Question

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DSL技术主要有以下几种：
1．不对称数字用户线（ADSL） ADSL是在无中继的用户环路网上，使用有负载电话线提供高速数字接入的传输技术。其特点是可在现有的任意双绞线上传输，误码率低，下行数字信道速率为6Mbit/s，上行数字信道可传送144kbit/s或384kbit/s中速数据。
2．高比特率数字用户线（HDSL） HDSL是在无中继的用户环路网上使用无负载电话线提供高速数字接入的传输技术，最早出现于20世纪80年代末，是DSL技术中比较成熟的一种，由于其价格比使用T1线路要低，所以电信公司通常用它通过无中继的非屏蔽双绞线来连接企业用户。 HDSL能够在现有的普通电话双绞铜线（两对或三对）上全双工传输2Mbit/s速率的数字信号，无中继传输距离达3-5km。现在仅利用一对双绞线的HDSL技术也已出现（如以色列Orckit 和Metalink公司的产品）。 HSDL技术最近又有了升级型号----HDSL2，它可单线提供速率为160kbit/s-2.3Mbit/s、距离达4km对称传输，若用2对双绞线，传输速率可翻一番，距离也可提高30％。
3. 甚高速数字用户线（VDSL） 在ADSL基础上发展起来的VDSL，可在很短距离的双绞铜线上传送比ADSL更高速的数据，其最大的下行速率为51-55Mbit/s，传输线长度不超过300m；当下行速率在13Mbit/s以下时，传输距离可达1.5km，上行速率则为1.6Mbit/s以上。 和ADSL相比，VDSL传输带宽更高，而且由于传输距离缩短，所以码间干扰小，数字信号处理技术简化，成本显著降低。它和光纤到路边（FTTC）相结合，可作为无源光网络（PON）的补充，实现宽带综合接入。
4．单线路数字用户线（SDSL） SDSL是对称的DSL技术，与HDSL的区别在于只使用一对铜线。SDSL可以支持各种上、下行通信速率相同的应用。该技术现在已实际使用，运行良好。不过标准尚未最终确立。 5．速率自适应数字用户线（RADSL） RADSL提供的速率范围与ADSL基本相同，也是一种提供高速下行、低速上行并保留原语音服务的数字用户线技术，与ADSL区别在于：RADSL的速率可以根据传输距离动态自适应，当距离增大时，速率降低。

Answer 1

DSL technology as follows:
1. Asymmetric Digital Subscriber Line (ADSL) ADSL is not in the loop on-line users of the relay, the use of load-line to provide access to high-speed digital transmission technology. Can be characterized by any of the existing twisted-pair transmission, low error rate, speed downlink digital channel for 6Mbit / s, up digital channels can be sent 144kbit / s or 384kbit / s speed of data.
2. High bit-rate digital subscriber line (HDSL) HDSL in the relay without the use of on-line subscriber loop no load line to provide access to high-speed digital transmission technology, first appeared in the late 1980s, DSL technology is more mature A, because of its price than the T1 lines to be low, so carriers are usually used relaying it through without the unshielded twisted-pair connections to business users. HDSL in the existing ordinary twisted-pair copper telephone (two or three) on full-duplex transmission 2Mbit / s rate of the digital signal, no relay transmission distance of 3-5km. Now only the use of a pair of twisted-pair HDSL technology has also (Metalink such as Israel and Orckit products). HSDL technology, there has been a recent escalation of models ---- HDSL2, it can provide one-way rate 160kbit/s-2.3Mbit/s, symmetric transmission distance of 4km, with 2 twisted pair, the transmission rate could double Distance can be increased by 30%.
3. Very High Speed Digital Subscriber Line (VDSL) in the ADSL developed on the basis of VDSL, in a very short distance on twisted-pair copper wires to send more than the ADSL high-speed data, the largest of its rate down to 51-55Mbit / s, Transmission line length of not more than 300m; rate in the current line of 13Mbit / s below, the transmission distance up to 1.5km, up rate for 1.6Mbit / s and above. Compared to ADSL and, VDSL higher bandwidth transmission, but also due to shortening the distance, the ISI of small, digital signal processing technology to simplify and reduce costs significantly. And its fiber to the curb (FTTC) combined can be used as passive optical network (PON) supplement to achieve a comprehensive broadband access.
4. Single-line digital subscriber line (SDSL) SDSL is a symmetric DSL technology, HDSL and the only difference is that the use of a pair of copper wires. SDSL can support, the same rate downlink communications applications. The technology is now practical use, good run. However, the final standard has not yet been established. 5. Adaptive rate digital subscriber line (RADSL) RADSL provided by the scope and speed ADSL is basically the same, but also to provide a high-speed downlink and uplink low-speed and voice services to retain the original digital subscriber line technology, ADSL and the difference is: RADSL based on the rate of transmission Adaptive distance dynamic, when the distance increases, the lower the rate.

Answer 2

DSL technologies are as follows:
1. Asymmetric Digital Subscriber Line (ADSL) ADSL is a relay in the absence of the subscriber loop network, the use of the load of high-speed digital telephone lines to provide access to the transmission technology. Its characteristics are available at any of the existing twisted-pair transmission, low error rate, downlink digital channel rate 6Mbit / s, uplink digital channel can send 144kbit / s or 384kbit / s medium-speed data.
2. High bit-rate digital subscriber line (HDSL) HDSL relay in the subscriber loop without the use of no-load-line telephone lines to provide access to high-speed digital transmission technology, first appeared in the 80's at the end of the 20th century, DSL technology is more mature A, because of its price than the use of T1 lines must be low, so telecommunications companies usually use it without relay through unshielded twisted pair to connect business users. HDSL to the existing ordinary telephone twisted-pair copper wires (two pairs or three pairs of) full-duplex transmission on 2Mbit / s rate digital signal, non-relay transmission distance up to 3-5km. Now using only a pair of twisted pair of HDSL technologies have emerged (such as Israel Orckit and Metalink's products). HSDL technology recently upgraded models ---- HDSL2, it can provide one-way rate of 160kbit/s-2.3Mbit/s, symmetrical transmission distance of 4km, if using two pairs of twisted-pair transmission rate can be doubled, Distance can also be increased by 30%.
3. Very high-speed digital subscriber line (VDSL) in ADSL developed on the basis of VDSL, can be in a very short-distance transmission of the twisted-pair copper wire more than the ADSL high-speed data, its largest downlink rate of 51-55Mbit / s, transmission line length of not more than 300m; current line speed in the 13Mbit / s below, the transmission distance up to 1.5km, uplink rate, compared with 1.6Mbit / s and above. And ADSL compared, VDSL higher transmission bandwidth, but also because of transmission distance shortened, so the small inter-symbol interference, digital signal processing technology to simplify and cost significantly reduced. It and the optical fiber to the curb (FTTC) combined can be used as passive optical network (PON) a supplement to the realization of broadband integrated access.
4. Single-line digital subscriber line (SDSL) SDSL is a symmetric DSL technology, with HDSL only difference is that the use of a pair of copper wires. SDSL can support a variety of on the same speed downlink communications applications. The technology is now actually used, to work well. However, the final standard has not yet been established. 5. Rate Adaptive Digital Subscriber Line (RADSL) RADSL rate provided by the scope and basically the same as ADSL, but also provides a high-speed downlink, low-speed uplink and retain the original voice services, digital subscriber line technology, with ADSL The difference is: RADSL transmission rate can dynamic adaptive distance, when the distance increases, the rate decreases.