TCP-IP network also roaming: mobile IP technology introduction
Generally speaking, mobile IP technology is a network technology that realizes the TCP / IP network roaming function. This technology mainly solves the problem that the local area network cannot be extended.
First make a simple analogy. As we all know, in the early 1990s, people broke the shackles of fixed phones and created early mobile phones. However, mobile phones at that time, so-called analog phones, could only talk in a certain area. If the user leaves this area to another area, he must reapply for a new phone number. This brings many inconveniences to people who pursue freedom and openness. The reason for the investigation was that the analog phones at that time did not support roaming services. At present, GSM mobile phones have been widely used by people. Now people can use a mobile phone number to communicate throughout the country and even the whole world.
Mobile IP technology is similar to this. The current network is based on the TCP / IP protocol for network communication, but the TCP / IP network protocol, like the analog mobile phone, does not support the roaming function. To give a most common example, an enterprise with a high degree of informatization generally has its own internal local area network, and all its employees work collaboratively on this network platform. If the employee of the enterprise leaves the office on a business trip or goes out, the employee can no longer use the internal network to work. At the same time, other employees will no longer have normal network contact with employees who have left. This situation is the main feature of the TCP / IP network, which does not support roaming.
Mobile IP technology is a new technology that is produced to solve this problem. It makes the necessary additions to the TCP / IP network protocol to support the roaming function of network extension. At this time, people in the online world can have a unique network IP address to maintain unified communication with the outside world. Well, the most vivid understanding of this technology can make this analogy: the computer is a bare metal of the user. The user's network IP address is the user's fixed mobile phone number. Computer users with fixed and unique network IP addresses can Enjoy roaming services like GSM mobile phone users.
Xi'an Xidian Jietong Wireless Network Communication Co., Ltd. has undertaken the research and development project of broadband wireless IP technology, which is the national 863 key research project. After nearly ten years of hard work, the research and development was finally announced in the spring of 2002 and won the national Aa certification of 863 acceptance group! Jietong Communication not only created the world's first mobile IP roaming system, but also ended the limitation of the "local area" of the local area network, and created a new network era in which TCP / IP networks support roaming.
From a technical point of view, mobile IP technology is a key technology for mobile terminals (PC / Sever / segment, etc.) to support mobile (roaming) in a relatively large range, it ensures that mobile terminals communicate normally during the movement, and With two-way connectivity. In Jietong Communication's mobile IP roaming system, we must first support a few new concepts:
Mobile node: a computing terminal, server, network segment, etc. that needs to roam across network segments.
Mobile IP server: It is a hardware device that implements mobile IP. It is called a home agent and a foreign agent according to the network segment to which the mobile node belongs.
Mobile IP terminal software: software installed on mobile nodes, mainly used to implement network communication functions with foreign agents and home agents.
Agent search: It is used by mobile nodes to determine whether they are roaming.
Care-of address: It is the temporary address obtained from the foreign agent when the mobile node moves to the external network.
Login: It is the process of a series of authentication, registration, and tunnel establishment when the mobile node reaches the external network.
Tunnel: is a two-way data channel temporarily established between the home agent and the foreign agent.
The working mechanism of the JITCOM mobile IP roaming system is shown in the figure below: 
First, users should register with the mobile IP server of the "home agent" in the original network. (You can use it for life for as long as you register once.) When a user travels from Beijing to Shanghai with a mobile terminal (such as a laptop), the user connects his computer to the local area network (wired network or wireless network environment) of a Shanghai enterprise . Then, open the mobile IP client software. At this time, the laptop will automatically perform an agent search to determine whether it is roaming. Next, the mobile IP server ("foreign agent") in the Shanghai local area network assigns the computer a care-of address. After obtaining the care-of address, the user's laptop must be authenticated and logged in. After successful authentication, the mobile IP roaming system establishes a tunnel between the two mobile IP servers in Beijing and Shanghai. At this point, the user's laptop can communicate normally with the outside world through the foreign agent. At the same time, the “home agent†mobile IP server forwards the other network information in Beijing to the user to the “home agent†mobile IP server in Shanghai. At this time, the “foreign agent†transfers the obtained information to the user ’s laptop.
During this process, the user's network IP address has not changed, and maintains a unified, two-way, instant communication contact with the original network.
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