ey detected? Equally important, how are the transmission impairments that they inevitably cause reported and cor- rected? There must also be an agreed upon set of rules that define exactly how the information is to be physically transmitted over the selected medium. For example, if the protocol to be used dictates that information will always be transmitted on pin 2 of a data cable, such as that shown in Figure 2-10, then the other end will have a problem, since its received signal will arrive on the same pin that it wants to transmit on! Further- more, there must be agreement on how information is to be physically represented, how and when it is to be transmitted, and how it is to be acknowledged. What happens if a very fast transmitter overwhelms the receive capabilities of a slower receiver? Does the slower receiver have the ability, or even the right, to tell it to slow down? Collectively, all of these problems pose what seem to be insur- mountable challenges to the transmission of data from a source to a receiver. And while the process is obviously complex, steps have been taken to simplify it by breaking it into logical pieces. Those pieces, as we described earlier, are protocols. Collections of protocols, carefully Send Data Figure 2-10 Ground Physical agreements Carrier Receive Data Request to Data Set Ready Clear to Send Data Terminal Ready 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 Protocols selected to form functional groupings, are what make data communi- cations work properly. Perhaps the best-known family of protocols is the International Orga- nization for Standardization's Open Systems Interconnection Reference Model, usually called the OSI Model for the sake of simplicity. Shown in Figure 2-11 and comprising seven layers, it provides a logical way to study and understand data communications and is based on the