 into small, easily routable pieces, called packets, prior to transmission. Of course, this adds an additional layer of complexity to the process: What happens if one of the packets fails to arrive at its destination? Or, what if the packets arrive at the destination out of order? Some process must be in place to manage these challenges and overcome the potentially disastrous results that could occur. Computer networks have a lot in common with modern freeway sys- items, including the tendency to become congested. Congestion results in delay, which some applications do not tolerate well. What happens if some or all of the packets are badly delayed, as shown in Figure 2-8? What is the impact on the end-to-end quality of the service? Another vexing problem that often occurs is errors in the bitstream. Any number of factors including sunspot activity, the presence of electric motors, and the electrical noise from fluorescent lights, can result in ones being changed to zeroes and zeroes being changed to ones, as shown in Figure 2-9. Obviously, this is an undesirable problem, and there must be a technique in place to detect and correct these errors when they occur. There may also be inherent problems with the physical medium over which the information is being transmitted. There are many different media including twisted copper wire pairs, optical fiber, coaxial cable, and wireless systems, to name a few. None of these are perfect transmis- sion media; they all suffer from the vagaries of backhoes, lightning Figure 2-8 Problems in the network cause delay and lost data. 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. Protocols Chapter 2 Figure 2-9 Bit errors 0110111X1111010X01111101 strikes, sunlight, earth movement, squirrels with sharp teeth, kids with BB guns, and other impairments far too numerous to name. When these problems occur, how are th