By Peter Beck
Chief Operating Officer
VideoLan Technologies
Louisville, Ky.
Broadband telecommunications and wide-area data
communications services continue to be stymied by
major technical, economic, or market problems
associated with last-mile technologies like "fiber to
the home," hybrid fiber/coax (HFC), ADSL, and a
number of others. Fiber and HFC are technically
feasible, but the massive construction programs
needed to bring them to the desktop are
uneconomical.
This problem is stimulating the development of
high-bandwidth transmission technologies for the existing twisted-pair copper wire infrastructure.
Such solutions, like ADSL/HDSL technology, are vastly more economical than fiber, but still have
bandwidth limitations or are specific to certain services or traffic forms. Consequently, they still
carry some market risk. VideoLan's patented Metallic Fiber technology resolves a number of
problems associated with other technologies and can compete effectively in a last-mile environment.
Metallic Fiber is a broadband carrier solution currently implemented on two otherwise unused
twisted pairs that are already part of existing in-building and on-campus EIA568 wiring plans.
VideoLan has successfully employed the technology in its first product, the VL2000 desktop
video-distribution network. Because it employs a broadband carrier, however, any number of other
traffic types and combinations can be modulated onto it using various modulation schemes.
This means it could also be engineered for use in a wide variety of analog and digital transmission
applications for local-exchange carriers' local loops, and for other service offerings that require a
range of bandwidths and distances and that support multiple traffic forms.
The great flexibility of Metallic Fiber, a generic transport, offers a number of advantages to users,
including a bandwidth that is two to 10 times that of other twisted-pair technologies, and support for
both analog and digital traffic or a combination of the two. And these traffic forms can be supported
in full-duplex mode.
Metallic Fiber embeds adaptive equalization to automatically support any transmission distance, up
to the maximum specified for the application. For example, in an application where the maximum
designed transmission distance might be 2,000 feet, Metallic Fiber allows the user to run that
product over any distance between zero and 2,000 feet simply by plugging in a wire of the desired
length. It automatically senses signal clarity, correctness, and gain; these characteristics, and thus the
quality of the signal, depend upon the distance the signal has traveled. This technique compares to
other systems which must be pre-set to specific distances or distance ranges.
Because Metallic Fiber is based on a broadband carrier, any variety of analog or digital can be
modulated on it. A variety of modulation methods can be used, depending on the traffic and
bandwidth desired. Many of these methods are already available in off-the-shelf chip sets.
The VL2000 implements the modulation techniques in a unique manner. Modulation and
demodulation occur at the outer bounds of the network, in modems at the desktop. The modulated
signals are then transmitted over two twisted pairs at a bandwidth of 15 MHz for distances of up to
2,000 feet. Video is modulated over a bandwidth of from 0 to 6 MHz; two 20-kHz audio channels
are centered on the frequencies of 8.7 MHz and 9.7 MHz; a 57.6-kbits/s data channel is centered
on a frequency of 10.7 MHz; and two control data channels (used for switch functions and internal
system control) are centered on the frequencies of 11.7 MHz and 12.7 MHz. The VL2000
implementation is full duplex, and this frequency budget is used on both transmit and receive pairs.
This is merely one example of what can be done in terms of modulating analog and digital signals on
the system, demonstrating that it is possible to simultaneously modulate multiple traffic streams and
multiple traffic forms, with appropriate separation bands. Alternatively, all available bandwidth could
be used for one traffic form, analog or digital, or for any combination of forms. While these
obviously are not new concepts, Metallic Fiber dramatically expands the amount of available
bandwidth.
Metallic Fiber is characterized by modulation at very low voltage levels-the video signal is
modulated at a maximum of 500 millivolts, while the analog and digital signals are modulated at a
maximum of 100 millivolts. These gain levels work very successfully in the VL2000, and they ensure
that RF emissions and crosstalk are negligible in multiconductor cable groups. Low interference is
critical to installation in typical teleco local loop architectures.
It is also critical in the VL2000, which puts video traffic in the LAN environment, although not
actually on the LAN=2E. The EIA568 wire plan used for LANs specifies four unshielded twisted
pair (UTP), Category 4 or 5 or data twist, to the desktop. LAN technologies such as 10BaseT
Ethernet, Token Ring, and others, however, employ only two of these pairs. Metallic Fiber splits the
other two pairs off with a Y connector and employs them for bi-directional transmission. Because
Metallic Fiber transmissions are completely independent of and parallel to the existing LAN, yet use
existing twisted pairs, the need to bring high-cost fiber or coaxial cable to the desktop is eliminated.
Easy adaptation
Metallic Fiber is also readily adapted to any analog or digital traffic form. The technology has
enough bandwidth available to handle not only video in the analog NTSC form, but also in JPEG,
MPEG 1, and MPEG 2 forms, all of which can be digitized at different bandwidths. Even ATV
could be distributed via VideoLan's technology. (ATV may use about 18 Mbits/s bandwidth for
local distribution, while MPEG 2 can employ up to 45 Mbits/s; Metallic Fiber has the capacity to
carry them in full-duplex mode.)
