Subject: [tsvwg] Comments on draft-thubert-tsvwg-detnet-transport-00

From: Ingemar Johansson S <[email-masked]>
Date: Wed, 25 Oct 2017 11:28:04 +0000

Hi

And thanks for a nice overview, well worth the time spent.

One thing that occurs to me is that we have (atleast?) two different technologies for low latency transport 
1) L4S technology, for instance TCP HULL can reach very low (or zero) queue delays, se e.g https://people.csail.mit.edu/alizadeh/papers/hull-nsdi12.pdf . It is however not perfectly safe against jitter casued by e.g large amounts of incast traffic. 
2) DetTrans/DetNet , can reach insanely (zero) queue delays and deterministic e2e delay if the packets are forwarded as they arrive at each node along the path.

These two technologies, can to some extent cover similar requirements. The difference is that DetNet can cover very extreme requirements, whereas L4S is likely more scalable.  
These are just my observations, not necessarily something that should go into the draft.

This work pinpoints a problem with the interaction with the application layer and that problem applies to both L4S and DetNet. While it is possible to achieve a deterministic (or close to deterministic) delay on the packet level, there will in both cases be necessary with a queue on the application layer to absorb changes in application layer bitrate. Small message driven traffic such as sensor data is perhaps not a big issue, especially if messages can be discarded on the sender side without problems. What is worse is for instance high bitrate real time compressed video where the bitrate can change a lot and is not guaranteed to match a given target rate. 
If one is to be able to fully use the potential of low latency transport it becomes necessary to integrate the application layer (or video coders) tightly with the transport. 
We already saw this challenge with commercial video coders in the development of the SCReAM congestion control in the RMCAT WG.
This application layer interaction problem is not mainly an IETF matter, but it is likely a headache for application developers later on.

/Ingemar

> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Tue, 24 Oct 2017 12:46:03 +0000
> From: "Pascal Thubert (pthubert)" <[email-masked]>
> To: "[email-masked]" <[email-masked]>, "[email-masked]"
> 	<[email-masked]>
> Subject: [tsvwg] FW: New Version Notification for
> 	draft-thubert-tsvwg-detnet-transport-00.txt
> Message-ID: <23ba09a493ec44ef8f37099afa00a78b@XCH-RCD-
> 001.cisco.com>
> Content-Type: text/plain; charset="utf-8"
> 
> Dear all:
> 
> At the last DetNet meeting in Prague, Janos introduced the DetNet SLA, and
> we discussed the need to adapt the application injection of data into packets
> that match this SLA.
> To my best understanding of what happened then, the chairs then insisted
> that this was beyond the current scope and we discussed in-room and then
> outside the room that there is a need for a component that relates to IETF
> transport in order to achieve the functions required by the architecture at
> the DetNet Service Layer.
> 
> I put together the thoughts I gathered from those discussions in the form of
> an early draft and posted to TSVWG, which appeared to me as the natural
> place to discuss the topic.
> Please find the references below, comments welcome!
> 
> Cheers,
> 
> Pascal
> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]
> Sent: mardi 24 octobre 2017 14:37
> To: Pascal Thubert (pthubert) <[email-masked]>
> Subject: New Version Notification for draft-thubert-tsvwg-detnet-transport-
> 00.txt
> 
> 
> A new version of I-D, draft-thubert-tsvwg-detnet-transport-00.txt
> has been successfully submitted by Pascal Thubert and posted to the IETF
> repository.
> 
> Name:		draft-thubert-tsvwg-detnet-transport
> Revision:	00
> Title:		A Transport Layer for Deterministic Networks
> Document date:	2017-10-24
> Group:		Individual Submission
> Pages:		21
> URL:            https://www.ietf.org/internet-drafts/draft-thubert-tsvwg-
> detnet-transport-00.txt
> Status:         https://datatracker.ietf.org/doc/draft-thubert-tsvwg-detnet-
> transport/
> Htmlized:       https://tools.ietf.org/html/draft-thubert-tsvwg-detnet-
> transport-00
> Htmlized:       https://datatracker.ietf.org/doc/html/draft-thubert-tsvwg-
> detnet-transport-00
> 
> 
> Abstract:
>    This document specifies the behavior of a Transport Layer operating
>    over a Deterministic Network and implementing a DetNet Service Layer
>    and a Northbound side of the DetNet User-to-Network Interface.
> 
> 
> 
> 
> Please note that it may take a couple of minutes from the time of submission
> until the htmlized version and diff are available at tools.ietf.org.
> 
> The IETF Secretariat
> 
> 
> End of tsvwg Digest, Vol 162, Issue 9
> *************************************