Telebit
From Wikipedia, the free encyclopedia
Telebit was a US-based modem manufacturer, most notable 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 90s.
Telebit was originally 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.
Contents |
[edit] PEP and the TrailBlazer
In contrast to then-existing ITU V-series protocols, notably the common 2400 bit/s V.22bis, the TrailBlazers' proprietary PEP (Packet Ensemble Protocol) modulation employed a large number (initially up to 512) of closely spaced carrier frequencies, each modulated at a leisurely 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.
The Trailblazer's high data rate mode was available in one direction only. At a time when modems were actually pretty simple devices and used modulation techniques labelled either "full duplex" or "half duplex", the Trailblazer was termed internally an "adaptive duplex modem". The modem was designed to use most of the bandwidth in a single direction, with a relatively low speed reverse channel. The modems at the two ends of the connection would negotiate line turnarounds, reversing the directions of the high-speed and low-speed channels, based on the amount of data queued for transmission in each modem.
While this adaptive duplex scheme was able to send large files quickly, for users accustomed to having the distant computer echo characters, the delay associated with having the DSPs take turns using the bandwidth tended make interactive typing difficult, as there could be as much as a second and a half delay for a single character echo. This also caused problems for file transfer protocols, e.g., UUCP 'g' or Kermit, where a small packet of data was sent by one computer, followed by a wait for acknowledgment ("send and wait").
The TrailBlazer addressed this problem through a technique known as "protocol spoofing". When the local computer sent a packet to the modem for transmission, the modem's controller immediately sent an ACK message generated locally. This fooled the computer into thinking the packet had already reached the far end, prompting it to send another packet. The error correction normally being applied in the protocol was instead handled using a proprietary replacement protocol operating on top of the MNP error-correcting protocols to talk to the remote modem. In general, spoofing worked well with any protocol that used small packets, and thus generated lots of ACK messages; support for XModem and Kermit followed.
Support for these features did not come easily; the TrailBlazer Plus, for instance, used a Motorola 68000 to drive its electronics. This meant that the TrailBlazers were generally very expensive. However, its spoofing ability made the TrailBlazer modems extremely popular in the Unix world, as it could dramatically improve UUCP throughput, even at low connection speeds on very noisy lines. Improvements of over 10 times over a 2400 bit/s modem were not uncommon. Sites that required long-distance telephone calls to exchange UUCP mail could pay for the price of a TrailBlazer in long-distance savings fairly quickly.
The Trailblazers also introduced an extensive set of commands for setting up its various options. While most of the simple commands were based on the Hayes command set, like dialing a number or hanging up a phone, their proprietary capabilities were supported by proprietary commands and syntax. Most of these took the form of register=value pairs, leading to extremely long and almost undecipherable setup strings.
In 1988 Telebit added the T1000, essentially a TrailBlazer limited to a lower-speed 9600 bit/s version of PEP, remaining compatible at that speed with existing TrailBlazers. The T2000 added support for synchronous communications, typically used between mainframe computers.
[edit] The NetBlazer
Another of Telebit's famous products was the world's first on-demand internet dialup router, the NetBlazer. The product was developed by a team led by Mike Ballard, formerly of Packet, who eventually became Telebit's CEO in 1986, and president in 1992.
The NetBlazer essentially consisted of a small-form-factor PC combined with custom software and one of a variety of modems or other connection systems (ISDN, etc.) combined into a large modem-like box. Users connected to it via ethernet, which was also used for maintenance commands and setup.
In its first release the NetBlazer's supported TCP/IP using SLIP, but a later upgrade added PPP as well as support for IPX and AppleTalk. Later versions of the hardware switched from the Intel 80386 to a low-cost microcontroller version of the Motorola 68030, the MC68EN360.
[edit] Increasing speeds
The original TrailBlazer, T1000 and T2000 were backwards-compatible with the 2400 bit/s V.22bis standard, allowing them to connect with what was then the most common modem speed when talking to other brands of modems.
The first multi-company standard for 9600 bit/s dialup modems was V.32, introduced in 1989. Initially V.32 modems were very expensive, but Rockwell introduced modules and eventually chipsets that brought the prices down. Telebit first offered V.32 support in the T2500, which used the Trailblazer/T2000 hardware with the addition of the Rockwell V.32 modem module. A version without PEP support was offered as the T1500. The later T1600 had basically the same feature set as the T1500, but used Telebit's own V.32 implementation rather than the Rockwell module, resulting in reduced production cost and better performance. Both the T1500 and T1600 had list prices over $1000, although at the time a "1st tier" product from Hayes or U.S. Robotics generally cost about $700.
The V.32bis standard, increasing the bit rate to 14,400 bit/s, was introduced in 1991, and most modem vendors quickly responded with upgrades and new modems. A particularly "upsetting" change was Rockwell's decision to introduce a V.32bis chipset at a seriously reduced price point, allowing complete modems to be sold for about $300. All of the 1st tier companies, Hayes, USR and Telebit, had serious difficulties adapting quickly to a market that was now filled with low-cost modems with similar or better performance than their own "high-end" models. Telebit started slipping in terms of relative performance, while still trying to sell their products at their traditional high price points.
Telebit finally introduced the T3000 with V.32bis but without PEP, though a PEP upgrade was planned. Instead, Telebit "re-released" it in early 1994 as the $1,099 WorldBlazer model; essentially a T3000 with the new 23,000 bit/s TurboPEP mode. An upgrade from the T3000 to WorldBlazer was sold, consisting of two firmware ROMs and a PAL chip.
