An analog modem designed for high-speed Internet and remote access over two analog telephone lines. Based on the synchronous integration of two 56-Kbps modems, a 112-Kbps dual-l
ine modem communicates over two standard analog telephone lines, providing aggregated, uncompressed download speeds of up to 112 Kbps -- nearly 3.5 times faster than the current ITU V.34 standard. Using the combined bandwidth of two telephone lines, though, the technology allows you to drop one line as needed for voice calls or faxes. Proposed and promoted by Texas Instruments and U.S. Robotics, the 112-Kbps analog modems that a number of Taiwan companies make should be in stores in the U.S. this quarter.
Cable Modem
Modems designed to provide high-speed services via cable networks. Cable modems are internal devices that connect PCs to cable networks. Many solutions are being developed, with speeds ranging from 64 Kbps to 30 Mbps. Taiwan's CIS Technology is working with Toshiba of Japan to develop a second-generation cable modem. The modem, featuring a downstream speed of 8 Mbps, will be available in the first half of 1998 from Toshiba.
Asynchronous Transfer Mode (ATM)
A high-ban
dwidth switching and multiplexing technology based on small, fixed-length cells that allocates physical channels for specific connections. Highly scalable, ATM provides an ideal upgrade path for supporting higher-bandwidth applications and enables the simultaneous transfer of voice, data, and video traffic at very high speeds, and supports both LANs and WANs.
CNet Technology, a networking hardware vendor in Taiwan, has unveiled a new ATM module that you can use with the company's Ethernet switches. The module includes 15 ports and costs less than $1000 per port.
Digital Subscriber Line (XDSL)
A collective term for DSL transceivers that provide voice, data, and video services at megabit rates over standard twisted-pair wires. The technology includes ADSL, HDSL, SDSL, VDSL, RADSL, and more.
These are interim technologies that were developed to get around the local-access bottleneck using the installed base of copper wiring from phone and cable companies.
High-Bit-Rate Digital Sub
scriber Line (HDSL)
A technology offering full-duplex E1/T1 access over two copper-wire pairs, without repeaters. HDSL specifications created by Bellcore use 2B1Q modulation techniques. The technology is frequently used to replace repeated T1 service over distances as long as 12,000 feet. Unlike ADSL, HDSL provides users with 1.5 to 6.1Mbps in both directions instead of just downstream.
Symmetric Digital Subscriber Line (SDSL)
Also known as single-line digital subscriber line, SDSL offers E1/T1 transmission speeds in upstream and downstream directions over a single copper-wire pair. SDSL is full-duplex, so it provides speeds of up to 1.5 Mbps both upstream and downstream.
The technology may be the preferred method for doing sophisticated real-time functions, such as conducting audio, data, and video communications, or remotely connecting to a corporate LAN.
Very High-Bit-Rate Digital Subscriber Line (VDSL)
An impending upgrade to ADSL, VDSL combines ADSL technology
with ATM to give users speedy communications and network access over a twisted-pair copper wire at speeds of up to 60 Mbps downstream and 2.3 Mbps upstream over distances of up to 300 meters.
Though VDSL promises an ultrahigh downstream bandwidth over copper wire, some developers question the viability of a near-term market for VDSL, because it requires that a fiber-to-the-curb switched digital-video infrastructure be in place.
Rate-Adaptive Digital Subscriber Line (RADSL)
A rival technology of ADSL, RADSL can boost speeds to up to 8.2 Mbps downstream and 1 Mbps upstream with discrete multitone (DMT) capability. Because its transmission speed is rate-adaptive, based on the length and signal quality of an existing telephone line, RADSL is not optimized for only one loop, but dynamically optimizes to each loop for the greatest throughput available.
Alternatives to ISDN and ADSL
