Re: [Detnet] DetNet - Migration path

[Rodney Cummings <[e-mail]>]

Thanks Ethan,

The current draft of 802.1Qcc has both for each flow (stream):

- AccumulatedLatency: This is provided from network to user, and it represents the currently configured maximum latency.

- MaxLatency: This is provided from user to network as the maximum latency that the application requires. If AccumulatedLatency exceeds this value, the network reports failure (flow not configured).

The assumption was that the network configuration may need to adapt to changing physical hardware and/or the requirements of new flows, and therefore AccumulatedLatency isn't always stable.

Early drafts of 802.1Qcc had a MinLatency requirement (for low jitter), but that was removed due to concerns that it would require significant buffering. Application representatives (e.g. automotive, industrial) did not make strong arguments to keep MinLatency.

Rodney
> -----Original Message-----
> From: Grossman, Ethan A. [mailto:[e-mail]]
> Sent: Friday, October 7, 2016 3:21 PM
> To: Rodney Cummings <[e-mail]>; [e-mail]
> Subject: RE: DetNet - Migration path
> 
> Thanks Rodney. On a peripherally related note, one thing you mention below
> about 802.1Qcc is "the user ... requests a maximum latency". In another
> current DetNet discussion there is the distinction between the user
> requesting a specific latency (presumably implying a reply from the
> network saying whether it was available or not) vs only being able to
> query the network about its latency performance. I thought we were
> converging on the latter model, but now I'm not as clear. Am I missing
> something here?
> Thanks,
> Ethan.
> 
> -----Original Message-----
> From: Rodney Cummings [mailto:[e-mail]]
> Sent: Friday, October 07, 2016 11:23 AM
> To: Grossman, Ethan A.; [e-mail]
> Subject: RE: DetNet - Migration path
> 
> Great topic,
> 
> I'm not completely clear on what it would mean for a router to support
> DetNet, but let's assume it means that the router:
> 1. Uses one of the solutions from draft-dt-detnet-dp-alt to identify flows
> of DetNet data.
> 2. Uses queuing/shaping/scheduling techniques from 802.1Q to provide
> DetNet guarantees for that data (e.g. max latency).
> 3. Provides YANG management for #1 and #2.
> 
> All of this could be done today using vendor-specific YANG modules, with
> centralized network management software from that vendor. That's not ideal
> of course, but it is useful.
> 
> How would a user application (protocol from draft-ietf-detnet-use-cases)
> use this?
> 
> I would argue that the user applications should use the "API" specified in
> 802.1Qcc clause 46 (currently in draft). That API is agnostic of layer 2/3
> details and the data-plane encoding. The user simply identifies the flows
> from the host perspective (e.g. UDP header fields), and requests a maximum
> latency. The API is used between the user's application and the
> centralized network management software. The API specifies YANG, so it can
> be implemented as a RESTful API or similar.
> 
> AVnu Alliance's goal is to certify conformance to standards (i.e. multiple
> vendors).
> 
> Can AVnu Alliance certify the vendor-specific router implementation? No
> Can AVnu Alliance certify the 802.1Qcc API between the user application
> and the vendor-specific network manager? Yes As time goes on and DetNet
> standards are published, can AVnu Alliance certification do deeper into
> the routers? Yes
> 
> That's one hypothetical intermediate plan.
> 
> Rodney
> 
> From: detnet [mailto:[e-mail]] On Behalf Of Grossman, Ethan
> A.
> Sent: Friday, October 7, 2016 12:42 PM
> To: [e-mail]
> Subject: [Detnet] DetNet - Migration path
> 
> Hi Folks,
> 
> I did a brief "DetNet Status" presentation to the AVnu Alliance Technical
> Working Group, which is an industry group that promotes AVB/TSN. The
> attendance at this particular meeting was mostly Pro Audio people, and
> their main line of questioning was "What is the plan for incrementally
> migrating users from where they are today to increasingly improved network
> performance, which would eventually culminate in "full DetNet"?"  Another
> way to put it might be "Can we leverage the work of DetNet to improve
> networking capabilities between now and when DetNet is implemented on most
> routers?"
> 
> As far as I know, we don't have a plan to roll out a "migration path" with
> intermediate performance levels, using today's protocols, perhaps with
> "minor" changes to support DetNet. We are designing an architecture and
> protocol extensions that will do the job, leveraging existing  protocols
> to the extent possible, but it is an end goal, not a roadmap.
> 
> Having said that, do we have any other more helpful reply to this line of
> questioning?
> 
> Thanks,
> Ethan.
>