Re: [Detnet] Traffic description in DetNet flow info model

[Lou Berger <[e-mail]>]

We certainly will need to coexist with existing IETF technologies.

(as contributor) I've been assuming that when using TE infrastructure,
that DetNet would co-exist with, and build on, existing service
definitions for LSPs (or equivalent).  This includes, for example,
DiffServ, controlled load (RFC 2211), Guaranteed Service (RFC2212) and,
perhaps, MEF10.1 (RFC6003).

Lou

On 07/15/2017 04:47 AM, Norman Finn wrote:
> You got it, Ethan.  No support for VBR.  I think that's clear in the
> architecture, but let's look at it.
> 
> -- Norm
> 
> ------------------------------------------------------------------------
> *From:* Grossman, Ethan A. [[e-mail]]
> *Sent:* Thursday, July 13, 2017 11:05 AM
> *To:* Norman Finn; Balázs Varga A; John Grant; DetNet WG
> *Subject:* RE: [Detnet] Traffic description in DetNet flow info model
> 
> Hi Norm,
> 
> Thanks for the offer :- ) The original question from Yiyong was:
> 
>  
> 
> The DetNet flow info model should provide some common concepts and
> description of the flow. One part is traffic specification of the flow.
> Here is something not clear, is DetNet dealing with VBR flows and what
> attributes are needed? And how to deal with VBR flow, for source
> guarantee purpose, do we need to define shaping parameters?
> 
> …
> 
> In architecture draft, section 4.1.2, “The traffic characteristics of an
> App-flow can be CBR (constant bit rate) or VBR (variable bit rate)”. In
> section 4.3.2, mentions synchronous flow and asynchronous flow, but no
> details of that.
> 
>  
> 
> So it sounds to me like this should be addressed in that section of the
> Arch draft (e.g. some statement that DetNet itself does not explicitly
> support VBR flow, however this could be implemented e.g. using a CBR
> tunnel + TCP) and thence in the traffic spec (again, DetNet doesn’t do
> VBR). AFAIK there isn’t any specific request for VBR support in the
> existing Use Cases, so no harm no foul? Does that sound right?
> 
>  
> 
> Ethan.
> 
>  
> 
> *From:*Norman Finn [mailto:[e-mail]]
> *Sent:* Thursday, July 13, 2017 1:08 AM
> *To:* Grossman, Ethan A. <[e-mail]>; Balázs Varga A
> <[e-mail]>; John Grant <[e-mail]>; DetNet WG
> <[e-mail]>
> *Subject:* RE: [Detnet] Traffic description in DetNet flow info model
> 
>  
> 
> Thanks for the clarification, Ethan.  Yes, I was absolutely talking
> about a "CBR tunnel" service, though which a customer would be running
> any mix of traffic of any kind.  Either the customer or the provider
> could operate the "tunnel entrance" that does most all of the packet
> dropping.  But, assuming that the dropping is done properly, there would
> be 0 congestion loss through the provider network.
> 
> I also think that this kind of service could be offered by an SP,
> offered by the IT department in an enterprise, or offered to the
> customers of a multi-tenant data center.  I agree with you, that this is
> the only use case I've seen for running TCP over DetNet.
> 
> Maybe I should offer some text for the use cases draft?
> 
> -- Norm
> 
> ------------------------------------------------------------------------
> 
> *From:*Grossman, Ethan A. [[e-mail]]
> *Sent:* Wednesday, July 12, 2017 11:25 AM
> *To:* Norman Finn; Balázs Varga A; John Grant; DetNet WG
> *Subject:* RE: [Detnet] Traffic description in DetNet flow info model
> 
> 1)      In the pro audio and video space it seems to me that constant
> bitrate is the norm; variable rate stream formats exist however they
> aren’t used that much in pro. One indication of that is that the
> (pre-packet-based A/V) industry is accustomed to point-to-point
> per-stream connections (in both analog and digital forms) for both audio
> and video.
> 
> 2)      To me the spirit of DetNet (and AVB/TSN) has been the notion of
> guaranteeing a fixed amount of bandwidth per flow, and I don’t exactly
> see how VBR would fit into the core of DetNet. Norm’s suggestion that a
> user could lease a fixed amount of DetNet-enabled bandwidth then use
> that to transmit multiple TCP streams (which are essentially VBR, and in
> aggregate might be advantageous for multi-stream VBR traffic) makes
> about as much sense as I can see right now. If I’m missing something
> please let me know.
> 
> Ethan.
> 
>  
> 
> *From:*detnet [mailto:[e-mail]] *On Behalf Of *Norman Finn
> *Sent:* Wednesday, July 12, 2017 12:34 AM
> *To:* Balázs Varga A <[e-mail]
> <mailto:[e-mail]>>; John Grant <[e-mail]
> <mailto:[e-mail]>>; DetNet WG <[e-mail]
> <mailto:[e-mail]>>
> *Subject:* Re: [Detnet] Traffic description in DetNet flow info model
