Q01. What does ADSL stands for ?
Q02. What is the difference between ADSL and DSL?
Q03. What is xDSL ?
Q04. What is the local loop?
Q05. What is Unshielded Twisted Pair (UTP) ?
Q06. What is DMT?
Q07. What is G.lite ?
Q08. How does ADSL work ?
Q09. Why is ADSL faster in some other countries ?
Q10. DSL modems aren't really modems, are they?
Q11. Will my telephone service remains in working order if a power cut  happens in my area?
Q12. What is a splitter ?
Q13. What does a POTS splitter do and when do I need one?
Q14. We have wall jacks in several rooms. Where should I put the splitter?
Q15. What are the basic requirement to get online with an ADSL device ?
Q16. What is ADSL2 ?
Q17. What is ADSL2+ ?
Q18. What is Reach-Extended ADSL2 (RE-ADSL2) ?
Q19. What is AWG ?
Q20. What is a Bridge Tap ?
Q21. What does VPI / VCI stand for ?
Q22. What is ATM ?
Q23. What does CRC stands for ?
Q24. What does DSLAM stands for ?
Q25. What is the effect of noise?
Q26. What is crosstalk?
Q27. What is attenuation?
Q28. What is modulation?
Q29. Will I need a free IRQ to install the PCI ADSL Modem?
Q30. Can I take my ADSL service with me if I move premises?
Q31. Will I have to get a new phone number?
Q32. What is involved in an ADSL service qualification check?
Q33. Does computer performance affect the access speed?
Q34. Are there any types of equipment that won't work with ADSL?
Q35. How do I tune my xDSL line for maximum performance?
Q36. Can I have more than one xDSL line in my home?
Q37. Is xDSL available in my area?
Q38. Can I use my 56K modem with my ADSL line?
Q39. How do I determine how far I am from my CO?
Q40. What are loading coils?
Q41. Do I need to protect my equipment against lightning?
Q42. Fixed or Dynamic IP ?
Q43. How are IP addresses assigned?
Q44. Is a static IP address service available?
Q45. I would like to set up a server using a global IP address. Is that possible?
Q46. Will I have a static IP address?
Q47. Can I use my own domain name?
Q48. How is the authentication ID set for PPP connection?
Q49. How is DNS information set?
Q50. Does "Always-on" access mean that my computer is vulnerable to hacker attacks?
Q51. NAT and no NAT?
Q52. What does VPN mean?
Q53. What is Telnet?
Q54. What is SNMP?
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Asymmetric Digital Subscriber Line. ADSL is a standard that enables devices attached to twisted-pair copper wiring to transmit data at rates of 8 Mbps downstream and 1 Mbps upstream. ADSL devices can transmit data at distances of up to 18,000 feet.

DSL : Digital Subscriber Line is a technology that exploits unused frequencies on copper telephone lines to transmit traffic typically at multi-megabit speeds. DSL can allow voice and high-speed data to be sent simultaneously over the same line.

ADSL is a type of DSL where the upstream and downstream speeds differ ( Hence the "asymmetric" part ).

xDSL is a generic abbreviation for the many flavors of DSL or Digital Subscriber Line technology. xDSL refers to the technology used between a customer's premises and the telephone company, enabling more bandwidth over the already installed copper cabling that users traditionally had. There are several variations of DSL:

ADSL	Asymmetric Digital Subscriber Line
HDSL	High Bit-Rate Digital Subscriber Line
IDSL	ISDN Digital Subscriber Line
RADSL	Rate-Adaptive Digital Subscriber Line
SDSL	Symmetric Digital Subscriber Line
VDSL	Very High Bit-Rate Digital Subscriber Line

 

The last segment of the carrier network. The local loop extends from a telephone company ( The Central Office (CO) ) to an end user (Residence), and is still primarily used for analog connections.

This loop provides a user with access to the global telecommunications infrastructure that is installed all over the world. The local loop has been historically designed to provide voice grade audio service.

