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Lecture Data communications and networks: Chapter 2 - Forouzan 

The two dominant networking models are the Open Systems Interconnection (OSI) and the Internet model (TCP/IP).The first is a theoretical framework; the second is the actual model used in today's data communications. In Chapter 2, we first discuss the OSI model to give a general background. We then concentrate on the Internet model, which is the foundation for the rest of the lecture. | Chapter 2 Network Models Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. 2-1 LAYERED TASKS We use the concept of layers in our daily life. As an example, let us consider two friends who communicate through postal mail. The process of sending a letter to a friend would be complex if there were no services available from the post office. Sender, Receiver, and Carrier Hierarchy Topics discussed in this section: 2. Figure 2.1 Tasks involved in sending a letter 2. 2-2 THE OSI MODEL Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. It was first introduced in the late 1970s. Layered Architecture Peer-to-Peer Processes Encapsulation Topics discussed in this section: 2. ISO is the organization. OSI is the model. Note 2. Figure 2.2 Seven layers of the OSI model 2. Figure 2.3 The interaction between layers in the OSI model 2. Figure 2.4 An exchange using the OSI model 2. 2-3 LAYERS IN THE OSI MODEL In this section we briefly describe the functions of each layer in the OSI model. Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer Topics discussed in this section: 2. Figure 2.5 Physical layer 2. The physical layer is responsible for movements of individual bits from one hop (node) to the next. Note 2. Figure 2.6 Data link layer 2. The data link layer is responsible for moving frames from one hop (node) to the next. Note 2. Figure 2.7 Hop-to-hop delivery 2. Figure 2.8 Network layer 2. The network layer is responsible for the delivery of individual packets from the source host to the destination host. Note 2. Figure 2.9 Source-to-destination delivery 2. Figure 2.10 Transport layer 2. . | Chapter 2 Network Models Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. 2-1 LAYERED TASKS We use the concept of layers in our daily life. As an example, let us consider two friends who communicate through postal mail. The process of sending a letter to a friend would be complex if there were no services available from the post office. Sender, Receiver, and Carrier Hierarchy Topics discussed in this section: 2. Figure 2.1 Tasks involved in sending a letter 2. 2-2 THE OSI MODEL Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. It was first introduced in the late 1970s. Layered Architecture Peer-to-Peer Processes Encapsulation Topics discussed in this section: 2. ISO is the organization. OSI is the model. Note