Summary

Chapter 8: Fundamental Networks 43At the network layer, each segment from the transport layer becomes a packet. The packetcontains logical addressing and other Layer 3 control information.At the data link layer, each packet from the network layer becomes a frame. The frame containsphysical address and error-correction information.At the physical layer, the frame becomes bits. These bits are transmitted one at a timeacross the network medium.At the receiving computer, the de-encapsulation process reverses the process of encapsulation.The bits arrive at the physical layer of the OSI model of the receiving computer. Theprocess of virtually traveling up the OSI model of the receiving computer brings the data tothe application layer, where an e-mail program displays the e-mail.NoteMnemonics can help you remember the seven layers of the OSI. Two examples are “All People SeemTo Need Data Processing” and “Please Do Not Throw Sausage Pizza Away.”Compare the OSI and TCP/IP ModelsThe OSI model and the TCP/IP model are both reference models used to describe the datacommunication process. The TCP/IP model is used specifically for the TCP/IP suite of protocols.The OSI model is used to develop standard communication for equipment and applicationsfrom different vendors.The TCP/IP model performs the same process as the OSI model, but it uses four layersinstead of seven. Figure 8-23 shows how the layers of the two models compare.Figure 8-23OSI Model and TCP/IP Model Compared