Consider more than bandwidth when choosing Internet access technology
Any agency building toward expanded online government will soon reach a fork in the road over its choice of Internet access technology.
Digital subscriber lines, Integrated Services Digital Network, 56-Kbps analog, T1, cable, fixed-point wireless and satellite all have virtues and drawbacks. Which is right for your agency?The one you select will depend on such things as your bandwidth requirements, budget and whether the necessary supporting infrastructure is available.Here's a look at what each one offers.This is the traditional telephone modem connection used to connect most computers to the Internet. Maximum speed is determined by the type of modem attached to the line. Most analog modems now are 56 Kbps, the highest speed possible on a normal dial-up line, although the actual transmission speeds usually are lower.Cable modems on average have a bandwidth of 1.544 Mbps. Fiber-optic cable connects the transmission center to local coaxial cable lines. Fiber-optic cabling takes up little conduit space and offers high security with high bandwidth. Cable also provides always-on availability.DSL is a term for any local digital network loop. In simple terms, DSL is an improved method for moving data over regular telephone lines. A DSL circuit, however, is much faster than a normal phone connection and, like cable, is always available.The circuits are configured to connect to two specific locations, similar to a leased line, allowing for download speeds of up to 1.544 Mbps. DSL is a popular alternative to ISDN and traditional leased lines because it is faster, less expensive and provides a dedicated line as well as unlimited usage for a monthly fee.A common configuration of DSL transmits data asymmetrically so that bandwidth usage is higher in one direction than in the other. Typical ADSL applications transmit at around 8 Mbps downstream and 768 Kbps upstream.'This is particularly beneficial for Internet access, remote access and video on demand, in which downstream usage far exceeds upstream usage. In addition, normal telephone use is unaffected.Unlike ADSL, HDSL lines use a symmetric method of transmitting data at rates up to 1.5 Mbps in both directions. Because of the symmetric properties, the highest transmission rates can be supported in lengths up to 15,000 feet. This makes HDSL suitable mainly for campus like environments and localized service.An extension of HDSL, VDSL supports data rates up to 52 Mbps downstream and 1.5 Mbps upstream over distances of 1000 to 4000 feet.Fixed-point wireless is a point-to-point system sending microwave transmissions from one fixed point'a microwave dish'to another. Though expensive, it offers a broader bandwidth and speeds up to 4,500 times faster than a 56-Kbps dial-up modem.ISDN networks transmit over copper wire at up to 128 Kbps. It can be expensive to install and operate, but costs'around 30 cents per minute'are steadily dropping. Because it is digital, it also supplies higher levels of speed and security than traditional phone lines.Transmissions are sent to an orbiting satellite and beamed down to an individual location. Satellites allow fast transmission over immense distances with no loss of signal.Transmission speeds are fast, but the service is expensive and travels only downstream; you still have to send from your PC over a phone line.T1 is a leased-line connection that functions at 1.544 Mbps. T1 is expensive but is one of the speediest methods available for connecting to the Internet, because of its bandwidth.There also is T3, which transmits at 4.5 Mbps.
Analog modem
Cable
DSL
Asymmetric DSL
High-bit rate DSL
Very high-bit rate DSL
Fixed-point wireless
ISDN
Satellite
T1
Drew Robb of Tujunga, Calif., writes about information technology.
By Drew Robb
Special to GCN
Any agency building toward expanded online government will soon reach a fork in the road over its choice of Internet access technology.
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Analog modem
Cable
DSL
Asymmetric DSL
High-bit rate DSL
Very high-bit rate DSL
Fixed-point wireless
ISDN
Satellite
T1
Drew Robb of Tujunga, Calif., writes about information technology.
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