什么是DSL？英文版
Digital Subscriber Line
Digital Subscriber Line, or DSL, is a family of technologies that provide digital data transmission over the wires used in the "last mile" of a local telephone network. Typically, the download speed of DSL ranges from 128 kilobits per second (Kbps) to 24,000 Kbps depending on DSL technology and service level implemented. Upload speed is lower than download speed for ADSL and symmetrical for SDSL.
History
The origin of Digital Subscriber Line technology dates back to 1988, when engineers at Bellcore (now Telcordia Technologies) devised a way to carry a digital signal over the unused frequency spectrum available on the twisted pair cables running between the telephone company's central office and the customer premises. Implementation of DSL could permit an ordinary telephone line to provide digital communication without interfering with voice services. However, incumbent local exchange carriers (ILEC) were not enthusiastic about DSL, since it was not as profitable as installing a second phone line for consumers who preferred simultaneous dial-up internet and voice connections, and the broadband data connection would cannibalize existing ISDN customers. This changed in the late 1990s when cable television companies began marketing broadband Internet access. Realizing that most consumers would prefer broadband Internet to dial-up Internet, ILECs rushed out the DSL technology, which they had delayed implementing, as an attempt to win market share from the broadband Internet access offered by cable television operators.
DSL is the principal competition of cable modems for providing high speed Internet access to home consumers in Europe and North America. Older ADSL standards can deliver 8 Mbit/s over about 1? miles (2 km) of unshielded twisted pair copper wire. The latest standard, ADSL2+, can deliver up to 24 Mbit/s, depending on the distance from the DSLAM.Some customers, however, are located farther than 1? miles (2 km) from the central office, which significantly reduces the amount of bandwidth available (thereby reducing the data rate) on the wires.
Operation
The local loop of the Public Switched Telephone Network was initially designed to carry POTS voice communication and signaling, since the concept of data communications as we know it today did not exist. For reasons of economy, the phone system nominally passes audio between 300 and 3,400 Hz, which is regarded as the range required for human speech to be clearly intelligible. This is known as commercial bandwidth. Dial-up services using modems are constrained by the Shannon capacity of the POTS channel.
At the local telephone exchange (UK terminology) or central office (US terminology) the speech is generally digitized into a 64 kbit/s data stream in the form of an 8 bit signal using a sampling rate of 8,000 Hz, therefore – according to the Nyquist theorem – any signal above 4,000 Hz is not passed by the phone network (and has to be blocked by a filter to prevent aliasing effects).
The local loop connecting the telephone exchange to most subscribers is capable of carrying frequencies well beyond the 3.4 kHz upper limit of POTS. Depending on the length and quality of the loop, the upper limit can be tens of megahertz. DSL takes advantage of this unused bandwidth of the local loop by creating 4312.5 Hz wide channels starting between 10 and 100 kHz, depending on how the system is configured. Allocation of channels continues at higher and higher frequencies (up to 1.1 MHz for ADSL) until new channels are deemed unusable. Each channel is evaluated for usability in much the same way an analog modem would on a POTS connection. More usable channels equates to more available bandwidth, which is why distance and line quality are a factor. The pool of usable channels is then split into two groups for upstream and downstream traffic based on a preconfigured ratio. Once the channel groups have been established, the individual channels are bonded into a pair of virtual circuits, one in each direction. Like analog modems, DSL transceivers constantly monitor the quality of each channel and will add or remove them from service depending on whether or not they are usable.
The commercial success of DSL and similar technologies largely reflects the fact that in recent decades, while electronics have been getting faster and cheaper, the cost of digging trenches in the ground for new cables (copper or fiber) remains expensive. All flavors of DSL employ highly complex digital signal processing algorithms to overcome the inherent limitations of the existing twisted pair wires. Not long ago, the cost of such signal processing would have been prohibitive but because of VLSI technology, the cost of installing DSL on an existing local loop, with a DSLAM at one end and a DSL modem at the other end is orders of magnitude less than would be the cost of installing a new, high-bandwidth fiber-optic cable over the same route and distance.
