CHAPTER I: DSL

DSL is an abbreviation for "Digital Subscriber Line". Digital Subscriber Line (DSL ) technology is a modem technology that uses existing twisted-pair telephone lines to transport high-bandwidth data, such as multimedia and video, to service subscribers. This is also known as “ 2Wire Digital Lifestyle”. DSL runs on regular copper phone wires which is a direct dedicated connection between your location and the phone company central office. A DSL modem is attached to the DSL phone line, and run another cable from the DSL modem to the computer. This aplication requires 10BaseT Ethernet card.Looking into internet, waiting for pages to be downloaded, modem to be connected to internet, busy signals, giving up phone line while surfing are the few very common scenarios that are faced by conventional 56.6Kbps internet user. DSL is here to soothe all those problems away!

Digital Subscriber Line (DSL) is a high-speed Internet connection over regular twisted copper pair phone lines that makes use of previously unused bandwidth on the phone line and uses it to transport large amounts of data to and from computers while allowing voice calls over the same line.

Figure 1.1: Signals In Copper Phone Line

As data's share of network traffic increases, Digital Subscribe Line (DSL) can offer numerous benefits for carriers which may need multiple DSL flavors to suit business and residential markets. As telephone technology enters its second full century, the business model for local exchange carriers is changing quickly from one based on providing circuit-switched voice services to one based on providing differentiated packet-switched voice and data services.

DSL has had incredible market acceptance spurred on by very aggressive pricing from companies like Pacific Bell (SBC) here in Northern California. Unfortunately, the pricing has been so low to attract customers (and keep them from trying cable), that many DSL service providers have been losing money on each account.

Most basic home DSL lines include the ability to connect regular analog phones to RJ-11 jacks, just like normal phone service. In some cases a POTS (Plain Old Telephone Service) splitter, which is basically a box that connects the analog phone wires is used.More expensive DSL service, sometimes called "enhanced" may provide higher data rates but more often than not is enhanced by the addition of features like static IP addresses (more than one).

1.2 ADVANTAGES AND DISADVANTAGES OF DSL

For the network access provider, the principal benefit of DSL is its ability to permit the rapid flow of information while using the existing copper wire foundation. Therefore, access providers do not need to install more copper or lay down miles of expensive fiber, as they would for other potential solutions.

DSL also eliminates providers' need to constantly upgrade their pricey Class 5 switch installations. If providers were to continue to provide data and voice services over the same network, they would have to buy more switches to ensure a congestion-free network.

As widely reported, a typical voice call lasts about five minutes, compared to an average 30 minutes for an Internet call. This means that for every new Internet customer, the carrier would need to provision six additional lines to guarantee the previous level of service availability to Plain Old Telephone Service (POTS) users.

DSL bypasses the Class 5 switch for data-only calls, so access providers can accept more traffic without investing in a huge switch upgrade. With DSL, voice and data paths are separated, which means that providers can meet the burgeoning need for high-speed data services without breaking their budgets. Furthermore, by keeping costs low, service providers can make money off the traditionally low-margin business of providing Internet access.

User Benefits

DSL offers customers access to a range of information services they previously could not receive through Internet communication. Users can experience high-speed Web browsing and can send and receive large documents.

Another benefit is to use DSL's always-on capability to receive information, such as news, video clips and stock quotes, that is pushed toward the user at the time it is generated, according to a personalized profile, without the need for the user to dial-up.

Always-on capability will help turn the PC into an appliance, making it easier for the mass consumer market to use. People will be able to walk to a PC and send e-mail, check for the latest airfare promotion or download a promotional clip for a new movie - and they will be charged on a usage basis, not a connect-time basis.

Consumers also may benefit by receiving all of their telephone-related services through a single provider. Customers are buried under a monthly pile of bills from utility service companies. By being able to receive voice and data services from one source-and paying for them through a single bill-consumers will gain significant added value from their service provider. This one-stop shopping will give providers an important means of differentiating their services from those of competitors such as cable companies.

