Subject: [core] Some comments on draft-shelby-core-coap-00

From: "Angelo P. Castellani" <[email-masked]>
Date: Wed, 31 Mar 2010 17:50:55 +0200

Dear all,
I've some questions on CoAP, to understand why you are doing things in this way:

1) Why is a TransactionID needed, cannot be used the UDP source port
of the requester to session mapping, it is the usual way to do it and
we can save bytes in the header?

In this way can also be exploited the 6lowpan UDP port compression, so
when a lot of sessions are active, the UDP source port field size will
automagically scale to a greater size.

In cases where source port mapping may be changed (?? PAT?) a
Transaction-ID Option can still be defined that will override the
assumption that request source port maps the session.

2) Why isn't defined a SUBSCRIBE method?

Isn't that one of the new "features" required?

3) The OPTIONS format is quite "big".

Why don't you avoid size byte for options where the size is
well-known? (from the draft: Content-type=2B, Uri-code=1B, Max-age=2B)

I'm asking this because I think that actual compression with respect
to a simple HTTP/1.0 request could be a lot better.. That I consider a
crucial requirement because could be the main motivation for actually
using CoAP and not the latter.

Best regards,
Angelo P. Castellani