Google's entry last week into the IM space gave a high-profile shot in the arm to the open IM protocol XMPP (Extensible Messaging and Presence Protocol). The decision to base Google Talk on the XML-based XMPP framework -- combined with Google's considerable market clout -- could shake up stalled IM interoperability efforts, or at the very least gives a big lift to a grassroots Internet standard.

When instant messaging started to surge in popularity a few years ago, a hot-button issue crept up around IM standards. At the time, two fledgling IM protocols were making their way through the Internet Engineering Task Force (IETF) standardisation process: SIMPLE, based on the SIP (Session Initiation Protocol) telephony protocol, and XMPP, based on XML.

Although a standards push among public IM networks never quite got off the ground, corporate vendors started taking sides. On one side, heavyweights Microsoft and IBM lined up behind SIP and SIMPLE, while XMPP gained traction with Jabber and implementations at companies including Apple, HP, and France Telecom. XMPP last year received official IETF ratification, while SIMPLE is still trudging through development in the IETF.

Google's choice to base its Google Talk IM on XMPP shakes up this landscape considerably. The company has said it is committed to enabling open communications, and selecting an open, XML-based protocol for its IM service is a step in that direction.

Meanwhile, public IM networks such as those from AOL, Yahoo, and MSN have closely guarded their subscribers and shied away from standards, although some have taken small steps at interoperability through individual agreements aimed at corporate users.

For example, AOL has established agreements between its AIM network and select vendors. AIM is the largest of the public networks with 41.6 million subscribers. Earlier this year AOL unveiled its Enterprise Federation Partner program, designed to allow select enterprise IM systems to add AIM and ICQ users to their IM contact lists and send and receive messages. In addition, this week enterprise IM vendor Antepo launched secure federation with users on the AIM network through its OPN System XT, an updated version of its server-based IM software. Antepo's product has native support for both SIP/SIMPLE and XMPP.

Although the Google Talk offering is aimed at consumers, the fact that it is based on the XMPP protocol encourages developers of all stripes to jump in.

"We want to encourage the developer community to create new and innovative applications that leverage our service. To enable this, Google Talk uses the standard XMPP protocol for authentication, presence, and messaging," Google officials wrote in the Google Talk release notes.

Google Talk also allows users to use other clients to connect to the Google IM service. Any client that supports XMPP can connect to Google Talk, Google officials said. This list includes: Adium, iChat, GAIM, and Trillian Pro, among others.

In an interesting twist, Google Talk enables voice call support through a custom XMPP-based signaling protocol and peer-to-peer communication mechanism, according to Google officials. Typically SIP, which is designed from the ground up for Internet telephony, is used to support voice. Google officials said it plans to add support for SIP in a future release.

According to Gartner research director Allen Weiner, Google Talk holds the potential to bring interoperability to the MSN, Yahoo, and AOL networks. But Google first will have to boost use of Gmail and get loyal IM users to switch to its service, Weiner wrote in a research note.

Google's entry into the IM space creates "a new dynamic that could lead to a market repositioning," according to Weiner.

Weiner also wrote that Google's selection of XMPP, as well as its considerable market power, could force changes in the IM market.

"This structure could bring about IM interoperability among the major players if Google gains enough market traction to force changes," he wrote.

Whatever its impact on IM interoperability, Google Talk adds fuel to XMPP's growing momentum, according to Peter Saint-Andre, executive director of the Jabber Software Foundation, a non-profit organization that builds open application protocols on top of XMPP.

Other recent boosts to XMPP's fortunes came from Apple, which earlier this year started supporting XMPP in its Tiger OS, and Sun Microsystems, which in March introduced XMPP support to its Sun Java System Instant Messaging product.

"A lot of people are getting onboard and deploying XMPP. Where it goes from here depends on the federation strategy Google puts together," Saint-Andre said.

Furthermore, whether Google can eventually help drive interoperability among IM networks remains to be seen, he said.

"I think what we will see first is more interoperability on a one-off basis. Everyone wants seamless communication [with IM] and Google has some market clout. It is definitely a step in right direction," Saint-Andre said.

One of the strongest reasons for XMPP's continuing, if quiet, success is that the protocol is reaching maturation and has received approval from the IETF. For its part, SIMPLE, which adds IM and presence extensions to the SIP telephony negotiation framework, is still not finished.

"Right now XMPP is a very modular and extensible technology," Saint-Andre said. "The early adopters who've pushed something out there, such as in the financial industry and government, are all using XMPP because they need something they can deploy today."