While the leading technical specification for server-to-server instant
messaging interoperability is coming closer to becoming an official
standard, the forces behind SIMPLE are already hard at work on beefing it up
and addressing lingering problems.
SIMPLE -- or Session Initiation Protocol (SIP) for Instant Messaging and
Presence Leveraging Extensions -- provides the guidelines for a chat session
between IM users on different servers. Late last month, the protocol's
draft received approval by the Internet's de facto standards body, the
Internet Engineering Task Force (IETF), and is awaiting official
publication, expected in a few weeks.
Now, the proponents of SIMPLE and SIP, the media-independent protocol on
which it is based, are gearing up to address a handful of shortcomings and
under-developed features.
Many of those problems stem from limitations inherent in SIP -- or
rather, they originate because SIP's very specific architecture is being
stretched to encompass an entire instant messaging session.
SIP's designers -- who include engineers at dynamicsoft, Columbia
University, Microsoft and Cisco --
intended it to oversee the creation of a connection between two or more
users of different media servers who want to communicate.
After establishing a link, SIP then would hand the connection to another
protocol, which would handle the transporting of actual content. SIP's
founders envisioned it being platform- and media-agnostic, so that the
protocol could handle media ranging from text (e.g., instant messaging), to
audio (conference calls) and video (videoconferencing). One of the
protocol's early trials successfully connected participants in an online
Quake game, for instance.
But under the soon-to-be-published SIMPLE specs, SIP does not hand off
control of the instant messaging conversation to another protocol. Instead,
it uses the same procedure that it follows in establishing the initial link
to carry each successive message.
In an online chat of some length, this practice creates lots of little,
unconnected SIP messages, as the protocol establishes a link, sends a user's
IM, then closes the link. That, in turn, leads to a significant chunk of
bandwidth being expended in simply opening and closing the link between
users. SIP also doesn't provide workarounds for network congestion, which
could result from such a system.
Having long recognized this shortcoming, SIMPLE's founders noted that the
protocol would best be suited for short, disconnected text messages --
analogous to a two-way pager -- rather than for a constant stream of
communications, such as required in telephone, videoconferencing or
longer-term instant messaging.
As a result, while many in the group has been working on receiving
approval for SIMPLE's "page-mode" spec, some also have been exploring ways
to implement "session-mode" instant messaging, in which a connection would
be maintained without the need for constant reconnection.
One proposed solution would incorporate what some have seen as a rival to
the SIMPLE protocol. Robert Sparks, co-chair of the IETF's SIMPLE working
group and a senior software architect at dynamicsoft, last month submitted a
draft by which SIP would hand off a connection to the Extensible Messaging
and Presence Protocol -- an XML-based IM specification promoted by Jabber,
Inc. and its open-source software foundation.
"SIP is really good at rendezvous, call control, mobility support -- none
of which exists in Jabber/XMPP," said Jonathan Rosenberg, dynamicsoft's
chief scientist and a co-author of SIP and SIMPLE. "Jabber is really good
at carrying blocks of data between Point A and Point B, through firewalls,
and with applications attached to the transport, like recording applications
and so on. By putting them together to take advantage of Jabber for
point-to-point messaging, it's really the ideal combination."
Such a move also would bring the community of Jabber developers into the
fold. In addition to Jabber, Inc., dozens of independent software
developers are using and building on Jabber's open-source protocol, which is
thought to run on thousands of servers.
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