Subscriber Line

Telecommunications Industry

Amitava Dutta , in Encyclopedia of Data Systems, 2003

Ii.E Digital Subscriber Line

Digital subscriber line (DSL) is a manual technology that achieves high speeds over existing twisted pair lines. To provide DSL service, a provider installs a digital subscriber line access multiplexer (DSLAM) at the company central role (CO). This is used to aggregate multiple customer DSL lines. At the customer location, a DSL modem is installed to finish the DSL connection.

DSL comes in a multifariousness of flavors and transmission speeds. To date, asymmetric digital subscriber line (ADSL) has been deployed the virtually. It offers speeds of up to 7   Mbps downstream but significantly lower upstream speeds. It is marketed primarily to the residential market for Internet activity. Loftier-speed digital subscriber line (HDSL) is also available. Information technology is a T1-like service having comparable bandwidth. Symmetric digital subscriber line (SDSL) allows for symmetrical data rates of up to 2.2   Mbps, which is adequate for small and medium-sized businesses.

The fact that DSL uses existing copper wire makes it particularly attractive to ILECs. There are, notwithstanding, some limitations. College frequency signals attenuate faster over metal loops. DSL service is therefore limited in distance to approximately 12,000 feet. It is adversely affected by network elements commonly found on voice copper lines, such as taps and loading coils. For these reasons, DSL service has not been deployed equally rapidly and extensively equally the ubiquity of twisted-pair infrastructure would suggest. Companies similar Rhythms, Covad, and Northpoint have positioned themselves to sell ADSL, SDSL, and HDSL to businesses around the United States. However, they often observe themselves at the mercy of the ILECs who own the existing copper loops. Analysts see vast growth in residential utilize of ADSL. While current penetration is approximately 1% of households, Goldman Sachs, amid others, predicts that DSL will be used in near 44.eight one thousand thousand homes by 2008.

Other DSL standards are emerging. These include Very High Information Rate Digital Subscriber Line (VDSL), designed to offer capacity suitable for video, and Rate-Adaptive Digital Subscriber Line (RADSL), which is able to arrange the commitment charge per unit based on line conditions.

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Domain 4: Communication and Network Security (Designing and Protecting Network Security)

Eric Conrad , ... Joshua Feldman , in CISSP Written report Guide (Third Edition), 2016

DSL

Digital Subscriber Line (DSL) has a "concluding mile" solution similar to ISDN: use existing copper pairs to provide digital service to homes and minor offices. DSL has found more widespread use due to college speeds compared with ISDN, reaching speeds of 10 megabits and more than.

Mutual types of DSL are Symmetric Digital Subscriber Line (SDSL, with matching upload and download speeds), Asymmetric Digital Subscriber Line (ADSL, featuring faster download speeds than upload), and Very High Rate Digital Subscriber Line (VDSL, featuring much faster asymmetric speeds). Another option is HDSL (High-data-rate DSL), which matches SDSL speeds using two pairs of copper; HDSL is used to provide inexpensive T1 service.

Symmetric DSL is also called Single-Line DSL. An advantage of ADSL is that information technology allows the simultaneous use of a POTS line, often filtered from the DSL traffic. As a general rule, the closer a site is to the Cardinal Role (CO), the faster the available service.

Table 5.9 summarizes the speeds and modes of DSL.

Tabular array 5.9. DSL Speed and Distances [10]

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Wide Expanse Networking

Naomi J. Alpern , Robert J. Shimonski , in Eleventh Hour Network+, 2010

Digital Subscriber Line

DSL is normally denoted as xDSL, where the x specifies what blazon of DSL is in use. DSL is usually used to access the Cyberspace from both residential and business concern locations to provide loftier-speed access to the Internet. DSL became very popular every bit dial-up technologies become increasingly unable to meet the need for fast access to the Cyberspace.

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DSL and other high-speed technologies are slowly displacing dial-up service to the Internet. DSL is one of the most highly used because it tin can utilise preexisting phone lines in your home, so installation is a bit cheaper and less intrusive.

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DSL is not a shared medium, unlike cable networks, which employ shared admission. Shared admission means that when there is heavy usage of the system, less bandwidth is bachelor to individual users. DSL has dedicated bandwidth, so the only 1 using that bandwidth is you.

DID You KNOW?

One drawback of DSL, withal, is that the QoS is dependent on the user's altitude from the primal office (CO). The CO is where the network endpoint is located and is mostly run by your Internet service provider (ISP). The farther you are from the CO, the slower the service is. There are many forms of DSL. The nearly common forms of DSL are asymmetric DSL (ADSL) and symmetric DSL (SDSL).

