Microsoft Notification Protocol
Mobile Status Notification Protocol (MSNP, which is not an acronym for "Microsoft Network Protocol" as is often believed) is the protocol employed by MSN Messenger and other clients like Trillian and Windows Messenger to communicate with the MSN Messenger switchboard servers.
Version History
MSNP1
MSNP1 has never been public, it is believed it was used during the early stages of design and development with MSN Messenger 1
MSNP2
Made available to developers in 1999 in an Internet Draft
MSNP3
MSNP4
MSNP5
MSNP6
MSNP7
MSNP8
Minimum version of the protocol accepted by the switchboard servers, rendering older and obsolete clients inoperable with their servers, forcing users to upgrade clients.
Currently the only "official" MSN Messenger client that still uses this protocol is Windows Messenger 4.6 through 4.8 and the 5.x series.
This protocol supported Windows Messenger-to-Windows Messenger webcam and voice capabilities.
MSNP9
Version of the protocol starting with MSN Messenger 6, adds support for display pictures, frame-by-frame webcam (rather than a traditional stream like Windows Media Player's WMV format and an improved voice system, as well as improved NAT traversal for file transfers.
MSNP10
Employed in MSN Messenger 6.1, after Microsoft decided to switch the internal configurations in October 2003. However, it was not a big overhaul, and most of the external features remained the same.
MSNP11
MSNP12
Newest used version of the protocol, employed by MSN Messenger 7.5
MSNP13
Newly discovered protocol version used in Windows Live Messenger 8.0