Telebit
Telebit Corporation 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. The high price of the Telebit modems was initially not a concern as their performance was equally high compared to other systems. However, as new designs using V.32 and V.32bis began to arrive in the early 1990s, Telebit's price/performance ratio was seriously eroded. A series of new designs followed, but these never regained their performance lead. By the mid-1990s the company had been part of a series of mergers and eventually disappeared in 1998 after being acquired by Digi International. Startup 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. PEP and the TrailBlazer 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' used a proprietary modulation system known as Packetized Ensemble Protocol (PEP), based on orthogonal frequency-division multiplexing (OFDM). It 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 in steps of 10 bps with decreasing line quality. Using a large number of carriers spread across the phone network's bandwidth meant that the chance that any one carrier would be subject to a problem was high. In order to correct for the unavoidable errors this would cause, the Trailblazers were one of the earlier implementations of the MNP error-correcting protocols. Although these protocols added overhead, and errors caused further overhead, the combination of all of these features still provided much higher throughput than conventional designs running on the same lines. In contrast, something like a 2400 bit/s modem might suffer from a smaller number of errors in a given time, but those errors would require longer to fix through re-transmission at the slower speed. If those errors were being caused by a constant source