Asymmetric DSL

ADSL is the most widely deployed form of DSL technology. Most homes and small businesses currently using DSL engineering science use ADSL. Characteristics of ADSL are as follows:

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ADSL is used to transmit digital data on preexisting phone lines.

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Unlike dial-upwardly, ADSL provides an ever on connexion to the Internet.

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ADSL is able to place voice and data information on the same line.

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ADSL is asymmetric. This means that ADSL is designed to provide more bandwidth in one management than in the other.

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ADSL generates downstream speeds of about viii Mbps and upstream speeds of upwards to 640 Kbps.

Symmetric DSL

SDSL is typically used in larger companies, and the upstream and downstream channels have the aforementioned size; that is, the download speed and upload speed are equal. SDSL operates at about 2 to 2.five Mbps.

EXAM Alert

Other forms of DSL are very-high-speed digital subscriber line (VDSL), high-speed digital subscriber line (HDSL), symmetrical high-speed digital line subscriber (SHDSL), ISDN digital subscriber line (IDSL), and HDSL Second Generation (HDSL-ii). Y'all volition accept to be familiar with ADSL and SDSL not only for the examination but also for your own use if you program to work on DSL. These are the most normally used types and will surely be something you lot volition want to know about in more depth if the state of affairs arises where you may exist working with this technology.

For the test, y'all will demand to know how to troubleshoot issues with DSL, although DSL itself may not be the problem. Look for misleading types of questions that inquire you virtually DSL technology, although the questions are non essentially focused on that particular applied science. The Network+ examination is notorious for these types of scenario questions. Be able to isolate what the cause of a problem may be, whether it exist an ISDN, DSL, or WISP (wireless ISP) connexion based on the engineering and the underlying network – every bit well every bit problems may also be occurring at that place that are misleading you into the wrong answer. Finally, make sure that you remember that DSL and ISDN are both digital technologies, non analog.

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Voice Communications

John Vargo , Ray Chase , in Encyclopedia of Information Systems, 2003

VII.B.4. xDSL Applied science

Digital subscriber line (DSL) standards include a range of variations including ADSL (asymmetric digital subscriber line), HDSL (loftier-bit-rate digital subscriber line) and SDSL (unmarried pair digital subscriber line). These standards support the transmission of loftier-speed digital information over vocalism-class lines, often aiming to deliver T1 or E1 speeds more than efficiently. This technology has go available in many areas and offers considerable benefits over the employ of a modem for transmission of data. Benefits include the ability to back up the simultaneous apply of a single line for telephone calls while transmitting data (web browsing, etc.). The engineering also supports much higher data transmission rates. ADSL, for instance, offers upward to 640  Kbps upstream (e.thou., for sending e-mail) and up to ix Mbps downstream (e.k., for downloading from the Internet).

The technology, every bit always, is not without its challenges however. For most implementations of DSL engineering science, the user must be located reasonably close to the telco switching substitution office. The further the user is from the switch, the slower the transmission speeds. If the user is too far from the exchange she cannot use DSL at all.

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Domain 4

Eric Conrad , ... Joshua Feldman , in Eleventh 60 minutes CISSP® (Third Edition), 2017

DSL

Digital subscriber line (DSL) has a "terminal mile" solution that uses existing copper pairs to provide digital service to homes and small offices.

Common types of DSL are symmetric digital subscriber line (SDSL, with matching upload and download speeds); asymmetric digital subscriber line (ADSL), featuring faster download speeds than upload speeds; and very loftier-charge per unit digital subscriber line (VDSL, featuring much faster asymmetric speeds). Some other option is loftier-data-charge per unit DSL (HDSL), which matches SDSL speeds using ii copper pairs. HDSL provides inexpensive T1 service. As a general rule, the closer a site is to the Fundamental Part (CO), the faster the bachelor service will be.

Table iv.iv summarizes the speeds and modes of DSL.

Tabular array 4.4. DSL Speed and Distances one

Type Download Speed Upload Speed Altitude from CO
ADSL one.5–9   Mbps 16–640   Kbps 18,000   ft
SDSL 1.544   Mbps 1.544   Mbps 10,000   ft
HDSL 1.544   Mbps 1.544   Mbps 10,000   ft
VDSL twenty–50   +   Mbps Up to xx   Mbps <   5000   ft

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Multicast for VPLS and Carrier Ethernet Networks

Vinod Joseph , Srinivas Mulugu , in Deploying Side by side Generation Multicast-enabled Applications, 2011

7.2.7.half dozen Standardizing IPTV Delivery

IPTV stressed the existing broadband connectivity model. Starting time, PPP is non well suited to deliver a unmarried stream to multiple subscribers ("multicast"). Second, Ethernet is emerging equally the networking technology of option for the WAN, specially for high-bandwidth applications such as IPTV.

