by Steve Church
Cleveland, Ohio, USA
Editor's note: this page is excerpted from our Introduction to Livewire System Design Reference & Primer.
As with analog audio installations, Livewire set-ups range from the very simple to complex facility-wide installations with hundreds of ports. This section is aimed primarily at those who will be building large systems.
Ethernet is balanced and transformer coupled, so has quite good resistance to interference and has no problem with ground loops. However, frequencies ranging to tens of megahertz are being used, so care must nevertheless be taken.
Charles Spurgeon in Ethernet: The Definitive Guide says that you should consider wiring to be the essential skeleton for your network installation. He goes on to point out that network cabling skeletons are often hidden in the time-honored place for skeletons: a closet. Rim shot.
In the bad old days, wiring was specific to the task – and often to the vendor. Each telephone, network, and audio had its own cable type and wiring protocols. The idea at standards bodies like the Telecommunications Industry Association (TIA) and the Electronic Industries Association (EIA) in the USA is to define classes or categories of cables and accessories that can be used for all applications specified for that class. With this, you have a vendor-independent way to wire buildings and facilities so that services from many vendors can be supported over time without replacing cabling and connectors. The name for this concept is structured wiring.
The long cables that go from equipment rooms to terminal locations are called horizontal cables. They usually terminate in RJ-45s, either in patchfields or on wall jacks. Patchcords with RJ-45s at each end complete the system, connecting the terminals and central equipment to the jacks.
Twisted-pair Cable Categories
Cable categories are key to the structured wiring concept. The cabling specifications for the various categories are in the TIA/EIA-568-A (and B) Commercial Building Telecommunications Cabling Standard. The following categories are defined:
These are used only for telephone and Ethernet 10BASE-T, so are not useful for Livewire installations.
This designation applies to 100 ohm unshielded twisted pair cables and associated connecting hardware whose transmission characteristics are specified up to 100MHz. Cat 5 cables are today’s most common because they support Ethernet 100BASE-TX.
This is enhanced Category 5 cable. The main application is for gigabit 1000BASE-T. While Cat 5 is acceptable for 1000BASE-T, 5e is preferred. We recommend Cat 5e for new LW installations. While LW terminals use 100BASE-T and have no “official” need for 5e, the cost increment is small and the “confidence-factor” that all will be well is higher. And if 1000BASE-T becomes common, you will be ready.
Cat 6 provides significantly higher performance that Cat 5e. You don’t need this level of performance for LW, but if the cable can be had with not too much price premium, it might make sense to use it. Belden has a Cat 6 cable called Mediatwist that looks very interesting. This product has the pairs bonded together so that the relationship between the wires remains fixed regardless of manufacturing tolerances, cable flexing, etc.
The most significant difference between cables from each category is the number of twists per foot and the tightness with which they are controlled at time of manufacture. The wire pairs in a voice-grade Category 3 cable usually have two twists per foot, and you may not even notice the twists unless you peel back quite a lot of the outer insulation. Category 5 is tightly twisted, something like 20 per foot. This results in superior crosstalk performance at higher frequencies.
Another characteristic of twisted-pair cables is the type of insulation used on the wires and the cable jacket. “Plenum rated” cables are more stable with changing temperatures due to their using Teflon rather than PVC insulation. Plenum rated cables are required in air handling spaces in order to meet fire regulations. Teflon produces less smoke and heat in the case of a fire than PVC and does not support the spread of flames.
Special Care for Ethernet Audio
“Normal” data over Ethernet is usually TCP/IP protocol. As discussed later, TCP has a re-transmission mechanism that detects errors and fixes them by requesting and obtaining replacement packets when one has been received with a defect. This mechanism is not used for audio – it can’t be when you need low delay and multiple receivers. So it could be possible that a network could be apparently OK with computer data, yet exhibit errors with audio because TCP is covering-up problems.
A particular concern is to prevent impedance reflections at cable termination points and to not disturb too much the position of the wires inside the cable. Here are some specific recommendations:
Use the minimum number of terminations and patches that will support your application.
Use patch cables, connectors, and other accessories rated at the same or higher category level as the cable you are using.
Keep a wire pair’s twist intact to as close as possible to any termination point. For Category 5, this should be to within 1.3 cm (.5 inch).
Maintain the required minimum bending radius. For a 4-pair 0.5 cm (.2 inches) diameter cable, the minimum bend radius is 4 times the diameter, or about 2 cm (.8 inches).
Minimize jacket twisting and compression. Install cable ties loosely and use Velcro fasteners that leave a little space for the cable bundle to move around. Do not staple the cable to backboards. If you tightly compress the jacket, you may disturb the twists inside and the relationship of one pair to another, which could cause crosstalk.
