Step 1: Get conneted either via Ethernet or WIFI (ad hoc network preferred)
Step 2: connect via the audio midi setup to the other persons computer
Step 3: In ableton assign who is master and slave by turning the sync button on for either the input(slave) or output(master) for the network session
Step 4: Hit EXT, and press play on master computer.
Hope you find this help full, if you have questions feel free to post a comment.