Design of wireless IP gateway

1 overview

In the actual network, many not the same location of the local area network need interactive information, in order to realize the Special wireless network (data chain) and the interconnection between the LAN, and developed the following functions of the gateway. First, IP-level interconnection: That is, the IP datagram of a LAN after the conversion of the gateway through the wireless network to another gateway, after conversion, the IP datagram can reach another local area network of the corresponding host, as shown in Figure 1, followed by the implementation of connection certification. When the gateway is started, the connection is authenticated with another gateway, and when the authentication is passed, the IP connection is established.

The experiment uses the Self-developed software, works under the Windows 9x operating system, obtains all IP datagram in the local area network, through judges, modifies the Ethernet header information, transmits the IP data to the serial port, sends out through the connection in the serial port wireless device, The wireless device connected on the gateway serial port of the destination network is received and forwarded to the destination computer via the gateway. From the function, the gateway computer realizes the function of the router.

The principle and function of the 2 router

2. 1 principle of the router

A router (router) is a typical network-layer device. It transmits data by IP datagram between two LANs, it is called intermediary system in OSI/RM, completes the task of network layer relay or third layer relay. Routers have the ability to judge network addresses and select paths, it can be in a multi-network environment, the establishment of flexible connections, can be completely different data groups and media access methods to connect various subnets, routers only accept the source station or other routers information, it does not care about the use of the subnet hardware devices, However, it requires running software that is consistent with the Network layer protocol. Routers are local routers and remote routers, the local routers are used to connect network transport media, such as optical fiber, coaxial cable, twisted pair; a remote router is used to connect remote transmission media and requires appropriate devices such as telephone lines to be equipped with modems, wireless via wireless receivers, transmitters.

The main task of the router is to find an optimal transmission path for each data frame passing through the router and to effectively transfer the data to the destination site. This shows that the choice of the best path strategy is the routing algorithm is the key to the router. To do this, the routing table (routing table), which holds data about various transmission paths in the router, is used for routing. The routing table holds the logo information of the subnet, the number of routers on the network, and the name of the next router. The routing table is divided into the following two categories:

1. Static routing Table

The system administrator has set up a fixed routing table called static routing table, usually in the system installation according to the configuration of the network preset, it will not change with the future network structure changes.

2. Dynamic routing Table

The dynamic routing table is a routing table which is automatically adjusted by a router according to the operation of the network system according to a certain routing algorithm. Routers, based on the functionality provided by the routing Protocol (routing protocol), automatically learn and memorize network operations and automatically calculate the best path for data transfer when needed.

2. 2 Router Features

There are five main features of the router:

1. The network intercepts the message which sends to the FAR ground network segment, plays the forwarding function.

2. Select the most reasonable route to boot traffic.

3. Routers in the process of forwarding messages, in order to facilitate the transmission of messages between the network, according to the predetermined rules of the large packet decomposition into the appropriate size of the packet, to arrive at the destination and then the decomposed packets into the original form.

4. Multi-protocol routers can connect network segments using different communication protocols and serve as a platform for communication between different communication protocol network segments.

5. The primary task of a router is to direct traffic to a destination network and then to a specific node station address. The latter function is done through network address decomposition.

From the above, according to the specific requirements of this project, the design of the wireless gateway function to achieve a part of the role of the router, but not a complete sense of the router. In the process of design and actual programming, reference is made to some implementation methods of existing routers, but it is simpler than the router as a commodity.

3 System design and implementation

3. 1 System structure

The system structure is shown in Figure 1.

For a LAN, a wireless data link is a protocol entity that is hidden within a gateway and is transparent to both LAN1 and LAN2. For external purposes, half Gateway 1 and half Gateway 2 is a monolithic gateway that completes IP-related information processing, routing, and internal LAN physical addressing. The IP datagram transfer process between two LANs is shown in Figure 2. Here the gateway mainly solves forwarding decision, delay processing and address conversion.