tailieunhanh - artech house a professionals guide to data communication in a tcp ip world 2004 phần 10

5 cho thấy rằng bit nhiều gấp hai lần được chứa trong sự bùng nổ tín hiệu. Với mỗi biểu tượng đại diện cho 2 bit, điều này đã được dự kiến . Trong những trường hợp này, các tín hiệu trong hình đạt được một tốc độ bit mà là hai lần tốc độ truyền. Trong những năm 1920, Harold Nyquist | 228 Glossary Outside plant In the public telephone network all wiring and facilities between the customers premises and the central office. Packet A sequence of as many as a few thousand bits. Some are users data the message and some are control overhead data. In the control data is destination information that guides the packet across a network. Passive OPEN function call See listening mode. Packet Layer Protocol In the packet layer or layer divides the user s data into fixed length segments and adds a 3-byte header. Paired cable Cable that has twisted pairs as conductors. Passband signal A complex signal produced by using a baseband signal to modify a property of another signal called the carrier signal . The energy of the passband signal occupies a range the passband that encompasses the frequency of the carrier signal or is contiguous with it. The sideband components of the passband signal carry the information contained in the baseband signal. A passband signal may be moved in the frequency plane by changing the frequency of the carrier signal. PCF interframe space See point coordination function interframe space. Peer-to-peer communication Communication between same layers of sending and receiving protocol stacks to set up and manage transfer of data. Permanent virtual circuit A virtual connection that is permanently assigned between two stations. Poll final bit In LAP-D the first bit of the second byte of the control field. In command frames it is known as the poll P bit. When set to 1 it identifies this frame as requiring a response from the receiver. When set to 0 a response is not required. In response frames the P F bit is known as the final F bit. When set to 0 it identifies this frame as one of a continuing sequence. When set to 1 it is the final frame in the sequence. Phase modulation The phase of the carrier is varied based on the value of the modulating signal. Phase-shift keying Digital modulating technique in which the carrier signal may .