Re: [6lowapp] Charter and transports

Hi,

(New thread title)

So to me the answer seems to be that TCP will work for some  
configurations, but obviously not for all networks, and not for all  
requirements (e.g. multicast).

On Nov 3, 2009, at 5:15 , Jonathan Hui wrote:
>
>>> But are TCP's services/constraints
>>> appropriate for the application?  I can think of a variety of LLN
>>> applications that work just fine with TCP and others that could  
>>> stand
>>> to use something else to improve latency, message efficiency, non  
>>> p2p
>>> flows, multihoming, mobility,  etc.
>>
>> That's another question, yes. But I'd see building new transport  
>> layer functions for 6LOWAPPs as an activity that would need some  
>> very strong ties to the TSV area, if it wouldn't be hosted there in  
>> the first place.
>
> Agreed.  Though the line seems to be a bit blurred because some  
> suggest building transport-like mechanisms in whatever "app-level"  
> protocol we're working on.

In the Stockholm BarBof, Lars had a very good explanation on this one.  
We very well may start TSV area work on transport improvements - but  
that is a long-term effort and won't happen in time for CoAP. I do  
think we should aim at starting that work eventually, but let's get  
CoAP started first.

Obviously UDP is something we will need to support as a transport for  
CoAP, and I argue that we also need to allow the use of CoAP over TCP  
as this is useful for some applications. When using UDP, some simple  
mechanism for reliability (e.g. stop-and-wait) would of course be  
needed along with a transaction ID (see e.g. 6lowapp-frank-chopan).  
When doing this we should of course cooperate with TSV people.

So this brings us to the next question, what should we say in the CoAP  
charter about transports? Right now it says

"The protocol will operate over UDP...".

I would suggest it says something more like:

"The protocol will operate over UDP by default, and should define an  
alternative binding to TCP or another suitable reliable transport  
layer."

What do you think?

Zach

>
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> Jonathan Hui
>
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Zach Shelby
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