Subscriber Line

Telecommunications Manufacture

Amitava Dutta , in Encyclopedia of Information Systems, 2003

II.Eastward Digital Subscriber Line

Digital subscriber line (DSL) is a transmission 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 office (CO). This is used to aggregate multiple customer DSL lines. At the customer location, a DSL modem is installed to terminate the DSL connection.

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

The fact that DSL uses existing copper wire makes information technology particularly attractive to ILECs. There are, nevertheless, some limitations. Higher frequency signals attenuate faster over metallic loops. DSL service is therefore limited in distance to approximately 12,000 feet. It is adversely affected by network elements commonly plant on phonation copper lines, such as taps and loading coils. For these reasons, DSL service has not been deployed as chop-chop and extensively every bit the ubiquity of twisted-pair infrastructure would suggest. Companies like Rhythms, Covad, and Northpoint have positioned themselves to sell ADSL, SDSL, and HDSL to businesses around the U.s.. Nevertheless, they often find themselves at the mercy of the ILECs who own the existing copper loops. Analysts encounter vast growth in residential utilize of ADSL. While current penetration is approximately 1% of households, Goldman Sachs, among others, predicts that DSL will be used in virtually 44.viii one thousand thousand homes by 2008.

Other DSL standards are emerging. These include Very High Data Charge per unit Digital Subscriber Line (VDSL), designed to offer capacity suitable for video, and Rate-Adaptive Digital Subscriber Line (RADSL), which is able to accommodate the delivery 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 Study Guide (3rd Edition), 2016

DSL

Digital Subscriber Line (DSL) has a "concluding mile" solution similar to ISDN: utilize existing copper pairs to provide digital service to homes and small-scale offices. DSL has plant more widespread use due to higher speeds compared with ISDN, reaching speeds of ten megabits and more than.

Common types of DSL are Symmetric Digital Subscriber Line (SDSL, with matching upload and download speeds), Disproportionate 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 2 pairs of copper; HDSL is used to provide inexpensive T1 service.

Symmetric DSL is as well called Single-Line DSL. An advantage of ADSL is that it allows the simultaneous use of a POTS line, often filtered from the DSL traffic. As a full general rule, the closer a site is to the Fundamental Office (CO), the faster the available service.

Table v.9 summarizes the speeds and modes of DSL.

Table 5.nine. DSL Speed and Distances [10]

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Wide Area Networking

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

Digital Subscriber Line

DSL is commonly denoted every bit xDSL, where the x specifies what type of DSL is in use. DSL is unremarkably used to access the Net from both residential and business organisation locations to provide loftier-speed admission to the Internet. DSL became very popular as dial-up technologies go increasingly unable to meet the demand for fast access to the Net.

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

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DSL is not a shared medium, unlike cable networks, which use shared access. Shared access ways that when there is heavy usage of the arrangement, less bandwidth is available to individual users. DSL has defended bandwidth, and so the merely ane using that bandwidth is you.

DID Y'all KNOW?

1 drawback of DSL, still, is that the QoS is dependent on the user's distance from the central office (CO). The CO is where the network endpoint is located and is more often than not 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 almost common forms of DSL are disproportionate DSL (ADSL) and symmetric DSL (SDSL).

Disproportionate DSL

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

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ADSL is used to transmit digital information on preexisting telephone lines.

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Unlike punch-up, ADSL provides an e'er on connexion to the Internet.

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ADSL is able to identify voice and data data on the aforementioned line.

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

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ADSL generates downstream speeds of nigh 8 Mbps and upstream speeds of up 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 nigh 2 to 2.5 Mbps.

EXAM WARNING

Other forms of DSL are very-loftier-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). You will take to be familiar with ADSL and SDSL non only for the examination but also for your own use if y'all program to piece of work on DSL. These are the most normally used types and will surely be something you will want to know almost in more than depth if the situation arises where you may be working with this technology.

For the test, you lot will need to know how to troubleshoot problems with DSL, although DSL itself may non be the problem. Look for misleading types of questions that ask you nearly DSL engineering science, although the questions are not substantially focused on that particular technology. The Network+ examination is notorious for these types of scenario questions. Be able to isolate what the cause of a problem may exist, whether it be an ISDN, DSL, or WISP (wireless ISP) connection based on the technology and the underlying network – also as problems may also be occurring there that are misleading you into the wrong reply. Finally, make sure that you call up that DSL and ISDN are both digital technologies, not analog.