Most residential and small-office DSL implementations reserve low frequencies for POTS service, so that with suitable filters and/or splitters the existing voice service continues to operate independent of the DSL service. Thus POTS-based communications, including fax machines and analog modems, can share the wires with DSL. Only one DSL modem can use the subscriber line at a time. The standard way to let multiple computers share a DSL connection is to use a router that establishes a connection between the DSL modem and a local Ethernet or Wi-Fi network on the customer's premises.
Once upstream and downstream channels are established, they are used to connect the subscriber to a service such as an Internet service provider.
Equipment
The subscriber end of the connection consists of a DSL modem. This converts data from the digital signals used by computers into a voltage signal of a suitable frequency range which is then applied to the phone line.
In the early days of DSL, installation required a technician to visit the premises. A "splitter" was installed near the demarcation point, from which a dedicated data line was installed. Today, many DSL vendors offer a self-install option, in which they ship equipment and instructions to the customer. In this case, since no changes are made to the cable plant on the customer premises, all the phone wires are carrying both POTS and DSL signal frequencies; therefore the customer generally needs to plug a DSL filter into each telephone outlet. However, this can sometimes cause degradation of the DSL signal (especially if more than 5 analogue devices are connected to the line) because the DSL signal is present on all telephone wiring in the building. A way to circumvent this is to install one filter upstream from all telephone jacks in the building, except for the jack to which the DSL modem will be connected. Since this requires wiring changes by the customer and may not work on some (poorly designed) household telephone wiring, it is rarely done. It is usually much easier to install filters at each telephone jack that is in use.
At the exchange a digital subscriber line access multiplexer (DSLAM) terminates the DSL circuits and aggregates them, where they are handed off onto other networking transports. It also separates out the voice component.
Protocols and configurations
Many DSL technologies implement an ATM layer over the low-level bitstream layer to enable the adaptation of a number of different technologies over the same link.
DSL implementations may create bridged or routed networks. In a bridged configuration, the group of subscriber computers effectively connect into a single subnet. The earliest implementations used DHCP to provide network details such as the IP address to the subscriber equipment, with authentication via MAC address or an assigned host name. Later implementations often use PPP over Ethernet or ATM (PPPoE or PPPoA), while authenticating with a userid and password and using PPP mechanisms to provide network details.
DSL also has contention ratios which need to be taken into consideration when deciding between broadband technologies
DSL technologies
The line length limitations from telephone exchange to subscriber are more restrictive for higher data transmission rates. Technologies such as VDSL provide very high speed, short-range links as a method of delivering "triple play" services (typically implemented in fiber to the curb network architectures).
Example DSL technologies (sometimes called xDSL) include:
High-bit-rate Digital Subscriber Line (HDSL), covered in this article
Symmetric Digital Subscriber Line (SDSL), a standardised version of HDSL
Asymmetric Digital Subscriber Line (ADSL), a version of DSL with a slower upload speed
Rate-Adaptive Digital Subscriber Line (RADSL)
Very-high-bit-rate Digital Subscriber Line (VDSL)
Very-high-bit-rate Digital Subscriber Line 2 (VDSL2), an improved version of VDSL
G. Symmetric High-speed Digital Subscriber Line (G.SHDSL), a standardised replacement for early proprietary SDSL by the International Telecommunication Union Telecommunication Standardization Sector
Powerline Digital Subscriber Line (PDSL), a high speed powerline communications solution which modulates high speed data onto existing electricity distribution infrastructure
Transmission methods
Transmission methods vary by market, region, carrier, and equipment.