There were some design studies of a possible full-duplex PEP using echo cancellation (as is used in V.32), and this technology was proposed to the CCITT (now known as the ITU-T) for possible adoption as the V.fast modem standard. However, more conventional modem technology was chosen and standardized as V.34. Telebit deemed full-duplex PEP to require more engineering effort than was justified by the shrinking market for PEP modems, and never introduced this feature.
[edit] The Octocom merger and the FastBlazer V.34 modem
The CCITT moved quickly to improve on V.32bis, and by 1993 it was clear that the ratification process for their new 28,800 bit/s V.34 standard was going to be finalized in 1994. Companies lined up to start production of new V.34 designs, some going so far to introduce models based on interim standards, notably V.FC.
Telebit's modem engineering team developed a plan for a V.34 modem, but the executive staff believed that it was important to get a product to market more quickly. To that end, they began looking for other modem companies to acquire, and in January 1993 announce that Telebit would acquire Octocom Systems, a small privately held modem company in Massachusetts. Octocom had a V.34 modem in development which was expected to be ready for shipment quickly. Almost all modem engineering activities at Telebit's California offices ceased, though NetBlazer engineering continued to be based in California until the end of 1995.
The Telebit FastBlazer 8840 V.34 modem was introduced in May 1994, in a release that is a textbook example of product mismanagement. When the FastBlazer was first introduced it did not include V.34 support, with management stating that they couldn't do so because the standard was not yet ratified. Although this was true (for one month anyway, it was ratified in June), the FastBlazer did not ship with an interim standard either; even AT&T's largely-ignored 19,200 bps v.32terbo would only be available as a post-release upgrade in July, there were no plans to support the widespread V.FC at all, and no date was set for full V.34 support other than "two or three months".
Making matters worse, the FastBlazer didn't include fax support, and while Telebit stated that an upgrade to add this would be available, they would be charging for it. Nor would the FastBlazer support PEP, which was now considered to be a minor consideration, but nevertheless one of the few reasons anyone purchased a Telebit modem in the "early days". For sites with Telebit modems at least one end of the link, a PEP-capable upgrade might be worthwhile if one side was being upgraded. Without PEP, any V.34 modem was a worthy competitor.
All this for an introductory price of $1,399, when V.32bis faxmodems were available for $200 or less, and industrial-quality V.34 designs were soon available for under $500.
It took a long seven months before Telebit finally introduced V.34 support in January 1995, also releasing the $399 TeleBlazer "low-end" model at the same time. By this point any goodwill the company had was lost, and even long-time supporters were publicly pooh-poohing the company on the UseNet, the medium that originally drove the widespread adoption of the TrailBlazer.
[edit] End of the company
The company quickly found itself in serious financial difficulty, which they were never able to address. Late in 1993 they completed their merger with Octocom, the idea being to use Octocom's Chelmsford, Massachusetts manufacturing capability, downsizing the existing Sunnyvale office to become a NetBlazer development site. The VP of Engineering quit in the spring, and the west-coast office was then closed.
As it turned out, the manufacturing costs at Octocom were actually higher than their original west-coast factory, and they failed to pay bills on time with one of their major component suppliers. New lines of credit were quickly arranged with various distributors, but this resulted in higher parts costs. This simply made matters worse, and by December 1995 it was publicly known that the company was up for sale.
In 1996 the bulk of their networking business were acquired by Cisco Systems for $200M, primarily for their channelized T1 digital modem technology. The offer was unsolicited, and likely a better price than the company as a whole was worth. Cisco was uninterested in the analog modem side of the business which was spun off to the existing management team to become Telebit Incorporated.
In the summer of 1997 they merged with another small company, ITK Telekommunikation, which was purchased a year later in July 1998 by Digi International, makers of the DigiBoard multi-port serial card for PCs. Digi was uninterested in the modem line, which was now hopelessly outdated, and immediately cancelled production. Remaining inventory was liquidated in March 1999.
[edit] Legacy
While the Trailblazers have generally been displaced by modems implementing the higher-rate V.34/V.90 series standards, and although they have been out of production since the mid-1990s, many TrailBlazers continue to be in operation to this date, and repair services are still available.
Orthogonal frequency-division multiplexing (OFDM), which is used in both the ITU Asymmetric Digital Subscriber Line (ADSL) and IEEE 802.11 Wireless LAN standards, has some of its roots in the Packet Ensemble Protocol. Notably, these protocol's reused PEP's concept of carrying a single data-link over many lower rate FDM sub-carriers.
[edit] Models
| Model | Year | Capabilities |
|---|---|---|
| Trailblazer | 1985 | Original model, approximately 18,000 bit/s |
| Trailblazer+ | ? | performance improvement, over 19,000 bit/s |
| T1000 | 1988 | lower-cost model limited to 9600 bit/s |
| T2000 | ? | synchronous link support |
| T2500 | ? | T2000 + V.32 (9600 bit/s) support added based on Rockwell module |
| T1500 | ? | V.32 (9600 bit/s) without PEP, Rockwell based |
| T1600 | ? | V.32, Telebit-internal implementation |
| T3000 | ? | V.32bis(14400 bit/s) and fax support |
| WorldBlazer | 1994 | T3000 with TurboPEP and, later, fax |
| FastBlazer | 1994 | V.34 (28800 bit/s) |
| TeleBlazer | 1995 | "low cost" V.34 |
| QBlazer | ? | V.32 (9600 bit/s) battery-powered portable modem |
| QBlazer+ | ? | V.32bis (14400 bit/s) version of the QBlazer |
| NetBlazer | ? | ethernet-connected on-demand SLIP and PPP router |
[edit] See also
