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2-1 LAYERED TASKSWe use the concept of layers in our daily life. As anexample, let us consider two friends who communicatethrough postal mail. The process of sending a letter to afriend would be complex if there were no servicesavailable from the post office. Topics discussed in this section: Sender, Receiver, and Carrier Hierarchy2.2
Figure 2.1 Tasks involved in sending a letter2.3
2-2 THE OSI MODELEstablished in 1947, the International StandardsOrganization (ISO) is a multinational body dedicated toworldwide agreement on international standards. An ISOstandard that covers all aspects of networkcommunications is the Open Systems Interconnection(OSI) model. It was first introduced in the late 1970s. Topics discussed in this section: Layered Architecture Peer-to-Peer Processes Encapsulation2.4
2-3 LAYERS IN THE OSI MODELIn this section we briefly describe the functions of eachlayer in the OSI model. Topics discussed in this section: Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer2.9