Recently from computer networking, where one computer (usually a client) will send a quick, pointless query to another computer (usually a server) in order to find out if it is still online and see how long the response takes.
Originally from the naval warfare practice of "active sonar" where one ship (usually a surface ship) will send out a given sound or "ping" in order to measure the direction and delay in the "echo" of that sound off of another body (usually a submarine.
I don't know... Ping me around eight and we'll see how things are going.
2) To call me
'ping' is a computer network utility program used to determine the accessability of another computer on a network. Information gathered from the 'ping' program can also show the amount of time it took to contact the other computer thereby establishing if there are network delays between the two systems.
The usage of this term probably originated with computer hobbyists or folks working in the computer industry.
2) "I'm not sure where on campus I'll be later, so ping me and I'll let you know"