多媒体网络基础-第1章 因特网.ppt

Commons Both are based on the concept of a stack of independent protocols. Functionality of the layers is similar. The layers above transport are application-oriented users of the transport service. Differences OSI Model TCP/IP Model Model /Protocol Model was devised before the corresponding protocols were invented The protocols came first ,and the model was really just a description of the existing protocols Layers 7 4 Network Layer Supporting both connectionless and connection-oriented communication Only supports connectionless communication Transport Layer Only connection-oriented communication Both connectionless and connection-oriented communication 只要遵循 OSI 标准，一个系统就可以和位于世界上任何地方的、也遵循这同一标准的其他任何系统进行通信。 在市场化方面 OSI 却失败了。 OSI 的专家们在完成 OSI 标准时没有商业驱动力； OSI 的协议实现起来过分复杂，且运行效率很低； OSI 标准的制定周期太长，因而使得按 OSI 标准生产的设备无法及时进入市场； OSI 的层次划分并也不太合理，有些功能在多个层次中重复出现。 Bad timing 时机 The apocalypse（启示） of the two elephants. ——M.I.T David Clark Both the model and protocols are flawed. Session and presentation are nearly empty. Data link and network are overfull The model and protocols are extraordinarily complex. Some function reappear again and again in each layer.Eg: Addressing, flow control, error control. Bad implementations 实现 Bad politics 政策 Beijing Institute of Fashion Technology LiuYi Basis of Computer Network： The goals of Computer networking are ： Communication 数据通信 and Resource Sharing 资源共享 Computer Technology 计算机技术 Communication Technology 通信技术 ——What’s the earliest computing tool ? ——What’s the earliest communication method ? 1. Classified by distance (most commonly used） WAN（Wide Area Network）广域网也叫远程网。 范围：几十公里到几千公里，覆盖国家、地区、大洲。 LAN（Local Area Network局域网）。 范围：一个实验室、大楼、校园。这是计算机网络中最活跃的领域。 MAN（Metropolitan Area Network）城域网 范围：介于广域网与局域网之间，一般是几十公里的大量企业、机关、公司大多个局域网互联的需求。 Classified by switching method: Circuit switching（电路交换）、Message switching（报文交换）、 Packet switching （分组交换） Classified by topology （Important）: Star、Bus、Ring、Tree、Network Classified by transmission media: Guided Trans