10 Myths About Cable and DSL Internet Technologies
The speed of hybrid fiber coax (HFC) cable and Digital Subscriber Line (DSL) Internet access services are comparable.
Fact: DSL Internet access offerings typically are not as fast as those offered via HFC. Depending on the DSL provider, service levels can range from 128Kbps to 7Mbps downstream from the Internet to the user while upstream service levels from the user to the Internet can range from 128Kbps to 1Mbps. Over HFC, service levels can range from 400Kbps to 10Mbps downstream and 128Kbps to 10Mbps upstream. Service levels depend on service agreements offered by each cable system operator per market, and depend on whether the access is for residential or commercial use. But typically, HFC has more bandwidth available than DSL.
Many homes and offices cannot get the higher speed DSL service because they are located too far from the telephone company's central office. DSL circuits are prevented from maintaining high-bandwidth connections past relatively short distances, such as 18,000 feet. In contrast, HFC technology provides all customers equal access to high-speed services.
DSL connections are "dedicated," whereas HFC cable connections are "shared." As more users are added to the cable-based Internet service, the speed of a user's Internet connection decreases.
Fact: All connections to the Internet, from nearly any provider, are shared at some point. In fact, the Internet itself is a network of networks, shared by millions of users worldwide. The only dedicated portion of a DSL circuit exists between the user's home or business and the telephone company's central office. Beyond that point, DSL subscribers are on the telephone company's central office. Beyond that point, DSL subscribers are on the telephone company's metropolitan network, shared with other DSL, data and telephone subscribers. The user's connection then is routed to an Internet Service Provider (ISP), where it is shared with all other ISP subscribers before being transmitted to the Internet. Therefore, both DSL and HFC technologies provide a shared access to the Internet - but in very different ways.
"Shared versus dedicated" really asks: What is the overall performance of the Internet connection? Cox Communications, among the largest U.S. cable broadband companies, is a leader in providing HFC-based Internet services. Several factors contribute to their success:
1. Cox's HFC network has been largely rebuilt over the past few years and is designed with growth in mind. The network is highly scalable, enabling expansion of available bandwidth to meet increasing customer demands without major network upgrades. Cox can add an additional channel for capacity, or create a new neighborhood "node," allowing bandwidth to double for a given group of users.
2. High-performance proxy/cache servers, installed locally for each market Cox serves, reduce the need to retrieve frequently requested content (popular Website pages) from the Internet, further enhancing the user's online experience.
3. Cox customers connect to the Internet via a nationwide, very high-speed, private Tier 1 backbone. A Tier 1 ISP is one whose backbone peers directly into national and regional Internet Network Access Points (NAPs). The private backbone ensures low network latency, and contributes to higher effective throughput. Tier 2 or below ISPs, some of whom provide DSL services, connect to the Internet via Tier 1 providers, thus reducing the speed and capacity of an Internet connection.
Because customers within an HFC neighborhood node are using a "shared" network, one user can more easily tap into the data stream of another local customer.
Fact: Cable networks are no less secure than phone networks. Currently, many cable systems use proprietary technology, which are inherently difficult to reverse engineer. Although cable modems share a common cable infrastructure that may serve many customers, each cable modem is addressed individually. In order for someone on the same cable segment to eavesdrop on another customer's data conversation, they would have to access the much more complex radio frequency (RF) signal by completely reverse engineering the proprietary cable system - a highly unlikely scenario.
In late 1999 and early 2000, Cox will be upgrading its cable systems to support DOCSIS (Data Over Cable Service Interface Specification)-compliant cable modems and equipment. Using the DOCSIS standard, Cox's HFC specifications will guarantee user data privacy across the cable network by encrypting customers' data traffic flow. With Baseline Privacy Interface (BPI), Cox controls distribution of encryption keys to its customers' cable modems from its master telecommunications centers and hub sites. Policing and filtering functions are used to reduce risks from attacks targeted at a customer's PC. These policing capabilities secure a customer's data via a state-of-the-art data encryption standard (DES) algorithm.
When a cable connection is delivering digitized video, voice and high speed data simultaneously to the home or office, the cable modem user will suffer from "congested" bandwidth, unlike a DSL user.
Fact: Because of the inherent ability of hybrid fiber-coax networks, cable companies can assign dedicated frequencies for delivering each video, voice and data service without conflict. Thanks to the 750MHz capacity of Cox's network and plant, additional bandwidth is reserved for the next generation of services yet to be developed. Cable networks can do this because they can deliver much more bandwidth to their customers than can telephone lines. Telephone lines are limited to approximately 1MHz of bandwidth, which must be shared between voice and data services. Since cable services all use distinctly different channels, you can watch TV, talk on the phone, and surf the Net simultaneously without impacting any individual service.
