es the token in the appro- priate field of the frame it builds (actually, the medium access control scheme, called a MAC scheme and implemented on the NIC card that builds the frame), adds the data and address, and transmits the frame to the next station on the ring. The next station-which also has a frame it wishes to send-receives the frame, notes that it is not the intended recipient, and also notes that the token is busy. It does not transmit, but instead passes the frame of data from the first station on to the next sta- tion. This process continues, station by station, until the frame arrives at the intended recipient on the ring. The recipient validates that it is the intended recipient, at which time it makes a copy of the received frame, Figure 5-23 A token- passing, distributed- polling LAN Token Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Premises Technologies Chapter 5 sets a bit in the frame to indicate that it has been successfully received, leaves the token set as busy, and transmits the frame on to the next sta- tion on the ring. Because the token is still shown as busy, no other station can transmit. Ultimately, the frame returns to the originator, at which time it is recognized as having been received correctly. The station, there- fore, removes the frame from the ring, frees the token, and passes it on to the next station (it is not allowed to send again just because it is in possession of a free token). This is where the overall fairness scheme of this technique shines through. The very next station to receive a free token is the station that first indicated a need for it. It will transmit its traffic, after which it will pass the token on to the next station on the ring, followed by the next sta- tion, and so on. This technique works very well for situations in which high traffic congestion on the LAN is the norm. St