Subject: HTTP over SCTP without chunked encoding

From: [email-masked]
Date: Thu, 02 Apr 2009 00:58:11 +0000

At the recent HTTP WG meeting the subject of HTTP over SCTP was discussed,
and in particular the question was raised as to whether or not SCTP could
be used to avoid chunked encoding.  There are two ways to do this, but one
of them (EXPLICIT_EOR socket option) conflicts with current thinking about
how best to send HTTP over multiple SCTP streams.  The other approach is
to use the payload protocol identified or PPID.

The PPID is an optional value that is set by the sender and read by the
receiver.  The approach would be to define two PPID values (allocated by
IANA), say HTTP_MESSAGE_PIECE and HTTP_MESSAGE_END.  The sender would set
the PPID to HTTP_MESSAGE_END for the last sctp_sendmsg() call for the
current HTTP object, thereby allowing the receiver to identify the end of
the current HTTP object.

I'm far from being an expert in HTTP, and I would be grateful for feedback
on the suitability of this mechanism.  Thanks very much.

- Jon Leighton

---

From: Mark Nottingham <[email-masked]>
Date: Wed, 8 Apr 2009 16:38:07 +1000

I'm far from an expert in SCTP, but at first glance, this is  
potentially attractive, but slightly more intrusive in the HTTP stack,  
because it's introducing a new way to frame messages, rather than  
reusing exising code to do so.

The current proposals (AIUI) are less intrusive, because at a certain  
point a SCTP stream just looks like a TCP connection.

Now, whether this trade-off is worth it or not is an open question, of  
course. I think most people are focused on the aspects of SCTP that  
relieve the problems experienced with pipelining, and while having a  
more efficient framing mechanism is interesting, it's not low-hanging  
fruit.

Perhaps this should be an open design question in a HTTP-over-SCTP  
draft, to try to get feedback from interested vendors...

Cheers,

--
Mark Nottingham     http://www.mnot.net/