The Gordian Knot

REVIEW

THE GORDIAN KNOT
Planning your cabling requirements for the future

by Peter H. Putman, CTS

Cable pulls used to be so easy. Need to run audio? Grab a spool of plenum wire. Video? Okay, how many signals you wanna move around? Control cables? Sure. Let me grab my soldering iron, some 9-pin RS-232 plugs and jacks, and multi-strand wire.

Now that you've got a system that works, the manufacturers are driving you crazy with "better" ways to move signals around. Cat 5 wire. Fiber optics. RF transmission. Pulse-width modulation. LEDs. Receivers and transmitters. Yeeesh!

Truth is, there really are better ways to transport video, audio, and data over hard wired connections, particularly in multi-room environments. Discrete analog wiring is a good thing as long as the cable runs aren't too long, or don't need to be split and re-distributed too many times.

But today's typical residential or commercial installation is a bit of a crap shoot - how future-proof can you make an installation, when you don't even know what types of analog and digital signals will need to move down those wires?

There are other considerations, not the least of which are labor costs and cable prices. It would be nice to realize significant reductions in both categories, yet be able to ensure some degree of future expansion capability for your clients.

ON THE BEAM

The most efficient way to transmit any combination of oddball signals is to multiplex them. Multiplexing isn't exactly a new idea. Television broadcast stations have been doing it for years, using a 6 MHz RF "pipe" to carry amplitude-modulated video, frequency-modulated audio subcarriers, and a color burst subcarrier that also contains horizontal and vertical sync pulses.

That makes wiring really easy - just one coaxial cable carries all the information from transmitter to receiver (via an antenna or a cable drop). Because the receiver has a great deal of selectivity and filtering, multiple channels of RF can be transported across that one cable. The only technical limitations are the losses in the cable, plus any signal degradation that occurs in the analog amplifiers, splitters, and distribution equipment.

So if this model works for the broadcast of TV signals (not to mention satellite), why not adopt the broadcast model for distribution of AV signals, and eliminate the need for all those cable pulls? Better yet, why not install a system of wiring that has sufficient bandwidth to handle all kinds of digital and analog signal sources, so it really won't matter what you decide to connect to the "pipe" you've provided?

THREE WAYS TO DO IT (SO FAR)

There are several ways to adopt the broadcast multiplex pipeline system for residential and commercial wiring. One that I have covered in previous issues of S&VC, and which is getting a lot of attention from the manufacturers of projectors and displays, is to use ordinary Cat5/6 wire to carry all signals as digital bits of information.

This pure packet system has many advantages. Because it's all digital, all that's required is that any 'receivers' of data have some sort of unique address, such as an IP address. With this system, audio, video, and data packets are received only by the equipment they are addressed to, and large volumes of packets containing everything from emails and still photos can be mixed in with multi-channel audio, video, computer display signals, control information, and even digital TV programs.

The downside to all this is that you will have to set up some sort of Local Area Network (LAN) within the facility to communicate with all of these devices. That might not be too daunting a task, but it does require a degree of system intelligence beyond simple wiring.

There are other potential roadblocks, too. Many companies with existing LANs do not want to have AV equipment connected into their network for now (doubting Thomases, I guess) and that means you'll need to set up a separate, parallel LAN for the immediate future until everyone in the IT departments are convinced your projector or plasma monitor won't crash their server when it sends out a service email.

Another problem is the availability of equipment with IP addresses. So far, only Sony has gone on record as saying they will build IP addressing into every product they make from now on, including their broadcast VTRs, digital cameras, display devices, and even DVD players. At present, if you want to build a pure LAN-equipped AV facility, you may still need to rely on RS-232 control for screens, audio amplifiers and mixers, drapes, etc.

LANs are also shared bandwidth networks. A 100 MB/s Ethernet connection means you have 100 MB/s maximum data rate (or headroom) available to all users on the network. It's easy to gobble up data, too. In a residential network, simply watching a streamed DTV program would chew up 20 MB/s of data. PVRs that stream programs like SONICblue's Replay system will also grab a chunk of data, as will high-resolution digital photos, music from CDs, and DVD movies.

This isn't to say that you should dismiss LANs for AV installations - far from it. But the concept is still in its infancy and it will take time for manufacturers to incorporate the necessary IP addressing into their products. The upside is that you'll only need to pull one type of cable (Cat5/6) for everything, which will considerably whittle down labor and product costs.

