Research Of Techniques On Wireless Access To Internet

Today, both of the wireless communications and Internet are growing rapidly, it is two sparkling spots in current information technology area. The main goal of this thesis is to design a wireless networks with various frequencies access to TCP/IP-based networks, and to study the key techniques involved in these wireless access networks.Firstly, the sketch to a wireless communication network system is presented, which includes different frequencies like HF, VHF and satellite channels. According to the characteristics of HF channel, the compatibility between HF networks and Internet is studied, and a new network protocols is figured about the HF network access to Internet. A LLC frame structure with alterable length is put forward, a protocol of selective repeat SW-ARQ is proposed. Furthermore, a HF agent protocol is proposed, which adopts I-TCP, SACK and the link layer protocol, the high bit error rate and the long delay would be overcome in this way.At the same time, the protocol stack of CDMA-based Internet access system is described. Based on snoop protocol, a protocol with delay DUPACK is presented, which adopts the limited recovery link layer scheme. It is fit for CDMA based cellular network to access to Internet. The analysis shows, TCP sender can be shielded from errors in mobile communication system with this novel protocol. Another advantage of this novel protocol is that base station doesn't need to check and remind the state of each TCP connection, so it is more likely to take place of the Snoop in the applications with security requirements. Performance measurements show that this scheme can often perform comparable to the Snoop.Generally, user's mobility means their access point to network may change. On the basis of MobileIP model, the traffic overhead to fix network for supporting user mobility is analyzed. At the same time, the mobile agent advertisement rate is studied, which trade off between the available bandwidth for data and the accessible period, the registration lifetime is discussed. Security problems brought by user's mobility is considered also. Finally, a protocol of public-key certificate-based security is proposed, it guarantees the end-to-end mutual authentication. it can also guarantees the privacy of communicating parties against the outsiders.