For the business customer, DSL represents a very compelling investment for several key reasons:

• First, DSL provides a cost-effective way for telecommuters and branch offices to access the corporate network, provisioned via secure virtual private network services.
• Additionally, a DSL-based approach can improve the quality and reduce the cost of communications among employees via videoconferencing. It also can improve productivity by making intranet applications available to the distributed work force and by creating a cost-effective communications channel with the corporation's partners via extranets.
• Finally, DSL can displace the costs associated with separate voice, data and video networks.

To the business, though, a faster pipe does not represent a significant advantage if the service provider cannot guarantee bandwidth on that pipe. The availability of different classes of services and quality of service, provisioned at different prices, are essential requirements for the business. The granularity of these service classes also will help the carrier market its services to multiple tiers of customers, helping to accelerate the return on its overall investment.

Advantages

• Fast - Modems are much faster than analog modems. Different varieties of DSL provide different maximum speeds, from twice as fast to approximately 125 times faster than a 56.6K analog modem. The only speed limit with DSL is the speed of the Internet and all the different computers attached to it. The speed can go up to 1.5Mbps.
• Doesn’t tie up to phone line - DSL doesn't interfere with phone calls, even though it uses regular phone line. This means that one can leave the Internet connection open and still use the phone line for voice calls.
• Always on - DSL connection is always available. No more traditional dialing-up procedure is required and user doesn’t have to be worried being line-dropped while browsing or downloading. One only need to set up the computer to check for new e-mail or to browse through the internet.
• Reliable - DSL is reliable said to be reliable since it runs on phone line and phone company networks are among the most reliable in the world, experiencing only minutes of downtime each year
• DSL doesn't necessarily require new wiring; it can use the phone line you already have.
• The company that offers DSL will usually provide the modem as part of the installation.
• A router, along with a DSL modem, allows up to eight computers to access the Internet over a single DSL line.
• DSL provides the bandwidth you need for high-bandwidth applications. Streaming audio and video will come across in real-time, rather than interrupted segments.
• DSL offers reliable high-speed Internet connections that are far less expensive than other options such as T1 lines.
• DSL is flexible and scalable, ideal for growing business computer networks.
• Enable users to work from home, listen to streaming audio or watch streaming video while working on your computer.

Disadvantages

• A DSL connection works better when user is closer to the provider's central office.
• The connection is faster for receiving data than it is for sending data over the Internet.
• The service is not available everywhere

1.3 TYPES OF DSL

The term xDSL covers a number of similar yet competing forms of DSL, including ADSL, SDSL, HDSL, RADSL, and VDSL. xDSL is drawing significant attention from implementers and service providers because it promises to deliver high-bandwidth data rates to dispersed locations with relatively small changes to the existing telco infrastructure. xDSL services are dedicated, point-to-point, public network access over twisted-pair copper wire on the local loop ("last mile") between a network service provider (NSP's) central office and the customer site, or on local loops created either intra-building or intra-campus. Currently the primary focus in xDSL is the development and deployment of ADSL and VDSL technologies and architectures. This chapter covers the characteristics and operations of ADSL and VDSL.

Table 1.1: Types Of DSL and Description

1.4 COMPARISON OF DSL TO OTHER TECHNOLOGY

Analog dial-up modems

Broadband is the name given to systems designed for high-speed transmission of huge amounts of electronic data. Think of a pipe carrying water. If you want to get more water down the pipe, and send it faster, you need a broader pipe.

A dial-up modem (narrowband) would have a small trickle of water flowing along the bottom of the pipe, while a broadband technology such as DSL or cable uses almost all of the available carrying capacity.