As of now, you can get a limited degree of LAN connectivity and enjoy some benefits such as remote diagnostics of equipment, automatic email alerts, and status monitoring. Streaming video and audio, and sharing presentations and still images, are not quite there yet for IP-connected AV devices.

AND IN THIS CORNER

The broadcast multiplex pipeline concept translates almost perfectly to twisted-pair systems that use Cat5/6 cable as inexpensive balanced transmission lines. Instead of moving digital data, a small transmitter modulates the video, audio, and sync signals as RF carriers and subcarriers. For a 5-wire signal system, the red, green, and blue channels are each discrete RF signals with sync and audio traveling as FM signals.

This concept has been around for a few years, and provides a simple way to accomplish point-to-point RF distribution of signals. Assuming the output of the transmitter is matched carefully to the transmission line (Cat5/6 cable), the signal losses due to attenuation are tolerable and allow cable runs of up to 1000 feet with baseband video and 640x480 (VGA) signals.

There are also RF signal multiplexers for Cat5/6 wiring, just as you'd have with CATV and MATV systems. If you need to move a signal to more than one display device, all you have to do is add such a splitter, which is nothing more than a broadband RF distribution amplifier with pads and terminations to accommodate Cat5/6 wiring.

But this system has a finite limit on the number of different video and audio signals you can move around, and that limit is determined by the operating frequency of the transmitter and receiver, plus roll-off in the Cat5/6 cable itself.

For example, the allowable cable lengths drop with an increase in resolution, horizontal scanning frequency, and refresh rate. Moving SXGA graphics or HDTV 1080i signals becomes problematic at lengths over 400 feet or so. UXGA images will cut that length to about 200 feet, according to the specifications I have seen from manufacturers of twisted-pair transmitters and receivers.

For that reason, I view twisted-pair interconnects as "bridge" technology. The Cat5/6 wire pulls needed to make up a twisted-pair system are perfectly suited for conversion to a full-blown LAN once the IP-addressed equipment and peripherals are available. All you need to in the future is to pull out and toss the transmitters and receivers, replacing them with hubs, servers, and other interconnections.

SEE THE LIGHT?

There's a third way to future connectivity, but it takes a different path than Cat5/6 LANs or RF networks. That's to do away with coax or twisted-pair wire altogether and use fiber optic cables. Yes, I've hear that fiber is expensive, difficult to terminate, fragile, etc. Maybe that was true once, but the situation today is much different.

Fiber optic cable has one big advantage over Cat5/6 cable - bandwidth. Single-mode cable drops about .25 dB of signal for every kilometer @ 1550 nanometers. That works out to about .4dB per mile of fiber, a figure that leaves conventional wiring gasping for air in its wake. Even multimode fiber can achieve about 5 dB/km performance at 850 nm. Because the bandwidth of fiber optic cable goes well into the terrahertz (THz) range, multiplexing of video, audio, and control signals is a pretty easy task.

The original implementations of fiber used analog signal transmission, similar to the concept of a preamplifier and amplifier. Variations in a sine wave were amplified (not always faithfully) and reproduced at the receiving end of the fiber link. But analog signal could easily be degraded by imperfections or light distortion and refraction in fiber.

The answer (like everything else these days) is to go digital, as there are less problems switching 1s and 0s. Because fiber is a two-way system (just like a LAN), the transmitter and receiver can move any kind of digital data and even provide for forward error correction (FER). At present, lasers and LEDs are both used for fiber transmitters, although LEDs are typically reserved for multimode fiber and lasers for single-mode.

The cost of fiber optic cable has come way down. With terminations, fiber can be had for about 15 cents per foot. The terminations have also become easier to use, eliminating the need for polishing and adopting a crimp-style connector that is about as complex to install as a BNC plug. For more secure connections, the polish-and-epoxy system is still used, albeit in a much more expedient way.

Like other systems, repeaters can be installed to boost fiber signals over really long runs. However, it's not possible to use a fiber distribution system to split fiber into multiple bundles. Rather; a signal distribution system working at the actual signal frequency is required, unless the fiber system is carrying pure digital packets around some sort of LAN.

There is another advantage to using fiber, and that is its immunity to crosstalk, EMI, RFI, lightning, and other AC-coupled interference that can be problematic with any copper-based system. No voltage flows through fiber, so it can be run alongside high-voltage or utility pipes and won't crate any hazards if it should break (unless it runs through a photographic darkroom).