CAP: Carrierless Amplitude Phase Modulation - deprecated in 1996
DMT: discrete multitone modulation, otherwise known as OFDM
OFDM: Orthogonal frequency-division multiplexing
數(shù)字用戶線路（Digital Subscriber Line或簡(jiǎn)稱DSL），是通過銅線或者本地電話網(wǎng)提供數(shù)字連接的一種技術(shù)。它的歷史要追溯到1988年，貝爾實(shí)驗(yàn)室一位工程師設(shè)計(jì)了一種方法可以讓數(shù)字信號(hào)加載到電話線路未使用頻段，這就實(shí)現(xiàn)了不影響話音服務(wù)的前提下在普通電話線上提供數(shù)據(jù)通信。但是貝爾的管理層對(duì)這個(gè)并不熱心, 因?yàn)槿绻脩舭惭b兩條線路會(huì)帶來更多的利潤(rùn)。這一狀況直到1990年代晚期有線電視公司開始推銷寬帶互聯(lián)網(wǎng)訪問時(shí)才得到改善。當(dāng)意識(shí)到大多數(shù)用戶絕對(duì)會(huì)放棄安裝兩條電話線訪問互聯(lián)網(wǎng)，貝爾公司才搬出他們已經(jīng)討論了10年的DSL技術(shù)，來爭(zhēng)奪有線電視網(wǎng)絡(luò)公司的寬帶市場(chǎng)份額。
到2005年, DSL技術(shù)是線纜調(diào)制解調(diào)器向歐洲和北美的家庭用戶的提供寬帶接入主要競(jìng)爭(zhēng)對(duì)手。
工作原理
電話系統(tǒng)設(shè)計(jì)之初，主要用來傳送話音呼叫，出于經(jīng)濟(jì)的考慮，電話系統(tǒng)設(shè)計(jì)傳送頻率范圍在300Hz到3.4kHz范圍的信號(hào)（盡管人的話音可以到15kHz,但是這個(gè)范圍內(nèi)還是很容易辨別對(duì)方的）。
然而本地電話網(wǎng)的到最終用戶的銅纜實(shí)際上可以提供更高的帶寬，至少從最低頻率到200-800kHz不等，這取決于電路質(zhì)量和設(shè)備的復(fù)雜度（一般認(rèn)為到最終用戶分線器之間接頭越少越有利于提高帶寬，線路傳輸路過的環(huán)境，電子干擾越小越有益于提高線路帶寬）。
DSL服務(wù)通過利用電話線的附加頻段成功克服了在話音頻帶上傳送大量數(shù)據(jù)的難題（參看香農(nóng)定理）。
DSL服務(wù)通常保留0.3-4kHz這個(gè)范圍的頻段給話音服務(wù)，也就是所謂的普通老式電話業(yè)務(wù)（{lang|en|POTS}}）使用的頻段, 使用這個(gè)范圍以外的頻率傳送數(shù)據(jù)。
DSL連接在用戶設(shè)備DSL調(diào)制解調(diào)器和電話交換機(jī)之間建立, 然后交換機(jī)通過一些其他的協(xié)議與用戶真正要連接的（典型的）ISP建立連接。這不同于普通的公共電話網(wǎng)與用戶端到端的電話連接 。如果用戶到交換機(jī)距離超過5.5公里，服務(wù)質(zhì)量會(huì)因?yàn)楦蓴_急劇下降。
設(shè)備
用戶終端設(shè)備是DSL調(diào)制解調(diào)器。它轉(zhuǎn)換二進(jìn)制數(shù)據(jù)到數(shù)字電脈沖，使得信號(hào)在數(shù)字音頻流的頻段內(nèi)傳輸。
另外如果用戶早同一根線路上使用老式電話，還需要加裝一個(gè)被動(dòng)電子濾波器（很多叫法，"濾波器"，"微分器"或者"分路器"）（可能還有助于改善DSL終端信號(hào)抑止回聲信號(hào)）。這樣就能保證DSL調(diào)制解調(diào)器和電話只接受他們?cè)O(shè)計(jì)使用的信號(hào)。如果使用"wires-only"服務(wù)，用戶可以把濾波器插入一個(gè)現(xiàn)有的電話插槽，或者DSL運(yùn)營(yíng)商可能安裝它。
在交換局端使用數(shù)字用戶線路訪問復(fù)用器（DSLAM）將DSL電路上的數(shù)據(jù)匯聚然后轉(zhuǎn)發(fā)到其他的網(wǎng)絡(luò)。它還能分離出語音部分。
協(xié)議和配置
很多DSL技術(shù)在低水平比特流的ATM層實(shí)現(xiàn)，以保證不同的技術(shù)能夠在相同的鏈路上實(shí)現(xiàn)。
DSL設(shè)備可以創(chuàng)建網(wǎng)橋或者路由網(wǎng)絡(luò)，在網(wǎng)橋模式，一組用戶的計(jì)算機(jī)可以方便的連接到一個(gè)子網(wǎng)。早期的設(shè)備使用DHCP服務(wù)來分配提供一些配置細(xì)節(jié)例如網(wǎng)卡的IP地址，基于MAC地址的認(rèn)證或者分配主機(jī)名。 后來的的設(shè)備一般使用PPPoE（以太網(wǎng)上的PPP）或者PPPoA（ATM網(wǎng)上的點(diǎn)到點(diǎn)協(xié)議), 驗(yàn)證的時(shí)候使用用戶名和密碼，然后使用PPP原理去分配網(wǎng)絡(luò)配置（IP地址，子網(wǎng)掩碼，網(wǎng)關(guān)，DNS等）
DSL技術(shù)
可達(dá)范圍(從電話交換中心到用戶的線路長(zhǎng)度)與數(shù)據(jù)速率成反比, 象VDSL這樣的技術(shù)只能提供短距離鏈路（典型的就是FTTC－光線到路邊）。
使用DSL技術(shù)的技術(shù)(有時(shí)也叫 xDSL)有:
ADSL（非對(duì)稱用戶數(shù)字線）
HDSL（高速用戶數(shù)字線）
RADSL（速率自適應(yīng)數(shù)字用戶線路）
SDSL（對(duì)稱數(shù)字用戶線路, 標(biāo)準(zhǔn)版HDSL）
VDSL（超高速用戶數(shù)字線）
G.SHDSL（ITU-T標(biāo)準(zhǔn)替換早期SDSL）
