High-speed Data Hits A Ceiling
Sydney Morning Herald
Sunday March 25, 1990
DENNIS HAYES, the president and co-founder of Hayes Microcomputer Products, was in London the other week. Although ostensibly visiting several European capitals to promote the introduction of X.32 inter-working on the Hayes "V" series of smart modems, he also revealed that the enhanced serial port (ESP) standard has reached the stage where real products are about to appear.
Rather than blind the poor reader with buzzwords, let me explain what X.32 is, then I'll move on to ESP.
* X.32 is the dial-up (that is, modem) equivalent of the X.25 standard, agreed by the CCITT communications regulatory body last year.
X.25 is really a fancy name for the bundling of packets of data from several calls and feeding them - conveyer belt style - over a single wide band communications link. At the other end of the X.25 link, the packages are all re-assembled back into their various data calls.
Using X.25 for data calls means that the cost of using a given call route is shared. This makes for lower call costs, although some telecommunications authorities seem to charge what they like here in Europe, which makes a mockery of the cost savings behind X.25 networks.
X.32 extends the X.25 concept to dial-up links. Under the CCITT X.32 standard, it's possible to "open up" four simultaneous channels of data over a single modem link.
This isn't as crazy as it sounds. Suppose you start downloading a program from an online service. Using X-Modem, data flows fairly freely in one direction, with the occasional "ACK" signal flowing back from your computer in the opposite direction.
Under X.32, there's room in the bandwidth for a lot more data to flow from your computer to the distant end of the modem link. Using an X.32 link you can be downloading a program on one channel, uploading a second program on the other channel, and browsing an airline timetable on a third channel. And if you really want to do fancy tricks, you could also open up a fourth channel to a chatline service on your favourite multi-user bulletin board.
Dennis Hayes is keen to see X.32 usage become more widespread.
Why? Because it encourages modem users to move on up to faster modems -upgrading means more modem sales.
Faster modems usually employ some form of data compression, the most popular of which is V.42bis at the moment. Using V.42bis, it's possible to squeeze a data throughput of 9,600 bits per second out of a 2,400 bits per second modem. Or, to put it another way, four 2,400 bits per second channels(using X.32) from a 2,400 bits per second modem.
As ever with the introduction of new technology, there's a small snag. When the IBM PC was first conceived in the US, back in the early 1980s, modems were slow and expensive machines, usually operating at a pedestrian 300 bits per second. The fast modems of today were in the realms of science fiction. As a result, the IBM engineers designed the PC's serial port with such speeds in mind.
Today, with modems of 9,600 bits a second beginning to appear, the older PCs cannot cope with such high data throughput. On a standard 4.77MHz 8086-based PC (the original IBM PC standard) for example, the serial port can scarcely keep up with 9,600 bits per second.
When you start to add features such as X.32 and V.42bis to the modem, you multiply the workload of the serial port, first by four and then by four again. Sure, you can get four 9,600 bits per second channels out of your 9,600 bits per second modem using X.32 and V.42bis, but can your PC's serial port cope?
No problem, you say. Let's soup up the PC's serial port. Hold on a minute, though - the UART chips are fundamental to the design of the PC's interface. Meddle with them and you cause problems with the addresses of the serial port in the PC's memory. Enter Hayes to the rescue with its enhanced serial port(ESP) specification.
ESP is a two-port serialcommunications board designed with a 1K data buffer for transmitted and received characters. The large buffer avoids problems with lost characters when using high data speeds.
Hayes plans to have an ESP card, which interfaces between the PC's bus and a high-speed modem or similar device, available towards the end of the second quarter of this year.
Despite Hayes's penchant for high modem prices, ESP will be surprisingly cheap. An ESP card for Micro Channel Architecture (MCA) PCs will set you back U$349, while an AT-bus version will cost U$299.
Interestingly, Hayes developed the ESP standard and consequent hardware when it hit the data throughput ceiling on ordinary PCs with its Ultra Smartmodem 9600, a high-speed modem supporting all speeds through to 9,600 bits per second, with V.32 and V.42bis specifications.
The ESP standard allows ordinary serial port devices to be plugged into the ESP socket on the relevant PC expansion card.
Because ESP is compatible with standard serial-port hardware, no software changes are required. Software developers can use the advanced features of ESP, such as direct memory access (DMA), to increase the performance of communications software.
Using DMA, for example, allows some of the processor-intensive duties of the PC's CPU to be handled by the ESP card. The result is a faster PC.
Great, you say, let's get an ESP card. What are the snags?
As with any PC card, the disadvantage is that your PC has one less slot for use with other expansion cards. In the longer term, Hayes hopes that internal card modem manufacturers will incorporate the ESP standard into their modem hardware. When this happens, internal modems will become even better value for money.
ESP represents a major step forward in allowing very fast serial port devices - not just modems - to be hooked up to a PC. Hayes is charging a modest licence fee to third-party companies wishing to incorporate the ESP standard in their peripherals. The ploy should work.
It very nearly didn't, however. Last year, when Hayes approached IBM with the idea, hoping to get Big Blue to embrace the design standard, their engineers were rebuffed. IBM took the attitude that the high-speed data throughput problems were caused by software, not hardware, so it felt it did not have a role to play.
Undeterred, Hayes's engineers went down the road to Microsoft, who welcomed the ESP standard with open arms. The result is that ESP hardware and software products will appear en masse later this year, supported by both companies.
© 1990 Sydney Morning Herald
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