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Three ways to break data gridlock
Technologies such as cable modems, dense wave-division multiplexing, and splitterless ADSL are working to unclog the information superhighway
By Julie Anne Schofield, Senior Editor -- Design News, October 18, 1998
1. Cable modems: That's entertainment
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| Cable modems allow high-speed Internet access via a cable TV network. A splitter lets users watch cable TV while still being |
Cable modems take advantage of the cable TV network to connect a PC to the Internet. Today's fastest analog modems operate at 56 kbps bidirectionally; cable modems permit downstream data rates up to 27 Mbps and upstream rates of up to 786 kbps.
Like all modems, cable modems work by modulating and demodulating signals. Because most cable networks are not now bidirectional, some cable modems today use standard telephone lines to transmit upstream information.
| Two-way cable modem system connects IP (Internet protocol) network via hybrid fiber coax to a home |
Motorola's (Mansfield, MA) Cable Comm technology uses the CyberSURFRTM cable modem at the subscriber premises and the Cable Router at the headend. The system offers downstream rates up to 30 Mbps, of which 10 Mbps is available to an individual modem. The upstream data rate is 768 kbps. This downstream rate is faster than a T1 line commonly used in office buildings.
2. Dense wave-division multiplexing (DWDM): Exponentially increasing fiber capacity
DWDM turns a single fiber-optic cable into a "virtual" cable with dozens of strands. It's a lot cheaper than laying more cable across the country.
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| Wave-division multiplexing (WDM) lets multiple data channels at different wavelengths share a common optical fiber. Dense WDM increases fiber capacity by assigning signals to specific frequencies within a designated frequency band and then multiplexing the resulting signals out onto one fiber. |
Wave-division multiplexing doubles the capacity of a fiber by making possible the simultaneous transmission of two optical signals at two discrete wavelengths. Dense WDM combines multiple optical signals so that they can be amplified as a group and transported over a single fiber to increase capacity. The signals can be different formats and running at different data rates.
GigaMuxTM from Osicom Technologies (Santa Monica, CA) is a 32-channel dense wavelength division multiplexer that transforms existing fiber-optic cable from a dedicated single-application medium into a conduit that can simultaneously transport multiple optical channels. The device supports multiple data formats including: SONET, ATM, G-Ethernet, fiber channel, and switched digital video. The technology increases a single fiber's bandwidth from 2.5 to 80 Gbps.
Future DWDM terminals will be able to carry up to 80 channels, or wavelengths, for a total bandwidth of 200 Gbps, or 40 wavelengths for a total of 400 Gbps.
3. Splitterless ADSL: Fast technology gets less complex, expensive
ADSL (asymmetric digital subscriber line) technology allows traditional voice and digital data to coexist on the same copper telephone line. The technique delivers high-bandwidth, multimedia applications such as streaming video, interactive gaming, and fast Internet access.
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| Splitterless ADSL uses modems with a high-pass filter to block interference from voice-range frequencies. A low-pass filter attached to telephones prevents data traffic from interfering |
Splitterless ADSL eliminates the need for an external splitter to separate voice traffic from high-speed data traffic. Practically, it means service providers won't have to physically install the splitter outside a customer's home. This reduces cost and complexity of ADSL, which--without the splitter--can deliver up to 1.5 Mbps downstream and 512 kbps upstream.
Texas Instruments (Houston) this year announced a splitterless ADSL implementation that uses its 1,600-MIPS TMS320C6000 DSP technology, as does TI's full-rate ADSL implementation, which provides data transfer rates up to 8 Mbps. Thus, the chip supports both full-rate ADSL and reduced rate splitterless options G.lite and Universal ADSL.
The DSP-based chipset is a programmable solution, so manufacturers and consumers using TI's splitterless ADSL can upgrade via software to the G.Lite standard once it is fully defined and approved next year. Once that occurs, TI will use the 'C6000 core to build a custom programmable chipset that conforms to the standard.
