Information for the availability service is provided via our open specifications document: [MS-OXWAVLS].
Information for the security model used in the availability service, please reference the following document: [MS-OXCPERM].

For more info, you can refer:

Availability Web Services Protocol specification: http://msdn.microsoft.com/en-us/library/cc463891(v=exchg.80).aspx or http://download.microsoft.com/download/5/D/D/5DD33FDF-91F5-496D-9884-0A0B0EE698BB/[MS-OXWAVLS].pdf or http://download.microsoft.com/download/5/D/D/5DD33FDF-91F5-496D-9884-0A0B0EE698BB/Exchange_Protocols.zip.