A Weak Cable Backbone Can Paralyze a Project

Bandwidth, Distance Make Fiber Popular for Security and IT Use

One cabling technology that will cross over to both sides of the converging market is fiber. On the security side, fiber has been used for years when video and data need to be sent over the long haul on large applications. Current fiber technology generally allows up to 32 cameras on a single strand point-to-point link, and hundreds on a drop-and-insert system.

For the network folks, fiber has traditionally been utilized for backbone and major trunk links. Usually found between buildings and campuses, fiber is increasingly finding its role as a “last mile” technology, whether to the home or the desktop.

Fiber is prevalent in both the security and data/communications industries for two basic reasons: the large amount of bandwidth it provides and the long distances it can send data. It is important, however, to take the time to design fiber installations properly. Because all sides of the converged market can take advantage of fiber, this extra care will ensure its viability for some time to come.  When considering fiber optics for your infrastructure, one thing frequently overlooked is optical budget. This is a very important calculation that can mean the difference between a successful, functioning installation and several money-losing return trips.

Put simply, the optical budget is the amount of light, or optical power, that is present at the receiver after passing through several conditions that induce loss. These loss-makers can be any number of things. The most obvious are splices and connections. Each one allows some amount of light to be lost into the space around it. Even a properly applied connector introduces some measure of loss, as there are always small gaps between the two ends of the fiber strand. Splicing can be very problematic because the alignment of the two spliced ends must be extremely precise. There are several types of splices for optical cable. Fusion splicing, where the two ends of the strand are heated and melded together, is the most effective and least lossy splice, but it requires a degree of skill and training not everyone possesses.

There are also mechanical splice kits available that make it possible for almost anyone who can install a BNC connector to also install a fiber connector. While these kinds of splices are far less expensive and easier to perform than fusion splicing, they also generally allow more light to escape than fusion splices. Another big way for light to escape is a faulty installation of the cable. Exceeding pull strengths and bend radiuses can cause cracks and breaks in the glass, allowing more light to be lost. Optical time domain reflectometers (OTDRs) and visual fault finders can show where and sometimes how much light is being lost. This is all part of the cable certification process we will discuss shortly.

All of these loss points may not be a big issue, however, if the optical budget is calculated properly. Each manufacturer of optical splices, connectors and cable rates their devices for optical loss. This rating is expressed in decibels (dB).  While there are a lot of factors, the basic formula is fairly simple. When you subtract the output power at the transmitter from the in
put sensitivity at the receiver, you get the power budget.

You then subtract the loss for each connection or splice, along with any measured loss indicated in test equipment from that budget. The budget number will usually be indicated in the spec sheets of the fiber transmitter and receiver products.

Also remember, you need a margin for unforeseen fluctuations. Make sure you add headroom into your calculations. Factors such as cost and performance requirements will affect this margin number, but it should usually be between 3dB and 10dB.

Another simple thing you can do to provide an infrastructure that will last into the future is provide room to expand. The majority of the cost of a fiber installation is in the labor, so why not leverage that labor cost to have more fiber available if needed?

Fiber-optic cables come in several configurations and fiber counts. It would not be a huge increase of cost to purchase a cable with a few more strands than you need in the beginning. Imagine the cost of having to pull a whole new cable after construction is finished if the customer wants to add devices or systems. Upgrading from six to 10 strands will seem like a drop in the bucket.

As mentioned above, unlike coax, fiber will have a strong presence in a converged market for a long time. It is very important you implement your fiber installations with that in mind.

Most UTP Works Fine for CCTV; Networking Can Be Another Story

UTP is another technology that serves us well today and will carry us into a converged world. It has become the force to be reckoned with in the infrastructure market. It seems to be a good fit for almost every application we run into.

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