Google Talk is a service offered by Google for Voice over IP and instant messaging. Google Talk beta was released on August 24, 2005 and consists of both a service and a client used to connect to the service. Unlike some other instant messaging services, Google Talk uses an open protocol, XMPP, for the IM part, and it encourages the use of clients other than their own in connecting to the Google Talk service.
As of the launch date, the Google Talk client is available only for Windows (2000, XP, Server 2003); users of other operating systems are provided with instructions for various popular Jabber clients, such as Psi or Miranda IM for older versions of Microsoft Windows, iChat or Adium for Mac OS X, and Gaim or Kopete for Unix-like systems. However, any program capable of using the Jabber protocol is sufficient, although the voice over IP service only works with the Google client. Google has released the VoIP portions as Jingle.
Google has announced that a major goal of the Google Talk service is interoperability. Google Talk uses Jabber and XMPP to provide real-time extensible messaging and presence events, including offline messaging (only through non-Google clients like Adium). On January 17, 2006, Google enabled server-to-server communications, federating itself with any Jabber server that supports the dialback protocol.
On December 15, 2005, Google released libjingle, a C++ library to implement Jingle, "a set of extensions to the IETF's Extensible Messaging and Presence Protocol (XMPP) for use in voice over IP (VoIP), video, and other peer-to-peer multimedia sessions." Libjingle is a library of the code that Google uses for peer-to-peer communication, and was made available under a BSD license.
Google Talk does not encrypt the Jabber stream, instead using an undocumented nonstandard way of authenticating to the service, retrieving a token from a secure web server. Other clients than Google's own are required to secure their streams with TLS before sending the password, causing them to stay encrypted throughout the whole session. Google claims that all messages (text and voice) will be encrypted in future releases.
Conversation logs can also now be automatically saved to a special folder in the user's Gmail account; this allows users to search within their chat logs easily, and to have them centrally stored no matter what computer is used to have conversations. Using Google's official client or through gmail.com, it is possible to enable "off the record" mode to prevent either user from being able to log the conversation, although this only affects the Gmail logging system and does not prevent logging by users whose IM client has its own logging capability, such as Gaim. It is important to note, however, that third party clients do not have the ability to go "off the record" at this moment, and all conversations through third party clients are logged into the user's Gmail account.
Offline messages are not supported so far and the configuration options available are very limited.