Subject: Re: [Lwip] [core] draft-arkko-core-cellular

From: Zhen Cao <[email-masked]>
Date: Sun, 29 Jul 2012 00:12:07 -0700

Dear Authors

I read the draft and found it very interesting and useful for me to
understand how to build energy efficient cellular M2M devices, not
only CoAP devices.

Although the draft is entitled with “CoAP devices”, its provided
recommendations are generally workable for any M2M devices that
provide sensing or actuator service. As what’s stated in Section 1.
   The recommendations in this memo should be taken as complementary to
   device hardware optimization, microelectronics improvements, and
   further evolution of the underlying link and radio layers.  Further
   gains in power efficiency can certainly be gained on several fronts;
   the approach that we take in this memo is to do what can be done at
   the IP, transport, and application layers to provide the best
   possible power efficiency…

I like the style of section 3, the analysis of the link layer
implications for energy-efficient application development. Some
questions and comments are listed separately as below.
- Public network. Is it just used as the adverse of “private network”?
- Point to point link. As analyzed in the draft, this is a normal case
for cellular connection, no way and no need to consider third party
devices. As to achieve energy efficient is always contradictory of
handling multicast/broadcast packets, it is relatively easier to be
efficient with PPP link. Or shall we make such recommendations?
- Radio technology. Radio proved to be the most energy consuming part,
and L2 mechanisms are most efficient in the optimization space. I
turned to believe that there is no need to optimize the upper layers
before I encounter the idea of message coordination. That is to reduce
the frequency of trigger link up by coordinating the send/recv
behavior of different protocols. For example, 6LOWPAN-ND advertises
sometime and wake the radio, and then radio/MAC layer optimization
turns it off before COAP protocol triggers a groupcomm afterwards. If
these send/recv of different protocols can be coordinated, I guess the
situation will be much better.

Section 7 on the “Real-time reachable device”.  For cellular devices,
there is one characterize to utilize: they are always reachable from
the circuit-switch side.  Take the CoAP protocol as an example, if it
is difficult to reach the device (as a CoAP server, or to initiate the
observe mode) from the packet side, we can trigger it via a SMS
message and let it behave as a client.  This is a rather special case
for cellular devices that developers can take advantage of.  I heard
of some usage in this regards.

Again, I believe the description and analysis in this document is
useful for the cellular M2M devices. Guidelines for CoAP and other
IETF protocols can be derived from it.

Best regards,
CZ

On Mon, Jul 9, 2012 at 4:43 AM, Jari Arkko <[email-masked]> wrote:
> Hi,
>
> We have written a draft that talks about how to apply CoAP in smart objects
> attached to the Internet via the cellular networks.
>
> Comments appreciated.
>
> Jari
>
> On 09.07.2012 14:37, [email-masked] wrote:
>>
>> A new version of I-D, draft-arkko-core-cellular-00.txt
>> has been successfully submitted by Jari Arkko and posted to the
>> IETF repository.
>>
>> Filename:        draft-arkko-core-cellular
>> Revision:        00
>> Title:           Building Power-Efficient CoAP Devices for Cellular
>> Networks
>> Creation date:   2012-07-09
>> WG ID:           Individual Submission
>> Number of pages: 17
>> URL:
>> http://www.ietf.org/internet-drafts/draft-arkko-core-cellular-00.txt
>> Status:          http://datatracker.ietf.org/doc/draft-arkko-core-cellular
>> Htmlized:        http://tools.ietf.org/html/draft-arkko-core-cellular-00
>>
>>
>> Abstract:
>>     This memo discusses the use of the Constrained Application Protocol
>>     (CoAP) protocol in building sensors and other devices that employ
>>     cellular networks as a communications medium.  Building communicating
>>     devices that employ these networks is obviously well known, but this
>>     memo focuses specifically on techniques necessary to minimize power
>>     consumption.
>>
>>
>>
>> The IETF Secretariat
>>
>
>
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