Developers add power, sensitivity to
extend Gigabit Ethernet's reach
(see about paragraph 6 or 7 for Nbase ref)
By Kristina B. Sullivan, PC Week Labs
04.22.98
Even before the Institute of
Electrical and Electronics
Engineers' 802.3z Gigabit
Ethernet standard is formally
adopted, developers are
unveiling plans to go beyond
its distance specifications.
Expected to be ratified in
June, IEEE 802.3z will support
device distances of 220
meters for 62.5-micron
multimode fiber and 5,000 meters for
single-mode fiber.
But for would-be users of Gigabit Ethernet now
running Fast Ethernet at its standard
specifications of 2,000 meters for multimode and
20,000 meters for single mode, the Gigabit
Ethernet standard doesn't go far enough.
Vendors are addressing the issue by developing
extended-length products that are nonstandard.
Prominet Corp., of Marlboro, Mass., which was
recently purchased by Lucent Technologies Inc.,
is now shipping the Long Distance Gigabit
Ethernet Module for its P550 Cajun Switch, which
extends standard single-mode fiber distances to
10,000 meters and 62.5-micron multimode fiber
to 440 meters. The product accomplishes this by
transmitting at a higher power and using a more
sensitive receiver.
"We expect to see this being useful in
environments where there is access to dark
fiber," said Doug Ruby, vice president of product
marketing for Lucent and a Gigabit Ethernet
Alliance steering committee member. "Instead of
running OC-3 or even OC-12 over ATM or
SONET [Synchronous Optical Network], users
will run switched Gigabit Ethernet for data
applications," Ruby said. Among sites interested
in extended-distance Gigabit Ethernet are
organizations that span metropolitan areas,
military bases and airports.
For example, a consortium of public schools and
facilities in the Northwest that comprises 13
agencies and 120 sites, became a candidate for
extended-distance Gigabit Ethernet when it
requested proposals for a new network to
support 20,000-meter distances. Packet Engines
Inc. proposed Gigabit Ethernet running on
single-mode fiber augmented by hot optics, which
transmit more power than specified in the
standard.
"By using very good fiber-optic cable and good
splicing with the hotter optics, we think we can
get up to 20 kilometers," said Brian MacLeod,
director of marketing for Packet Engines, in
Spokane, Wash. (He didn't identify the
consortium because no contract has not been
awarded.)
Nbase Communications Inc. is also extending the
Gigabit Ethernet standard with an add-on module
now in beta testing. The Network Converter
works with any 1000Base-LX Gigabit
Ethernet-standard switch to cover 18,000
meters, said Mannix O'Connor, national sales
manager for Nbase, in Chatsworth, Calif.
Gigabit Ethernet defines two standards for
fiber-optic cabling: 1000Base-SX, with short
wavelength transceivers, and 1000Base-LX, with
longer wavelength transceivers. The
1000Base-LX products work with multimode fiber
to achieve distances of 550 meters. Only
1000Base-LX products work with single-mode
fiber to reach the 5,000 meter specification.
There are significant cost differences between
the 1000Base-LX and 1000Base-SX products.
Lucent quotes $2,200 per Gigabit Ethernet port
with SX vs. $3,600 per port for LX switches;
Packet Engines charges $1,295 for the SX
version of its G-NIC and $2,695 for the LX
model, and 3Com Corp.'s SuperStack II Switch
3900 Downlink Modules are priced at $1,445 for
the SX format and $1,995 for the LX type.
The IEEE 802.z committee recently reduced the
distance specification for 1000Base-SX from 260
to 220 meters to avoid DMD (differential mode
delay), which causes jitter as light beams inside
the fiber move at different speeds. The DMD
problem was also addressed by qualifying the
launch of the laser transmitter, increasing
receiver sensitivity and reallocating the jitter
budget within the transceiver, according to the
Gigabit Ethernet Alliance.
"We feel confident that we have this licked," said
Jeff Martin, product marketing manager for Bay
Networks Inc., of Santa Clara, Calif., and vice
chairman of communications for the Gigabit
Ethernet Alliance. "We've created a situation
where we avoid DMD, and as distances go
longer, you have to tighten constraints," Martin
said.
Others point out that extended distances can be
achieved without adding nonstandard modules.
"The IEEE specification is based on the lowest
common denominator fiber," said MacLeod, of
Packet Engines. With 1000Base-LX running on
single-mode fiber, Packet Engines has
successfully tested distances of 7.6 kilometers,
he said.
To show that the standard's ratings are
conservative, the Gigabit Ethernet Alliance will
run 1000Base-SX over 500 meters of cable at
NetWorld+Interop, in Las Vegas, on May 5,
Martin said.
Transceiver vendors also expect to reach 10,000
meters without changing the existing standard.
"They can take their standard offering for LX
transceivers and guarantee 10 kilometers," said
Bob Gohn, 3Com Corp.'s program manager for
Gigabit Ethernet, in Boxboro, Mass.
Developers do not expect the IEEE to address
extended-length distances any time soon. "These
are more proprietary-oriented solutions driven by
optics vendors," Gohn said. "I don't expect the
IEEE to extend the standard for applications that
go beyond the scope of a local-area
environment."
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