Telebit

Telebit was a US-based modem manufacturer, known for their TrailBlazer series of high-speed modems. One of the first modems to routinely exceed 9600 bit/s speeds, the TrailBlazer used a proprietary modulation scheme that proved highly resilient to interference, earning the product an almost legendary reputation for reliability despite mediocre (or worse) line quality. They were particularly common in Unix installations in the 1980s and 1990s.

Telebit was founded by Paul Baran, one of the inventors of the packet switching networking concept. Baran had recently started a networking company known as Packet Technologies on Bubb Road in Cupertino, California, which was working on systems for interactive television. While working there, he hit on the idea for a new way to implement high-speed modems, and started Telebit across the street. Packet Technologies was a major beta customer for Telebit in late 1985. Packet Technologies later failed, and several of their employees were folded into Telebit, while most of the others formed StrataCom, makers of the first Asynchronous Transfer Mode (ATM) switches.

In contrast to then-existing ITU Telecommunication Standardization Sector (ITU-T) V-series protocols, such as the common 2400 bit/s V.22bis, the TrailBlazers' proprietary (PEP) modulation employed a large number (initially up to 512) of closely spaced carrier frequencies, each modulated at 6 baud, encoding 0, 2, 4 or 6 bits per interval. Under favorable conditions, the devices could reach data rates of 6 baud x 6 bits-per-baud x 512 carriers = 18432 bits per second. If a particular carrier was distorted, attenuated or interfered with, it could be turned off, allowing the data rate to degrade gracefully with decreasing line quality.

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