Single-chip transceiver serves dual standards
GEORGE KOTELLY
To support both 1.25-Gbit/sec Gigabit Ethernet and 1.062-Gbit/sec Fibre Channel data rates over fiber-optic or coaxial-cable interfaces, Applied Micro Circuits Corp. (amcc) in San Diego has produced the S2052 single-chip, dual-frequency transceiver (see photo). This supplier of bipolar application-specific integrated circuits (asics) has condensed a transmitter and receiver pair into one compact package that serves as a common communications device for two data transmission technologies. With this same transceiver, network and equipment designers can easily move from established Fibre Channel applications to the onslaught of Gigabit Ethernet applications expected soon (see Gigabit Ethernet Update). Moreover, cost savings come into play because one device can be adapted to multiple deployments.
For example, the transceiver accommodates applications ranging from Fibre Channel adapter cards, servers, and raid (redundant array of independent disk) storage devices to Gigabit Ethernet network interface cards and high-speed ports on switches and hubs. Fabricated by a low-power bipolar process, the device performs parallel-to-serial and serial-to-parallel conversion and framing for 10-bit block-encoded data. Internal clocking and control functions are transparent to the user.
According to Tim Thompson, amcc product marketing manager, "The S2052 is our base platform, which will expand and evolve to satisfy customers` needs." With this transceiver, experienced Fibre Channel network planners and providers can readily move up to Gigabit Ethernet implementations because the physical interfaces of both architectures are the same.
A combination of proven Synchronous Optical Network interface and phase-locked-loop (pll) techniques helps the chip meet both ansix3t11 Fibre Channel and Gigabit Ethernet jitter specifications. Armed with this capability, the device`s differential pecl-compatible input/output for fiber-optic interfaces decreases crosstalk and increases data integrity. (pecl is positive-referenced emitter-coupled logic.) The transceiver contains an internal clock that is frequency-locked to the reference clock and can run at either 1.062 GHz for Fibre Channel use or at 1.25 GHz for Gigabit Ethernet applications.
Thompson says that a key attribute of the transceiver is that it does not need external capacitors; all the pll filtering is incorporated internally. In this way, the device avoids picking up external ground and power noise or coupling from external capacitors that could cause jitter or performance difficulties.
Another transceiver advantage, says Thompson, "is a unique lock-detect function that provides a combination of transition density and no-loss-of-synchronization indicator that differs from other products in looking for that information." The lock-detect function monitors the state of the receiver`s pll clock-recovery unit.
Adds Tom Palkert, amcc systems engineer, "The lock-detect feature also eliminates the signal-detect function in a fiber-optic module and maintains downstream clocking despite operational problems."
Several large manufacturers of data communications equipment have been evaluating and testing the part in Ethernet switches, Gigabit Ethernet adapter cards, and serial backplanes since December. In fact, early adopters favor Gigabit Ethernet applications over those for Fibre Channel.
With the S2052 transceiver in production, the company plans to release a line of similar products later this summer. q
Gigabit Ethernet Update
Categorized by industry experts as the next dominant backbone transmission technology, Gigabit Ethernet is gaining widespread acceptance because it builds upon the established Fibre Channel ansi standard. For example, Gigabit Ethernet standards are being adapted from Fibre Channel for their complete physical link, optical-to-electrical converters, and transceivers. As a result, new physical-layer devices are not needed.
Still under study, Gigabit Ethernet standards are being developed for completion in July 1998 through the efforts of the Gigabit Ethernet Alliance and its ieee 802.3z Task Force. "The development of the standard is on schedule and progressing well," says Bob Grow, alliance spokesperson, "and the lack of significant change in direction from the basic proposals corroborates this fact."
Recent refinements and additions to the draft standard include the general management structure, link startup protocol, optical physical layer interface specifications, and electrical specifications for the gigabit media-independent interface.
To maintain the aggressive schedule for the Gigabit Ethernet standards, the task force is planning to complete the specification by July 1997 and then initiate the ballot process. As an industry testimonial, alliance membership continues to grow steadily and, at press time, had reached 99 participating companies.
Standards notwithstanding, the Dell`Oro Group, a Portola Valley, CA-based market-research company, estimates that worldwide sales of Gigabit Ethernet products for servers and local area backbone networks should reach approximately $1.3 billion by the year 2000.
For updated information on Gigabit Ethernet, the Gigabit Ethernet Alliance has established a World Wide Web site at www.gigabit-ethernet.org.
