Broadband Internet

Broadband Internet access, often referred to as "broadband Internet" or simply "broadband", is an internet connection with a high data-transmission rate. DSL and cable modem, both popular consumer broadband technologies, are typically capable of transmitting 256 kilobits per second or more, at approximately nine times the speed of a modem using a standard digital telephone line.

Broadband Internet access became a rapidly developing market in many areas in the early 2000s; one study found that broadband Internet usage in the United States grew from 6% in June 2000 to over 30% in 2003. Modern consumer broadband implementations, up to 20 Mbit/s, are several hundred times faster than those available at the time of the popularization of the Internet (such as ISDN and 56 Kbit/s) while costing less than ISDN; though performance and costs vary widely between countries.

Overview

Broadband is often also referred to as high-speed Internet, due to its usually high rate of data transfer. In general, any connection to the customer of 256 Kbit/s (0.256 Mbit/s) or higher is considered broadband Internet. The International Telecommunication Union Standardization Sector (ITU-T) recommendation I.113 has defined broadband as a transmission capacity that is faster than primary rate ISDN, at 1.5 to 2 Mbit/s. The FCC definition of broadband is 200 Kbits/s (0.2 Mbit/s) in one direction, with advanced broadband being at least 200 kbit/s in both directions. The OECD has defined broadband as 256 Kbit/s in at least one direction. Though there is no specific bit rate defined by the industry, the one defined by the OECD is the one used most often as the common baseline around the world. Broadband can mean lower-bit rate transmission methods though, which some Internet Service Providers (ISPs) use to their advantage, marketing lower-bit rate connections as broadband.

In practice, the advertised bandwidth is not always reliably available to the customer; ISPs often allow a greater number of subscribers than their backbone connection can handle, under the assumption that most users will not be using their full connection capacity very frequently. This aggregation strategy works more often than not, so users can typically burst to their full bandwidth most of the time. However, peer-to-peer file sharing systems, often requiring extended durations of high bandwidth, stress these assumptions and can cause major problems for ISPs who have excessively overbooked their capacity. For more on this topic, see network traffic engineering. As take up for these introductory products increases, telcos are starting to offer higher bit rate services. For existing connections, this usually involves reconfiguring the existing equipment at each end of the connection.

As the bandwidth delivered to end-users increases, it is expected that video on demand services being streamed over the Internet, which currently require specialized networks, will become more popular. Currently, the data rate typical on most broadband services is not sufficient to provide good quality video, as MPEG-2 quality video requires about 6 Mbit/s for good results. Adequate video for some purposes becomes possible at lower data rates, with rates of 768 kbit/s and 384 kbit/s used for some video conferencing applications. The MPEG-4 format, at the higher end of cable modem and ADSL performance, delivers high-quality video at 2 Mbit/s. The Ogg Tarkin format is intended to deliver similar performance.

Increased bandwidth has already made an impact on newsgroups: postings to groups such as alt.binaries have grown from JPEG images to entire CD and DVD images. According to NTL, the level of traffic on their network increased from a daily inbound news feed of 150 gigabytes of data per day and 1 terabyte of data out each day in 2001 to 500 gigabytes of data inbound and over 4 terabytes out each day in 2002.

Digital Subscriber Line, or DSL, is a family of technologies that provides digital data transmission over wires used in the "last mile" of a local telephone network. Typically, the download speed of DSL ranges from 128 kilobits per second (Kbps) to 24,000 Kbps depending on DSL technology and service level implemented. Upload speed is lower than download speed for ADSL and symmetrical for SDSL.

Hardware

The subscriber end of the connection consists of a DSL modem. This converts data from the digital signals used by computers into a voltage signal of a suitable frequency range to be applied to the phone line.