Figure 1.2: Bandwidth Usage

Analog modems have reached their technical limit in V90 technology that delivers up to 56.6 kilobits per second. Cheap cost and compatibility with most phone lines have made them the communication technology of choice for individual PC users. It is widely believed that a 56K, V.90 modem squeezes close to the maximum amount of data that can be fit on an analog phone line, and you can only get that bandwidth if your ISP has V.90-compatible equipment on their end. In addition, the modem only achieves its top speed if the signal only goes through one analog-digital conversion and the quality of the line is good, which means that most V.90 modems rarely deliver the full 56 kilobits per second.

The only analog trick left is to bond two 56K modems together for more bandwidth, sometimes referred to as the "shotgun" setup. This increases your Internet access costs, and can be frustrating to set up. To try this, an ISP that can support this method and two telephone lines are required. Even if 112K is obtained out of this arrangement, it still has drawbacks when compared to the other technologies. A 56K modem is not good enough for a more-than-casual Internet user. For the near future, problems caused by congestion of the public phone network, which was not designed to carry Internet traffic can be expected.

Cable modems

Cable modems are the primary competitor to DSL. They offer high-bandwidth Internet access over cable TV lines, the service is reasonably reliable, and the service costs approximately $40-60/month (plus a $100-175 installation fee). Cable modems are used primarily for residential Internet access because office buildings and business parks aren't usually wired for cable television service.

Table 1.2 : Cable and DSL speed rates

There are two types of cable modems. The most prevalent is the hybrid fiber/coax (HFC) modem, which runs over HFC cable networks and offers theoretical download speeds from 3 to 30 megabits per second; however, real-world data indicate that speeds from 400 to 1440 kilobits per second can be expected.

The other, older type is a one-way modem that runs over standard cable coaxial networks. These modems offer up to 2 megabits per second download speeds, but they offer no upload capacity because cable networks were not originally designed for two-way communication. With the older system, in order to send out information over the Internet, a separate phone line, modem and ISP are required. This one-way approach is being dumped as cable companies upgrade to two-way infrastructure.

In order to offer the two-way service, the cable company must first upgrade your neighborhood to hybrid fiber/coax cable lines. As of early 1999, only about 30% of the total cable lines in the United States have been converted to HFC. One reason for the spotty availability of cable modem service is that upgrading lines is very expensive. In addition, cable lines are not likely to be located around office buildings and business parks, so high-bandwidth options for businesses probably won't include cable.

Cable networks differ from DSL networks in their basic structure. With a cable modem, you are sharing access to the Internet, unlike DSL which runs on a dedicated connection. Cable modem service is set up like a local area network (LAN), making it possible for many users to share the same bandwidth. The downside of shared access is security where experienced hackers may be able to break into other computers on the same cable network in the neighborhood. Also, as more users in a neighborhood send and receive information, it is possible that the available bandwidth for individual users could shrink, slowing speeds similar to the rush hours on a city highway.

It is worth asking about content restrictions before purchasing the cable modem service. Some cable systems would prefer that you use the cable TV service for watching video, so as to restrict the amount of streaming video accessible with cable modem! One company is trying to require cable modem subscribers to take its proprietary content. In other words, one would see what the company wants him/her to see, and wouldn't be able to venture beyond that area to the whole Internet. The Consumers Union and the Consumer Federation of America are attempting to stop these practices by convincing the Federal Communications Commission that cable systems are common carriers like phone networks. If successful, the FCC could legally prevent cable companies from putting any restrictions on Internet access.

Satellite access

The most widely available high-bandwidth Internet access technology in a geographic sense is Direct Broadcast Satellite (DBS), also known as Digital Satellite Service (DSS), a competitor to cable television that 6.6 million Americans were using in 1998. As long as there is a clear line of sight to the southern sky, a special type of Internet access through DBS service can de ordered.

DBS service requires a small dish (usually 18 to 21 inches across), mounted outdoors to receive data sent from a stationary satellite. A recent test showed that DBS service providers can deliver download speeds in the neighborhood of 350 kilobits per second.