Digital Subscriber Line
Digital Subscriber Line, or DSL, is a family of technologies that provide digital data transmission over the wires used in the "last mile" of a local telephone network. Typically, the download speed of DSL ranges from 128 kilobits per second (Kbps) to 24,000 Kbps depending on DSL technology and service level implemented. Upload speed is lower than download speed for ADSL and symmetrical for SDSL.
History
The origin of Digital Subscriber Line technology dates back to 1988, when engineers at Bellcore (now Telcordia Technologies) devised a way to carry a digital signal over the unused frequency spectrum available on the twisted pair cables running between the telephone company's central office and the customer premises. Implementation of DSL could permit an ordinary telephone line to provide digital communication without interfering with voice services. However, incumbent local exchange carriers (ILEC) were not enthusiastic about DSL, since it was not as profitable as installing a second phone line for consumers who preferred simultaneous dial-up internet and voice connections, and the broadband data connection would cannibalize existing ISDN customers. This changed in the late 1990s when cable television companies began marketing broadband Internet access. Realizing that most consumers would prefer broadband Internet to dial-up Internet, ILECs rushed out the DSL technology, which they had delayed implementing, as an attempt to win market share from the broadband Internet access offered by cable television operators.
DSL is the principal competition of cable modems for providing high speed Internet access to home consumers in Europe and North America. Older ADSL standards can deliver 8 Mbit/s over about 1? miles (2 km) of unshielded twisted pair copper wire. The latest standard, ADSL2+, can deliver up to 24 Mbit/s, depending on the distance from the DSLAM.Some customers, however, are located farther than 1? miles (2 km) from the central office, which significantly reduces the amount of bandwidth available (thereby reducing the data rate) on the wires.
Operation
The local loop of the Public Switched Telephone Network was initially designed to carry POTS voice communication and signaling, since the concept of data communications as we know it today did not exist. For reasons of economy, the phone system nominally passes audio between 300 and 3,400 Hz, which is regarded as the range required for human speech to be clearly intelligible. This is known as commercial bandwidth. Dial-up services using modems are constrained by the Shannon capacity of the POTS channel.