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Voice Communications

John Vargo , Ray Hunt , in Encyclopedia of Data Systems, 2003

Vii.B.4. xDSL Technology

Digital subscriber line (DSL) standards include a range of variations including ADSL (asymmetric digital subscriber line), HDSL (high-chip-rate digital subscriber line) and SDSL (single pair digital subscriber line). These standards support the transmission of high-speed digital information over voice-grade lines, often aiming to evangelize T1 or E1 speeds more efficiently. This engineering science has become available in many areas and offers considerable benefits over the use of a modem for transmission of information. Benefits include the ability to support the simultaneous employ of a single line for phone calls while transmitting data (web browsing, etc.). The technology besides supports much higher data transmission rates. ADSL, for case, offers upwards to 640  Kbps upstream (eastward.g., for sending e-mail) and up to nine Mbps downstream (e.1000., for downloading from the Cyberspace).

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

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Domain 4

Eric Conrad , ... Joshua Feldman , in Eleventh Hr CISSP® (Tertiary Edition), 2017

DSL

Digital subscriber line (DSL) has a "last 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 high-rate digital subscriber line (VDSL, featuring much faster disproportionate speeds). Another option is high-data-charge per unit DSL (HDSL), which matches SDSL speeds using 2 copper pairs. HDSL provides inexpensive T1 service. Equally a full general rule, the closer a site is to the Central Office (CO), the faster the available service volition be.

Table 4.4 summarizes the speeds and modes of DSL.

Table four.iv. DSL Speed and Distances 1

Type Download Speed Upload Speed Altitude from CO
ADSL 1.5–9   Mbps xvi–640   Kbps 18,000   ft
SDSL one.544   Mbps 1.544   Mbps x,000   ft
HDSL i.544   Mbps 1.544   Mbps 10,000   ft
VDSL xx–50   +   Mbps Up to 20   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

vii.two.7.6 Standardizing IPTV Delivery

IPTV stressed the existing broadband connectivity model. Start, PPP is not well suited to deliver a unmarried stream to multiple subscribers ("multicast"). Second, Ethernet is emerging as the networking technology of choice for the WAN, specially for loftier-bandwidth applications such as IPTV.

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

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Ethernet delivery using the N:ane (or services VLAN or Due south-VLAN) or 1:i (customer VLAN or C-VLAN) model. Service VLANs evangelize each service (vocalism, video, and data) to a defended client 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 unmarried logical connectedness (Ethernet VLAN), allowing all bandwidth to be shared amid all services.

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In addition to PPP, the operator could use the simpler (only less functional) IP over Ethernet (IPoE) model. The DHCP proponents fence that the "PPP login" is no longer required, and PPP does not support multicast IPTV well. However, this simplistic argument downplays many of PPP's benefits. PPPoE and DHCP tin be used concurrently to evangelize different services, even to the aforementioned subscriber.

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Utilize of a single B-RAS to support all traffic (single edge) or the ability to use a separate edge router to support IPTV traffic (multi-edge).

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Connecting to the Internet

January L. Harrington , in Ethernet Networking for the Small Function and Professional Home Role, 2007

DSL Pluses and Minuses

Like cable access, DSL is a viable choice for Cyberspace access for a small or home business. The positive aspects of DSL service include:

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Skilful performance: DSL is a dedicated line over the local loop to the CO. Information technology therefore is non bailiwick to the slowdowns that tin occur with cablevision service when traffic to and from the fiber optic node is very heavy. (To be fair, most users won't encounter cablevision 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 blazon of service you purchase, DSL will price anywhere from $15 to $150 a month.

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

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

Note: The DSL-versus-cable admission choice can be a tough one. Both cost about the same, provide good functioning, don't require a dedicated phone line, and are very reliable. Often the choice is based just on which service is available in a given area. If you have both available, then you can look at parcel content and prices.

DSL does have several disadvantages:

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

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Even within the 15,000 foot limit, the farther you become from the CO, the slower the manual speed.

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

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

Note: Which exercise I use? DSL. Why? Because when arranged with my phone service, DSL is $15 a month cheaper than the cable service. (I have satellite TV rather than cable.) In add-on, my premises are only i,250 feet from a CO. The service might be rated at upwardly 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 access technology that provides connection speeds in the megabit per second (Mbps) range. Characteristics of cable modems are every bit follows:

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They use the broadband technology of cable television lines.

