Re: [iot-wg] CoAP and CGN

[Roger Light <roger@xxxxxxxxxx>]

Hi Julien,

I should have been clearer as well - my point was just to give another
useful datapoint. Comparing DTLS+PSK to TLS+x509 doesn't tell you a
great deal because both parts are different. With TLS+PSK as well it
is clearer which parts add the overhead.

Cheers,

Roger


On Mon, Nov 30, 2015 at 3:24 PM, Julien Vermillard
<jvermillard@xxxxxxxxx> wrote:
> Sorry, I probably miss phrased "usual TLS/TCP".
>
> Yes TLS PSK is also quite compact, but mosquitto is the only broker I know
> which support it.
> (ex: hivemq or aws iot doesn't support it). So in my view it's not "usual".
> For example it's not working for Paho Java because TLS PSK is not in the
> Java JDK :(
>
> For CoAP it's somewhat the default ciphersuite because it's in specified as
> "mandatory" in the RFC.
> It's often the X.509 authentication which are not supported on constrained
> CoAP nodes and networks.
>
> --
> Julien Vermillard
>
> On Mon, Nov 30, 2015 at 4:05 PM, Roger Light <roger@xxxxxxxxxx> wrote:
>>
>> On Mon, Nov 30, 2015 at 8:30 AM, Julien Vermillard
>> <jvermillard@xxxxxxxxx> wrote:
>>
>> > 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 completeness, I just used wireshark to grab packets when
>> connecting with a mosquitto_sub that had been nobbled not to send any
>> real data to a mosquitto instance listening with TLS-PSK  over TCP.
>> The total on the wire byte count was 1419.
>>
>> Cheers,
>>
>> Roger
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>
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