SO MANY CHOICES

There is no clear-cut advantage here. Twisted-pair wire is a practical solution for many applications, but it is bandwidth limited and not practical in really long runs. Cat 5/6 in a LAN configuration using pure digital data is a very practical solution, but the network needs to be setup to run Gigabit Ethernet or Fibre Channel to allow streaming of bandwidth-hogging video and audio.

If more products were available to support IP addressing, then the Cat5/6 LAN approach would make good sense. It's pretty simple to set up a small AV network and add hubs and routers as needed. All that really needs future upgrading from that point on is the equipment, as the wiring should be good for 100 to 200 Mb/s applications.

Fiber optics cable brings beacoup bandwidth to the table and super-long transmission distances, plus competitive prices when compared to Cat5/6 cable (some spec sheets I saw recently showed single-mode fiber at $0.75 per foot, as opposed to Cat 5 bulk cable at $0.12 per foot). But you'll need to do signal distribution and splitting post-fiber to make it practical.

If I had to make a choice, I might pull both for a commercial installation. The fiber links would be for serving up high-bandwidth video and computer graphics from a central location, or for point-to-point. For lower-bandwidth applications including networked displays, I'd haul in some Cat5/6.

With this setup, you could eliminate a lot of bundles of control, audio, and analog video wiring, not to mention a bunch of distribution amplifiers, and be future-proof for an all-digital signal distribution system. The cable is certainly inexpensive enough, and there are plenty of interfaces available for both systems.

At present, Extron, FSR, Altinex, and InLine are supporting twisted-pair connections, and some of these companies are taking baby steps into pure LAN and IP interfaces. They are joined in that market by Sony, Epson, Sharp, InFocus/Proxima, and other display manufacturers that are incorporating IP addresses into their projectors and monitors. I suggest you check out all the offerings from these companies and pay careful attention to bandwidth specifications before choosing the wire for your future installs.

On the fiber side, the lone voice of any substance is Communications Specialties, who has quite a few RGB, video and audio interfaces for fiber connectivity. (My thanks to John LoPinto of CSI who provided background materials on fiber for this feature.) I've covered twisted-pair and LAN connectivity in previous issues of S&VC, but if you want more information on fiber, CSI has a couple of educational booklets that are yours for the asking. Drop them an email at info@commspecial.com.

Copyright ©2002 Primedia Business Media / Peter H. Putman
This article appears in the July 2002 issue of Sound and Video Contractor.