A cable with one or more twisted copper wires bound in a plastic sheath. Preferred method to transport data and voice to business workstations and telephones. Unshielded wire is preferred for transporting high speed data because at higher speeds, radiation is created. If shielded cabling is used, the radiation is not released and creates interference.

Several DSL technologies use a modulation technique known as Discrete Multitone, or DMT. DMT divides the upstream and downstream bands into a collection of smaller frequency ranges of approximately 4 kHz each, called subchannels. During transmission, each 4 kHz subchannel carries a portion of the total data rate. By dividing the transmission bandwidth into a collection of subchannels, DMT is able to adapt to the distinct characteristics of each telephone line and maximize the data transmission rate.


The ITU has approved a global industry standard for full-rate ADSL, known as G.992.1, or G.dmt. This specification calls for operation rates of up to 8 Mbps downstream and up to 1 Mbps upstream when operating over telephone lines at distances of up to 18,000 feet.

G.lite technology delivers data transmission greater than 1.5 Mbps downstream and up to 512 kbps upstream. G.lite enables simultaneous voice traffic and data traffic without requiring installation of a voice-data splitter and without requiring microfilters on every phone or answering machine. In the absence of any splitter, the frequencies used by the G.lite signal are subjected to numerous voice traffic phenomena. ITU approved the G.lite or G.992.2 standard in June 1999.

The service makes use of your existing telephone line. It splits the signal into two channels, one for voice communications (POTS) and the other for the high speed ADSL data connection (Upstream/Downstream ).
An ADSL Modem provides high-speed Internet access over existing phone lines by making use of previously unused frequency bandwidth above the voice band. By placing ADSL signals above the frequency of the voice signal, ADSL service can coexist on the same line with your telephone service. ADSL is asymmetric in that it provides a higher data rate in the downstream (receive) direction than in the upstream (transmit) direction. Asymmetric operation is ideal for typical home and small office use where files and information are downloaded more frequently than uploaded.


Although POTS and ADSL occupy distinct channels, they might influence one another. Telephone devices can possibly experience audible disruption whilst ADSL signals can experience interference resulting in throughput deterioration. To avoid this mutual interference, a splitter is required.
Graphically, it looks like this:

Technically, ADSL can run at data speed of up to 8Mbps, but that rate is effected considerably by line length (The further you are from the exchange or CO, the less speed you can get) from a copper pair. If you are very close to the exchange ( < 1Km ) then you could run the line at 8Mbps downstream.

No, they're not. People call them DSL "Modems" because the term describes the gear in ways people understand today. Actually, the DSL equipment is a network termination device with a micro-router inside. It doesn't really make calls the way a traditional modem does. Nor can it be used to place calls to a traditional modem.

Your phone service will still work even if you completely disconnect all your DSL gear from the system.
Power outages and failed DSL gear do not affect voice phone service.
(Of course, if there are problems with the phone line, the DSL will probably have problems as well.)

An ADSL Splitter is a three-port device, with one port for the external connection to the telephone exchange, one for the internal analog telephone connection and one for the internal ADSL connection. The ADSL data signal and the regular voice signal are carried down the same line, each operating in a different part of the spectrum.

In order to have the ADSL data signal not interfering with your regular telephones, fax machines and answering machine, you will need to fit a Splitter. The Splitter strips out the data signal so  your phones can receive the normal voice signal without interference.

An ADSL splitter is required in ADSL systems for a broadband signal and a conventional telephone signal to be carried over the same channel.

A POTS splitter uses a low pass filter to separate the low end frequencies of the telephone audio spectrum from the higher frequencies of the xDSL signals. The splitter should be a passive device, not requiring power so that voice service can be provided as has been in the past. This splitter allows for the traditional voice service that consumers are accustomed to. A splitter is required at both the customer premises and at the far end ( CO ).

Connect the splitter to the wall jack closest to the cable entry of your premises.
Branch the telephone cable from the splitter's connector, and connect the separate cables to each room.
In the event of noise on the line, you may be able to eliminate the noise by attaching a splitter and telephone to each wall jack.

