Chapter 10 Mobile IP TCP/IP Protocol Suite Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

OBJECTIVES: To discuss addressing issues related to a mobile host and the need for a care-of address. To discuss two agents involved in mobile IP communication, the home agent and the foreign agent, and how they communicate. To explain three phases of communication between a mobile host and a remote host: agent discovery, registration, and data transfer. To mention inefficiency of mobile IP in two cases, double crossing and triangular routing, and a possible solution. TCP/IP Protocol Suite

Chapter Outline 10.1 Addressing 10.2 Agents 10.3 Three Phases 10.4 Inefficiency in Mobile IP TCP/IP Protocol Suite

10-1 ADDRESSING The main problem that must be solved in providing mobile communication using the IP protocol is addressing. TCP/IP Protocol Suite

Topics Discussed in the Section Stationary Host Mobile Host TCP/IP Protocol Suite

固定主机 IP地址由两部分组成：前缀和后缀 路由器利用IP地址的前缀为分组(数据报)选择路由 主机移动时不能携带固定不变的IP地址 前缀是某个特定网络的地址 前缀使得主机与某个网络相关联 路由器利用IP地址的前缀为分组(数据报)选择路由 主机移动时不能携带固定不变的IP地址 TCP/IP Protocol Suite

Note The IP addresses are designed to work with stationary hosts because part of the address defines the network to which the host is attached. TCP/IP Protocol Suite

移动主机 当主机从一个网络移动到另一个网络时，IP编址结构需要修改 解决方案 改变地址 两个地址 TCP/IP Protocol Suite

改变地址 移动主机在移动到新网络时改变它的IP地址 缺点：不透明(P228) TCP/IP Protocol Suite

两个地址 归属地址(home address)：主机原始地址 转交地址(care-of address)：外地网络临时地址 TCP/IP Protocol Suite

Figure 10.1 Home address and care-of address TCP/IP Protocol Suite

mobile host moves from one network to another. Note Mobile IP has two addresses for a mobile host: one home address and one care-of address. The home address is permanent; the care-of address changes as the mobile host moves from one network to another. TCP/IP Protocol Suite

10-2 AGENTS To make the change of address transparent to the rest of the Internet requires a home agent and a foreign agent. TCP/IP Protocol Suite

Topics Discussed in the Section Home Agent Foreign Agent TCP/IP Protocol Suite

家乡(归属)代理 移动主机家乡网络上的路由器 当远程主机向移动主机发送分组时，家乡代理充当该移动主机 先由家乡代理接收分组，然后再将分组发送给处地代理 TCP/IP Protocol Suite

外地代理 移动主机当前所在的外地网络路由器 外地代理接收家乡代理发送过来的分组，并把分组交付给移动主机 移动主机也可充当外地代理。此时转交地址称为同址转交地址(colocated care-of address) TCP/IP Protocol Suite

Figure 10.2 Home agent and foreign agent TCP/IP Protocol Suite

Note When the mobile host and the foreign agent are the same, the care-of address is called a colocated care-of address. TCP/IP Protocol Suite

10-3 THREE PHASES To communicate with a remote host, a mobile host goes through three phases: agent discovery, registration, and data transfer. The first phase, agent discovery, involves the mobile host, the foreign agent, and the home agent. The second phase, registration, also involves the mobile host and the two agents. Finally, in the third phase, the remote host is also involved. We discuss each phase separately. TCP/IP Protocol Suite

Figure 10.3 Remote host and mobile host configuration TCP/IP Protocol Suite

Topics Discussed in the Section Agent Discovery Registration Data Transfer TCP/IP Protocol Suite

代理发现 发现家乡代理 发现外地代理 TCP/IP Protocol Suite

代理发现报文 代理通告(agent advertisement) 代理询问(agent solicitation) TCP/IP Protocol Suite

代理通告 在ICMP通告报文后附带代理通告 TCP/IP Protocol Suite

Note Mobile IP does not use a new packet type for agent advertisement; it uses the router advertisement packet of ICMP, and appends an agent advertisement message. TCP/IP Protocol Suite

