 number of stations trying to send is high, a significant delay will result. How- ever, if the stations had only options 0 or 1 from which to choose, and if there were 100 workstations, it would take years to have a successful transmission. Data Communications No simple mathematical solution is available to estimate CDMA/CD delays accurately. Practical experience has proved that to have reasonable per- formance out of 802.3 the loading has to be kept to the order of 40% or less on average of the maximum physical data rate. The CSMA/CD as a MAC sublayer operation provides no acknowl- edgments and garbled frames are just discarded. If higher protocol layers use acknowledgments, they appear just like other frames in the network. Figure 6.30 shows an example in which there are three active stations in the CDMA/CD network. At time instant 0, both stations A and B transmit simultaneously and collision is detected. Then station A decides to transmit again but station B decides to wait for one contention slot time. Station C transmits at the same time as station A and a second collision occurs. Now both A and C decide to skip one slot and station B seizes the net- work. Both A and C transmit when the network is free again and a third col- lision occurs. Now station A has suffered from three collisions and its range for the second transmission is zero to seven slots. Station A has now a wide range and it selects most probably a higher number than station C, which has had only two collisions. In the example shown in Figure 6.30, station C picks 1, waits one contention slot, and transmits. Station A picks 2 and transmits immediately when C has finalized its transmission. T = Transmits C = Collision W = Wait L = Listen Station A Station B Station C Selection Selected Selection Selected Selection Selected Instant range number range number range number 0...1 0...1 0...3 0...1 0...7 0...3 Figure 6.30 Contention example. Introduction to Telecommunications Network Engineering 6.5.6 Twisted-Pair Ethernet Ethernet today is always w