> 
>  
> 
> Certainlly UDP is typical for applications in the industrial space.
> 
> But, given that DetNet can defend itself against misbehaving
> transmitters (by dropping packets), one could certainly supply an
> application with a CBR-like service over which one runs TCP.
> 
> In one sense, you might be better off using some technique like WFQ, so
> that you can get more bandwidth if it's available.  But, if the cost
> parameters are favorable, you can certainly imagine an SP using DetNet
> to offer CBR-over-best-effort services, over which TCP can certainly be
> run.  The downside compared to the usual techniques for this is that
> oversubscription of reservations is not allowed.  The upside is that the
> user gets every last bit of his contracted bandwidth, without random
> variations due to other customers' activity.
> 
> -- Norm
> 
> ------------------------------------------------------------------------
> 
> *From:*detnet [[e-mail]] on behalf of Balázs Varga A
> [[e-mail]]
> *Sent:* Tuesday, April 25, 2017 1:20 AM
> *To:* John Grant; DetNet WG
> *Subject:* Re: [Detnet] Traffic description in DetNet flow info model
> 
> Hi,
> 
>  
> 
> Good discussion.
> 
>  
> 
> As a general comment I think applications requiring DetNet transport
> should be UDP
> 
> based and not TCP (as retransmission would violate the transport
> parameters the
> 
> DetNet flow requires).
> 
>  
> 
> I think what Yiyong is looking for whether we can make better resource
> reservation
> 
> for DetNet flow being VBR than reserving for peak rate? With CBR we are
> on the safe
> 
> side, no doubt. However for example not all TSN queuing method (e.g.,
> time gated
> 
> queues, etc.) can ensure that unused resources can be used by non-DetNet
> traffic.
> 
>  
> 
> Additionally, would be good to have feedback on how much applications
> would “like”
> 
> the shaping of DetNet flows. Shaping could help for better resource
> utilization,
> 
> but is it a good idea for DetNet?
> 
>  
> 
> I would like to ask the authors of the use-cases to comment what type of
> traffic is
> 
> used in their use-cases (CBR, VBR, something else). Maybe that would
> help to sort
> 
> this out.
> 
>  
> 
> Cheers
> 
> Bala’zs
> 
>  
> 
> *From:*detnet [mailto:[e-mail]] *On Behalf Of *John Grant
> *Sent:* 2017. április 21. 16:20
> *To:* DetNet WG <[e-mail] <mailto:[e-mail]>>
> *Subject:* Re: [Detnet] Traffic description in DetNet flow info model
> 
>  
> 
> TCP isn't really intended for use with the kind of flows that would use
> CBR or VBR.
> 
>  
> 
> The main facilities provided by TCP are rate control and retransmission
> of lost packets. When transferring a block of data (such as, say, an
> image or a pre-recorded video or a PDF) over a best-effort service,
> these allow the transfer to make best use of what the network provides.
> But if the network service guarantees a particular data rate you don't
> need the kind of rate control that TCP does, and if the network hardly
> ever loses a packet you don't need frequent acknowledgements.
> 
>  
> 
> For instance, if you are sending live audio with a sampling rate of 48k
> samples per second, and packing 12 samples in a packet, you need to send
> a packet every 250 microseconds, so you need CBR with a rate of 4000
> packets (of a certain size) per second.
> 
>  
> 
> The VBR service that was defined for ATM was intended for sending
> compressed video at constant quality, so that "busy" content needs more
> bits per frame than content with less detail. The peak rate is the bit
> rate for the "busiest" content, and the average bit rate was also
> signalled. I think the idea was that you could "overbook" a link by
> routing flows whose peak rates add up to more than the link capacity, in
> the expectation that they wouldn't all be demanding the peak rate at the
> same time. I think something similar is done with digital television
> multiplexes.
> 
>  
> 
> Note that with CBR (and VBR) the rate is determined by the application's
> requirements, whereas with TCP it is determined by what the best-effort
> service delivers.
> 
>  
> 
> John Grant
> Nine Tiles, Cambridge, England
> [phone] and [phone]
> http://www.ninetiles.com
> <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.ninetiles.com&d=DwMF-g&c=lI8Zb6TzM3d1tX4iEu7bpg&r=ZcHC6wX_gDwPDcfMaFNZiQ&m=tS5EY8SXaTQuzywNz5HT0Jrgxk9GSRF2WhaHXBOAl4k&s=RmSC6BBktJC1J2slxfA-haYqlf34eB0oLtUd-Z-oSHY&e=>
> 
>  
> 
> On 21 Apr 2017, at 08:37, zhayiyong wrote:
> 
>  
> 
>     Hi John,
> 
>      
> 
>     Thank you for the reply. I agree that make reservation on peak rate
