Hey Michael, Got it. Thanks a lot. On 17 Oct 2017 00:25, "Scharf, Michael (Nokia - DE/Stuttgart)" < [email protected]> wrote:
> Hi Abhijan, > > > > I fully agree that for some use cases basically the known TCP > optimizations for short flows apply. Version -01 already includes quite > some new wording on TCP stacks that use a window of some (few) MSS. The > plan is to better organize that content in -02. > > > > Specifically, version -01 already includes guidance regarding limited > transmit in Section 4.3, in order to address your feedback from the Prague > meeting: > > > > <snip> > > For bulk data transfers further TCP improvements may also be useful, > such as limited transmit [RFC3402]. > > </snip> > > > > Yet, I now realize that there is a typo in this reference. Instead of RFC > 3042, version -01 wrongly refers to RFC3402, which doesn’t make any sense > ;-) I apologize for that mistake. This typo will be fixed in -02. > > > > Of course, further comments would be welcome. > > > > Thanks > > > > Michael > > > > > > *From:* Lwip [mailto:[email protected]] *On Behalf Of *Abhijan > Bhattacharyya > *Sent:* Monday, October 16, 2017 12:25 PM > *To:* [email protected] > *Cc:* [email protected]; Abhijan Bhattacharyya <[email protected]>; > [email protected] > *Subject:* Re: [Lwip] I-D Action: draft-ietf-lwig-tcp- > constrained-node-networks-01.txt > > > > Hi Carles, > > This is indeed an important piece of work. The fact that this draft is > maturing in tandem with the evolution of the CoAP-on-TCP darft is really > beneficial for the IoT technology space. > > During the last Prague meeting I made some comments towards the end of the > presentation. I take this opportunity to put those comments in the mailing > list in a more organized form. See if you and your co-authors find them > useful. > > One thing that I would like to stress upon is that, I would like to see > TCP in IoT as an inheritance of a more generalized class of problem related > to TCP performance for short flows. This is an old problem and has been > studied in many literatures (Example: [1-3]). The case for IoT is a > specialization (the word "specialization" would most likely attribute to > the factors like scalability, h/w constraints, etc.). In [4] one can find a > mathematical definition for short flows for TCP. > > (In fact, going by [5], it will not be too wrong to say that IoT is > basically a culmination of different existing technological issues under > one umbrella that predominantly deals with constrained devices and > networks.) > > > > So, just check if you can deliver the problem statement in a bit > generalized manner if the above makes sense. > > Coming to the problem with short flows, the basic problem is the > sub-optimal performance of slow-start and non-availability of enough > duplicate ACKs (dupacks) to start the fast-retransmission. Now , your draft > very rightly takes into account the cases where the window may run over > more than one (and only a few) MSS. While you have mentioned about the > utility of ECN and SACK, probably it would also be useful to mention about > the "limited transmit" algorithm [6]. I do not have readily available > statistics about its implementation in Kernels at present. But, probably it > is available. [6] essentially optimizes on how the fast re-transmit works > for short-flows which do not run over enough segments to ensure sufficient > number of dupacks to indicate a 'softer' congestion and thus prevents the > sender from going into the costly slow-start phase (as RTO remains the only > option to detect congestion in the absence of enough dupacks). Combination > of SACK and [6] may benefit the system. However, I do not have any readily > available study on the performance benchmark for this. But it is an option > worth keeping in this work, I think. > > > Thank you. > Best wishes for your draft. > > ------------------------ > [1] H. Balakrishnan, et al, “TCP Behavior of a Busy Internet Server: > Analysis and Improvements “, in Proc. Of IEEE Infocomm ’98, CA, USA, March, > 1998. > [2] N. Cardwell, et al, “Modeling the Performance of Short TCP > Connections”, Technical Report, University of Washington, October, 1998 ( > http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1. > 30.2099&rep=rep1&type=pdf ) > [3] K. Avrachenkov, et al, “Differentiation between short and long TCP > flows: predictability of the response time”, INFOCOM 2004 > [4] N. Kartik, “TCP optimized for short flows”, Stanford University, June > 2003, (http://web.stanford.edu/class/ee384y/projects/download03/nitin3.pdf > ). > [5] Karen Rose, Scott Eldridge, Lyman Chapin, "THE INTERNETOF THINGS:AN > OVERVIEW", October, 2015. > [6] M. Allman, H. Balakrishnan, S. Floyd, RFC 3042, “Enhancing TCP's loss > recovery using limited transmit” , January, 2001. > > > > On Mon, Oct 16, 2017 at 12:02 AM, <[email protected]> wrote: > > > A New Internet-Draft is available from the on-line Internet-Drafts > directories. > This draft is a work item of the Light-Weight Implementation Guidance WG > of the IETF. > > Title : TCP Usage Guidance in the Internet of Things > (IoT) > Authors : Carles Gomez > Jon Crowcroft > Michael Scharf > Filename : draft-ietf-lwig-tcp- > constrained-node-networks-01.txt > Pages : 20 > Date : 2017-10-15 > > Abstract: > This document provides guidance on how to implement and use the > Transmission Control Protocol (TCP) in Constrained-Node Networks > (CNNs), which are a characterstic of the Internet of Things (IoT). > Such environments require a lightweight TCP implementation and may > not make use of optional functionality. This document explains a > number of known and deployed techniques to simplify a TCP stack as > well as corresponding tradeoffs. The objective is to help embedded > developers with decisions on which TCP features to use. > > > The IETF datatracker status page for this draft is: > https://datatracker.ietf.org/doc/draft-ietf-lwig-tcp- > constrained-node-networks/ > > There are also htmlized versions available at: > https://tools.ietf.org/html/draft-ietf-lwig-tcp- > constrained-node-networks-01 > https://datatracker.ietf.org/doc/html/draft-ietf-lwig-tcp- > constrained-node-networks-01 > > A diff from the previous version is available at: > https://www.ietf.org/rfcdiff?url2=draft-ietf-lwig-tcp- > constrained-node-networks-01 > > > 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. > > Internet-Drafts are also available by anonymous FTP at: > ftp://ftp.ietf.org/internet-drafts/ > > _______________________________________________ > Lwip mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/lwip > > > > > -- > > Regards, > > Abhijan Bhattacharyya, > > *Scientist @ TCS Research, India* >
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