Chapter6WirelessandMobileNetworks.ppt

* * * * * * * * * * * * 6: Wireless and Mobile Networks 6-* Chapter 6 outline 6.1 Introduction Wireless 6.2 Wireless links, characteristics CDMA 6.3 IEEE 802.11 wireless LANs (“wi-fi”) 6.4 Cellular Internet Access architecture standards (e.g., GSM) Mobility 6.5 Principles: addressing and routing to mobile users 6.6 Mobile IP 6.7 Handling mobility in cellular networks 6.8 Mobility and higher-layer protocols 6.9 Summary 6: Wireless and Mobile Networks 6-* 无线和移动对上层协议的影响 逻辑上，没什么影响： 为上层协议提供的仍然是尽力而为的服务 TCP和UDP也可以运行无线网络上 性能上，有很大影响: 传输出错或切换都会导致丢包（丢包率高），链路层重传会产生很大延迟 TCP将丢包（长延迟也当作丢包）解释为拥塞，不必要地减小拥塞窗口，导致应用吞吐率很低（无线链路的带宽本来就很低） 6: Wireless and Mobile Networks 6-* Chapter 6 Summary Wireless wireless links: capacity, distance channel impairments CDMA IEEE 802.11 (“wi-fi”) CSMA/CA reflects wireless channel characteristics cellular access architecture standards (e.g., GSM, CDMA-2000, UMTS) Mobility principles: addressing, routing to mobile users home, visited networks direct, indirect routing care-of-addresses case studies mobile IP mobility in GSM impact on higher-layer protocols * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 6: Wireless and Mobile Networks 6-* frame control duration address 1 address 2 address 4 address 3 payload CRC 2 2 6 6 6 2 6 0 - 2312 4 seq control 802.11帧格式 Address 2: 发送节点的MAC地址 Address 1: 接收节点的 MAC 地址 Address 3: 连接AP的路由器接口的MAC 地址 Address 4: 只在自组织模式中使用 6: Wireless and Mobile Networks 6-* Internet router AP H1 R1 AP MAC addr H1 MAC addr R1 MAC addr address 1 address 2 address 3 802.11 frame R1 MAC addr H1 MAC addr dest. address source address 802.3 frame 802.11帧: 寻址举例 6: Wireless and Mobile Networks 6-* frame control duration address 1 address 2 address 4 address 3 payload CRC 2 2 6 6 6 2 6 0 - 2312 4 seq control Type From AP Subtype To AP More frag WEP More data Power mgt Retry Rsvd Protocol version 2 2 4 1 1 1 1 1 1 1 1 802.11帧（续） duration of reserved transmission time (RTS/CTS) frame seq # (for reliable ARQ) frame type (RTS, CTS, ACK,