There's even enough bandwidth to handle multiple video channels, both uncompressed and
compressed. This flexibility opens up a wide variety of new product opportunities, and Video-Lan
plans future product implementations. The ability to transmit multiple signals like multimedia and
control data over the same set of wires distin-guishes Metallic Fiber from other desktop video
products that carry audio and control data band, typically on the LAN. This ability to carry multiple
traffic forms is important for telephone companies, where wires start in a central office, emerge as a
cable group consisting of as many as 600 wire pairs, break down into small groups of 25 pairs, and
finally enter individual homes in small groups of two to four pairs.
In a corporate setting, a larger group of cables enters a building at the D-mark. It is even possible
(though not implemented in the VL2000) to carry voice traffic (e.g., POTS) in addition to video and
other traffic on Metallic Fiber.
Metallic Fiber also has more than enough bandwidth to carry LAN traffic such as 10 Base T and
token ring, which may be implemented in a new generation of VideoLan products. Its ability to
carry the LAN signal has been demonstrated in the lab. It can even carry ATM traffic. VideoLan
has successfully tested a number of modulation methods and expects to employ frequency-shift
keying (2 bits/Hz), quadrature-amplitude modulation (QAM) (4 bits/Hz), and 64 QAM (5 bits/Hz).
As a result, Metallic Fiber could deliver ATM to the desktop at the STS-1 rate, at least. At
distances shorter than 2,000 feet and using more wire pairs, it is expected to deliver even higher
ATM rates.
Metallic Fiber might even be used as a carrier system for HDSL/ADSL. The protocol specifies a
certain format and clock rate, and other requirements; there is no reason that Metallic Fiber can't be
the carrier and provide even better transmission than is available now.
The Metallic Fiber broadband carrier signal can be and has been passed through fiber, using fiber
transceivers as gateways to private networks or metropolitan-area fiber networks. This requires that
the gain be adjusted and the mode converted from bipolar to common if the signal is to pass through
off-the-shelf fiber transceivers. However, to interface directly with fiber links and transceivers is
inexpensive. This extends the twisted-pair infrastructure, as it normally is through the telephone
networks on existing fiber, and can be done in cases where the fiber is dark, i.e., not in service by a
public carrier.
WAN combos
The ability to interface to fiber is useful, as large corporations and universities already employ a
combination of fiber and twisted pair in the wide-area networks. Typically, multistory buildings have
multiple strands of fiber on risers; some strands are lit and some dark. The Metallic Fiber signal can
even be interfaced to a microwave link, provided it has sufficient bandwidth. (Not all microwave has
15-MHz capacity.)
The figure (p.54) illustrates how VideoLan's first product, the VL2000 desktop-video and
multimedia-conferencing network combines Metallic Fiber and broadband-switching technology
with products and technologies from other vendors into a system that encompasses both local and
remote users. At the desktop, the system consists of: a modem-like Metallic Fiber card that can be
installed in PCs as well as interfaced to video storage devices such as VCRs and CDs; a video
overlay card; and a user interface consisting of a camera, microphone, and external speakers.
Twisted-pair leads from the card to a broadband-switching hub that handles local video
transmission and switching. This in turn connects to any number of wide-area video gateways that
provide access to public carrier networks. For small, remote locations, Video-Lan provides
stand-alone video workstations that connect directly to the public carrier.
In its current implementation, the VL2000 has a bandwidth of 15 MHz, and uses Metallic Fiber for
up to a maximum of 2,000 feet of untwisted pair. The analog NTSC signal is employed in the
system, rather than a digitized video signal, because it allows the system to access VCRs, laser
disks, and live video feeds without having to do expensive digital encoding and decoding. Use of
NTSC also allows Video-Lan to address the new and fast-growing video-distribution market, in
addition to the teleconferencing market. It also allows the use of relatively inexpensive off-the-shelf
products such as video cameras and televisions, thus reducing the cost of the video network while
maintaining maximum performance.
The VL2000 currently employs video gateways to access carrier networks via T-1 switched and
T-1 dedicated lines or ISDN BRIs. As stated earlier, it is also possible to terminate at a fiber
transceiver for access to private or metropolitan area networks. VideoLan's gateways digitize and
compress video signals, using any number of possible schemes, such as the H.320 standard for
video conferencing. This can be transmitted well within T-1 data rates and multiplexed into data
rates on fiber.
The system can also handle compressed JPEG, MPEG 1, and MPEG 2, all at various bit rates,
giving users the choice of how to handle transmission and quality issues.
Metallic Fiber has great potential as a local-loop transmission technology, although like any other
transmission technology it has distance-vs.-bandwidth tradeoffs. The VL2000 employs a 15-MHz
bandwidth for broadband video and multimedia applications on short local loops that are entirely
appropriate for corporate and institutional use. But because it can be re-engineered for different
combinations of distances, and because it can incorporate any number of already available
modulation schemes, it has the potential to carry almost any form of analog or digital traffic at rates
that have heretofore been possible only on fiber or coaxial cable.
The technology also can be adapted to a wide range of local loop lengths. And, while the current
product employs wire pairs in category 4, 5, or data twist, Metallic Fiber can also be run on
category 3 telephone-quality wires.
The technology has been run successfully in large cable loops in the presence of various other traffic
forms, and testing is in progress for multiconductor cable groups typical of teleco plants, and at
various distances. In addition, Metallic Fiber can be interfaced to various public network
architectures with existing termination equipment such as multiplexers and channel banks.
BTW, I bought this stcok at 3 3/8 . What do you think JW? |