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

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The manual speeds are typically around 1.544 Mbps, but broadband Internet tin can provide greater speeds allowing a download path of up 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 Isp (Internet service provider).

Characteristics of DSL modems are as follows:

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They allow simultaneous voice and information communications.

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They transmit and receive information digitally beyond the telephone line'southward twisted-pair cable providing Internet admission using existing phone wiring.

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They provide manual speeds of ane.544 Mbps and tin can go up to data transfer rates of 6.1 Mbps.

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The speed of DSL decreases the further you lot are from a telephone company's offices or a repeater that regenerates the betoken. The closer you are to the telephone company'south offices, the faster your DSL connection will be.

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There are several dissimilar variations of DSL available (shown in Tabular array 3.2), which offer different information transfer rates and distance limitations.

Table 3.2. Types of DSL

Type of DSL Bandwidth Distance Limitations
Asymmetric digital subscriber line (ADSL) Downstream: ane.544 to 6.1 Mbps Upstream: 16 to 640 Kbps Speeds decrease over distance. i.544 Mbps at 18,000 ft., ii.048 Mbps at sixteen,000 ft., 6.312 Mbps at 12,000 ft., and 8.448 Mbps at 9,000 ft.
Consumer digital subscriber line (CDSL) Downstream: 1 Mbps Upstream: Under 1 Mbps 18,000 ft.
DSL Lite or Chiliad.Light 1.544 to 6 Mbps xviii,000 ft.
ISDN digital subscriber line (IDSL) 128 Kbps xviii,000 ft.
High digital subscriber line (HDSL) Varies depending on twisted-pair lines. 1.544 Mbps duplex on 2 twisted-pair lines or 2.048 Mbps duplex on three 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: 1.5 to 2.3 Mbps Speeds decrease over distance. iv,500 ft. at 12.96 Mbps, 3,000 ft. at 25.82 Mbps, and 1,000 ft. at 51.84 Mbps

Fast Facts

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

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ISDN Channels An ISDN transmission excursion consists of a logical grouping of data channels which deport voice and data. Each ISDN connexion consists of two channels, a B channel and a D channel, each with their ain function and bandwidth constraints. The bearer channels (B channels) transfer data and offering a bandwidth of 64 Kbps per each channel, and the data aqueduct (D aqueduct) handles signaling at 16 or 64 Kbps and so that the B channel doesn't have to exercise information technology. This includes the session setup and teardown using a communications linguistic communication known as Digital Subscriber Signalling System No. one (DSS1). The bandwidth available for the D channel is dependent upon the type of service – basic charge per unit interfaces (BRIs) unremarkably require sixteen Kbps and main rate interfaces (PRIs) apply 64 Kbps. Typically, ISDN service contains 2 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 (half dozen 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 (30 B channels) – Europe

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ISDN Interfaces There are two bones types of ISDN service:

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BRI consists of two 64 Kbps B channels and one xvi Kbps D aqueduct 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 basic blazon of service today intended for minor business concern or home use. To use BRI services, you must subscribe to ISDN services through a local telephone company or provider. By default, you must be within xviii,000 ft. (almost 3.4 miles) of the telephone company's primal part for BRI services.

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PRI requires T1 carriers to facilitate communications. Ordinarily, the channel structure contains 23 B channels plus one 64 Kbps D channel for a full of 1536 Kbps. This standard is used only in North America and Japan. European countries support a different kind of ISDN standard for PRI. It consists of 30 B channels and one 64 Kbps D channel for a total of 1984 Kbps. A technology known as Non-Facility Associated Signaling (NFAS) is bachelor to enable yous to support multiple PRI lines with 1 64 Kbps D aqueduct.

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

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ISDN reference points They are used to define logical interfaces. They are, in effect, a type of protocol used in communications. The following list contains the reference points:

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

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

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T defines reference point between NT1 and NT2 devices.

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U defines reference point betwixt NT1 devices and line termination equipment. This is ordinarily the fundamental switch.

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ISDN identifiers They use five separate identifiers when making a connection. The provider assigns two of these when the connection is first prepare up: the service profile identifier (SPID) and the directory number (DN). These are the most common numbers used because the other three are dynamically gear up each fourth dimension a connection is made. The three dynamic identifiers are terminal endpoint identifier (TEI), bearer lawmaking (BC), and service access point identifier (SAPI).

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