ADSL vs CABLE MODEM vs WIRELESS

Introduction

As the Internet moves from dial up connections to high bandwidth links, three principle Technologies vie for user’s attention. Cable modems, which allow users to connect using the cable television network, seem to be first out of the gate with broader availability and lower costs with some concern about the security issues. ADSL, a service available through the telephone network, is reputed by some sources to offer greater potential for the future. And last but not least is Wireless Broadband; this is a newer technology, which use’s a satellite signal, from the satellite you will then run the coaxial cable into the wireless router, then run the RJ45 into your hub, switch, or computer.As the use of information technology grows, both personally and commercially, we see hardware capability expand continuously. At the same time the demands of users and the software they employ promptly exploits new capacity to its limits. The explosion in use of the Internet that has occurred in recent years leaves us with the limited bandwidth available as a bottleneck in the continued growth of the systems we use. Those who have been using dial up connections since the mid-eighties will know that each time the technology moves to a higher speed, whether from 300 baud to 1200, the great leap to 9600 baud or the more recent move to 56k baud, we are told that we are approaching the limits of what is possible using ordinary telephone lines. Each time, the pundits have been wrong but now, at 56k it seems they may finally be right and the search for alternatives is on (Clark, 99). The Internet has gone from a small user base of email correspondents to wide consumer use for web-based information over the past few years. These uses approach the limits of present telephone dial up connections. Audio and video need more bandwidth to come into their own. If, as some predict, we will move to the use of thin clients with programs residing on distant servers, higher bandwidth will be a necessity. “There are alternatives to telephone dial up lines such as ISDN, T1 or T3 leased lines, and others however it seems that they do not offer the combination of speed, economy and availability users want”(Angell, 01). This paper will examine the present state of the three technologies, ADSL, Cable, and Wireless. I will review cost, speed, availability and security of these services as we consider these to be the principle criteria by which users choose between them. I will offer my conclusions and sources of information for further research. Before examining these details, some background on these technologies may be of use to the reader.

Cable Modem Technology

Cable modems use the television cable network. This is an always-on service, which offers significant bandwidth improvement over dial up service. Unlike xDSL service, subscribers share a connection. This presents security issues and can affect speed as the bandwidth is shared between a numbers of users. The cable network is a broadcast oriented system. The two way connection users require has required upgrades to the cable system to provide a network connection.More than 105 million homes in North America are passed by broadband coaxial cable plant and more than 75 million homes are cable TV subscribers. With near-ubiquitous coverage, coaxial cable connections provide a powerful platform for providing residences and small business with high-speed data access. However, one-way cable television systems must be upgraded into modern two-way networks to support advanced communications services, a technically complex and capital-intensive proposition. So far, cable operators have upgraded networks serving 60 percent of North American cable homes to support broadband Internet access.To deliver data services over a cable network, one television channel (in the 50 – 750 MHz range) is typically allocated for downstream traffic to homes and another channel (in the 5 – 42 MHz band) is used to carry upstream signals.

A headend cable modem termination system (CMTS) communicates through these channels with cable modems located in subscriber homes to create a virtual local area network (LAN) connection. Most cable modems are external devices that connect to a personal computer (PC) through a standard 10Base-T Ethernet card or Universal Serial Bus (USB) connection, although internal PCI modem cards are also available.

The cable modem access network operates at Layer 1 (physical) and Layer 2 (media access control/logical link control) of the Open System Interconnect (OSI) Reference Model. Thus, Layer 3 (network) protocols, such as IP traffic, can be seamlessly delivered over the cable modem platform to end-users.

A single downstream 6 MHz television channel may support up to 27 Mbps of downstream data throughput from the cable headend using 64 QAM (quadrature amplitude modulation) transmission technology. Speeds can be boosted to 36 Mbps using 256 QAM. Upstream channels may deliver 500 Kbps to 10 Mbps from homes using 16QAM or QPSK (quadrature phase shift key) modulation techniques, depending on the amount of spectrum allocated for service. This upstream and downstream bandwidth is shared by the active data subscribers connected to a given cable network segment, typically 500 to 2,000 homes on a modern HFC network.Most cable modem systems rely on a shared access platform, much like an office LAN. Because cable modem subscribers share available bandwidth during their sessions, there are concerns that cable modem users will see poor performance as the number of subscribers increases on the network. “Common sense dictates that 200 cable data subscribers sharing a 27-Mbps connection would each get only about 135 Kbps of throughput — virtually the same speed as a 128-Kbps ISDN connection — right? Not necessarily (Crockett, 99)”.

Unlike circuit-switched telephone networks where a caller is allocated a dedicated connection, cable modem users do not occupy a fixed amount of bandwidth during their online session. Instead, they share the network with other active users and use the network’s resources only when they actually send or receive data in quick bursts. “So instead of 200 cable online users each being allocated 135 Kbps, they are able to grab all the bandwidth available during the millisecond they need to download their data packets — up to many megabits per second (Fitzgerald, 99)”.

If congestion does begin to occur due to high usage, cable operators have the flexibility to add more bandwidth for data services. A cable operator can simply allocate an additional 6 MHz video channel for high-speed data, doubling the downstream bandwidth available to users. Another option for adding bandwidth is to subdivide the physical cable network by running fiber-optic lines deeper into neighborhoods. This reduces the number of homes served by each network segment, and thus, increases the amount of bandwidth available to end-users.

ADSL Technology

Although we tend to refer to this technology as ADSL (which is an acronym for Asymmetric Digital Subscriber Line) it is actually a subset of a broader group of standards that are referred to as xDSL (Hawley, Oct 99). It is Asymmetric in that users demand greater download bandwidth than upload bandwidth. The service is designed to sacrifice upload bandwidth in favor of download bandwidth. The service is carried over the unshielded twisted pair lines offered by telephone companies. “Greater speed is achieved by utilizing bandwidth beyond the regular voice range (300 Hz to 3,200 Hz)”( Berst, 01). Upgrading of telephone company equipment is sometimes required and there are distance limits between the Telco switch and the subscriber location that affect availability. It is an always-on connection and can share the line with regular voice service concurrently. Unlike cable, each user has a dedicated line. To use DSL you need a special DSL modem. These modems are not widely available, yet, other than from service providers. This modem is connected between an Ethernet card in the computer and a telephone connection.

Wireless Technology

The fixed wireless headend is the control point for the broadband access network. A carrier-class IP switch or router interfaces with the backbone data network offering connectivity to remote content servers, as well as the global Internet.This switch/router also connects to a wireless cable modem termination system (CMTS) that coverts data from a wide area network (WAN) protocol, such as packet over SONET, into digital signals that are modulated for transmission over the wireless network. These signals are then converted into wireless microwave frequencies through a transceiver and broadcast through an antenna to customer home or business locations. Like their counterparts that operate over cable TV systems, a wireless CMTS unit typically provides a dedicated 27 Mbps per downstream 6 MHz data channel that is shared by active users. Upstream speeds are typically below 1 Mbps.Content and application servers are typically located at the fixed wireless headend, as are network management and operations support systems. If the carrier were offering IP telephony, voice calls would be directed by the headend router to an IP telephony gateway, and then onto the public switched telephone network (PSTN).

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Most cable modem systems rely on a shared access platform, much like an office LAN. Because cable modem subscribers share available bandwidth during their sessions, there are concerns that cable modem users will see poor performance as the number of subscribers increases on the network. They are able to grab all the bandwidth available during the millisecond they need to download their data packets.

sumber : Scott Whitlow