HFC cable services are less reliable than the data services of a telephone company.
Fact: Cox's HFC cable services run over a ring-in-ring redundant network. The ring architecture provides multiple paths to each of Cox's HFC nodes serving 1,000 or fewer customers. Should even one of the fibers to that node break, user traffic can continue to flow uninterrupted across another redundant fiber path. As such, the self-healing ring-in-ring distribution offers the user a continuous, secure connection to the Internet.
When looking at price/performance, DSL is the obvious choice.
Fact: When compared to Integrated Services Digital Network (ISDN) or other high-cost services offered by many of the large telephone companies, Internet access using DSL does offer price savings. But cable offers a surprisingly low cost per user, typically lower than DSL. And, cable connection speeds typically start where DSL tops out.
Often, the price quoted for DSL service does not include the cost for an ISP's Internet access and features such as email. It's important to check that the DSL service price offered contains Internet access and related features. To accurately compare the cost of DSL and HFC Internet solutions, you must combine the price of the DSL circuit from the home or business to the telephone company's central office, along with the Internet access service charge from a DSL-capable ISP. With Cox's primary HFC Internet services, Cox High Speed Internet and Cox High Speed Internet business product, the cost of Internet access is built into the monthly pricing, unless otherwise indicated.
DSL service allows its customers to choose their own ISP; cable doesn't.
Fact: DSL providers frequently deliver ISP services packaged with a DSL circuit. As such, most DSL customers cannot choose an ISP other than the one already packaged with the DSL service. Cox provides its residential customers the ability to access the content of other.
ISP content and services delivered by the DSL provider typically are designed for 28.8K, or in some cases, 56K modems, in order to accommodate their most "common denominator" access speed customers. As part of its residential service, Cox provides near-instant video, high-quality sound, rich graphics and easy-to-use Web guides that utilize the high bandwidth available through HFC cable.
DSL is a new digital connection technology.
Fact: DSL technology comes in a variety of flavors, some of which are delivered over the old copper, twisted-pair wiring used for Plain Old Telephone Service (POTS). DSL was created to squeeze more speed and capacity out of this existing wiring system, which was designed for low-speed, low-capacity voice communications. Much of this wiring may have been installed decades ago. In contrast, HFC cable architecture is relatively new. An HFC network can deliver high-speed, high-capacity video, voice and data services to homes and businesses without relying on the local telephone network.
DSL is widely available today, because it's based on an existing network that reaches most homes and offices.
Fact: DSL services are not widely available for several reasons. To deploy DSL services upon the older copper-based network, the telephone companies must install new equipment in their central offices to combine DSL circuits together into a shared network. Connections to ISPs must also be established. Furthermore, they need to modify and upgrade the copper circuits to a home or business. Several obstacles either delay or prevent these circuits from being used to deliver DSL services:
· the existence of bridge taps, load coils, and changes in wire gauge; and
· the presence of "cross-talk," a type of interference between signals carried on separate wires in close proximity to each other, such as in a telephone wire bundle. Cross-talk interference increases proportionally with faster DSL speeds and with the number of similar signals carried in the same bundle. Because of cross-talk limitations, many DSL customers are not able to receive the highest speeds DSL marketers promote.
As stated in Myth #1, the distance from a home or business to the telephone company's central office also dictates what levels of service a customer can receive - if at all. Typically, only a small percentage of customers, those located within 18,000 feet of the central office, can obtain the optimal connection of 7Mbps speeds from DSL. Connection speeds drop dramatically to just 64Kbps, or less, for users outside of this range. Many DSL providers cannot tell you what speed is available to your home or business until they individually test your line.
High-speed cable connections aren't widely available, since most cable networks have not upgraded their systems to HFC networks for two-way communication.
Fact: HFC cable access reaches far more households and businesses than does DSL at this time. According to the Yankee Group, the number of cable modem subscribers in the U.S. is projected to surpass one million at year-end 1999, while the number of DSL subscribers is projected at 250,000 for the same period. Additionally, 25 percent of U.S. homes will have cable modem service availability at year-end 1999 as compared to 10 percent of U.S homes for DSL availability. At year-end 2000, those numbers are projected to increase to 43 percent for cable modem-ready U.S. homes and 20 percent for DSL-ready U.S. homes. At year-end 1999, Cox expects for nearly 65 percent of its homes passed to be HFC Internet ready.