AT&T's LightWire Pushes Into Phase 3
Thread,
First, before anyone accuses me of being un-American, the score is 6-0 St. Louis.
----
It appears that T is meeting most of our criteria for a digital baseband approach to tranport, like we've been calling for here, over a fiber architecture using Fast Ethernet and GbE to homes. But they continue to promote the use of black coax in the last couple thousand feet to the residence. It appears that they are going to rest on their laurels for a while, after finding a way of eliminating the active amplifiers in the coax section. Thus, removing the impetus to move anymore radically. But in the process, they are addressing a distibuted CMTS schema which looks interesting, but needs to be explained further.
Also, according to this piece T appears to be tracking lambda slicing capabilities and other developments at both S-A and Bookham, closely.
While this third phase of LW appears promising, it may be useful to keep in mind that the timing of Phase 2 has yet to be announced. Let's hope that the insulation on the black coax doesn't decompose before they get to Phase 3.
This article was originally sighted on the HLIT Thread, with thanks going to Mr. Miller. Enjoy.
Regards, Frank Coluccio
ps - it's still 6-0, St. Louis.
---------
Broadband Week for January 31, 2000
LightWire Pushes Into
Phase 3
multichannel.com
By FRED DAWSON January 31, 2000
AT&T Broadband & Internet Services has
pushed its thinking about the evolution of its
passive "LightWire" hybrid fiber-coaxial
architecture into a third phase, in which highly
integrated optoelectronic components and
digital technology will radically alter the way
services are delivered today.
The three-phase approach to implementing
LightWire was outlined by AT&T Broadband
vice president of engineering Oleh Sniezko at
the recent 2000 Conference on Emerging
Technologies sponsored by the Society for
Cable Telecommunications Engineers.
While elements of the strategy have been
known for some time, Sniezko's description
provided new insight into the company's
thinking about using digital-baseband and
dense-wavelength-division-multiplexing
technologies and about the evolution to what it
calls a "distributed CMTS
(cable-modem-termination-system)"
environment.
"We want to do distributed processing,"
Sniezko said. "I'd guess that in five years,
distributed CMTS will be used in 80 percent of
our systems."
The idea is to trim functions at the primary
hubs to bundling and routing, while moving
MAC (media-access-control) functions to the
mini-nodes in the LightWire architecture.
These points of final fiber termination serve
about 70 homes passed via passive coaxial
cable -- coax that has no in-line amplifiers
between the node and the end-user.
Each mini-node will handle local policing and
resolve upstream contention within the serving
area, independent of the rest of the network,
Sniezko explained. This will require converting
signals to the time-division-multiplexed
baseband domain, first in the upstream and
eventually in the downstream.
Already, Sniezko noted, Broadcom Corp. and
other chip suppliers offer
100-megabit-per-second and gigabit Ethernet
chips that would make it possible to interact
with end-users on the coax as if they were
service nodes on a local-area network.
"We want to push the HFC [hybrid
fiber-coaxial] network to look exactly like a PON
[passive optical network], while still using the
coax," Sniezko said.
PONs -- which, in a telecommunications
environment, typically use fiber-to-the-curb or
fiber-to-the-home architectures -- use several
techniques to transport signals, including TDM,
DWDM and subcarrier multiplexing, depending
on carrier and vendor designs. "We want to
use all of these technologies to our
advantage," he added.
The game now is to plot the migration strategy,
which has evolved from a two- to a
three-phased approach in the company's
current thinking.
As AT&T moves into the first phase of
LightWire upgrades -- retaining current modes
of signal delivery in the downstream and
upstream paths -- the fast-falling cost curves
are opening opportunities to make more
efficient use of this architecture through
changes in those delivery modes.
The first such shift can already be seen in
adopting baseband-return signaling between
secondary and primary hubs, which AT&T
expects to extend to nodes and mini-nodes
over the next year or so.
In phase two -- the timing of which is still to be
determined -- using digital baseband for
dedicated signals in the downstream, as well
as upstream, will allow the MSO to
"daisy-chain" mini-nodes via a two-fiber strand.
One fiber carries the broadcast analog signals,
and the other operates as an OC-48
(2.5-gigabit-per-second) bus, allowing use of
TDM devices to add and drop signals from the
bus at each mini-node.
This daisy-chaining makes adding mini-nodes
easy and greatly simplifies management and
restoration of services, Sniezko said.
"LightWire III" would entail a shift to the use of
DWDM to deliver dedicated signals to each
mini-node in the daisy chain.
This version of LightWire would rely on very
low-cost LEDs (light-emitting diodes) and a
new generation of integrated optoelectronic
devices to create an all-passive environment
from the secondary hub all the way to the
mini-nodes, Sniezko said.
"If the network capacity is enough between the
primary and secondary hubs, the narrowcast
part of the
subcarrier-multiplexing system can disappear,"
he noted.
The architecture would use DWDM to deliver
dedicated baseband signals to secondary
hubs, then use DWDM at secondary hubs to
partition signals across multiple wavelengths,
so each wavelength would carry signals
dedicated to a specific mini-hub.
One could use inexpensive LEDs at the
secondary hubs, rather than high-cost
wavelength-specific lasers, by employing
optical add/drop multiplexers to deliver a "slice"
of each LED's output over a narrow
wavelength into the fiber, Sniezko explained.
The key is a new generation of optical devices
that can be tightly integrated onto electronic
circuits. "The enabling devices exist today, but
that must be packaged to our specifications,"
he said.
Such packaging is under way through the work
Scientific-Atlanta Inc. is doing with Bookham
Technology Ltd., a U.K.-based developer of
such devices.
"We're still a long way from the ultimate in
solid-state optical networking, but we're moving
a good way up the scale from where we've
been," Bookham vice president of business
development Robert Green said.
Bookham developed a way to form complex
optical circuits on mass-produced silicon chips,
with the potential to miniaturize and cut costs
of products to be used in DWDM, return-path
transmissions and fiber optic nodes.
An early Bookham product is an integrated
transmitter/receiver being used by Japan's
Nippon Telephone & Telegraph Corp. and
other entities around the world to help lower
the cost of FTTH systems.
Bookham -- backed by the likes of Cisco
Systems Inc. and Intel Corp. -- is working with
S-A to develop a number of cable applications
for its patented "ASOC" (application-specific
optical-circuit) technology, Green said.
One application the two companies are
exploring is integrating a wavelength
demultiplexer and photoreceiver onto the chip.
This would create a miniaturized, low-cost
means of handing off a wavelength from a
multiwavelength stream at a mini-node on the
cable plant -- which is what AT&T wants in the
third phase of LightWire.
Early results of the Bookham/S-A collaboration
suggested that some existing capabilities in
Bookham products can be readily transferred
to cable applications, possibly this year, Green
said. But the DWDM add/drop capability is not
one of them.
AT&T officials acknowledged that they are
closely following the S-A/Bookham
developments. |
