The message used in Windows Messenger for isTyping indication is like the
following.

      MSG 11 U 9
3..MIME-Version:
 1.0..Content-Ty
pe: text/x-msmsg
scontrol..Typing
User: xiaotaow@h
otmail.com......

If I use Windows Messenger's communication service (using SIP), the
messenger uses SIP INFO method for the isTyping event.

INFO ...
Content-Type: application/xml
<?xml version="1.0"?>
<KeyboardActivity>
  <status status="type"/>
</KeyboardActivity>

The behavior for Window messenger handling the isTyping event is like:

At the sender side, it periodically check the input window, if there are
changes in the input window, it will send the event notification out.

At the receiver side, when it receives the event, it will display
<name> is typing. After about 5 seconds, if no new isTyping event
received, it will clean up the '<name> is typing'.