Re: [Detnet] L2/L3 model?

Dear all,

I'd think that the whole idea is that the physical resources of all machines can ultimately be abstracted in terms of line rate, time, buffers and queues regardless of whether the forwarding decision happens at L2 or L3.

It would make sense to compute a path based on such terms, wouldn't it?

For Erik's initial question, there may be a need for end-to-end detnet for a 6TiSCH network federated by a backbone, not that the latency of gigE would affect anything but to avoid congestion loss in large deployments.

Cheers,

Pascal

> Le 17 nov. 2014 à 13:32, Anca Zamfir (ancaz) <ancaz@cisco.com> a écrit :
> 
> Hi Philippe,
> My understanding is that QoS (delay, jitter, b/w, etc) must be guaranteed
> for the end-to-end path, whether the path spans L3 only, L2 only or a
> mixture. One solution would be for PCE to get the L2 and L3 island
> topologies (yes, make PCE work at L2 with SPB + extensions which is new)
> and create a single heterogeneous view of the network. Once the path is
> computed, PCE can determine how the different segments (could be TE LSPs
> in L3 or multicast groups for L2) should be created. I think PW-s (if
> used) would be carried inside these segments and it would be good to only
> expose the label at the termination point (listener or the node that
> eliminates the duplicates). This is to avoid having to do stitching.
> There are other possibilities to explore, with some (like where L2 and L3
> islands independently establish these paths) I am struggling with the
> end-to-end guarantee.
> 
> thanks
> -ana
> 
>> On 11/17/14 8:02 PM, "Philippe Klein" <philippe@broadcom.com> wrote:
>> 
>> Erik,
>> In my humble view, the L3 must only indicate the L3 router path over of
>> the L2 island with its path attributes  and let the L2 protocol select
>> the constrained path.
>> Essentially the inner L2 topology could be ignored by the L3.
>> 
>> /Philippe
>> Broadcom
>> 
>> Sent from my iPhone
>> 
>>> On Nov 17, 2014, at 20:11, "Erik Nordmark" <nordmark@acm.org> wrote:
>>> 
>>> 
>>> 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
>>> 
>>> _______________________________________________
>>> detnet mailing list
>>> detnet@ietf.org
>>> https://www.ietf.org/mailman/listinfo/detnet
>> 
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