>     is a simple solution. But the “peak rate” here depends on the
>     observation interval times max packets per interval, which means for
>     same flow, different interval leads to different peak rate. Below is
>     a little testbed we built to test the burstness feature of TCP flow.
> 
>     For the same 25Mbps TCP flow with no shaping:
> 
>      
> 
>     <image007.jpg>
> 
>     1s observation interval, peak rate 450Mbps.
> 
>      
> 
>     <image008.jpg>
> 
>     100ms observation interval, peak rate 900Mbps.
> 
>      
> 
>     <image009.jpg>
> 
>     10ms observation interval, peak rate 1Gbps, which is the link
>     speed/physical port speed.
> 
>      
> 
>     And further test shows that, 8 of these TCP flows to a 1Gbps port
>     cause packet loss. So my question is how can we make reservation
>     based on “peak rate”? E.g., for the same flow, if we take 1s
>     observation interval, we can serve 2 flows. But for 10ms observation
>     interval, only 1 flow, which does not make sense. And it is hard to
>     say long observation interval can guarantee delay and loss, since
>     buffer in router is only milliseconds level.
> 
>      
> 
>     Another thing is how to guarantee the source with max packets within
>     the interval. If shaping is necessary, what kind of parameters are
>     needed.
> 
>      
> 
>     Cheers,
> 
>     Yiyong
> 
>     *From:* detnet [mailto:[e-mail]] *On Behalf Of *John
>     Grant
>     *Sent:* Thursday, April 20, 2017 5:27 PM
>     *To:* DetNet WG
>     *Subject:* Re: [Detnet] Traffic description in DetNet flow info model
> 
>      
> 
>     As pointed out in 4.1.2, for a VBR flow you have to make a
>     reservation for the peak rate, and there isn't any reason to do
>     anything other than use the service that is already defined for CBR.
>     With circuit-switched systems any part of the reservation that
>     wasn't used was wasted, but in packet-based systems it can be used
>     for best-effort traffic, as stated in 4.3.2.
> 
>      
> 
>     Regarding synchronous flows, the first paragraph of 4.3.2 explains
>     that if the reservations on incoming and outgoing links are
>     time-aligned then the latency, and hence the amount of buffer space
>     required, can be minimised. The details mechanism for achieving that
>     would, I think, be out of scope for an architecture document.
> 
>      
> 
>     For a description of a system that implements synchronous flows, see
>     clause 5 of ETSI GR NGP 003, available from the "specifications" tab
>     at http://www.etsi.org/technologies-clusters/technologies/next-generation-protocols
>     <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.etsi.org_technologies-2Dclusters_technologies_next-2Dgeneration-2Dprotocols&d=DwMF-g&c=lI8Zb6TzM3d1tX4iEu7bpg&r=ZcHC6wX_gDwPDcfMaFNZiQ&m=tS5EY8SXaTQuzywNz5HT0Jrgxk9GSRF2WhaHXBOAl4k&s=ML38iAvI654emuUqPEQU1n8X7v3dy0G3x6FIlK2yFhA&e=>
> 
>      
> 
>     John Grant
>     Nine Tiles, Cambridge, England
>     [phone] and [phone]
>     http://www.ninetiles.com
>     <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.ninetiles.com_&d=DwMF-g&c=lI8Zb6TzM3d1tX4iEu7bpg&r=ZcHC6wX_gDwPDcfMaFNZiQ&m=tS5EY8SXaTQuzywNz5HT0Jrgxk9GSRF2WhaHXBOAl4k&s=JAKBl0WO6WGg8P0NfwBx-dcUfmUZ9AvKKEwQKEIx_p4&e=>
> 
>     On 20 Apr 2017, at 08:38, zhayiyong wrote:
> 
>      
> 
>     Hi All,
> 
>      
> 
>     Recently we have some discussion among authors of the two flow info
>     model draft. The DetNet flow info model should provide some common
>     concepts and description of the flow. One part is traffic
>     specification of the flow. Here is something not clear, is DetNet
>     dealing with VBR flows and what attributes are needed? And how to
>     deal with VBR flow, for source guarantee purpose, do we need to
>     define shaping parameters?
> 
>      
> 
>     In architecture draft, section 4.1.2, “The traffic characteristics
>     of an App-flow can be CBR (constant bit rate) or VBR (variable bit
>     rate)”. In section 4.3.2, mentions synchronous flow and asynchronous
>     flow, but no details of that.
> 
>     In use case draft, for some cases such as industrial and BAS, it can
>     assumes that the traffic is periodic with constant rate. For cases
>     such as Cellular Radio and M2M, there is usually no assumption on
>     the traffic. E.g., CoMP traffic is between two eNBs, it is hard to
>     say the flow is constant rate.
> 
>      
> 
>     Cheers,
> 
>     Yiyong
> 
>  
> 
>  
> 
> 
> 
> _______________________________________________
> detnet mailing list
> [e-mail]
> https://www.ietf.org/mailman/listinfo/detnet
>