31 Days Before Your CCNA Exam

Day 30Network Models and ApplicationsCCNA 640-802 Exam Topics■Describe common networked applications, including web applications.■■Describe the purpose and basic operation of the protocols in the OSI and TCP models.Describe the impact of applications (Voice over IP and Video over IP) on a network.Key PointsAs a new student to networking, one of the very first topics you probably learned was the layers ofthe OSI and TCP/IP models. Now that you have completed your studies and are reviewing for theCCNA exam, you more than likely can see the benefit of using these models. Each helps our understandingof networks in its own way. Today we review the OSI and TCP/IP models, as well as theapplications and protocols that are commonly used in networks.The OSI and TCP/IP ModelsTo understand how communication occurs across the network, we use layered models as a frameworkfor representing and explaining networking concepts and technologies. Network models providea variety of benefits:■■■■■■Reduce complexityStandardize interfacesAssist understandingPromote rapid product developmentSupport interoperabilityFacilitate modular engineeringInitially, networks were built on proprietary standards and hardware. Layered models, such as theTCP/IP and OSI models, support interoperability between competing vendor product lines.The OSI model development began in the 1970s with the goal to provide a standards-based suite ofprotocols that would allow communication between all computer systems. Although the U.S. governmentrequired the use of OSI products in the 1980s and 1990s, the Defense Advanced ResearchProjects Agency (DARPA) under the Department of Defense—and with the help of researchers atvarious universities—had designed the competing TCP/IP model. For various reasons, including thepopularity of TCP/IP, by 1983 the ARPANET had chosen TCP/IP as its principle protocol suit. By1994, all U.S. government agencies were required to switch over from OSI protocols to TCP/IP.