Connecting to an ADSL system requires the use of an ADSL modem. To use the ADSL Router in your network you must have:
    > ADSL service
    > A splitter or microfilter
    > An account with an ISP
    > Ethernet network card (NIC) or built-in networking for each computer
    > Operating Systems ( Windows, Mac OS, Linux or UNIX )
    > Internet Explorer 5.0 or later; Netscape Navigator 4.7 or later

ADSL2 standards, completed and approved by the International Telecommunications Union (ITU) in 2002, supersede existing ADSL standards. The standards are "G.dmt.bis" and "G.lite.bis", designated as G.992.3 and G.992.4 for full-rate ADSL and splitterless ADSL, respectively.

ADSL2+ reached consent at the ITU in January 2003, joining the ADSL2 standards family as G.992.5. ADSL2+ doubles the downstream bandwidth, increasing the downstream data rate to as much as 25 Mbps.
ADSL2+ specifies a downstream frequency up to 2.2 MHz. The result is a significant increase in data rates on shorter phone lines.

Reach-Extended ADSL2 (RE-ADSL2) is the new ADSL2 Annex L was approved by the ITU in October 2003. Annex L proposes new power spectral density (PSD) masks that can result in a significant increase in ADSL's reach. RE-ADSL2 extends a 768 kbps downstream service by approximately 3,000 feet to 19,000 feet. As a result, the coverage area for this service increases by 37%.

AWG (American Wire Gauge) is a measure of the thickness of copper, aluminum and other wiring in the U.S. and elsewhere. The "Gauge" means the diameter of the wire which commonly measured in Millimeter. Copper cabling typically varies from 18 to 26 AWG. The higher the number, the thinner the wire. The thicker the wire, the less susceptible it is to interference. Thicker wire is better for longer distances. For this reason, if extended distance was critical as a result of attenuation and crosstalk, a company installing a network might prefer telephone wire with the thicker gauge of AWG 24 to AWG 26.

AWG	Metric Size ( mm )	Loop Resistance ( Ohms/Mile )
28	0.32	685
26	0.4	441
24	0.5	277
22	0.63	174

In some countries, there is a common practice of splicing a branching connection onto a cable. A Bridge Tap is a length of wire pair that is connected to a loop at one end and is unterminated at the other end. Sometimes, several Bridge Taps might exist on a single loop. Bridged taps create an impairment to the transmission system. The reflection of signals from the unterminated Bridged Taps results in signal loss and distortion and thus affect the ADSL connection and performance.

VPI : Virtual Path Identifier is a virtual path used for cell routing that is identified by an eight-bit field in the ATM cell header. The VPI field specifies this eight-bit identifier for routing. The range for VPI field is 0-255.

VCI : A Virtual Channel Identifier is a virtual channel that is identified by a unique numerical tag that is defined by a 16-bit field in the ATM cell header. The purpose of the virtual channel is to identify where the cell should travel. The VCI field specifies this 16 bit numerical tag that determines the destination. The range for VCI field is 0-65535.

Asynchronous Transfer Mode. This refers to a packet switching or transfer technology which supports a variety of service-specific segmentation and reassembly (SAR) of information for adaptation – using a separate ATM adaptation layer or AAL – to transfer information using fixed-size (53 Bytes; 5 Byte header and 48 Byte information) packets called Cells. The transfer mode is asynchronous because the information from an individual user or application does not need to appear in periodic or synchronous fashion for transmission.

Cyclic Redundancy Check. CRC is an error-detection method that uses a mathematical divisor to check the integrity of the data in a transmitted packet.

Digital Subscriber Line Access Multiplexer. This refers to a network element residing in the PSTN Central Office (CO) which multiplexes (or combines) signals from multiple DSL customers, and splits the information so that voice call related traffic can be routed to the PSTN Switch, and data traffic can be routed to the Internet backbone.