						REVIEW
					THE GORDIAN KNOT Planning your cabling requirements for the future


					by Peter H. Putman, CTS Cable pulls used to be so easy. Need to run audio? Grab a spool of plenum wire. Video? Okay, how many signals you wanna move around? Control cables? Sure. Let me grab my soldering iron, some 9-pin RS-232 plugs and jacks, and multi-strand wire. Now that you've got a system that works, the manufacturers are driving you crazy with "better" ways to move signals around. Cat 5 wire. Fiber optics. RF transmission. Pulse-width modulation. LEDs. Receivers and transmitters. Yeeesh! Truth is, there really are better ways to transport video, audio, and data over hard wired connections, particularly in multi-room environments. Discrete analog wiring is a good thing as long as the cable runs aren't too long, or don't need to be split and re-distributed too many times. But today's typical residential or commercial installation is a bit of a crap shoot - how future-proof can you make an installation, when you don't even know what types of analog and digital signals will need to move down those wires? There are other considerations, not the least of which are labor costs and cable prices. It would be nice to realize significant reductions in both categories, yet be able to ensure some degree of future expansion capability for your clients. ON THE BEAM The most efficient way to transmit any combination of oddball signals is to multiplex them. Multiplexing isn't exactly a new idea. Television broadcast stations have been doing it for years, using a 6 MHz RF "pipe" to carry amplitude-modulated video, frequency-modulated audio subcarriers, and a color burst subcarrier that also contains horizontal and vertical sync pulses. That makes wiring really easy - just one coaxial cable carries all the information from transmitter to receiver (via an antenna or a cable drop). Because the receiver has a great deal of selectivity and filtering, multiple channels of RF can be transported across that one cable. The only technical limitations are the losses in the cable, plus any signal degradation that occurs in the analog amplifiers, splitters, and distribution equipment. So if this model works for the broadcast of TV signals (not to mention satellite), why not adopt the broadcast model for distribution of AV signals, and eliminate the need for all those cable pulls? Better yet, why not install a system of wiring that has sufficient bandwidth to handle all kinds of digital and analog signal sources, so it really won't matter what you decide to connect to the "pipe" you've provided? THREE WAYS TO DO IT (SO FAR) There are several ways to adopt the broadcast multiplex pipeline system for residential and commercial wiring. One that I have covered in previous issues of S&VC, and which is getting a lot of attention from the manufacturers of projectors and displays, is to use ordinary Cat5/6 wire to carry all signals as digital bits of information. This pure packet system has many advantages. Because it's all digital, all that's required is that any 'receivers' of data have some sort of unique address, such as an IP address. With this system, audio, video, and data packets are received only by the equipment they are addressed to, and large volumes of packets containing everything from emails and still photos can be mixed in with multi-channel audio, video, computer display signals, control information, and even digital TV programs. The downside to all this is that you will have to set up some sort of Local Area Network (LAN) within the facility to communicate with all of these devices. That might not be too daunting a task, but it does require a degree of system intelligence beyond simple wiring. There are other potential roadblocks, too. Many companies with existing LANs do not want to have AV equipment connected into their network for now (doubting Thomases, I guess) and that means you'll need to set up a separate, parallel LAN for the immediate future until everyone in the IT departments are convinced your projector or plasma monitor won't crash their server when it sends out a service email. Another problem is the availability of equipment with IP addresses. So far, only Sony has gone on record as saying they will build IP addressing into every product they make from now on, including their broadcast VTRs, digital cameras, display devices, and even DVD players. At present, if you want to build a pure LAN-equipped AV facility, you may still need to rely on RS-232 control for screens, audio amplifiers and mixers, drapes, etc. LANs are also shared bandwidth networks. A 100 MB/s Ethernet connection means you have 100 MB/s maximum data rate (or headroom) available to all users on the network. It's easy to gobble up data, too. In a residential network, simply watching a streamed DTV program would chew up 20 MB/s of data. PVRs that stream programs like SONICblue's Replay system will also grab a chunk of data, as will high-resolution digital photos, music from CDs, and DVD movies. This isn't to say that you should dismiss LANs for AV installations - far from it. But the concept is still in its infancy and it will take time for manufacturers to incorporate the necessary IP addressing into their products. The upside is that you'll only need to pull one type of cable (Cat5/6) for everything, which will considerably whittle down labor and product costs. As of now, you can get a limited degree of LAN connectivity and enjoy some benefits such as remote diagnostics of equipment, automatic email alerts, and status monitoring. Streaming video and audio, and sharing presentations and still images, are not quite there yet for IP-connected AV devices. AND IN THIS CORNER The broadcast multiplex pipeline concept translates almost perfectly to twisted-pair systems that use Cat5/6 cable as inexpensive balanced transmission lines. Instead of moving digital data, a small transmitter modulates the video, audio, and sync signals as RF carriers and subcarriers. For a 5-wire signal system, the red, green, and blue channels are each discrete RF signals with sync and audio traveling as FM signals. This concept has been around for a few years, and provides a simple way to accomplish point-to-point RF distribution of signals. Assuming the output of the transmitter is matched carefully to the transmission line (Cat5/6 cable), the signal losses due to attenuation are tolerable and allow cable runs of up to 1000 feet with baseband video and 640x480 (VGA) signals. There are also RF signal multiplexers for Cat5/6 wiring, just as you'd have with CATV and MATV systems. If you need to move a signal to more than one display device, all you have to do is add such a splitter, which is nothing more