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

John Grant
Nine Tiles, Cambridge, England
+44 1223 862599 and +44 1223 511455
http://www.ninetiles.com

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
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