Noise may be defined as the combination of unwanted interfering signal sources whether it comes from crosstalk, radio frequency interference, distortion, or random signals created by thermal energy.

The maximum data rate of a modem is limited by the available frequency range (bandwidth) and signal-to-noise ratio (SNR).

On a communications channel, extraneous signals degrade the quality or performance of the link.

Crosstalk refers to the interference between channels. In the ADSL world, the interference between nearby cables can have a negative impact on the performance of the affected cables.

Near-end crosstalk (NEXT) is a major impairment for systems that share the same frequency band for upstream and downstream transmission. NEXT noise is seen by the receiver located at the same end of the cable as the transmitter that is the noise source.

Far-end crosstalk (FEXT) is the noise detected by the receiver located at the end of the cable from the transmitter that is the noise source. FEXT is less severe than NEXT because the FEXT noise is attenuated by traversing the full length of the cable.

Attenuation is signal loss due to the diminishing availability of signal energy, or signal power. As an analog or digital signal traverses across a medium, it fades. High attenuation may lead to the inability to recover the signal on the far end.

Baseband transmission is extremely limited to attenuation.

Modulation is a prescribed method of encoding digital (or analog) signals onto a waveform (the carrier signal). Once encoded, the original signal may be recovered by an inverse process called demodulation. Modulation is performed to adapt the signal to a different frequency range than that of the original signal.

Yes, you'll need a free IRQ.

This depends on whether the premises that you are moving into belongs to an ADSL enabled exchange.

No, your phone number will remain unchanged.

There are many requirements to be met before an ADSL service can be provided. Not all telephone services belonging to an ADSL covered exchange can necessarily have an ADSL service.

A service qualification check will test whether your telephone line will meet the following requirements:

Your telephone line belongs to an ADSL enabled exchange.
Your home or business is within a certain distance from the CO.
Your telephone line is a straight PSTN service without any ADSL incompatible equipment such as PABX.

Computer performance affects how fast received data can be processed. So this can make a difference to access speeds in environments that are otherwise identical.

You cannot use ADSL if you have a PBX or key telephone system. ADSL signals cannot travel through these systems. To use ADSL, you will need to have your telephone system rewired to bypass such equipment to avoid interferes with the high frequency spectrum used by ADSL.

ADSL is not possible if you have a multiple phones on a single line. ADSL signals cannot go through these systems.

There is little you can do to really tune your DSL line. You're generally relying on the cabling plant installed in your house all the way through to the provider's network and your speed is typically determined at provisioning time.

Yes, generally this is not a problem. The telephone company will provide as many lines, each on a separate copper pair into your house as you want.

To find out, you can check a number of sources.
A. You can check with your local telephone company to see if they are providing xDSL services.
B. Check around with your local Internet Service Providers (ISPs).
C. Try the competitive local exchange companies (CLECs) in your area.
D. There are some sites which claim to tell you if DSL is available in your area simply by filling in a online form.
Unfortunately you cannot rely upon these sites for 100% accuracy. Even if you're told xDSL is available in your area, you still might be not able to get it. Often providers will need to perform a Qualification test to determine if they can send and receive a signal within their parameters. Long local loops and poor cabling plants are common reasons for failing a loop qualification test.

Theoretically yes. However, most ADSL providers have been installing separate ADSL circuits to the remote user without using a splitter to separate out the voiceband bandwidth. If a splitter was used, you could use a traditional POTS modem over the voiceband frequency spectrum of your phone line as you always did. In most cases however, the line is dedicated for ADSL Modem only.

You can call your service provider and ask them for the address of your local CO and get an approximate distance from your residence to the CO.

Loading coils are used to extend the range of a local loop for voice grade communications. They are inductors added in series with the phone line which compensate for the parallel capacitance of the line. They benefit the frequencies in the high end of the voice spectrum at the expense of the frequencies above 3600Hz.

