Thanks Eric. More from the last article:
As currently deployed, LightWire extends fiber to
"minifiber nodes" at interface points on the existing
coaxial cable plant. That extension eliminates the need
for in-line amplifiers between the node and end users. By
pushing fiber deeper into the network, LightWire not only
does away with maintenance and performance hassles
re-lated to those amps, but also reduces the number of
people contending for bandwidth over any coaxial serving
area, says Oleh Sniezko, vice president of engineering
at AT&T Broadband and Internet Services.
But the long-term benefits of LightWire could be much
greater, as reflected in the company's thinking about the
project's second and third phases. Rather than keep all
the cable modem termination system functions that
control distribution of data services in the headend, as is
now the case, AT&T could use LightWire to put most
CMTS functions in the minifiber nodes. This limits the
tasks performed at the primary hubs to bundling and
routing while moving other functions to the minifiber
nodes, which will serve about 70 homes each.
"I'd guess that in five years, distributed CMTSes will be
used in 80 percent of our systems," Sniezko says.
The key to this step is to use Time Division Multiplexing
technology to distribute all traffic to and from the
headend over the fiber portion of the cable network.
Today's cable networks use the more
processing-intensive and costly amplitude modulation
scheme to carry traffic. By using TDM to deliver
interactive, dedicated signals, AT&T will be able to use
off-the-shelf components common to local area networks
(LANs) in its minifiber nodes, Sniezko says.
Already, chip suppliers such as Broadcom are offering
100-megabit-per-second and Gigabit Ethernet integrated
circuits that would make it possible to interact with end
users on the coax portion of the network as if they were
service nodes on a LAN. "We want to push the HFC
network to look exactly like a passive optical network
[PON] while still using the coax," Sniezko says. In the
second phase, AT&T will use digital baseband for
dedicated signals both upstream and downstream. This
enables AT&T to "daisy-chain" its minifiber nodes using
a two-fiber strand, in which one fiber carries conventional
video programming and the other operates as an OC-48
(2.5-gigabit-per-second) bus, allowing the use of TDM
devices to add and drop signals from the bus at each
minifiber node.
The third phase of LightWire will involve the use of Dense
Wavelength Division Multiplexing to deliver dedicated
baseband signals to secondary hubs and then use
DWDM at the secondary hubs to partition those signals
across multiple wavelengths, so that each wavelength
would carry signals for a specific minifiber hub, Sniezko
says.
The key is a new generation of optical devices that can
be integrated onto electronic circuits.
No other cable company has moved this far into the
future. The advanced phases of LightWire address the
need to not only efficiently manage such traffic across a
streamlined optical infrastructure, but also to simplify
provisioning of an elaborate array of services to
subscribers using straightforward digital
telecommunications protocols instead of the more
complex ones defined in current cable data and packet
voice standards. |
