America Online's indirect endorsement of K56Flex
raises the number of ISPs indirectly supporting Rockwell's protocol to 116; the
number of ISPs directly supportive remains 0.
Hayes ships a version in a PC-card form factor -- Groups push pulse-code-modulated
modems
By Loring Wirbel
Norcross, Ga. - Progress on a standard for pulse-code-modulated (PCM) modems is
proceeding swiftly on both sides of the Atlantic, and products are being rushed to
market. But the modems, billed as capable of 56 kbits/second, are not without their
snags.
The U.S. Telecommunications Industry Association's TR-30.1 "fast-track" committee,
which met here last week, and the International Telecommunications Union's Study
Group 16 V.pcm have approved similar near-term standards for modems that will use
digital PCM coding downstream, and traditional V.34 coding on the return path.
Hayes Microcomputer Products Inc. (Atlanta) last week became the first OEM to ship
PCM modems in a PC-card form factor. And Telecom Analysis Systems Inc.
(Eatontown, N.J.) has introduced dedicated test sets for the new modems.
Few of the production modems using either the Rockwell Semiconductor
Systems/Lucent Technologies "K56flex" code or the U.S. Robotics Inc. "X2" code
achieve true 56-kbit/s transmission. Modem analyst Ken Krechmer of Action
Consulting Inc. (Palo Alto, Calif.) calls the 56k tag a misnomer, saying such systems
rarely will hit 56 kbit/s downstream in the field.
Hayes modem-product-line manager Patrick Kennedy said most vendors recognize
the need to explain to consumers that their telephone- or Internet-service providers
must be digitally terminated for the new PCM modems if the units are to work
properly. "We've had to deal with an 'actual mileage may vary' scenario since the days
of V.FC [V. Fast Class, an early Rockwell version of V.34]," Kennedy said. "We are
working diligently to include the Lucent and Rockwell K56flex logos in our material,
pointing out that users should be aware of what is in their local central offices."
Hayes sees typical throughput of 42 to 46 kbits/s on its modems, and expects those
numbers to improve, the company said.
America Online's decision, announced last Thursday, to standardize on the use
of Ascend Communications' equipment for PCM modems is an indirect
endorsement of K56flex, since Ascend's central-office equipment is based on the
chip sets of Rockwell Semiconductor Systems (Newport Beach, Calif.). Lucent and
Rockwell representatives pointed out that the endorsements by IBM and
Hewlett-Packard that were part of the AOL announcement indicates that most large
OEMs and service providers have turned to their the companies' jointly-developed
technologies.
On the standards front, TIA working group chairman Barry O'Mahony of Intel Corp.
said the biggest surprise was finding that the technical proposals from the
Rockwell/Lucent and U.S. Robotics camps are strikingly similar. Some differences in
startup sequences for modems and signal constellations for PCM code must be
resolved, he said, but "most of the interoperability issues were magnified by marketing
staffs."
O'Mahony and Krechmer said the prevailing sentiment at an ITU study-group meeting
in Geneva late last month was that standards would soon be achieved. "Coordination
opportunities look good enough that it may end up that the TIA standard and the ITU
recommendations will be essentially the same document," O'Mahony said.
One sticking point is that Europe uses A-law coding, whereas North America and
Japan have opted for mu-law PCM. It is uncertain whether an A-law variant will
become part of a merged ITU/TIA standard or will be handled in a separate
document.
ITU Study Group 16 is slated to consider a fast-track standard in January. That would
require that a draft TIA standard be ready for presentation by September. Intel will
host a meeting that month to review the TIA work and prepare a reference document
for the ITU.
Copyright r 1997 CMP Media Inc.
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