Microsoft Notification Protocol

~ the eulogy ~

Every MSN window in Turkey between 2002 and 2010 was a thin shell over a protocol almost none of us could have named. You typed, you hit enter, and somewhere underneath, a plain-text command went out over a socket with a transaction number on it. That was MSNP. It arrived with MSN Messenger 1.0 on 22 July 1999 and it stayed in service for nineteen years and eight months.

Microsoft never treated it as a public standard, though it came close once: MSNP2 was handed to developers in 1999 as an Internet Draft, and the version that actually shipped differed from it. After that the specification went private and the version numbers went up, and everything the outside world knew about the protocol came from people watching the packets. The MSNPiki wiki and a long line of third-party clients were built entirely on that reverse-engineering work.

I was on MSN for the whole TTNet years. University, then the internet cafe window where the client was already installed and still logged into somebody else's account. I knew none of this. The protocol is the part you never meet; what you meet is the status change and the little sound that goes with it.

~ the dossier ~

~ the version ladder ~

You can read the whole history of the product off the version numbers. MSNP3 added the command that managed switchboard sessions, which is how group chats worked. MSNP8 brought in Passport authentication and became the floor: in October 2003 Microsoft started refusing connections from anything below it, which quietly killed off every unmaintained client at once. MSNP9 added the data messages that carried custom emoticons and display pictures, plus frame-by-frame webcam feeds. MSNP14 added interoperability with Yahoo! Messenger, the one time two of the big walled gardens agreed to talk.

Then on 11 September 2007, Microsoft forced most MSN Messenger users onto Windows Live Messenger 8.1 for security reasons, and MSNP15 with its single sign-on became the new floor. Eleven versions later the numbering stopped at 24.

~ the afterlife ~

Here is the part that makes MSNP strange. Microsoft retired the Messenger service globally in April 2013 and moved everyone to Skype, which should have been the end of the protocol too. It was not. Microsoft deprecated the old Skype protocol on 20 June 2014, and by the second week of that August Skype was running on Microsoft Notification Protocol 24. The messaging stack Microsoft had bought for 8.5 billion dollars was quietly repaved with the messaging stack it already owned.

So MSNP outlived the brand it was named for by five years. Messenger itself held on longest in mainland China, where it was not retired until 31 October 2014, by which point the protocol had already changed employers. The end came when Skype moved to a web-based backend and MSNP24 stopped answering. A client library that had been built against it posted the obituary in a single line: "As of 2019/04/09, MSNP24 is gone for good."

~ what it gave away ~

The early versions were unencrypted, and a 2007 security analysis out of UBC concluded that the design "did not follow several principles of designing secure systems," then demonstrated the point by successfully spoofing a user's identity. For most of its life anybody sharing your network segment could read your conversation off the wire.

That is worth sitting with, given how much of a decade went through it. Every argument and every long conversation conducted in a window with a flashing taskbar button went through it. Twenty years of talk in plain text, over a protocol whose documentation was written by strangers who had to guess.

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