Avoid stretching the cable. The official recommendation is to use less than 25 lbs. pulling pressure.
Avoid close proximity to power cables and equipment that generate significant magnetic fields. The official recommendation is minimum 6.4 cm (2.5 inches) from power cables when the Cat 5 is either inside a conduit or shielded. Care should be taken also with fluorescent lighting fixtures, motors and transformers.
The pins on RJ-45 plugs are gold plated. But not all connectors are. For maximum reliability, use connectors with 50m gold plating.
To Shield or Not to Shield
Unless you are in a high RF environment or you intend to run your network cables close to audio cables with equipment that has poor balancing on the inputs, you should be able to use unshielded twisted pair for your Ethernet connections. If you decide to shield, the usual procedure to attach it only at one end applies in order to prevent ground loops.
More than Four Pairs in a Cable
Back in the 10BASE-T days, it was usual to have phone-type 25-pair cables carrying data signals. But the standards for Cat 5 and better call for individual cables for each connection due to the possibility of multiple disturber near end crosstalk –or many signals adding up to create combined crosstalk at too high a level.
On the other hand, Belden has some papers on their website proposing that their finest cable, Mediatwist, would support even 100BASE-T and analog audio inside a shared sheath. Nevertheless, they offer the cable in only 4-pair versions at this time.
Patch panels come in versions for rack or wall mount and with varying numbers of jacks. Your horizontal cables are punched down at the rear into 110-style insulation displacement connectors using a tool very similar to the one that is used with traditional “66 blocks.”
Cat 5e RJ-45 Patch Panels, in Rack and Wall-mount Versions
Paladin 3570 punch tool for 110-style IDC connectors
Again 110-style IDC connectors terminate the cable. Then these wired-up “Keystone” RJ-45 jacks are pushed into a hole in the wall plate to complete the job.
There are a lot of ways to build a Livewire network. For many people a simple one-switch layout will be perfectly sufficient. Others will want to build sophisticated networks to support multiple studios and perhaps hundreds of audio channels. Fortunately, Ethernet scales easily– so too your LW installation.
Here are some examples and ideas to get you started:
Common 1U switches can have as many as 48 ports. That is a lot of audio! Here’s a setup that supports an on-air studio and a production studio.
One-Studio, One-Switch Layout
The switch is a 24-port 100BASE-TX + 2-port 1000BASE-T/GBIC fiber version.
There is the microphone version of the LW terminal in the on-air studio and the 8x8 line version in the central rack. The production studio connects with a Router version terminal, which has one send channel and a selectable receive channel.
The Surface power supply includes plenty of GPIOs for starting CD players, lighting on-air lamps, remote mic on-off, etc.
The Studio Engine connects with a 1000BASE-T copper link to one of the two 1000BASE-T ports.
The delivery PC connects directly to the audio network with the Livewire PC Suite software. Control for it may be directly over the network or could be with a hardware parallel connection. Servers and additional PCs can be connected to the switch.
Peripherals such as codecs, telephone systems, and satellite receivers may be connected into the network wherever it is convenient. In the diagram, the Zephyr codec is shown attached to a LW terminal and that is how most equipment will initially attach for now. But soon this equipment and others will have direct LW connection ports.
You could expand this to two Surfaces and Engines to support two studios since the switch has two 1000BASE-T ports. Or you could substitute an all 1000BASE-T switch to support as many studios as you want.
Central Rack Installation
In the photo you can see a typical set-up with a terminal, engine, switch, and patchbay. (This one is at WEGL, Auburn University.) The patchbay is being used to terminate cables from remote locations before being connected to the switch with short patch jumpers, while the terminal and engine connect directly using longer patch cords. Using a patchbay and off-the-shelf patch cords in this fashion minimize the need to install RJ-45 plugs.
Daisy Chained Switches
While one switch can support multiple studios, you would have a single point of failure. Here’s another approach that gives each studio its own switch. The example uses three switches, one for each studio group. This layout style could easily be expanded to any number of switches and studios.
Daisy-chained Switches to Support Multiple Studios
The switches are connected together so that audio sources are shared. A 1000BASE-T link between the switches allows hundreds of audio channels to flow from one group to another. With more than two switches you could have a “circular backbone” with redundant spanning-tree links (described below) between the switches.
Peripherals that are used in common such as codecs could be plugged to any of the studio switches, or there could be a separate switch to pick up such feeds.
This is a layout that could support a very large facility. A gigabit switch is at the center and 100/1000 switches are used at the edge with one for each studio or logical group.
A Two-Level Layout for Larger Studio Facilities
A Router Selector terminal is kept in the central equipment room for test and monitoring. Additional terminals could link audio from non-Livewire studios.
While we could plug the Engines into the central switch, if we keep them coupled to the individual studio switches, there is no single point of failure for any studio.
