both L2 and L3 have 
queues and clocks, but the interaction with the control plane and the 
approach might be different for different forms of combinations.

First of all we have 6TISCH which is an L3-only network.

But in combined L2/L3 networks we could have at least
  - interconnecting L2 islands using L3
  - arbitrary topologies with mixtures of L2 and L3 forwarding devices

A suggestion (at the mike during the BoF) was to consider pseudo-wires. 
That might make sense when interconnecting L2 islands.
But with arbitrary topologies one could end with with a path that as a 
mixture of bridges and routers e.g.

      Sender - B1 - B2 - R1 - B3 - B4 - B5 - R2 - R3 - Listener

Are there use cases that result in such topologies/paths?

Would one need one controller which is aware of both the L2 and L3 
devices and can pick paths (with resources) that include both?
(Typically we separate the layers thus we might have a PCE which sees 
the L3 topology but not the L2 devices in between the routers.)

I think it would be good to explore the combined L2/L3 use cases and 
models in more detail.

    Erik

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