In the early days of DSL, installation required a technician to visit the premises. A "splitter" was installed near the demarcation point, from which a dedicated data line was installed. Today, many DSL vendors offer a self-install option, in which they ship equipment and instructions to the customer. In this case, because no changes are made to the cable plant on the customer premises, all phone wires are carrying both POTS and DSL signal frequencies. Therefore, customers generally need to plug a DSL filter into each telephone outlet. However, this can sometimes cause degradation of the DSL signal (especially if more than 5 analogue devices are connected to the line) because the DSL signal is present on all telephone wiring in the building. A way to circumvent this problem is to install one filter upstream from all telephone jacks in the building, except for the jack to which the DSL modem will be connected. Because this requires wiring changes by the customer and may not work on some (poorly designed) household telephone wiring, it is rarely done. It is much easier to install filters at each telephone jack in use. In the past, establishing new cable modem or satellite broadband service generally did require a visit by a technician to the premises, but this too has changed. Cable companies now deploy self install kits which enable their customers to get set up without a truck roll.

At the exchange, a digital subscriber line access multiplexer (DSLAM) terminates the DSL circuits and aggregates them, where they are handed off onto other networking transports. It also separates out the voice component.

Protocols & Configurations

Many DSL technologies implement an ATM layer over the low-level bit stream layer to enable the adaptation of a number of different technologies over the same link.

DSL implementation may create bridged or routed networks. In a bridged configuration, the group of subscriber computers connect into a single subnet. The earliest implementations of the bridged configuration used DHCP to provide network details, such as the IP address, to the subscriber equipment, with authentication via MAC address or an assigned host name. Later implementations often use PPP over Ethernet or ATM (PPPoE or PPPoA), while authenticating with a user id and password and using PPP mechanisms to provide network details.

DSL also has contention ratios which need to be taken into consideration when deciding between broadband technologies.

The origin of Digital Subscriber Line technology dates back to 1988, when engineers at Bellcore (now Telcordia Technologies) devised a way to carry a digital signal over the unused frequency spectrum available on the twisted pair cables running between the telephone company's central office and the customer premises. Implementation of DSL could permit an ordinary telephone line to provide digital communication without interfering with voice services. However, incumbent local exchange carriers (ILEC) were not enthusiastic about DSL. It was less profitable than installing a second phone line for consumers who preferred simultaneous connections and had the capability to cannibalize existing ISDN customers. This changed in the late 1990s when cable television companies began marketing broadband Internet access. Realizing that most consumers would prefer broadband Internet to dial-up Internet, ILECs rushed out the DSL technology, which they had delayed implementing, as an attempt to win market share, which was being consumed by these cable television operators.

DSL is the principal competition of cable modems for providing high speed Internet access to home consumers in Europe and North America. Older ADSL standards can deliver 8 Mbit/s over about 2 km (1.24 miles) of unshielded twisted pair copper wire. The latest standard, ADSL2+, can deliver up to 24 Mbit/s, depending on the distance from the DSLAM. Some customers, however, are located farther than 2 km (1.24 miles) from the central office, which significantly reduces the amount of bandwidth available (thereby reducing the data rate) on the wires.

A cable modem is a special type of modem, designed to modulate a data signal over cable television infrastructure. Cable modems are primarily used to deliver broadband Internet access, taking advantage of unused bandwidth on the cable television network. There were 22.5 million cable modem users in the United States during Q1 2005, up 17.4 million from Q1 2004. Cable modems are also commonly found in Canada and Latin America.

Cable modems should not be confused with older LAN systems such as 10base2 or 10base5 that used coaxial cables — and especially not with 10broad36, which actually utilized the same sort of cable as CATV systems.

Cable Modems and VOIP

With the advent of Voice over IP telephony, cable modems can also be used to provide telephone service. Many people who use cable modems have opted to eliminate their Plain Old Telephone Service (POTS). Because most telephone companies do not offer naked DSL (DSL service without a POTS line), many VoIP users prefer cable modems.

