tailieunhanh - Wireless Data Technologies reference phần 8

Quá trình mã hóa WEP sử dụng một chìa khóa đối xứng và một thuật toán toán học để chuyển đổi dữ liệu vào một định dạng không đọc được gọi là thuật toán mã hóa văn bản. Trong mật mã học, một khóa đối xứng là một giá trị chiều dài thay đổi được sử dụng để mã hóa hoặc giải mã một khối dữ liệu. Bất kỳ thiết bị | 160 WIRELESS DATA NETWORKS address with its home agent using message-exchange defined by Mobile IP. In the registration development the mobile node requests service from a foreign agent - one is present on the link. The home agent or some other router on the home link advertises reachability to the network-prefix of the mobile node s home address thus drawing packets that are intended for the mobile node s home address. The home agent captures these packets and tunnels them to the care-of address that the mobile node registered earlier. At the care-of address the original packet is removed from the tunnel and then sent to the mobile node. In the reverse direction packets sent by the mobile node are routed directly to their target without any requirement for tunneling. The foreign agent serves as a router for all packets created by a visiting mobile node. 9 RFID Introduction Radio Frequency Identification RFID Technology is about to enter a boom phase. Whereas in the past its progress was limited due to the lack of technological costeffective solutions and therefore served largely specialized niche markets recent developments now allow for the remaining hurdles to be overcome. What are RFID Systems RFID stands for radio frequency identification. It is a widely varied collection of technologies for various applications ranging from the high-speed reading of railway containers to applications in retail that can be regarded as a potential successor to the bar-coding technologies in use today. RFID is based around radio or electromagnetic propagation. This has the ability to allow energy to penetrate certain goods and read a tag that is not visible thereby to identify those goods remotely either in the form of an identity code or more simply that something is present EAS . Different frequencies of the radio system result in different reading ranges and properties of the system. RFID systems generally comprise two components namely transponders that are .