《计算机网络——自顶向下方法与Internet特色》幻灯片Lecture51.pptVIP

Chapter 5: The Data Link Layer and Local Area Networks Chapter 5: The Data Link Layer and Local Area Networks The goals of this chapter: understand principles behind data link layer services: framing error detection, correction sharing a broadcast channel: multiple access link layer addressing reliable data transfer, flow control: done! instantiation and implementation of various link layer technologies 第五章 数据链路层和局域网络 本讲目标: 了解数据链路层服务原理: 形成帧 Framing 错误检测, 校正 共享广播信道 链路层编址 可靠数据传输, 流量控制: 已经接触过了! 各类链路层技术的实现和实例 基本内容: 链路层的服务 错误检测, 校正 多点访问技术和LAN 链路层寻址, ARP 特定的链路层技术: 以太网 集线器, 网桥, 交换机 IEEE 802.11 LANs PPP ATM Chapter 5: The Data Link Layer and Local Area Networks The fundamental channels in link layer: Broadcast channel (广播信道): Many hosts are connected to the same communication channel Used in LANs, Wireless LANs, Satellite networks, hybrid fiber coaxial cable (HFC) access networks Medium access protocol is needed to coordinate transmission and avoid collisions Point-to-point communication link (点对点通信链路) Contents of this Chapter 5.1 Introduction and services 5.2 Error detection and correction 5.3 Multiple access protocols 5.4 Link-Layer Addressing 5.5 Ethernet 5.6 Hubs and switches 5.7 PPP Link Layer: Introduction Some terminology: hosts and routers are nodes communication channels that connect adjacent nodes along communication path are links wired links wireless links LANs layer-2 packet is a frame, encapsulates datagram 链路层概述 LINK：连接两个物理设备的通道: 主机-路由器, 路由器-路由器, 主机-主机 数据单元: frame（帧） Link layer: context Datagram transferred by different link protocols over different links: e.g., Ethernet on first link, packet-over-WAN on intermediate links, 802.11 on last link Each link protocol provides different services e.g., may or may not provide RDT over link transportation analogy Package from Daqing to Beijing Drive package to Railway station train to Beijing Railway station Van to specific address package = datagram transport segment = communication link transportation mode