At the local telephone exchange (UK terminology) or central office (US terminology) the speech is generally digitized into a 64 kbit/s data stream in the form of an 8 bit signal using a sampling rate of 8,000 Hz, therefore – according to the Nyquist theorem – any signal above 4,000 Hz is not passed by the phone network (and has to be blocked by a filter to prevent aliasing effects).
The local loop connecting the telephone exchange to most subscribers is capable of carrying frequencies well beyond the 3.4 kHz upper limit of POTS. Depending on the length and quality of the loop, the upper limit can be tens of megahertz. DSL takes advantage of this unused bandwidth of the local loop by creating 4312.5 Hz wide channels starting between 10 and 100 kHz, depending on how the system is configured. Allocation of channels continues at higher and higher frequencies (up to 1.1 MHz for ADSL) until new channels are deemed unusable. Each channel is evaluated for usability in much the same way an analog modem would on a POTS connection. More usable channels equates to more available bandwidth, which is why distance and line quality are a factor. The pool of usable channels is then split into two groups for upstream and downstream traffic based on a preconfigured ratio. Once the channel groups have been established, the individual channels are bonded into a pair of virtual circuits, one in each direction. Like analog modems, DSL transceivers constantly monitor the quality of each channel and will add or remove them from service depending on whether or not they are usable.
The commercial success of DSL and similar technologies largely reflects the fact that in recent decades, while electronics have been getting faster and cheaper, the cost of digging trenches in the ground for new cables (copper or fiber) remains expensive. All flavors of DSL employ highly complex digital signal processing algorithms to overcome the inherent limitations of the existing twisted pair wires. Not long ago, the cost of such signal processing would have been prohibitive but because of VLSI technology, the cost of installing DSL on an existing local loop, with a DSLAM at one end and a DSL modem at the other end is orders of magnitude less than would be the cost of installing a new, high-bandwidth fiber-optic cable over the same route and distance.
Most residential and small-office DSL implementations reserve low frequencies for POTS service, so that with suitable filters and/or splitters the existing voice service continues to operate independent of the DSL service. Thus POTS-based communications, including fax machines and analog modems, can share the wires with DSL. Only one DSL modem can use the subscriber line at a time. The standard way to let multiple computers share a DSL connection is to use a router that establishes a connection between the DSL modem and a local Ethernet or Wi-Fi network on the customer's premises.
Once upstream and downstream channels are established, they are used to connect the subscriber to a service such as an Internet service provider.
Equipment
The subscriber end of the connection consists of a DSL modem. This converts data from the digital signals used by computers into a voltage signal of a suitable frequency range which is then applied to the phone line.
In the early days of DSL, installation required a technician to visit the premises. A "splitter" was installed near the demarcation point, from which a dedicated data line was installed. Today, many DSL vendors offer a self-install option, in which they ship equipment and instructions to the customer. In this case, since no changes are made to the cable plant on the customer premises, all the phone wires are carrying both POTS and DSL signal frequencies; therefore the customer generally needs to plug a DSL filter into each telephone outlet. However, this can sometimes cause degradation of the DSL signal (especially if more than 5 analogue devices are connected to the line) because the DSL signal is present on all telephone wiring in the building. A way to circumvent this is to install one filter upstream from all telephone jacks in the building, except for the jack to which the DSL modem will be connected. Since this requires wiring changes by the customer and may not work on some (poorly designed) household telephone wiring, it is rarely done. It is usually much easier to install filters at each telephone jack that is in use.
At the exchange a digital subscriber line access multiplexer (DSLAM) terminates the DSL circuits and aggregates them, where they are handed off onto other networking transports. It also separates out the voice component.
Protocols and configurations
Many DSL technologies implement an ATM layer over the low-level bitstream layer to enable the adaptation of a number of different technologies over the same link.