DSL Forum TR-101 defines the technologies for delivering IPTV service besides equally for using Ethernet as the underlying network technology instead of ATM. Unlike the previous DSL Forum implementation standards, TR-101 provides numerous alternatives rather than dictating a single approach. Some of the primal alternatives include:

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Ethernet delivery using the N:i (or services VLAN or S-VLAN) or 1:i (customer VLAN or C-VLAN) model. Service VLANs deliver each service (vocalism, video, and data) to a defended customer such as a PC or STB and allocate a fixed amount of bandwidth to each service. Customer VLANs deliver all services to each subscriber via a single logical connection (Ethernet VLAN), allowing all bandwidth to be shared among all services.

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In addition to PPP, the operator could utilise the simpler (but less functional) IP over Ethernet (IPoE) model. The DHCP proponents argue that the "PPP login" is no longer required, and PPP does not support multicast IPTV well. Even so, this simplistic argument downplays many of PPP'due south benefits. PPPoE and DHCP can be used concurrently to evangelize different services, even to the same subscriber.

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Apply of a single B-RAS to support all traffic (unmarried edge) or the power to use a dissever border router to support IPTV traffic (multi-border).

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Connecting to the Cyberspace

Jan Fifty. Harrington , in Ethernet Networking for the Small Office and Professional Home Office, 2007

DSL Pluses and Minuses

Similar cable access, DSL is a feasible option for Cyberspace access for a small-scale or dwelling business. The positive aspects of DSL service include:

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Good performance: DSL is a defended line over the local loop to the CO. It therefore is not subject field to the slowdowns that can occur with cable service when traffic to and from the cobweb optic node is very heavy. (To exist fair, almost users won't meet cable service slowdowns from heavy traffic; this simply occurs in very high-density, heavy-usage areas.)

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Reasonable cost: Depending on the speed and type of service you purchase, DSL will cost anywhere from $15 to $150 a month.

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High reliability: DSL has very high uptime, with relatively few service outages.

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Loftier speed: DSL is very fast compared to dial-up access.

Note: The DSL-versus-cable access choice can be a tough one. Both cost virtually the same, provide expert operation, don't crave a dedicated phone line, and are very reliable. Often the pick is based simply on which service is available in a given expanse. If y'all have both bachelor, then y'all can look at package content and prices.

DSL does have several disadvantages:

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DSL is generally express to a distance of fifteen,000 feet from the CO. This measurement relates to cable length rather than physical altitude.

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Even within the xv,000 foot limit, the farther yous become from the CO, the slower the manual speed.

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DSL requires a telephone landline. If you are a "cell telephone merely" user, then this could be a major stumbling block.

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DSL's availability is more limited than that of cable access.

Notation: Which do I utilise? DSL. Why? Because when bundled with my telephone service, DSL is $15 a calendar month cheaper than the cable service. (I accept satellite TV rather than cable.) In addition, my premises are only 1,250 feet from a CO. The service might be rated at up to three Mbps, but I've had much faster downloads.

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Network Devices

Naomi J. Alpern , Robert J. Shimonski , in Eleventh Hour Network+, 2010

Digital Subscriber Line and Cable Modems

Cablevision modems and digital subscriber line (DSL) modems admission engineering science that provides connection speeds in the megabit per 2nd (Mbps) range. Characteristics of cable modems are every bit follows:

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They employ the broadband technology of cable television lines.

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They transmit data into a coaxial-based technology, which is used to split Internet access from television signals.

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The transmission speeds are typically around ane.544 Mbps, but broadband Internet can provide greater speeds allowing a download path of upwardly to 27 Mbps.

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Cable modems communicate with a cablevision modem termination system (CMTS) and provide a constant connection to the cable service provider that also acts in the role of an Cyberspace service provider (Isp).

Characteristics of DSL modems are equally follows:

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They allow simultaneous vocalism and data communications.

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They transmit and receive data digitally across the phone line's twisted-pair cable providing Cyberspace access using existing phone wiring.

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They provide transmission speeds of i.544 Mbps and can go upwardly to data transfer rates of six.1 Mbps.

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The speed of DSL decreases the further you are from a telephone visitor'south offices or a repeater that regenerates the signal. The closer y'all are to the telephone company'due south offices, the faster your DSL connection will exist.

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There are several different variations of DSL available (shown in Table 3.2), which offer different data transfer rates and distance limitations.

