Subject: [core] Congestion control (was Re: draft-tschofenig-core-coap-tcp-tls-03)

From: "Carles Gomez Montenegro" <[email-masked]>
Date: Fri, 1 May 2015 19:36:29 +0200

Hi Hannes,

I have a comment and a question on draft-tschofenig-core-coap-tcp-tls-03,
related with congestion control.

Comment
*******

I am particularly concerned with the following paragraph:

   As an additional usage scenario, some environments benefit from the
   more advanced congestion control and flow control capabilities
   provided by TCP.  While there is ongoing work to add more
   sophisticated congestion control to CoAP, see
   [I-D.bormann-core-cocoa], it is still far less efficient than
   functionality provided by TCP.        ^^^^^^^^^^^^^^^^^^

In its current form, the last sentence states in absolute terms that CoCoA
is "far less efficient" than TCP congestion control, whereas the
performance results we (the CoCoA authors) obtained in experiments
(presented e.g. in the CoRE WG meeting in Honolulu and in the ICCRG
meeting in Dallas) indicate just the opposite, at least in the scenarios
we considered.

TCP congestion control is of course great for many environments, and it
may indeed be a better choice for back-end communications in a cloud
infrastructure. However, in constrained node networks (CNNs), CoCoA seems
to work better than TCP RTO algorithms (e.g. Linux or Peak-Hopper), which
is reasonable since it has been specifically designed and tuned
considering CNN characteristics. In fact, Linux and Peak-Hopper
underperform even default CoAP in some scenarios.

(Note: in our work we have just considered NSTART = 1, since the CoRE WG
feedback has so far been that there have not been use cases for NSTART >
1.)

So I think the aforementioned paragraph should be modified accordingly.

Question
********

Is CoAP over TCP expected to run in constrained devices (e.g. due to the
NAT traversal issue described in your draft) ?

If the answer is yes, which RFC 7228 class(es) of devices are expected to 
run CoAP over TCP ?

I think it would be good to clarify these aspects in the draft.

Thanks!

Carles Gomez

> Hi all,
>
> I have just submitted -03 of the CoAP TCP document:
> http://tools.ietf.org/html/draft-tschofenig-core-coap-tcp-tls-03
>
> I updated the introduction to include the additional use cases discussed
> at the CORE WG session at IETF#92. Version -02 already contained some
> text about the requested use cases but I extended the text and shorted
> the introduction.
>
> I believe that this document is ready for a call for adoption by the WG
> chairs.
>
> Ciao
> Hannes
>
> _______________________________________________
> core mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/core
>

---

From: "weigengyu" <[email-masked]>
Date: Tue, 5 May 2015 14:57:23 +0800

> I think it would be good to clarify these aspects in the draft.

It is required to be clarified.
I think that CoAP over TCP may be used in the following scenarios:

1 in traditional Internet;
2 in less constrained networks, as smart phones in mobile communication 
networks, in LTE or LTE-A;
   or mobile termianls with WiFi;
   The class is C2. The power is Ps and E1.
   Mostly the termianl's resources are better.
3 in some specific constrained networks.  One example I see is a kind of 
in-house devices of Wi-SUNJ for smart grid.
   Its devices are supplied by Mains-power; probably battery with backup 
Mains-power.
   The class is  C2. The power is Et and E9.

Regards,

Gengyu WEI
Network Technology Center
School of Computer
Beijing University of Posts and Telecommunications
-----原始邮件----- 
From: Carles Gomez Montenegro
Sent: Saturday, May 02, 2015 1:36 AM
To: Hannes Tschofenig
Cc: Ilker Demirkol ; August Betzler ; [email-masked] WG
Subject: [core] Congestion control (was Re: 
draft-tschofenig-core-coap-tcp-tls-03)

Hi Hannes,

Comment
*******

Question
********

Thanks!

Carles Gomez