The downside is that the competitively-priced services are receive-only, much like the one-way cable modem setup. A phone line and modem are still needed to request information from the Internet. Also, satellites are slow for Internet usage. Let's say you have a DBS Internet access provider and you click a link to pull up a web page. Clicking that link is actually a request for information that travels out on your phone line, through the ISP, through the normal paths on the Internet, and is finally answered. The information you requested is then sent 22,300 miles up to the satellite, and then back down 22,300 more miles to your DBS dish. Even at the speed of light, this method of communication is slow enough to cause a noticeable lag between click and response. This is not a big problem for downloads, but if you're a chat junkie, or you use the Internet for a lot of live, two-way communications, DBS may not be the best choice for you.

Setup is a bit more of a hassle with DBS, too. Getting the DBS hardware to "talk" to your computer is an issue, and satellites can have technical problems. Historically, they have been very reliable, but when they quit working, there is no quick fix. It's possible that there's no service for a while. One may be able to switch to another satellite, possibly requiring the repositioning of dish and/or retuning satellite receiver.

One of the most well-known companies in DBS Internet access services is charging $179 - $229 for installation, and the dish and satellite modem together cost about $350. Monthly service rates range from $20 for 25 hours per month of online usage, up to $110 for 200 hours per month. Additional hours are billed at $1.99. (If you would like to receive DirecTV/USSB television with your Internet access, you can pay $400 - $500 for a dish that can receive both data and television signals. This cost includes the satellite modem, but the TV receiver will cost you more.)

ISDN

ISDN is a widely available, faster alternative to analog modems. ISDN works over standard copper phone wiring, like DSL, and gives you three data channels to work with. The two B channels operate at 56 kilobits per second or 64 kilobits per second, depending on how phone company has configured them. These two channels can be "bonded" together to double the speed. The D channel is used to connect your calls and uses only 16 kilobits per second of bandwidth. With the right hardware however, 9.6 kilobits per second of this bandwidth can be used as an always-on Internet connection. This feature is called Always-On/Dynamic ISDN (AO/DI). It is useful for low-bandwidth applications such as e-mail and stock quotes. In addition, when the capacity hits the 9.6 kilobits per second limit, the hardware can bring up a B channel to accommodate it. When the capacity need falls back down, the B channel is dropped.

Always-On/Dynamic ISDN is just catching on. If interested, one will have to buy an AO/DI modem, buy a Dial-Up Networking Patch for Windows, and find an ISP that can support it.

Depending on how much high-speed access competition there is in the market, installation and setup charges for ISDN range from $125 to $400 including a good adapter to connect the computer to the network. Monthly service costs range from around $20 to $80.

1.5 DSL FOR HOME AND TELECOMMUTER

G. Lite ADSL - G.Lite ADSL is a new standard for DSL service that will be available in mid to late 1999. It is the most consumer-friendly version of DSL. The cost for equipment and service will be less than other varieties. It will also be easier to install than other varieties - you will be able to do it yourself. It is based on ADSL, and offers downstream speeds up to 1.5 megabits per second and a maximum upstream data rate of 384 kilobits per second. Many DSL service providers will let you order lower bandwidths for a lower monthly cost. One common service will include a downstream speed of 384 kilobits per second with an upstream speed of 128 kilobits per second.

G.dmt ADSL - G.dmt ADSL is the other standard for home DSL service. It is an asymmetric technology, offering more downloading than uploading capacity. The big difference between these two technologies is speed. Sometimes called "Full-rate ADSL," the G.dmt variety can download data at -up to 8 megabits per second, and send data upstream at up to 1.5 megabits per second, if the modem is located within 10,000 - 12,000 feet of the phone company's CO (central office). Up to 18,000 feet away from the CO, G.dmt ADSL can reach up to 1.5 Megabit per second downstream. This type of DSL requires the telephone company to install a device called a "splitter" on the phone line, requiring an installation visit to your home.