Figure 10.4 Agent advertisement TCP/IP Protocol Suite

TCP/IP Protocol Suite

代理询问 移动主机移到外地网络，但没有收到代理通告时，发起代理询问 TCP/IP Protocol Suite

Mobile IP does not use a new packet type for agent solicitation; Note Mobile IP does not use a new packet type for agent solicitation; it uses the router solicitation packet of ICMP. TCP/IP Protocol Suite

登记 移动主机移至外地网络并发现外地代理，它必须进行登记 TCP/IP Protocol Suite

登记四个要素 移动主机必须向外地代理登记 移动主机必须向家乡代理登记 登记截止期到了之后，移动主机必须更新登记 移动主机回到家乡网络，必须取消登记 TCP/IP Protocol Suite

登记请求 移动主机将登记请求发送给外地代理，以变登记外地代理的转交地址，同时告知外地代理移动主机的家乡地址和家乡代理的地址 外地代理将登记请求转发给家乡代理 家乡代理收到登记请求后就获知外地代理的地址 TCP/IP Protocol Suite

Figure 10.5 Registration request format TCP/IP Protocol Suite

TCP/IP Protocol Suite

登记应答 登记应答由家乡代理发送给外地代理，然后再转发给移动主机 用于确认或拒绝登记请求 TCP/IP Protocol Suite

Figure 10.6 Registration reply format TCP/IP Protocol Suite

封装 登记报文被封装成UDP数据报 代理使用周知端口434 移动主机使用临时端口 TCP/IP Protocol Suite

Note A registration request or reply is sent by UDP using the well-known port 434. TCP/IP Protocol Suite

数据传送(1) 从远程主机到家乡代理 从家乡代理到外地代理 从外地代理到移动主机 从移动主机到远程主机 TCP/IP Protocol Suite

数据传送(2) 从远程主机到家乡代理 源地址：远程主机地址 目的地址：移动主机的家乡地址 家乡代理代理移动主机 TCP/IP Protocol Suite

数据传送(3) 从家乡代理到外地代理 从外地代理到移动主机 从移动主机到远程主机 家乡代理使用隧道技术将分组发往外地代理 外地代理将分组发给移动主机(依据转交地址) 从移动主机到远程主机 源地址：移动主机家乡地址 目的地址：远程主机地址 在外地网络发送 TCP/IP Protocol Suite

数据传送(4) 透明性 数据传送阶段，远程主机不知道移动主机的任何移动(早期方案) TCP/IP Protocol Suite

Figure 10.7 Data transfer TCP/IP Protocol Suite

Note The movement of the mobile host is transparent to the rest of the Internet. TCP/IP Protocol Suite

10-4 INEFFICIENCY IN MOBILE IP Communication involving mobile IP can be inefficient. The inefficiency can be severe or moderate. The severe case is called double crossing or 2X . The moderate case is called triangle routing or dog-leg routing. TCP/IP Protocol Suite

Topics Discussed in the Section Double Crossing Triangle Routing Solution TCP/IP Protocol Suite

两次穿越 当移动主机移至远程主机所在网络时 移动主机向远程主机发送分组时，借助外地代理(远程主机所在网络的路由器)，无问题 远程主机向移动主机发送数据时，仍需要错助家乡代理进行数据传送，即发生两次穿越问题 TCP/IP Protocol Suite

Figure 10.8 Double crossing TCP/IP Protocol Suite

三角路由(1) 发生三角路由问题的根源是移动主机的移动对远程主机来说是透明的 解决方法 去掉透明性：远程主机同时知道移动主机的家乡地址与转交地址 当家乡代理收到远程主机发给移动主机的第一个分组时，它将此分组发给外地代理，并向远程主机发送更新绑定分组(update binding packet)，让远程主机获知移动主机当前转交地址 TCP/IP Protocol Suite

Figure 10.9 Triangle routing TCP/IP Protocol Suite

三角路由(2) 当移动主机与远程主机不在同一个网络时 移动主机给远程主机发送分组理，无问题 远程主机给移动主机发送分组时，需要借助家乡代理，发生三角路由问题 TCP/IP Protocol Suite