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Re: [iot-wg] CoAP and CGN
Hi,
Few things to add to Kai answer.
On mobile network we see only a few applications are really fine to keep the communication open all the time (for those one I prefer to use MQTT).
Why? Cost and power consumption.

In practice the device communicates regularly with the server (for example: every 15 min to once a week) or when some data are ready to send.
For that CoAP beat MQTT in byte consumption because DTLS PSK both way handshake is ~800 bytes where a usual TLS/TCP handshake is 4k~6k and piggybacked ack save also few more bytes over TCP ACKs.

For server to device communication, a lot of people use SMS as a way to wakeup the device (or you can put CoAP message in SMS).
Being attached on the network passively for receiving SMS and without an active IP session cost nothing and consume a fraction of the power of keeping a TCP/IP connection open.

Also a CoAP over TCP draft exists: https://datatracker.ietf.org/doc/draft-ietf-core-coap-tcp-tls/
The idea is draft is to solve your issue and some compatibility problems with enterprise network which are blocking UDP.

Julien

On Mon, Nov 30, 2015 at 8:52 AM, Hudalla Kai (INST/ESY) <Kai.Hudalla@xxxxxxxxxxxx> wrote:

Hi Dominik,

 

I am glad that you find Californium to be of help for your work J

 

Regarding your question: you are right in assuming that the direction Californium -> Device over a CGN does not work easily out-of-the-box. In particular, it is hard to initiate communication with a device from the back-end. I am afraid, though, that there also is no silver bullet for solving these issues. I think it mainly depends on your use case at hand. Many IoT scenarios only require the periodic transmission of sensor readings from the device to a (cloud) back end. These cases should work out-of-the-box as you already realized.

 

In order to be able to talk to a device from the back end side, one approach to keeping the CGN’s routers “open” is to periodically send a “heart beat” message from the device to the back end. When using LWM2M this could either be done “explicitly” by frequent “update registration” messages sent by the device (LWM2M client) or “implicitly” by periodic “notifications” sent by the device for a resource observed by the back end (LWM2M server). Using any of these approaches, you should be able to also send “requests” initiated from the back-end to a device.

 

BTW I think the Californium [1] or leshan [2] developer mailing lists would be a better place for continuing this discussion J

 

[1] https://dev.eclipse.org/mailman/listinfo/cf-dev

[2] https://dev.eclipse.org/mailman/listinfo/leshan-dev

 

Mit freundlichen Grüßen/ Best regards

 

Kai Hudalla

Chief Software Architect

 

Bosch Software Innovations GmbH

Schöneberger Ufer 89

10785 Berlin

GERMANY

www.bosch-si.de

 

Mobile +49 (151) 54336335 

Phone +49 (30) 726 112-145

kai.hudalla@xxxxxxxxxxxx

 

Registered office: Berlin, Register court: Amtsgericht Charlottenburg, HRB 148411 B

Executives: Dr.-Ing. Rainer Kallenbach; Michael Hahn

 

 

 

From: iot-wg-bounces@xxxxxxxxxxx [mailto:iot-wg-bounces@xxxxxxxxxxx] On Behalf Of Dominik Obermaier
Sent: Saturday, November 28, 2015 12:13 AM
To: iot-wg@xxxxxxxxxxx
Subject: [iot-wg] CoAP and CGN

 

First of all, congratulations to all people involved in Californium for the new release! I’m very excited about it and I took the opportunity to dig deeper into CoAP recently.

 

There is one thing I don’t understand about CoAP and Carrier-Grade-Networks (CGN). Let’s say there is a Californium cloud deployment, which serves mobile clients. How would CoAP (which uses UDP by default if I’m not mistaken) work with CGNs? Would it be possible to traverse CGNs? Device -> Californium is obviously not a problem, but I can’t wrap my head around how the Californium -> Device way would work, since UDP hole punching seems not to be a working and reliable option with CGNs.

 

Are there any experiences with that? My understanding is, that if CoAP is used with IPv6, there wouldn’t be a problem. I didn’t find any good resources on that topic, so I would be glad if someone could clarify the current state with CoAP and mobile networks.

 

Thanks,

Dominik

 

-- 

Dominik Obermaier
   
dc-square GmbH - Software Solutions
Innere Münchener Straße 30
84036 Landshut
 
 
Tel. +49 871 - 97506300
Fax. +49 871 - 97506329
Web. www.dc-square.de
 
 
Geschäftsführer Christian Götz, Dominik Obermaier
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