VoIP and other new data services that require broadband Internet access are driving demand for increased bandwidth delivery via cable modems. As of 2005, several national cable systems in the United States have announced plans to upgrade their networks to meet this demand.

Both DSL and cable speeds exceed those of competing Internet services. Are DSL or cable any faster than each other? More importantly, are you getting all of the performance you should from your Internet connection? Follow along as we explain the speed difference between DSL and cable and offer tips for maximizing your performance.

DSL and Cable Speed - Bottom Line

Cable modem Internet services on average promise higher levels of bandwidth than DSL Internet services, which translates roughly to raw speed. However, while cable Internet will theoretically run faster than DSL, several technical and business factors can reduce or even eliminate this advantage.

DSL vs. Cable Raw Speed - Advantage Cable

In terms of theoretical peak performance, cable modem runs faster than DSL. Cable technology supports approximately 30 Mbps of bandwidth, whereas most forms of DSL cannot reach 10 Mbps.

One type of DSL technology, VDSL, can match cable's performance, also supporting 30 Mbps. However, Internet service providers generally do not offer VDSL, but rather the cheaper and slower ADSL or SDSL services.

DSL vs. Cable - Real-World Speed

In practice, cable's speed advantage over DSL is much less than the theoretical numbers suggest. Why?

Cable modem services can slow down significantly if many people in your neighborhood access the Internet simultaneously.

Both cable modem and DSL performance vary from one minute to the next depending on the pattern of use and traffic congestion on the Internet.

DSL and cable Internet providers often implement so-called "speed caps" that limit the bandwidth of their services.

Some home networks cannot match the speed of the Internet connection, lowering your performance

DSL and Cable Speed Caps

Both cable and DSL service providers commonly employ bandwidth / speed caps for residential customers. Bandwidth caps place an artificial limit on the maximum speed a customer can achieve by monitoring their individual traffic flow and throttling network packets if necessary. Bandwidth caps can reduce a 30 Mbps service down to 3 Mbps or lower.

Service providers may have several motivations for imposing speed caps including the following:

1. Providers concerned about the capacity limits of their network may implement a cap so in order to accommodate more customers.

2. Providers may believe that the vast majority of customers do not actually need any more bandwidth than that allowed under the cap.

3. Providers may want to create a fair-and-equal distribution of bandwidth of customers. Without a cap, for example, some DSL subscribers would enjoy much higher bandwidth levels than others in the same neighborhood.

4. Providers may want to charge higher or lower rates for greater or lesser bandwidth levels.

In 2001, about 5 million households in the United States subscribed to either cable modem or DSL Internet service.

DSL and cable together represent approximately 90% of the total broadband market in the U.S. As illustrated in the chart, cable modem technology has consistency led DSL in number of subscribers.

The USA possesses more broadband Internet subscribers than any other country. However, the People's Republic of China may surpass the U.S. as soon as the year 2007.

Each year, J.D. Power and Associates surveys thousands of U.S. residential customers on both DSL and cable modem Internet services. The survey assesses seven key factors that contribute to overall satisfaction with a high-speed Internet service:

Billing

Provider's business image

Cost of service

Customer service / technical support

Email services

Offerings and promotions

Performance and reliability

The 2004 survey includes results comparing DSL and cable modem. What's the bottom line? In each of the seven categories listed above, survey respondents gave DSL the edge over cable.

The graphic above displays results by service provider in this survey. The top two rated providers offer DSL service, while the lowest three rated providers offer cable modem service. Be sure to note where your local provider(s) rate in this survey.

When debating the relative merits of cable modem and DSL service, network security might be the most controversial item on the comparison chart. At first glance it appears one clearly wins the security battle over the other, but does this commonly-held opinion stand up to closer scrutiny? (See below)

DSL's Leg Up

Conventional wisdom holds that DSL service inherently offers better security than cable modem service. Some proponents of this view also happen to be DSL providers. Novia, for example, claims:

"DSL technology is clearly a superior choice compared to cable modems because DSL is more secure and can assure you access to higher bandwidth on busy networks."

