[政史地]ch02_Network Models.pptVIP

Figure 2.14 Application layer The application layer is responsible for providing services to the user.应用层负责向用户提供服务 Note Figure 2.15 Summary of layers 各层任务小结 7. 应用层：允许访问网络资源 6.表示层：负责翻译、压缩和加密数据 5.会话层：负责对话的控制和同步 4. 传输层：提供可靠的进程到进程的报文传输和错误恢复 3. 网络层：将分组从资源转移到目的；提供网络互连 2. 数据链路层：将比特组织成帧；提供跳到跳的传输 1. 物理层：通过介质传送比特流；提供机械及电气规格说明 2-4 TCP/IP PROTOCOL SUITE The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application. Physical and Data Link LayersNetwork LayerTransport Layer Application Layer Topics discussed in this section: Figure 2.16 TCP/IP and OSI model Data Communications Networking * * * McGraw-Hill The McGraw-Hill Companies, Inc., 2000 Chapter 2 Network Models 网络模型 Department of Electronic and Communication Engineering NCEPU KEY WORDS Reference model 参考模型 Layer 层 Interface 接口，界面 Function 功能 Header 头部 Trailer 尾部 Source address 源地址 Destination address 目标地址 Physical address 物理地址 Logical address 逻辑地址 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 发送方、接收方和载体Hierarchy 层次结构 Topics discussed in this section: Figure 2.1 Sending a letter 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 层次结构Peer-to-Peer Processes 对等进程