ts until the transmission has finished. As soon as the carrier is free it begins to transmit data, while at the same time continuing to listen for other transmissions. If it detects another device transmitting at the same time (collision detection), it stops transmitting and sends a short jam signal to tell other devices that a collision has occurred. Each of the devices that were trying to transmit then computes a random backoff period within a range 0 to tmax, and tries to transmit again when this period has expired. The device that by chance waits the shortest time will be the next to gain access to the medium, and the other devices will sense this transmission and go back into carrier sensing mode. A very busy medium may result in a device experiencing repeated collisions. When this happens tmax is doubled for each new attempt, up to a maximum of 10 doublings, and if the transmission is unsuccessful after 16 attempts the frame is dropped and the device reports an "excessive collision error". Other Wired Network MAC Methods Another common form of media access control for wired networks, defined by the IEEE 802.5 standard, involves passing an electronic "token" between devices on the network in a pre-defined sequence. The token is similar to a baton in a relay race in that a device can only transmit when it has captured the token. Wireless Network Logical Architecture If a device does not need control of the media to transmit data it passes the token on immediately to the next device in the sequence, while if it does have data to transmit it can do SO once it receives the token. A device can only keep the token and continue to use the media for a specific period of time, after which it has to pass the token on to the next device in the sequence. Media Access Control in Wireless Networks The collision detection part of CSMA/CD is only possible if the PHY layer transceiver enables the device to listen to the medium while transmitting. This is possible on a wired network, where invalid voltages resulting from coll