Mobile IP technology in wireless access

Introduction
With the rapid development of the Internet, people increasingly want to be flexible, fast, low-cost, anytime and anywhere access to the Internet. Because of these features, wireless communication technology is increasingly used in Internet access. In IMT-2000, it is stipulated that the third generation mobile communication system must support mobile IP packet service.

A The way and system of wireless access
Wireless communication technology can be broadly divided into mobile phone systems, wireless communications systems and satellite communications systems 3 categories. The mobile phone system is mainly amps, GSM and IS-95. In these systems, the mobile operators put forward the scheme of providing data service respectively.

The CDPD developed on the amps system completely uses the original spectrum and facilities, in addition to the base station and the antenna and the AMPS system shared, the network management system is independent, uses the special frequency method or the frequency hopping way to transmit the data. Circuit-switched cellular data technology is also used for amps systems, but it is not a CDPD mode of packet switching, but circuit switching mode.

GSM system providers use the 1.9GHz PCs network to provide mobile data services, known as PCS1900.

In addition, the IS-95CDMA mobile phone system proposed by the Qualcomm company also plans to provide data services.
1. Satellite communication systems use satellites to provide mobile and stationary wireless internet services.
2. Wireless communication system is mainly used in the ISM (industry, scientific Research, medical) band and u-nii (national information infrastructure is not open) band. The ISM band system is mainly used for wireless communication within the building and the university campus. U-nii Band of equipment are used LBT (listen-before-talk) wireless communication protocol.

Two. Mobile IP technology
For the fixed wireless communication access solution is relatively easy, as long as the original communication system on the basis of a little improvement on it, it is difficult in the mobile wireless users how to access the Internet, and at the same time meet the IMT-2000 two requirements:
One, ip-based wireless voice (Wireless Voice over IP) transmission delay can not exceed the CDMA and TDMA voice frame interval of 20ms;
Second, the transmission process, must provide similar to the traditional wireless communication seamless switching quality, with the smallest packet loss rate.

The IETF Network Working group has proposed the RFC2002 standard, elaborated the mobile IP principle, the realization as well as each kind of detail question in detail. Subsequently, the RFC2003 standard of IP encapsulation in IP, the RFC2004 standard of minimum encapsulation within IP, and the RFC2290 standard of mobile IPV4 configuration options for PPP IPCP were presented. Here is a detailed introduction to mobile IP related technologies.
Traditional IP technology hosts use a fixed IP address and TCP port number to communicate with each other. During the communication, their IP address and TCP port number must remain unchanged, otherwise communication between IP hosts will not continue. While mobile IP host may need to be on the network during the communication, its IP address may change frequently. In the traditional way, the change of IP address will lead to communication terminal. To solve this problem, mobile IP technology refers to the principle of processing cellular mobile phone calls, so that mobile nodes adopt a fixed IP address, a login can be achieved in any location to maintain a single link layer with the IP host, so that communication continues. Before introducing mobile IP technology, here are a few important concepts to start with:
Mobile Agent (mobility agent): Also divided into the attribution agent and the Outer zone agent two categories. The attribution agent is the mobile agent that belongs to the Internet, it has at least one excuse to belong to the Internet. The responsibility is to intercept packets to that point when the mobile node is moved to the extranet, and to forward the packets to the transfer node of the mobile node using tunneling techniques. The outer zone agent, located on the current outer area of the mobile node, is responsible for releasing the original packet's tunnel encapsulation, fetching the original packet, and forwarding it to the mobile node.
Mobile IP Address: Mobile IP node has two IP addresses. One is the home address, the address that is used when the mobile node is connected to the ownership network, regardless of where the mobile node is moved to the network, its attribution address remains unchanged. The second is the address of the end of the tunnel, which may be the forwarding address of the outer zone agent, or the local forwarding address. Typically, the outer zone proxy forwarding address is used. In this address mode, the outer-zone proxy is the end of the tunnel, it receives the tunnel packets, unlocks the packet's tunneling package, and forwards the original packets to the mobile node.
Location Registration (registration): The mobile node must register its location information with its attribution agent to be found. There are two different kinds of registration procedures. One is through the outer zone agent, the mobile node to the external agent to send the registration request message, then relay the message to the mobile node's attribution agent, the attribution agent after processing the registration request message to the outside district agent to send the registration reply message (Accept or reject the registration request), the outer Area agent processing registers the reply message, and forwards it to the mobile node. The other is directly to the attribution agent registration, that is, the mobile node to its attribution agent to send the registration request message, the Attribution agent processing to the mobile node to send a registration reply message.
Agent Discovery (Agent Discovery): First, passive discovery, that is, mobile node waiting for the local mobile agent periodic broadcast agent notification message, the second is the active discovery, that is, mobile node broadcast a request agent message.
Tunneling Technology (tunneling): When a mobile node is on an external network, the attribution agent needs to transfer the original datagram to the registered outer-area agent. This is where the attribution agent uses IP tunneling technology to encapsulate the original IP packet in the forwarded IP packet so that the original IP packet is forwarded intact to the forwarding address at the end of the tunnel. At the forwarding address, remove the tunnel, take out the original packet, and send the original packet to the mobile node. When the forwarding address is the mainstream local address, the mobile node itself is the end of the tunnel, it itself to remove the tunnel, take out the original data packet work. Two types of tunnel encapsulation techniques are defined in RFC2003 and RFC2004 respectively, as shown in Figure 1.
The mobile IP protocol works roughly as follows:
1. The mobile agent (that is, the outer zone agent and the attribution Agent) broadcasts its existence through an agent notification message. The mobile node can select the agent notification message to the local mobile agent through the proxy request message.
2. Mobile node After receipt of these agent notices, distinguish whether they are on the Internet or on an outside area.

3. When a mobile node detects that it is on the web, it does not need a mobile service to work. If the mobile node returns from the registered other extranet network, by exchanging its accompanying registration request and registering reply message, the mobile node needs to revoke the registration information from its attribution agent.
4. When a mobile node detects that it has wandered to a foreign area network, it obtains a referral address on the outer area web. This referral address may be obtained through a notification of an outside agent, or through an external allocation mechanism, such as DHCP (a local-resident forwarding address).
5. A mobile node that leaves the home network registers its new referral address with the vesting agent by exchanging its accompanying registration request and registration reply message, and it may also register with the attribution Agent with the help of the outer zone agent.
6. Packets destined for the mobile node are received by their attribution agent, the attribution agent encapsulates the packet using tunneling technology and sends the encapsulated packet to the mobile node's forwarding address, which is received by the tunnel endpoint (the outer-zone agent or the mobile node itself), is encapsulated, and eventually transferred to the mobile node.
In the opposite direction, using the standard IP routing mechanism, the packets sent by the mobile node are transmitted to the destination without the need to be forwarded through the attribution agent. Regardless of whether the mobile node is in or out of the network, all packets between the IP host and the mobile node are used as the location of the mobile node, and the forwarding address is only used for the connection with the mobile agent, and is not detected by the IP host. Figure 2 illustrates how mobile IP works when mobile nodes are on the Internet.
1. IP hosts pass the standard IP route and send packets to the mobile node to the destination network.
2. The packet is received by the attribution agent, and the registry indicates the associated address of the mobile node.
3. The transfer address of the "tunneling technology" to the mobile node, that is, the outer zone agent.
4. The Outer zone agent unlocks the tunnel, takes out the original packet, and forwards the original packet to the mobile node.
5. The packets emitted by the mobile node are sent to the destination via standard IP routing procedures (the default router for the mobile node is the foreign-Chinese agent in this figure).