Gigabit links are used between the edge switches and the center. These could be copper or fiber with a suitable switch.
The physical location of the switches is a matter of taste and trade-off. Putting the edge switches near the studios saves cable runs, but locating all the gear in a central room simplifies engineering activities.
As this is written, an appropriate switch for the center costs $2k and the studio switches $700. So this is a quite reasonable-cost option that provides a lot of power, flexibility, and expandability. Dozens of studios and thousands of audio channels are possible.
Ethernet switching has a built-in scheme for redundancy, called spanning-tree and standardized as 802.1D. A newer variant is called fast spanning-tree. Switches with spanning-tree enabled exchange information with each other about the topology of the overall network. You can have redundant backup links that are automatically activated in the case that a main link has failed. Depending on the switch and layout, it could take as little as a second or as much as a half-minute for a redundant link to be connected.
Link aggregation (sometimes called port trunking) is another method. With spanning-tree, even if you have two links between two switches, only one of them at a time will be active. But, it’s often better to have both active simultaneously because you get twice the bandwidth during normal operation and instantaneous backup should one fail. The link aggregation standard is 802.3ad. To use it, you usually have to specifically enable it on your switch. Incidentally, this is supported on some PC network interface cards intended for servers, so its not only for switch-switch links.
Most Ethernet switches offer a redundant power supply option.
We’ve been talking here about automatic on-line redundancy, but there is also manual swap-out as a reasonable option. Because RJ-45s are so easy to unplug and re-plug and because switches and other Livewire components are much cheaper than traditional alternatives, you can have spare units on the shelf for fast substitution.
Fiber optic links can extend the range of Ethernet. Because they are not subject to crosstalk and magnetic interference, they also can solve problems that might crop up in difficult locations with copper cables.
External media converters can be very simply plugged to LW terminal and switch 100BASE-T ports to convert copper connections to fiber.
This unit from Allied-Telesyn uses 100Mbps ST multimode fiber for up to 2km range. Units supporting SC single mode fiber can extend up to 75km.
Modern Ethernet switches often have the option to plug a media converter directly into a special socket so that fiber may easily be connected from switch to switch. This is useful to make high capacity backbone links without any external boxes.
Here is a typical case. There are two “uplink” ports for 1000BASE-T copper paired with SFP/mini-GBIC sockets. When the fiber adapters are plugged-in, the copper ports are automatically disabled. In the photo, there are no fiber adapters installed into the Mini-GBIC slots and the “T” LED is illuminated to show that the copper jacks are active.
The devices above are typical modern media adapters in the “SFP/mini-GBIC” size – about the same in width and height as an RJ-45 jack. The one on the left is for 1000BASE-SX and the one on the right is for 1000BASE-LX. Generally, SX cables have a range to 500 meters, LX to 5km, and LH to 70km.
There are Ethernet radios with surprisingly high bandwidth – and at surprisingly low cost. Interesting products are the Adtran Tracer, the Motorola Canopy, and units from Proxim and Redline Communications. Website addresses for these companies are in the Resources section. Most of these operate in the unlicensed ISM bands, but with modern spread-spectrum technology and elevated directional antennas, interference doesn’t look to present much problem. Licensed radios following the new IEEE 802.16 “Wimax” standard are starting to appear.
Bitrates range to 48 Mbps and distance to 50 miles depending on power level, antenna, and terrain.
For studio-to-transmitter link, remote pick-up, and studio-to-studio applications, these offer multiple channels of uncompressed audio, two-way transmission, and the ability to multiplex VoIP telephone, remote control, and general data. When audio and general data are mixed, the Ethernet switch provides the prioritization function. As with all LW elements, you can check them with a web browser on a network-attached PC.
You will have 100% security if you keep the Livewire system completely isolated from any other network, local or wide area. Those very concerned with protecting the studio system may well want to take this approach.
But there are advantages to sharing with or linking to an office network. You can configure and monitor the system from any connected PC and audio can be monitored on any desktop. In this case, separate switches or VLANs (described later) can be used to provide isolation. An IP router passes only the correct packets from one to the other and thus provides a firewall function.
The next step up in connectivity would be to have a network linking co-owned or otherwise affiliated stations. In this case, a network engineer is probably in the picture and he can take the necessary steps to protect your audio.
Connection to the public internet brings the advantage that you can monitor and configure from a remote site, but you now have much risk from unwanted intruders, viruses, etc. A qualified network engineer should be consulted to be sure you have an appropriate firewall and other protections in place.
In LW terminals, web and Telnet access are password protected to provide some measure of security. But we do not use exotic techniques like SSL (Secure Sockets Layer), so please understand that our devices were not designed to be exposed to the public internet without external protection.