The most common federation is the PIC (Public IM Connectivity) federation. This type of federation enables interoperability between unified communication platforms and Public IM services, such as AOL and Yahoo. As a result, end-users can use their UC clients, such as Microsoft Office Communicator (MOC), to chat with users on AOL IM service (AIM) or Yahoo! IM (YIM).
The other type of federation is the external or direct federation. Direct federation allows two organizations to federation their respective UC environments. This allows employee to collaborate with their colleagues using their UC clients. Direct Federation provides a secure B2B communication link.
Today, UC vendors only offer direct federation across similar UC systems. For example, IBM Sametime only allows cross-enterprise federation with other IBM Sametime platforms.
Over the past two years a number of announcements has been made about UC vendors working together to address the interoperability problems between their UC platforms. The reality is federation between dissimilar UC systems is difficult, and none of the UC vendors is going on a limb to be the first to offer it.
Moreover, providing direct federation is a slippery slope. Going beyond IM and presence federation and offering any-to-any federation across different communication modes, such as multi-user chat or persistent char rooms, is a huge challenge.