systat/udp
Description
Returns packets containing a list of active users.
Protocol
Client sends a packet. The server returns packets containing the
list of active users. The only condition is that lines of the list
of users must not cross packet boundaries.
There are obvious security concerns about having access to a list of active users.
Notes
This is also alternatively referred to as the USERS protocol.
Implementation
This seems to be most often the who command in unix.
RFCs
RFC-866
Reference Person
Jon Postelpostel@isi.edu