DSL implementations may create bridged or routed networks. In a bridged configuration, the group of subscriber computers effectively connect into a single subnet. The earliest implementations used DHCP to provide network details such as the IP address to the subscriber equipment, with authentication via MAC address or an assigned host name. Later implementations often use PPP over Ethernet or ATM (PPPoE or PPPoA), while authenticating with a userid and password and using PPP mechanisms to provide network details.
DSL also has contention ratios which need to be taken into consideration when deciding between broadband technologies
DSL technologies
The line length limitations from telephone exchange to subscriber are more restrictive for higher data transmission rates. Technologies such as VDSL provide very high speed, short-range links as a method of delivering "triple play" services (typically implemented in fiber to the curb network architectures).
Example DSL technologies (sometimes called xDSL) include:
High-bit-rate Digital Subscriber Line (HDSL), covered in this article
Symmetric Digital Subscriber Line (SDSL), a standardised version of HDSL
Asymmetric Digital Subscriber Line (ADSL), a version of DSL with a slower upload speed
Rate-Adaptive Digital Subscriber Line (RADSL)
Very-high-bit-rate Digital Subscriber Line (VDSL)
Very-high-bit-rate Digital Subscriber Line 2 (VDSL2), an improved version of VDSL
G. Symmetric High-speed Digital Subscriber Line (G.SHDSL), a standardised replacement for early proprietary SDSL by the International Telecommunication Union Telecommunication Standardization Sector
Powerline Digital Subscriber Line (PDSL), a high speed powerline communications solution which modulates high speed data onto existing electricity distribution infrastructure
Transmission methods
Transmission methods vary by market, region, carrier, and equipment.
CAP: Carrierless Amplitude Phase Modulation - deprecated in 1996
DMT: discrete multitone modulation, otherwise known as OFDM
OFDM: Orthogonal frequency-division multiplexing
