Google has made its instant messaging service fully inter-operable with the XMPP protocol, opening the doors to a rapid expansion of the IM market.

When Google launched Google Talk in August, it was compatible with device applications that support XMPP (Extensible Messaging and Presence Protocol), such as Trillian, but not at the server-to-server level.

That is now done - something that Google hopes will foster a federation of XMPP networks, including ones from ISPs, vendors and private businesses.

Networks now fully inter-operable with Google Talk include EarthLink's Vling IM and voice service, as well as XMPP-based networks run by corporations, universities and individual users.

Google hopes its efforts will help "build a lot of momentum so the remaining major service providers of IM will follow as well," said Mike Jazayeri, Google Talk product manager.

A major problem of IM services up until now has been the lack of inter-operability among the major providers AOL, Yahoo and Microsoft. Each are based on proprietary protocols and users can't communicate across networks.

Last year, Yahoo and Microsoft announced plans to link their products. Later, Google and AOL announced a similar scheme.