One might dismiss such claims as a sales gimmick from over exuberant DSL networking companies. However, the same sentiment is expressed by many non-commercial organizations as well. At Northwestern University, Kellogg Information Systems actually recommends cable over DSL, but not because they believe cable offers better security:

"If ease of installation is important to you, KIS suggests a cable modem over DSL. The slightly more secure environment offered by DSL is not enough to justify the added cost and installation hassle."

No matter their origins, the claims of superior security for DSL all relate more to a perceived weakness in cable modem security than to any unique advantage DSL might hold.

Cable's Network Neighborhood

Cable modem service uses a shared cable line to provide service to an entire neighborhood. Essentially, all cable customers in a region belong to the same local area network (LAN). Without any security measures in place, anybody in the neighborhood might technically be able to click on their Windows Network Neighborhood icon and actually see the computer names and addresses of their neighbors on the service. If a customer enables file sharing on any drives, neighbors could even download copies of their data!

Although some cable customers have encountered this problem in the past, many providers avoid this problem today by bundling security features in the cable modem hardware. In particular, basic network firewall capabilities will prevent files from being viewed or downloaded. Most cable modems today also implement the Data Over Cable Service Interface Specification (DOCSIS). DOCSIS includes support for cable network security features including authentication and packet filtering.

DSL uses dedicated rather than shared cabling, and DSL customers in a given neighborhood do not appear as nodes on a LAN. From this, many have concluded DSL service provides better security. However, this argument is, at best, an oversimplified one.

Considerations for Both DSL and Cable

Both DSL and cable provide always-on connection capability. By design, DSL and cable customers can stay logged into the Net indefinitely if they choose. This feature provides great convenience but also creates a security risk. First, the "law of averages" means that by simply being online longer a user increases their chance of attack. More importantly, the always-on feature typically means the customer will be using the same network address -- a static IP address -- for the duration of their online session. (See below)

Static IP addresses provide network attackers with a fixed target. The analogy to baseball and other sports applies: a moving target will generally be harder to "hit”. Many DSL and cable providers offer DHCP address assignment, which causes one's address to change each time they sign on. However, this feature is only slightly helpful if users remain online for days or weeks.

How do attackers actually penetrate a home or small office network? In general, they exploit weaknesses in applications or in the underlying operating system. Typically vulnerable applications include email, databases, and instant messaging and conferencing tools. Operating systems contain many potentially vulnerable network services like FTP that utilize specific network ports.

Many DSL and cable modem customers choose to purchase routers to protect their internal systems. A DSL or cable router enhances the functionality of the basic modem with security features such as packet filtering and network address translation (NAT). One can usually build an equivalent security system with the basic modem and proxy software installed on the computer directly connected to the modem. Broadband routers simply provide a convenient and operating system-independent packaging of security features.

Both DSL and cable provide reasonably safe Internet access as long as one follows reasonable security precautions. Considering the numerous security holes found in operating systems and applications in the past, these precautions should be followed regardless of the form of Net access one uses.

Customers of DSL or cable can choose from a number of possible precautions including use of a broadband router, firewall software, or proxy server software. When possible, one should also disable network file sharing on the internal LAN. Anytime a user signs up for new Internet service, or changes providers, they should immediately perform vulnerability tests. A number of different security testing tools exist for popular operating systems.

Finally, when evaluating cable modem service providers, consider the technology they offer. Does their modem implement DOCSIS, for example, and if so, what security options have been enabled? Does the provider offer dynamic IP assignment, and does one's IP address change at a periodic interval, or only upon first connection?

The growing popularity of DSL and cable is helping to raise awareness of private network security issues, but these services add very little in the way of new security holes themselves. Home networkers who haven't yet studied the security of their LAN should do so immediately regardless of whether they use DSL, cable, ISDN, or traditional dial-up access.