Re: [Detnet] DetNet - Migration path

["Grossman, Ethan A." <[e-mail]>]

Thanks Rodney. Since a DetNet network must provide bounded latency and jitter, once the network promises an AccumulatedLatency value to a flow, doesn't it have to maintain that value at least for the duration of the flow? We haven't discussed much about the consistency over time of such things as latency and jitter, but I assumed they would be within some given bound over time, right? Or is it an enduring property of the given network? Isn't that in effect a MinLatency value? 
Ethan.

-----Original Message-----
From: detnet [mailto:[e-mail]] On Behalf Of Rodney Cummings
Sent: Tuesday, October 11, 2016 5:54 AM
To: Grossman, Ethan A.; [e-mail]
Subject: Re: [Detnet] DetNet - Migration path

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.
> 

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