Does Cable Modem Phone Need A Data Line Cord

When you lot connect to the Net, you might connect through a regular modem, through a local-area network connection in your office, through a cable modem or through a digital subscriber line (DSL) connexion. DSL is a very loftier-speed connection that uses the same wires every bit a regular telephone line. Here are some advantages of DSL:

You tin can go out your Internet connection open and nevertheless apply the phone line for vocalization calls.
The speed is much college than a regular modem
DSL doesn't necessarily require new wiring; it tin can use the phone line you already have.
The visitor that offers DSL will usually provide the modem as part of the installation.

But there are disadvantages:

A DSL connexion works better when you are closer to the provider's primal role. The further away yous get from the central part, the weaker the bespeak becomes.
The connection is faster for receiving data than it is for sending information over the Internet.
The service is not available everywhere.

In this commodity, we explain how a DSL connection manages to squeeze more information through a standard phone line -- and lets you make regular telephone calls even when y'all're online.

Telephone Lines

If you take read How Telephones Work, and so you know that a standard telephone installation in the Us consists of a pair of copper wires that the telephone company installs in your home. The copper wires have lots of room for carrying more than than your phone conversations -- they are capable of handling a much greater bandwidth, or range of frequencies, than that demanded for phonation. DSL exploits this "extra capacity" to carry information on the wire without disturbing the line's ability to acquit conversations. The unabridged plan is based on matching particular frequencies to specific tasks.

To empathize DSL, you first need to know a couple of things about a normal telephone line -- the kind that telephone professionals call POTS, for Plain Old Phone Service. One of the ways that POTS makes the most of the telephone visitor'due south wires and equipment is past limiting the frequencies that the switches, telephones and other equipment volition acquit. Human voices, speaking in normal conversational tones, can be carried in a frequency range of 0 to 3,400 Hertz (cycles per second -- see How Telephones Piece of work for a great demonstration of this). This range of frequencies is tiny. For example, compare this to the range of virtually stereo speakers, which cover from roughly xx Hertz to xx,000 Hertz. And the wires themselves have the potential to handle frequencies up to several million Hertz in nigh cases.

The utilise of such a small portion of the wire'due south total bandwidth is historical -- think that the telephone system has been in identify, using a pair of copper wires to each home, for about a century. By limiting the frequencies carried over the lines, the telephone system can pack lots of wires into a very pocket-sized space without worrying about interference between lines. Modern equipment that sends digital rather than analog data can safely use much more of the telephone line's chapters. DSL does but that.

A DSL cyberspace connection is one of many constructive communication tools for keeping employees in impact with the part.

Asymmetric DSL

Most homes and small business users are connected to an asymmetric DSL (ADSL) line. ADSL divides upwards the available frequencies in a line on the assumption that nearly Net users look at, or download, much more information than they send, or upload. Nether this supposition, if the connexion speed from the Internet to the user is three to four times faster than the connection from the user back to the Internet, then the user volition run across the near benefit almost of the fourth dimension.

Precisely how much benefit yous see from ADSL will profoundly depend on how far you are from the key function of the visitor providing the ADSL service. ADSL is a altitude-sensitive technology: Every bit the connection'south length increases, the signal quality decreases and the connection speed goes down. The limit for ADSL service is 18,000 feet (five,460 meters), though for speed and quality of service reasons many ADSL providers identify a lower limit on the distances for the service. At the extremes of the altitude limits, ADSL customers may see speeds far below the promised maximums, while customers nearer the central office accept faster connections and may run into extremely high speeds in the future. ADSL technology tin can provide maximum downstream (Internet to client) speeds of up to 8 megabits per 2nd (Mbps) at a distance of nigh half-dozen,000 feet (one,820 meters), and upstream speeds of upwards to 640 kilobits per second (Kbps). In practice, the best speeds widely offered today are i.five Mbps downstream, with upstream speeds varying betwixt 64 and 640 Kbps. Some vast improvements to ADSL are available in some areas through services called ASDL2 and ASDL2+. ASDL2 increases downstream to 12 Mbps and upstream to 1 Mbps, and ASDL2+ is even improve -- information technology improves downstream to equally much as 24 Mbps and upstream to 3 Mbps.

