Converging media types simplify network management

Aug. 1, 1999

If you were to examine the campus backbone in today's enterprise networks, it would be no surprise to find a mixture of media types. Campus backbones typically include fiber, twisted-pair, and coaxial cables. These cables are more than likely "owned" by more than one department and have different physical routings that lead to inefficiencies in operation and maintenance. As you move to the horizontal runs, you also find a hodgepodge of solutions designed to support your network growth to higher transmission speeds. Standardizing your network on optical fiber can simplify network maintenance, lower operating costs over the life of your network, and provide you with a viable upgrade path as your network needs increase.

Typically, the terms "campus backbone" or "enterprise network" bring data-networking applications to mind. These are the networks that support all desktop computers, corporate databases, printer and file sharing, and, of course, the Internet.

For many years, the only practical way to connect campus buildings was to use router technology, which would be interconnected using technologies such as T1/E1 or Digital Data Service (DDS). As network traffic demands increase, these solutions become less and less desirable because of their lower operating speeds and the unacceptable latency they add to the network. As an alternative, as well as to achieve full network speed, fiber is used to directly connect buildings in the campus network. This approach allows full-speed operation at almost any distance (depending on whether multimode fiber or singlemode fiber is used).

However, the campus network does not end with meeting the needs of data transfer. Typical campus environments must also address voice, building automation, and security.

Voice interconnections typically take one of three forms: a T1/E1, multiple discrete voice lines, or a vendor-specific interface. T1/E1 circuits are the most common of the three. One or more T1/E1 circuits are used between private branch exchange, (PBXs) in each of the buildings. In larger campuses, this setup can require the use of mid-span repeaters every 5000 ft. But these repeaters are not the preferred solution, since they require power and add jitter and are an additional point of failure. In climates where lightning is common, copper wires can pick up noise and energy that can damage the equipment to which it is connected.

Building automation also requires a network. These systems control everything from the lights to climate and often share data among buildings. This data sharing is essential in how these systems regulate equipment. It keeps overall energy use for the entire campus intact, while maintaining an acceptable level of comfort. Building automation systems use a variety of interconnects, but most can be categorized as either RS-422/RS-485, proprietary, or Ethernet. In any case, unshielded twisted-pair (UTP) is most often used, resulting in lower speeds and increased noise emissions and interference in the network.

Security and video systems have some unique requirements. While I am not addressing deployments that are life critical, in many cases, improvements can be made in the design of building interconnects. For instance, security cameras are often deployed in remote areas. The transmissions from these cameras are usually fed back to a central security desk using coaxial cable. This cable has distance limitations and is also susceptible to electrical interference and lightning strikes.

The expenses associated with maintaining multiple media are cumulative. For example, each cable type requires unique testing equipment, which adds extra cost to the capital budget. UTP networks require unique cable testers and a time-domain reflectometer (TDR). Some coaxial installations require the use of an oscilloscope for troubleshooting. Fiber requires, at a minimum, a light source and one power meter, and for some larger networks, an optical TDR (OTDR). Each of these pieces of equipment carries a capital equipment cost as well as a training and maintenance cost.

When separate networks are added piecemeal, cost sharing is practically nonexistent. Parallel networks probably do not even share the same closet space, which leads to operation efficiencies and the related costs.

Instead of replacing all of the disparate media simultaneously, conversion technology allows the migration to fiber while protecting the investment already made in the network's infrastructure. Rather than face the expense of a forklift upgrade, the upgrade can be made in stages as your budget allows. You can keep up with technology for mission-sensitive areas and stay on budget for less-critical segments of the network. But the sooner you move to an all-fiber network, the better your return on investment; migrating to an optical-fiber-based network helps you get off the costly and time-consuming cabling treadmill perpetuated by copper. While UTP cables typically are "upgraded" every few years to support increased data rates, the optical fiber you install today has the bandwidth to support your future needs as well.

The data network is probably the easiest to interconnect with fiber. Many local area network (LAN) equipment manufacturers provide solutions with fiber interfacing. For those cases when a fiber interface is not available, media conversion can be deployed to convert the media interface to fiber. Media-conversion technology can also be used to connect fiber-optic cabling to UTP ports and is especially useful in migrating an existing or installed base of equipment to fiber. The biggest advantage of these fiber interconnects is that they operate at the same speed (or even greater speed) as the rest of the network.

The solution for voice service will most likely involve converting T1/E1 to fiber. Some systems have a proprietary fiber interface that can be used to interconnect PBXs, but most do not. When interconnecting several discrete lines between buildings, it may be necessary to first aggregate the channels into a T1/E1 using a channel bank. Once this aggregation has been done, a T1/E1 converter can be used to connect to the fiber.

Building automation systems that have adopted Ethernet for connectivity can be interconnected using standard LAN Ethernet media converters. Other systems use RS-422/RS-485, which need serial-data media converters (often referred to as fiber modems). When converting to fiber, it's important to note whether the data is synchronous or asynchronous in nature to determine the type of conversion technology needed.

When converting T1/E1 and serial data to fiber, there is often a concern that the fiber bandwidth is being "under-used." This situation is compared to using a sledgehammer to kill a fly. While it's true that fiber can carry much more data than a single T1/E1 circuit, the efficiency of having only one media type makes the deployment cost-effective.

Security systems often use the same type of data interfaces as building automation systems. Also, these systems often include surveillance video circuits, which connect cameras from several locations back to a central location in a star configuration. The signal is a composite video signal, typically National Television Standards Committee (NTSC) format and carried on a coaxial cable. By using conversion technology, these systems can use fiber to carry the signal from the video source, typically a camera, to the monitor. Most systems will need only a single strand of fiber. However, some systems require two fibers. In these instances, one fiber is used to carry the video signal from the camera to the monitor. The second fiber is used to carry pan, tilt, and zoom (often listed as PTZ) information back to the camera to control it.

By using the available media-interface and media-conversion technology, backbone cabling can converge to a single media type through fiber. Thus, deploying fiber in a unified cabling plant provides economies of scale. This convergence to a single media type will not only yield cost savings today, but will also establish the infrastructure needed to support the convergence of service offerings that is certain to happen in the future.

Steve Stange is chair of the Fiber Optics LAN Section (FOLS) of the Telecommunications Industry Association (TIA) and senior product manager for Transition Networks (Minneapolis, MN). He can be reached via e-mail at [email protected].

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