If two devices transmit simultaneously, it is detected and both devices retract to wait. It is a 'first come first served' system and there are no limits on the time that the DTE can transmit. It works well on point-to point circuits, light traffic networks, sporadic transmissions or fast networks. It is a fairly easy system with flexible standards, is widely used and compatible with many operating systems. It is not a fair system and does not work well on heavy load multi point circuits.
Some systems have polling lists which specify the sequence of the terminals to be polled.
The Reservation method allocates time slots with priority for important terminals and more time for busy terminals. Polling is a fair system, not very effective on low traffic circuits since it leaves a lot of empty time slots but good for lengthy transmissions . This protocol is known as IEEE 802.4 . The token indicates whether the the circuit is busy or free. A DTE waits for a free token to transmit, sets it to 'busy' and attaches the message to it.