Bandwith Issues

xDSL, present and future. By IcePick [email protected] email me if you use this. 26-April-1998 Since the birth of the World Wide Web, bandwidth has been a concern. Computer users surfing the Web are always in need of more bandwidth. In an effort to attract more surfers, content providers are jazzing up their pages using more multimedia than ever. The new generation of multimedia-laced Web pages contain bigger pictures and have embedded sound files; all these items take more bandwidth to download. The growth of the World Wide Web and its large content pages has led many computer users to seek faster ways of connecting than through analog modems. ADSL and the other products in the xDSL family are leading the way to faster Internet connections. The main advantage of xDSL is that the service is provided using digital signals as opposed to the analog signals used with regular voice modems. Digital circuits use signal levels or changes in signal levels to represent binary 1s and 0s. Digital signals are less susceptible to line noise then analog signals. Circuits based on digital signals can be manipulated using Digital Signal Processors, which have the ability to filter out line noise and other undesirable properties of a circuit. Analog signal transmissions manipulate properties of a carrier signal using either one or a combination of the following to convey data: amplitude, frequency, and phase (Cisco NA). xDSL is a family of products and standards that allows telephone companies to use existing copper-based POTS (plain old telephone service) lines to bring high speed digital services to consumers (Strauch 1997). The x in xDSL stands for one of many implementations of the family of products known as Digital Subscriber Line technology (UUNET 1997). Except for the relatively slow analog connection from the user\'s computer and the ISP\'s (Internet Service Provider) modems, the Internet is based on high speed digital circuits. The influx of slow connections from users\' computers and ISP modems creates a bottle-neck. xDSL is designed to eliminate the existing bottle- neck (TeleChoice DSL White Paper 1997). "DSL can literally transform the existing public information network from one limited to voice, text, and low resolution graphics to a powerful, ubiquitous system capable of bringing multimedia, including full motion video, to everyone\'s home this century" (ADSL Tutorial 1998). The different DSL products include High bit rate Digital Subscriber Line (HDSL); Asymmetric Digital Subscriber Line (ADSL); Universal Asymmetric Digital Subscriber Line, (UADSL); Single-line High bit rate Digital Subscriber Line (S-HDSL); ISDN-based Digital Subscriber Line (IDSL); Rate Adaptive Digital Subscriber Line, (RADSL); and Very high bit rate Digital Subscriber Line (VDSL). S-HDSL is also known as SDSL, Symmetric Digital Subscriber Line (UUNET 1996). Many differences exist between the members of the xDSL family and some differences exist among companies on how to implement individual types of xDSL. Advanced digital signal processing is used with xDSL to increase the throughput and signal quality (ADSL Tutorial 1997). While not all members of the xDSL family exist in any form save on paper, HDSL is a proven product with years of service. It is estimated that there are over 200,000 HDSL installations (Strauch 1997). Bellcore developed HDSL as a way of establishing T-1/E-1 links between the PSTN (Public Switched Telephone Network) and the customer\'s premises (PairGain 1996). HDSL is a symmetric system using two pairs of copper cables. HDSL can deliver between 512Kbps and 2.048Mbs (Scheuble NA). HDSL links can be established over spans 3.6 km using 24-gauge wire. Longer distances can be reached using heavier gauge copper (PairGain 1996). Due to the successful track history and ease of installation HDSL is well suited for use in PBX systems, campus-based networks, and digital loop services (Aber 1997). SDSL uses only one pair of copper wires and can be used to transmit data 384Kbps at 18,000 feet and can approach T-1 speeds of 1.544Mbs with loops of less than 10,000 feet (Cisco 1998). ADSL uses one pair of copper lines and operates in the frequency range of 4Khz to 2.2Mhz (ADSL Forum FAQ 1997). "ADSL provides asymmetric transfer rates of 1.5Mbs to 9Mbps downstream, 15Kbps to 640Kbps upstream" (Scheuble NA). The asymmetric nature of ADSL is provided by the fact that the upstream and downstream transfer rates are different. This asymmetric setup complements the