Protocols/MSNP/MSN Protocol Version 15
MSNP15 is the protocol version introduced with Windows Live Messenger 8.1 on 8 September 2006. It is based on MSNP14 but uses a different authentication mechanism called RPS "Relying Party Suite". Where TWN "Tweener" authentication is used on protocol versions 14 and below, RPS authentication will be used on protocol versions 15 and above.
In addition to a new authentication mechanism, Microsoft is also planning on making more of the properties of the user roaming. That is, the user's display picture, and in the future personal status messages, will be the same wherever the user signs in.
Furthermore, support for user locations has been added to the Personal Status Message, although this feature was later removed from the Windows Live Messenger 8.1 client.
Important note: All SOAP requests that used the ApplicationId 09607671-1C32-421F-A6A6-CBFAA51AB5F4 will now return error 500. This is because the Id is from an old beta client that has since been blocked by Microsoft. You must use the ApplicationId of Windows Live Messenger 8.5 (which is CFE80F9D-180F-4399-82AB-413F33A1FA11) or another valid messenger version for your SOAP requests to work.
- Blog post by ZoRoNaX