Tabular array iii.2. Types of DSL

Type of DSL Bandwidth Altitude Limitations
Asymmetric digital subscriber line (ADSL) Downstream: i.544 to vi.1 Mbps Upstream: sixteen to 640 Kbps Speeds subtract over altitude. ane.544 Mbps at 18,000 ft., 2.048 Mbps at 16,000 ft., 6.312 Mbps at 12,000 ft., and 8.448 Mbps at 9,000 ft.
Consumer digital subscriber line (CDSL) Downstream: one Mbps Upstream: Nether ane Mbps xviii,000 ft.
DSL Lite or 1000.Lite 1.544 to 6 Mbps 18,000 ft.
ISDN digital subscriber line (IDSL) 128 Kbps 18,000 ft.
High digital subscriber line (HDSL) Varies depending on twisted-pair lines. i.544 Mbps duplex on two twisted-pair lines or 2.048 Mbps duplex on 3 twisted-pair lines 12,000 ft.
Symmetric digital subscriber line (SDSL) 1.544 Mbps 12,000 ft.
Very high digital subscriber line (VDSL) Downstream: 12.9 to 52.8 Mbps Upstream: i.5 to 2.3 Mbps Speeds decrease over altitude. four,500 ft. at 12.96 Mbps, iii,000 ft. at 25.82 Mbps, and one,000 ft. at 51.84 Mbps

Fast Facts

An Integrated Services Digital Network (ISDN) is a system of digital telephone connections that enables information to be transmitted simultaneously end to end. Information technology consists of multiple components:

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ISDN Channels An ISDN transmission circuit consists of a logical grouping of data channels which carry vocalization and data. Each ISDN connexion consists of ii channels, a B aqueduct and a D aqueduct, each with their ain function and bandwidth constraints. The bearer channels (B channels) transfer information and offer a bandwidth of 64 Kbps per each channel, and the information channel (D aqueduct) handles signaling at 16 or 64 Kbps so that the B channel doesn't accept to do information technology. This includes the session setup and teardown using a communications language known as Digital Subscriber Signalling System No. 1 (DSS1). The bandwidth bachelor for the D channel is dependent upon the blazon of service – basic rate interfaces (BRIs) usually require 16 Kbps and primary rate interfaces (PRIs) use 64 Kbps. Typically, ISDN service contains two B channels and a single D aqueduct. H channels are used to specify a number of B channels. The following list shows the implementations:

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H0 384 Kbps (six B channels)

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H10 1472 Kbps (23 B channels)

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H11 1536 Kbps (24 B channels)

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H12 1920 Kbps (xxx B channels) – Europe

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ISDN Interfaces There are two bones types of ISDN service:

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BRI consists of 2 64 Kbps B channels and 1 16 Kbps D channel for a total of 144 Kbps. Only 128 Kbps is used for user data transfers. BRIs were designed to enable customers to use their existing wiring. This provided a low-cost solution for customers and is why it is the most bones blazon of service today intended for minor business organization or home apply. To use BRI services, yous must subscribe to ISDN services through a local telephone company or provider. Past default, yous must exist within eighteen,000 ft. (nearly three.iv miles) of the telephone company'south cardinal part for BRI services.

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PRI requires T1 carriers to facilitate communications. Unremarkably, the channel structure contains 23 B channels plus 1 64 Kbps D channel for a total of 1536 Kbps. This standard is used merely in North America and Japan. European countries support a different kind of ISDN standard for PRI. It consists of 30 B channels and i 64 Kbps D channel for a total of 1984 Kbps. A technology known as Not-Facility Associated Signaling (NFAS) is available to enable you to support multiple PRI lines with ane 64 Kbps D channel.

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ISDN devices The standard refers to the devices that are required to connect the end node to the network.

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ISDN reference points They are used to ascertain logical interfaces. They are, in issue, a type of protocol used in communications. The following listing contains the reference points:

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R defines reference bespeak between a TE2 device and a TA device.

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South defines reference point between TE1 devices and NT1 or NT2 devices.

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T defines reference point betwixt NT1 and NT2 devices.

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U defines reference indicate between NT1 devices and line termination equipment. This is usually the central switch.

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ISDN identifiers They use five separate identifiers when making a connection. The provider assigns 2 of these when the connection is first set up: the service contour identifier (SPID) and the directory number (DN). These are the most mutual numbers used because the other three are dynamically set upwardly each time a connection is made. The 3 dynamic identifiers are terminal endpoint identifier (TEI), bearer lawmaking (BC), and service access indicate identifier (SAPI).

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