You might wonder -- if distance is a limitation for DSL, why is it not also a limitation for voice telephone calls? The respond lies in small amplifiers called loading coils that the telephone company uses to heave voice signals. Unfortunately, these loading coils are incompatible with ADSL signals, so a voice coil in the loop between your telephone and the telephone company'due south central office will disqualify you lot from receiving ADSL. Other factors that might disqualify you from receiving ADSL include:

Bridge taps - These are extensions, between yous and the fundamental office, that extend service to other customers. While you wouldn't discover these bridge taps in normal phone service, they may take the full length of the excursion across the distance limits of the service provider.
Cobweb-optic cables - ADSL signals can't pass through the conversion from analog to digital and back to analog that occurs if a portion of your telephone circuit comes through fiber-optic cables.
Altitude - Fifty-fifty if y'all know where your primal function is (don't be surprised if you don't -- the telephone companies don't advertise their locations), looking at a map is no indication of the altitude a signal must travel between your house and the office.

Next, we'll await at how the signal is split and what equipment DSL uses.

Splitting the Indicate

The CAP System

In that location are two competing and incompatible standards for ADSL. The official ANSI standard for ADSL is a system called detached multitone, or DMT. According to equipment manufacturers, near of the ADSL equipment installed today uses DMT. An before and more easily implemented standard was the carrierless aamplitude/phase (CAP) system, which was used on many of the early installations of ADSL.

CAP operates by dividing the signals on the telephone line into iii distinct bands: Vox conversations are carried in the 0 to 4 KHz (kilohertz) ring, as they are in all POTS circuits. The upstream channel (from the user back to the server) is carried in a band between 25 and 160 KHz. The downstream channel (from the server to the user) begins at 240 KHz and goes up to a point that varies depending on a number of conditions (line length, line noise, number of users in a item phone company switch) but has a maximum of virtually 1.5 MHz (megahertz). This system, with the three channels widely separated, minimizes the possibility of interference between the channels on one line, or betwixt the signals on dissimilar lines.

The DMT Organization

DMT also divides signals into split up channels, merely doesn't use two fairly broad channels for upstream and downstream information. Instead, DMT divides the data into 247 separate channels, each 4 KHz wide.

One way to retrieve nigh it is to imagine that the phone company divides your copper line into 247 dissimilar iv-KHz lines and and so attaches a modem to each one. You get the equivalent of 247 modems connected to your computer at one time. Each channel is monitored and, if the quality is too impaired, the betoken is shifted to another channel. This arrangement constantly shifts signals between different channels, searching for the best channels for transmission and reception. In add-on, some of the lower channels (those starting at virtually viii KHz), are used as bidirectional channels, for upstream and downstream information. Monitoring and sorting out the data on the bidirectional channels, and keeping up with the quality of all 247 channels, makes DMT more than circuitous to implement than CAP, but gives it more than flexibility on lines of differing quality.

Filters

CAP and DMT are similar in one mode that yous can see as a DSL user.

If y'all accept ADSL installed, yous were about certainly given small filters to attach to the outlets that don't provide the indicate to your ADSL modem. These filters are low-pass filters -- simple filters that block all signals above a certain frequency. Since all voice conversations take place beneath iv KHz, the low-pass (LP) filters are built to block everything above 4 KHz, preventing the data signals from interfering with standard telephone calls.

DSL Equipment

ADSL uses two pieces of equipment, one on the customer cease and one at the Internet service provider, telephone company or other provider of DSL services. At the customer's location there is a DSL transceiver, which may also provide other services. The DSL service provider has a DSL Access Multiplexer (DSLAM) to receive customer connections.

The Transceiver

Well-nigh residential customers call their DSL transceiver a "DSL modem." The engineers at the telephone company or Internet service provider call information technology an ATU-R. Regardless of what it's called, it's the point where data from the user's computer or network is connected to the DSL line.