數(shù)字用戶線路（Digital Subscriber Line或簡(jiǎn)稱DSL），是通過銅線或者本地電話網(wǎng)提供數(shù)字連接的一種技術(shù)。它的歷史要追溯到1988年，貝爾實(shí)驗(yàn)室一位工程師設(shè)計(jì)了一種方法可以讓數(shù)字信號(hào)加載到電話線路未使用頻段，這就實(shí)現(xiàn)了不影響話音服務(wù)的前提下在普通電話線上提供數(shù)據(jù)通信。但是貝爾的管理層對(duì)這個(gè)并不熱心, 因?yàn)槿绻脩舭惭b兩條線路會(huì)帶來更多的利潤(rùn)。這一狀況直到1990年代晚期有線電視公司開始推銷寬帶互聯(lián)網(wǎng)訪問時(shí)才得到改善。當(dāng)意識(shí)到大多數(shù)用戶絕對(duì)會(huì)放棄安裝兩條電話線訪問互聯(lián)網(wǎng)，貝爾公司才搬出他們已經(jīng)討論了10年的DSL技術(shù)，來爭(zhēng)奪有線電視網(wǎng)絡(luò)公司的寬帶市場(chǎng)份額。
到2005年, DSL技術(shù)是線纜調(diào)制解調(diào)器向歐洲和北美的家庭用戶的提供寬帶接入主要競(jìng)爭(zhēng)對(duì)手。
工作原理
電話系統(tǒng)設(shè)計(jì)之初，主要用來傳送話音呼叫，出于經(jīng)濟(jì)的考慮，電話系統(tǒng)設(shè)計(jì)傳送頻率范圍在300Hz到3.4kHz范圍的信號(hào)（盡管人的話音可以到15kHz,但是這個(gè)范圍內(nèi)還是很容易辨別對(duì)方的）。
然而本地電話網(wǎng)的到最終用戶的銅纜實(shí)際上可以提供更高的帶寬，至少從最低頻率到200-800kHz不等，這取決于電路質(zhì)量和設(shè)備的復(fù)雜度（一般認(rèn)為到最終用戶分線器之間接頭越少越有利于提高帶寬，線路傳輸路過的環(huán)境，電子干擾越小越有益于提高線路帶寬）。
DSL服務(wù)通過利用電話線的附加頻段成功克服了在話音頻帶上傳送大量數(shù)據(jù)的難題（參看香農(nóng)定理）。
DSL服務(wù)通常保留0.3-4kHz這個(gè)范圍的頻段給話音服務(wù)，也就是所謂的普通老式電話業(yè)務(wù)（{lang|en|POTS}}）使用的頻段, 使用這個(gè)范圍以外的頻率傳送數(shù)據(jù)。
DSL連接在用戶設(shè)備DSL調(diào)制解調(diào)器和電話交換機(jī)之間建立, 然后交換機(jī)通過一些其他的協(xié)議與用戶真正要連接的（典型的）ISP建立連接。這不同于普通的公共電話網(wǎng)與用戶端到端的電話連接 。如果用戶到交換機(jī)距離超過5.5公里，服務(wù)質(zhì)量會(huì)因?yàn)楦蓴_急劇下降。
設(shè)備
用戶終端設(shè)備是DSL調(diào)制解調(diào)器。它轉(zhuǎn)換二進(jìn)制數(shù)據(jù)到數(shù)字電脈沖，使得信號(hào)在數(shù)字音頻流的頻段內(nèi)傳輸。
另外如果用戶早同一根線路上使用老式電話，還需要加裝一個(gè)被動(dòng)電子濾波器（很多叫法，"濾波器"，"微分器"或者"分路器"）（可能還有助于改善DSL終端信號(hào)抑止回聲信號(hào)）。這樣就能保證DSL調(diào)制解調(diào)器和電話只接受他們?cè)O(shè)計(jì)使用的信號(hào)。如果使用"wires-only"服務(wù)，用戶可以把濾波器插入一個(gè)現(xiàn)有的電話插槽，或者DSL運(yùn)營(yíng)商可能安裝它。
在交換局端使用數(shù)字用戶線路訪問復(fù)用器（DSLAM）將DSL電路上的數(shù)據(jù)匯聚然后轉(zhuǎn)發(fā)到其他的網(wǎng)絡(luò)。它還能分離出語音部分。
協(xié)議和配置
很多DSL技術(shù)在低水平比特流的ATM層實(shí)現(xiàn)，以保證不同的技術(shù)能夠在相同的鏈路上實(shí)現(xiàn)。
DSL設(shè)備可以創(chuàng)建網(wǎng)橋或者路由網(wǎng)絡(luò)，在網(wǎng)橋模式，一組用戶的計(jì)算機(jī)可以方便的連接到一個(gè)子網(wǎng)。早期的設(shè)備使用DHCP服務(wù)來分配提供一些配置細(xì)節(jié)例如網(wǎng)卡的IP地址，基于MAC地址的認(rèn)證或者分配主機(jī)名。 后來的的設(shè)備一般使用PPPoE（以太網(wǎng)上的PPP）或者PPPoA（ATM網(wǎng)上的點(diǎn)到點(diǎn)協(xié)議), 驗(yàn)證的時(shí)候使用用戶名和密碼，然后使用PPP原理去分配網(wǎng)絡(luò)配置（IP地址，子網(wǎng)掩碼，網(wǎng)關(guān)，DNS等）
DSL技術(shù)
可達(dá)范圍(從電話交換中心到用戶的線路長(zhǎng)度)與數(shù)據(jù)速率成反比, 象VDSL這樣的技術(shù)只能提供短距離鏈路（典型的就是FTTC－光線到路邊）。
使用DSL技術(shù)的技術(shù)(有時(shí)也叫 xDSL)有:
ADSL（非對(duì)稱用戶數(shù)字線）
HDSL（高速用戶數(shù)字線）
RADSL（速率自適應(yīng)數(shù)字用戶線路）
SDSL（對(duì)稱數(shù)字用戶線路, 標(biāo)準(zhǔn)版HDSL）
VDSL（超高速用戶數(shù)字線）
G.SHDSL（ITU-T標(biāo)準(zhǔn)替換早期SDSL）