The DqDb forms the basis of the IEEE 802. 6 standard for MANs DQDB is descended from the earlier QPSX, which was developed at the University of Western Australia and Telecom Australia. DQDB uses two unidirec tional linear fiber-optic buses. Stations are connected to both buses. Through the clever use of counters the DQDB protocol provides approximate first in, first out(FIFO) service to arriving packets. There are no collisions in DQDB, so utilization can approach 100%. Bus speeds of 150 Mbps are possible. 92.4 Wide Area Networks Data are generally transmitted over long distances by wide area packet networks. These networks generally lease telephone lines from telecommunications carriers that are used to carry data exclusively Packet switching technology was first used on a large scale in the arpanet beginning in the 1960s. The Internet(which replaced the earlier ARPANET)serves to connect universities, industrial and government research centers, and private users One problem area unique to wide area packet networks is that of routing. Unlike the previously mentioned networks, there are usually multiple routes available between sources and destinations. Distributed routing algorithms have been developed that route based on current traffic conditio 92.5 The future The future is likely to see an increase in data rates as fiber-optic cables are widely deployed. This will spur the development of faster switching nodes through the use of parallel processing and VLSI implementation. Protocols will have to be simplified to increase processor throughput. New forms of traffic such as video and graphics will become more important. Computer networks will proliferate throughout the world, making possible the ubiquitous transport of data between any two points. These networks are likely to consist of both private networks and new service offerings from telecommunications companies. Defining Terms Area networks: LAN, within single building: MAN, metropolitan-sized region; WAN, national/international Coaxial cable: A shielded cable that conducts electrical signals and is used in bus-type local area networks. Fiber-optic cable: a glass fiber cable that conducts light signals and can be used in token ring local area networks and metropolitan area networks. Fiber optics can provide higher data rates than coaxial cable. They are also immune to electrical interference. IEEE standards: 802.3, CSMA/CD bus; 802.4, token bus; 802.5, token ring; 802.6, DQDB MAN. Related Topics 72. 3 Local-Area Networks .75.3 Stochastic Processes References U. Black, Data Networks: Concepts, Theory and Practice, Englewood Cliffs, N.J. Prentice-Hall, 1989 M. De Prycker, Asynchronous Transfer Mode: Solution for Broadband ISDN, New York: Simon and Schuster, 1991 A. De Simone and S Nanda,Wireless data: Systems, standards, services, Wireless Networks, 1(3): 241-253, 1995 N. J. Muller, Wireless Data Networking, Boston, Mass: Artech House, 1995 L. Peterson and B Davie, Computer Networks: A System Approach, San Francisco, Calif Morgan Kaufman, 1995 T G. Robertazzi, Performance Evaluation of High Speed Switching Fabrics and Networks: ATM, Broadband ISDN and MAN Technolgoy, Piscataway N.J. IEEE Press, 1993 P Scherer, The 100 Mbps Ethernet Standard In Distinguished Lecture Series(IX)(videotape), Stanford, Calif Univ Video Communications, 1994 e 2000 by CRC Press LLC© 2000 by CRC Press LLC DQDB The DQDB forms the basis of the IEEE 802.6 standard for MANs. DQDB is descended from the earlier QPSX, which was developed at the University of Western Australia and Telecom Australia. DQDB uses two unidirec￾tional linear fiber-optic buses. Stations are connected to both buses. Through the clever use of counters the DQDB protocol provides approximate first in, first out (FIFO) service to arriving packets. There are no collisions in DQDB, so utilization can approach 100%. Bus speeds of 150 Mbps are possible. 92.4 Wide Area Networks Data are generally transmitted over long distances by wide area packet networks. These networks generally lease telephone lines from telecommunications carriers that are used to carry data exclusively.Packet switching technology was first used on a large scale in the ARPANET beginning in the 1960s. The Internet (which replaced the earlier ARPANET) serves to connect universities, industrial and government research centers, and private users. One problem area unique to wide area packet networks is that of routing. Unlike the previously mentioned networks, there are usually multiple routes available between sources and destinations. Distributed routing algorithms have been developed that route based on current traffic conditions. 92.5 The Future The future is likely to see an increase in data rates as fiber-optic cables are widely deployed. This will spur the development of faster switching nodes through the use of parallel processing and VLSI implementation. Protocols will have to be simplified to increase processor throughput. New forms of traffic such as video and graphics will become more important. Computer networks will proliferate throughout the world, making possible the ubiquitous transport of data between any two points. These networks are likely to consist of both private networks and new service offerings from telecommunications companies. Defining Terms Area networks: LAN, within single building; MAN, metropolitan-sized region; WAN, national/international region. Coaxial cable: A shielded cable that conducts electrical signals and is used in bus-type local area networks. Fiber-optic cable: A glass fiber cable that conducts light signals and can be used in token ring local area networks and metropolitan area networks. Fiber optics can provide higher data rates than coaxial cable. They are also immune to electrical interference. IEEE standards: 802.3, CSMA/CD bus; 802.4, token bus; 802.5, token ring; 802.6, DQDB MAN. Related Topics 72.3 Local-Area Networks • 75.3 Stochastic Processes References U. Black, Data Networks: Concepts, Theory and Practice, Englewood Cliffs, N.J.: Prentice-Hall, 1989. M. De Prycker, Asynchronous Transfer Mode: Solution for Broadband ISDN, New York: Simon and Schuster, 1991. A. De Simone and S. Nanda, “Wireless data: Systems, standards, services,” Wireless Networks, 1(3):241–253, 1995. N. J. Muller, Wireless Data Networking, Boston, Mass: Artech House, 1995. L. Peterson and B. Davie, Computer Networks: A System Approach, San Francisco, Calif.: Morgan Kaufman, 1995. T. G. Robertazzi, Performance Evaluation of High Speed Switching Fabrics and Networks: ATM, Broadband ISDN and MAN Technolgoy, Piscataway N.J.: IEEE Press, 1993. P. Scherer, The 100 Mbps Ethernet Standard. In Distinguished Lecture Series (IX) (videotape), Stanford, Calif.: Univ. Video Communications, 1994