When lightning strikes, the current from the lightning can travel through the telephone cables, power cables, or Ethernet cables, damaging your ADSL modem or other peripherals. To protect your equipment from a lightning strike during a lightning storm or if there is any risk of lightning, we recommend that you remove the modular telephone cables attached to your ADSL modem and splitter. A variety of lightning protectors are available commercially. As some products may affect ADSL transmission quality, consult the retailer or manufacturer when you make your purchase.

This is mainly relevant for internet service providers. Your computer has an IP address when connected to the internet. When you use a modem and dial up, you are provided with an IP address. This IP is normally dynamic which means it changes each time you connect to the Internet.

The same can be true of ADSL. There is a log in procedure, and you are then connected. You can then stay connected forever if you want.

If your ISP provides a fixed IP address then you can run servers on your machine, and people can access it. This means you can have email actively delivered instead of collected periodically by POP3. You can run web and games servers. Generally it is a much better service.

If you have dynamic IP then your address changes. This makes it much harder for people to get hold of you unless they know your IP address. You cannot easily have a name for your machine (or web site or email) as this would have to be updated every time you change your IP address.

A corporate network can set up their own private fixed addressing for a wide area network.

With a router-type modem : A global IP address is assigned dynamically to the WAN side of the ADSL modem with a point-to-point protocol ( PPP ) connection. For PCs on a LAN, private IP addresses can be assigned, and the PCs access the Internet using network address translation (NAT).
For the PCI/USB type ADSL modem : You use the Windows dial-up function to establish a PPP connection, and a global IP address would be assigned.
A static IP addressing service may also be available, depending on the Internet Service Provider.

It depends on the Internet Service Provider. Check your ISP for the details.

It depends on the Internet Service Provider. Please choose a service where you can be assigned a fixed global IP address. Check the ISP's service options to find out whether this type of service is available.

In most cases, NO. Basically, client-side DSL has IP addresses assigned using Dynamic Host Configuration Protocol (DHCP). With DHCP, IP addresses are assigned out of a pool of available addresses. Thus you may get a different IP address every time you connect.

For most people, this is the preferred approach, because it is invisible to you and requires no special set-up on your side.

However, in a few cases people or companies might require a static IP address. In those cases, server-enabled DSL will be required.

Conditions of service, including user domain names and the availability of e-mail services and hosting services, are at the discretion of each ISP and may vary.
Please ask the service providers before you sign up.

For USB/PCI ADSL Modem, you use the Windows dial-up function to establish a PPP connection, and the PC obtains the DNS information.

For USB/PCI ADSL Modem, you use the Windows dial-up function to establish a PPP connection, and the PC obtains the DNS information.

We cannot tell whether the data communications that customers have with people outside their network constitute an attack in any particular instance.
You will need to make your own security arrangements.

NAT stands for Network Address Translation. For the Ethernet connected ADSL service, the line can be provided with a single IP address (Fixed or Dynamic) and a block of private addresses or it can be provided with a block of fixed IP addresses.

With a single address there are no incoming connections allowed. Only replied to outgoing connections using NAT can be received. However, with your own router you could configure port forwarding of certain ports to certain internal machines if you like.

With a block of addresses the connection is an unfiltered connection, normally to the internet. The ISP could provide NAT or filtering at their end if they wish.

All of this is in your control if you have your own equipment.

VPN : Virtual Private Network. A VPN is a network that has been implemented by overlaying point-to-point links over leased lines or over the public Internet. This can be implemented in the networking hardware/firmware using a software-only solution, such as Microsoft's point-to-point tunneling protocol (PPTP). When the public Internet is used, all communication must be encrypted to ensure security.

A protocol that links two computers in order to provide a terminal connection to the remote machine. Instead of dialing into the computer, you connect to it over the Internet using Telnet. When you issue a Telnet session, you connect to the Telnet host and log in. The connection enables you to work with the remote machine as though you were a terminal connected to it.

SNMP, Simple Network Management Protocol. SNMP is a network management protocol used almost exclusively in TCP/IP networks. SNMP provides a means to monitor and control network devices, and to manage configurations, statistics collection, performance, and security.