If more than one station transmits simultaneously, contention is detected and both stations select a random number 0 or 1 and transmit again immediately or wait for one contention slot (51.2 microseconds). Depending on how many collisions have occurred, random number is selected from the set 0 (2'-1), where is the number of detected collisions If 10 or more collisions have occurred, selection range is 0 1,023. When 16 collisions have occurred, the problem is reported to higher layers. Figure 6.29 Contention algorithm of CDMA/CD. slot time is set to be 512 bit times (51.2/ us), the time that the transmission of a minimum size frame (64 bytes) takes at the data rate of 10 Mbps. After the first collision, each station waits randomly either 0 or 1 con- tention slot times before trying again. If two stations collide and each one picks the same random number, they will collide again. After the second col- lision, each station picks 0, 1, 2, or 3 at random and waits that number of contention slots. If a third collision occurs, then the next time, the number of slots to wait is chosen at random from the interval of 0 to 23 - 1. In general, after i number of collisions, a random number between 0 and 2i - 1 is chosen, and that number of slots is skipped. The probability of the next collision decreases with the number of previous collisions. After 10 collisions have been reached, the randomization interval is frozen at the maxi- mum of 1,023 slots. After 16 collisions, the controller reports failure back to the computer. Further recovery is up to the higher layers and typically an error message is prompted. The probability of this situation is SO small that it does not occur in normal operation but it may happen, for example, if the coaxial cable is cut off. Then each transmitted frame is reflected from the bro- ken end of the cable and collision is detected for each transmission. This described algorithm, called binary exponential backoff [3], was chosen to dynamically adapt to the number of stations trying to send. If the