tailieunhanh - sams teach yourself tcp ip in 24 hours phần 5

Bit mặt nạ mạng con đại diện cho ID mạng địa chỉ IP và ID của các mạng con là 1 bit. Các bit đại diện cho ID lưu trữ địa chỉ IP là 0 bit. Điều này có nghĩa là (với một vài ngoại lệ hiếm và bối rối) 1 bit được tất cả các bên trái và 0 bit được tất cả các bên phải. Bất kỳ octet đầy đủ các số 1 trong mặt nạ mạng con sẽ xuất hiện như | 164 HOUR 9 Getting Connected Because wireless networks are inherently slower and less reliable than cable-based networks the WAP protocols are designed to deliver maximum performance. Some WAP protocols are in a binary format that must be translated to the text-based format of the TCP IP protocols for the WAP device to receive Internet-related data transmissions. A device called a WAP gateway translates the WAP protocol information to an Internet-compatible format see Figure . an Internet-compatible format. FIGURE A WAP gateway translates the WAP protocol information to WAP Protocols Application Transport Lower-Layer Proprietary Wireless Protocols Bearer Internet Network Access The WAP suite includes other related protocols and languages not depicted in Figure such as WMLScript a scripting language and WBMP a bitmap format . More recent WAP standards have proposed greater compatibility with TCP IP and also greater compatibility with XML and HTML through XHTML which will replace WML as the WAP markup language. Mobile IP You might have noticed that devices moving around the world pose a significant problem for delivering responses to Internet requests The Internet addressing system is organized hierarchically with the assumption that the target device is located on the network segment defined through the IP address. Because a mobile device can be anywhere the rules for communicating with the device become much more complicated. To maintain a TCP connection the device must have a constant IP address which means that a roaming device cannot simply use an address assigned by the nearest transmitter. Significantly because this problem relates to Internet addressing it can t be solved strictly at the Network Access layer and requires an From the Library of Athicom Parinayakosol Wireless Networking 165 extension to the Internet layer s IP protocol. The Mobile IP extension is described in RFC 3220. Mobile IP solves the addressing problem by associating a .