Fwd: In the firing line

References: <1048264190.513.76.camel@fred>
 <p05200f01baa14fa16f87@[203.32.153.158]>
 <[email protected]>
Date: Mon, 24 Mar 2003 10:12:46 +1030
To: "clemens fischer" <[email protected]>
From: Andrew Rutherford <[email protected]>
Subject: Re: In the firing line

At 1:28 PM +0100 22/3/03, clemens fischer wrote:

>sorry, i may have missed something or working too long:  the acronym
>SIP is unknown to me.  would you please provide a pointer?

Session Initiation Protocol, originally RFC 2543 (March 1999), 
updated by RFC 3261 (June 2002).

SIP was designed to handle the requirements of voice over IP 
signalling (by carrying an SDP payload) and instant messaging. 
Basically on the wire it looks a lot like HTTP, but requires a lot of 
email like headers ("From", "To", etc.) SIP addresses are of the form 
sip:[email protected], that is, they have a user and a domain part.

SIP uses DNS SRV records to perform much the same functions an MX records.

It has a REGISTER mechanism to channel messages to a device (usually 
authenticated via HTTP's MD5 Digest mechanism), so all messages for 
sip:[email protected] can be forwarded by iagu.net's proxy server 
(think HTTP proxy server) directly to my laptop.

It also has a more selective SUBSCRIBE mechanism to indicate interest 
in certain classes of events, used by the proxy to generate or 
channel NOTIFY messages. Currently the primary use is to let you know 
when other parties have performed registration, to let those in the 
messaging world know that their "buddies" are logged in. Also used to 
send voice mail message waiting alerts, more relevant to us.

Given SIP is very good at moving small MIME body-parts directly to 
the end user, you could use NOFITY's or similar with a Content-Type 
of message/external-body to send the notification of a new message 
somewhere on a server associated with the sender. SIP Proxies would 
have to be extended to maintain a cache of notifications for those 
off-line, but this would be much smaller than a mail spool including 
the actual content.

-- 
Andrew Rutherford      sip:andrewr AT iagu.net
Iagu Networks
http://www.iagu.net/