The transceiver can connect to a client'southward equipment in several ways, though most residential installation uses USB or 10 base-T Ethernet connections. While most of the ADSL transceivers sold past ISPs and telephone companies are simply transceivers, the devices used by businesses may combine network routers, network switches or other networking equipment in the aforementioned platform.

The DSLAM

The DSLAM at the admission provider is the equipment that really allows DSL to happen. A DSLAM takes connections from many customers and aggregates them onto a unmarried, loftier-capacity connexion to the Cyberspace. DSLAMs are generally flexible and able to support multiple types of DSL in a single central part, and different varieties of protocol and modulation -- both CAP and DMT, for example -- in the same type of DSL. In improver, the DSLAM may provide additional functions including routing or dynamic IP address assignment for the customers.

The DSLAM provides 1 of the main differences between user service through ADSL and through cable modems. Because cablevision-modem users generally share a network loop that runs through a neighborhood, adding users means lowering performance in many instances. ADSL provides a dedicated connection from each user back to the DSLAM, significant that users won't come across a performance decrease equally new users are added -- until the total number of users begins to saturate the unmarried, high-speed connection to the Internet. At that point, an upgrade by the service provider tin can provide additional operation for all the users connected to the DSLAM.

For data on ADSL rates and availability in the United States, go to Broadband Reports. This site tin can provide information on ADSL service companies in your surface area, the rates they charge, and customer satisfaction, every bit well every bit estimating how far yous are from the nearest primal part.

ADSL isn't the only type of DSL, and it'due south not the merely way to get high-speed Cyberspace admission. Next, we'll look at ADSL alternatives.

Alternatives to ADSL

There are lots of variations in DSL technology -- many of them address DSL's distance limitations in ane way or another. Other types of DSL include:

Very high fleck-charge per unit DSL ( VDSL ) - This is a fast connection, but works simply over a short distance. It is capable of handling Internet access, HDTV and on-need services at rates of 52 Mbps downstream and 12 Mbps upstream.
Symmetric DSL (SDSL) - This connectedness, used mainly by small businesses, doesn't allow you to use the phone at the aforementioned time, but the speed of receiving and sending information is the same.
Rate-adaptive DSL (RADSL) - This is a variation of ADSL, but the modem can adjust the speed of the connection depending on the length and quality of the line.
ISDN DSL (IDSL) - This is a combination of the Integrated Services Digital Network (ISDN) and DSL technology. ISDN was the solution to dial-up Internet -- it allowed vocalization, text graphics, video and other data to share ane telephone line. This made it possible to talk on the phone and employ the Cyberspace at the same time. IDSL is faster than ISDN connections but slower than DSL. It tin travel a longer distance of 5 to 6 miles, so it is usually a good option for people who tin't get DSL in their expanse.
Universal DLS (Uni -DSL) - This emerging engineering, developed by Texas Instruments, is backwards compatible with all existing versions of DSL. It offers somewhat of a centre ground betwixt ASDL and VDSL -- at longer distances, information technology can attain the speeds of ASDL, but information technology can provide greater speeds than VDSL at shorter distances. In some locations, Uni-DSL can provide four times the amount of speed equally VDSL.

Alternatives to DSL

With DSL'due south distance limitation and lower availability, what are another options? At that place are 2 major alternatives to DSL -- cable and wireless.

Cable and DSL are the two big rivals in the globe of broadband. Cablevision isn't limited past distance like DSL -- cable wires reach virtually neighborhoods, and bespeak strengths don't weaken over long distances. While DSL allows y'all to use the phone and Net simultaneously, cable lets users sentinel television and surf the Internet at the same time. Many cablevision companies are likewise beginning to bundle services with cablevision Goggle box, Cyberspace and digital telephone on 1 bill. Although cable and DSL speeds are most the same, the 1 disadvantage with cable is bandwidth -- connection speeds tin can slow down if too many people are using a cablevision service at the same time.

A new technology, known every bit WiMax or 802.16, looks to combine the benefits of broadband and wireless. WiMax will provide high-speed wireless Internet over very long distances and will about likely provide admission to big areas such every bit cities. WiMax technology will be bachelor in most American cities in 2008.

To learn more about DSL and other topics, read on to the next page.

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