1.6 SECURITY ISSUES

People are often surprised to discover that their DSL (or cable modem) connection is not secure. If file sharing is turned on, for example, it's possible for someone out on the Internet to easily hack into your computer and view or modify your files. DSL and cable modem connections, despite advertising claims to the contrary, are often architected as "shared" connections. The nature of your connection exposes you to significant danger if you don't have protection. If you are connecting your network to the Internet via DSL or Cable Modem, make sure you have a device or software that provides protection. If you have a single computer, you either want to turn off file-sharing, or better yet, install a personal firewall. McAfee, among other companies, offers personal firewall products.

1.7 ADDRESSING ISSUES

DSL accounts come with either a dynamically assigned TCP/IP address or static address(es). Most low-cost accounts designed for home offices or very small businesses offer a single dynamically assigned address. The benefit to the provider is that they can use a smaller pool of addresses to support a larger number of users. Although these providers will claim that their DSL service is "always on" the truth is that your connection, when idle, times out. Each time A user wants to use the Internet after an idle timeout period, he will have to reconnect and obtain an IP address. Granted, this may take a couple of seconds, but he's not really always on! A common protocol used to provide your DSL connection and IP address in this scenario is the Point to Point Protocol over Ethernet (PPPoE). The provider will give the subscribers PPPoE software for their PC or Macintosh. Other software available on the Internet can also be used. With a dynamically assigned address, it is more difficult to share a DSL account with multiple users on the same LAN, although not impossible. It is also more difficult to host an email server, web site or FTP site on DSL connection, although again, not impossible. Slightly more expensive accounts come with at least one fixed IP address. With fixed addresses, it is easier to share the DSL connection and host email and web servers.

1.8 CHOOSING SERVICE PROVIDER

DSL Provider Monthly Notes   $49/month to $750/month (Business or Residential Package) ADSL to T1 Speed (1.5MB solid connection) Speakeasy, rated NUMBER 1 by DSLReports.com in customer satisfaction, Choose from an array of bandwidth packages for both residential and business customers, from ADSL to full T1 speeds. Prices range from $49/month to $750/month  Static IP Unlimited Dialup Verizon DSL $34.95 768 Kbps / 128 Kbps Free DSL Modem $29,95 for months 2 and 3 ($34.95/month thereafter). Free first month $25 Virtual MasterCard Gift Card. Earthlink DSL: $21.95/mo for 3 months and $49.95 thereafter. Business and residential plan available. 1.5Mbps Down, 256Kbps Up FREE DSL Modem Free Installation 1 Year/No Annual Contract Option Available Static IP Connect Multiple Computers Pac Bell Basic DSL $49.95 Dynamic IP $99 for DSL Modem (free for annual contract) Southwestern Bell DSL $49.95 $200  for technician install (free if customer self-install) $99 for DSL Modem Verizon/GTE DSL (Silver) $49.95 (768 Kbps/ 128 Kbps) $59.95 for Enhanced Bronze Package (1.5 Mbps/128 Kbps)  XO Communication Business DSL $149.00 $ 54.95 for 608/128 Kbps  $ 79.95 for 1.5 Mbps/384 Kbps  $225 for DSL Modem    AT&T DSL $54.95     Bellsouth Standard DSL $49.95 $199.95  for technician install (free if customer self-install) $99.95 for Service Activation Fee  $150 for basic Modem (PCI or USB)  Prodigy DSL $49.95 Dynamic IP 1-Year contract $99.00 for modem Sprint FastConnect DSL $50.00 $49.99 for activation and $9.95 for S&H Dynamic IP Verizon DSL $59.95 (1.5 Mbps/128 Kbps) $125 equipment fee will apply Earthlink DSL $49.95 Dynamic IP ($64.95 per month for static IP package) $129 per month for Biz DSL

Table 1.4: Some Foreign DSL Providers's Information

1.9 HARDWARE INFORMATION