than a broadband RF distribution amplifier with pads and terminations to accommodate Cat5/6 wiring. But this system has a finite limit on the number of different video and audio signals you can move around, and that limit is determined by the operating frequency of the transmitter and receiver, plus roll-off in the Cat5/6 cable itself. For example, the allowable cable lengths drop with an increase in resolution, horizontal scanning frequency, and refresh rate. Moving SXGA graphics or HDTV 1080i signals becomes problematic at lengths over 400 feet or so. UXGA images will cut that length to about 200 feet, according to the specifications I have seen from manufacturers of twisted-pair transmitters and receivers. For that reason, I view twisted-pair interconnects as "bridge" technology. The Cat5/6 wire pulls needed to make up a twisted-pair system are perfectly suited for conversion to a full-blown LAN once the IP-addressed equipment and peripherals are available. All you need to in the future is to pull out and toss the transmitters and receivers, replacing them with hubs, servers, and other interconnections. SEE THE LIGHT? There's a third way to future connectivity, but it takes a different path than Cat5/6 LANs or RF networks. That's to do away with coax or twisted-pair wire altogether and use fiber optic cables. Yes, I've hear that fiber is expensive, difficult to terminate, fragile, etc. Maybe that was true once, but the situation today is much different. Fiber optic cable has one big advantage over Cat5/6 cable - bandwidth. Single-mode cable drops about .25 dB of signal for every kilometer @ 1550 nanometers. That works out to about .4dB per mile of fiber, a figure that leaves conventional wiring gasping for air in its wake. Even multimode fiber can achieve about 5 dB/km performance at 850 nm. Because the bandwidth of fiber optic cable goes well into the terrahertz (THz) range, multiplexing of video, audio, and control signals is a pretty easy task. The original implementations of fiber used analog signal transmission, similar to the concept of a preamplifier and amplifier. Variations in a sine wave were amplified (not always faithfully) and reproduced at the receiving end of the fiber link. But analog signal could easily be degraded by imperfections or light distortion and refraction in fiber. The answer (like everything else these days) is to go digital, as there are less problems switching 1s and 0s. Because fiber is a two-way system (just like a LAN), the transmitter and receiver can move any kind of digital data and even provide for forward error correction (FER). At present, lasers and LEDs are both used for fiber transmitters, although LEDs are typically reserved for multimode fiber and lasers for single-mode. The cost of fiber optic cable has come way down. With terminations, fiber can be had for about 15 cents per foot. The terminations have also become easier to use, eliminating the need for polishing and adopting a crimp-style connector that is about as complex to install as a BNC plug. For more secure connections, the polish-and-epoxy system is still used, albeit in a much more expedient way. Like other systems, repeaters can be installed to boost fiber signals over really long runs. However, it's not possible to use a fiber distribution system to split fiber into multiple bundles. Rather; a signal distribution system working at the actual signal frequency is required, unless the fiber system is carrying pure digital packets around some sort of LAN. There is another advantage to using fiber, and that is its immunity to crosstalk, EMI, RFI, lightning, and other AC-coupled interference that can be problematic with any copper-based system. No voltage flows through fiber, so it can be run alongside high-voltage or utility pipes and won't crate any hazards if it should break (unless it runs through a photographic darkroom). SO MANY CHOICES There is no clear-cut advantage here. Twisted-pair wire is a practical solution for many applications, but it is bandwidth limited and not practical in really long runs. Cat 5/6 in a LAN configuration using pure digital data is a very practical solution, but the network needs to be setup to run Gigabit Ethernet or Fibre Channel to allow streaming of bandwidth-hogging video and audio. If more products were available to support IP addressing, then the Cat5/6 LAN approach would make good sense. It's pretty simple to set up a small AV network and add hubs and routers as needed. All that really needs future upgrading from that point on is the equipment, as the wiring should be good for 100 to 200 Mb/s applications. Fiber optics cable brings beacoup bandwidth to the table and super-long transmission distances, plus competitive prices when compared to Cat5/6 cable (some spec sheets I saw recently showed single-mode fiber at $0.75 per foot, as opposed to Cat 5 bulk cable at $0.12 per foot). But you'll need to do signal distribution and splitting post-fiber to make it practical. If I had to make a choice, I might pull both for a commercial installation. The fiber links would be for serving up high-bandwidth video and computer graphics from a central location, or for point-to-point. For lower-bandwidth applications including networked displays, I'd haul in some Cat5/6. With this setup, you could eliminate a lot of bundles of control, audio, and analog video wiring, not to mention a bunch of distribution amplifiers, and be future-proof for an all-digital signal distribution system. The cable is certainly inexpensive enough, and there are plenty of interfaces available for both systems. At present, Extron, FSR, Altinex, and InLine are supporting twisted-pair connections, and some of these companies are taking baby steps into pure LAN and IP interfaces. They are joined in that market by Sony, Epson, Sharp, InFocus/Proxima, and other display manufacturers that are incorporating IP addresses into their projectors and monitors. I suggest you check out all the offerings from these companies and pay careful attention to bandwidth specifications before choosing the wire for your future installs. On the fiber side, the lone voice of any substance is Communications Specialties, who has quite a few RGB, video and audio interfaces for fiber connectivity. (My thanks to John LoPinto of CSI who provided background materials on fiber for this feature.) I've covered twisted-pair and LAN connectivity in previous issues of S&VC, but if you want more information on fiber, CSI has a couple of educational booklets that are yours for the asking. Drop them an email at info@commspecial.com. Copyright ©2002 Primedia Business Media / Peter H. Putman This article appears in the July 2002 issue of Sound and Video Contractor.