Instant Messaging in MSN Messenger is session based . The people in between whom the conversation is going to take place have to be in a session mode. We cannot send/receive messages unless we start a chat session with a user. 

There are basically two methods in  which a user can be in a chat session                                                           

 

User sends a chat session request

 

The client(user) sends a command to the server asking it for the address of the SwitchBoard(SB) server. All instant messaging conversation take place via the switchboard server.

XFR 9 SB

The server(SB) replies back with the ip address of the switchboard server(SB),the port on which to connect and a CKI hash. CKI is a security package and the client has to use the hash to connect to the switchboard server.

 XFR 9 SB 64.4.13.88:1863 CKI 989487642.2070896604     

Now we have to make another  new connection this time to the switchboard server. Our previous connection to the MSN messenger server  must be kept as it is. If we loose connection with that server we would log out.

After we have connected to the switchboard server(SB) we send the following command to the switchboard server.

USR 1 venky_dude@hotmail.com  989487642.2070896604  

If the CKI hash sent by us is right the server(SB) responds back with this

USR 1 OK venky_dude@hotmail.com venkat

After this has been done the user has to "Call" the other user to the chat session. This is done by sending the following command.

CAL 2 deadxxx@hotmail.com 

The server replies back with the a session id which it will pass on to the other user

CAL 2 RINGING 11717653

When the other user replies and is ready for a chat the server(SB) sends us this command

JOI deadlee@hotmail.com Venkatesh

This indicates that the other user has joined in the conversation and we are now ready to send and receive messages.

 

User receives a chat session request

When we are being invited to a chat session by a user the server(NS) send us the following message.

 

RNG 11742066 64.4.13.74:1863 CKI 989495494.750408580 deaxxxx@hotmail.com Venkatesh

Here the server(NS) sends us the session id ,the ip address of the SwitchBoard server to connect to,the port on which to connect to ,the CKI hash and the user trying to start a conversation with us.

Now we have to make another  new connection this time to the switchboard server. Our previous connection to the MSN messenger server  must be kept as it is. If we loose connection with that server we would log out.

We  connect to the switchboard server and send the following command

ANS 1 venky_dude@hotmail.com 989495494.750408580 11742066

Here we send our login name ,the CKI hash that was sent to us and the session Id that was sent to us

The server responds back with 

IRO 1 1 1 deaxxxx@hotmail.com Venkatesh

and

ANS 1 OK

We are now ready to send and receive messages.

 

Before sending/receiving messages let us see how the message is constructed.

When we are sending a message we build the header information  in the following way

MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
X-MMS-IM-Format: FN=Microsoft%20Sans%20Serif; EF=; CO=0; CS=0; PF=22

While sending a message we send it this way

MSG  2  N 137                                                                                                                       MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
X-MMS-IM-Format: FN=Microsoft%20Sans%20Serif; EF=; CO=0; CS=0; PF=22

hello

Here 2 is the trial id which has to incremented each time we send a message. 137 is the total length of the message i.e length of the header and length of the actual message that we are sending in this case it is 'hello'.

 While receiving the message it is more or less similar

Here is an example of a message received

MSG deaxxxx@hotmail.com Venkatesh 137
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
X-MMS-IM-Format: FN=Microsoft%20Sans%20Serif; EF=; CO=0; CS=0; PF=22

hello

 

When the other user is typing a message we receive the foll message

MSG deaxxxx@hotmail.com Venkatesh 100
MIME-Version: 1.0
Content-Type: text/x-msmsgscontrol
TypingUser: deaxxxx@hotmail.com

 

I guess now u guys are well on your way to make your own version of  MSN messenger.If u guys have any doubts regarding this messenger or vb/c++ in general send me a mail at venky_dude@yahoo.com or you could go to my askme page and ask me a question.Do visit my projects page at http://www.geocities.com/venky_dude/venkwork.htm

 

 

References:

You could take a look at these sites for more information

This is the original protocol published by microsoft.

http://www.ics.uci.edu/~impp-1/knowledge.html

This is the MD5 homepage where u can find programs/codes for doing the MD5 encryption

http://userpages.umbc.edu/~mabzug1/cs/md5/md5.html

 

                                                                         

You can download a sample application from here Unify.zip