Advantages of Biscuit Jacks

Biscuit jacks offer a few advantages in your structured-cabling design. First of all, they are very inexpensive compared to other types of surface-mount wiring systems, which is why many houses that had the old four-pin telephone systems now have biscuit jacks—you could buy 20 of them for around $25. Even the biscuits that support multiple jacks are still fairly inexpensive.

Another advantage of biscuit jacks is their ability to work in situations where standard modular or fixed-design wall plates won't work and other types of surface-mount wiring are too bulky. The best example of this is office cubicles (i.e., modular furniture). A biscuit jack has an adhesive tab on the back that allows it to be mounted anywhere, so you can run a telephone or data cable to a biscuit jack and mount it under the desk where it will be out of the way.

Finally, biscuit jacks are easy to install. The cover is removed with one screw. Inside many of the biscuit jacks are screw terminals (one per pin in each jack), as shown in Figure 1. To install the jack, you just strip the insulation from each conductor and wrap it clockwise around the terminal and between the washers and tighten the screw. Repeat this process for each conductor in the cable. These jacks are not high-speed data compatible and are capable of Category 3 performance at best.

 
Figure 1: Screw terminals inside a biscuit jack

Note

Not all biscuit jacks use screw terminals. The more modern data communications jacks use IDC connectors to attach the wire to the jack.

Disadvantages of Biscuit Jacks

The main disadvantage to biscuit jacks is that the older biscuit jacks are not rated for high-speed data communications. Notice the bunch of screw terminals in the biscuit jack shown in Figure 1. When a conductor is wrapped around these terminals, it is exposed to stray electromagnetic interference (EMI) and other interference, which reduces the effective ability of this type of jack to carry data. At most, the older biscuit jacks with the screw terminals can be rated as Category 3 and are not suitable for the 100Mbps and faster communications today's wiring systems must be able to carry.

Advantages of Fiber-Optic Cabling

The following advantages of fiber over other cabling systems explain why fiber is becoming the preferred network cabling medium for high-bandwidth, long-distance applications:

• Immunity to electromagnetic interference (EMI)
• Higher data rates
• Longer maximum distances
• Better security

Immunity to Electromagnetic Interference (EMI)

All copper-cable network media share one common problem: they are susceptible to EMI. EMI is stray electromagnetism that interferes with electrical data transmission. All electrical cables generate a magnetic field around their central axis. If you pass a metal conductor through a magnetic field, an electrical current is generated in that conductor.

When you place two copper communication cables next to each other, EMI will cause crosstalk; signals from one cable will be picked up on the other. The longer a particular copper cable is, the more chance for crosstalk.

Fiber-optic cabling is immune to crosstalk because optical fiber does not conduct electricity and uses light signals in a glass fiber, rather than electrical signals along a metallic conductor, to transmit data. So it cannot produce a magnetic field and thus is immune to EMI. Fiber-optic cables can therefore be run in areas considered to be "hostile" to regular copper cabling (such as elevator shafts, electrical transformers, in tight bundles with other electrical cables, and industrial machinery).

Higher Possible Data Rates

Because light is immune to interference, can be modulated at very high frequencies, and travels almost instantaneously to its destination, much higher data rates are possible with fiber-optic cabling technologies than with traditional copper systems. Data rates far exceeding the gigabit per second (Gbps) range and higher are possible, and the latest IEEE standards body is working on 100Gbps fiber-based applications over much longer distances than copper cabling. Multimode is the preferred fiber-optic type for 100–550 meters seen in LAN networks, and since single-mode fiber-optic cables are capable of transmitting at these multi-gigabit data rates over very long distances, they are the preferred media for transcontinental and oceanic applications.

You will often encounter the word "bandwidth" when describing fiber-optic data rates. With optical fiber, bandwidth does not refer to channels or frequency, but rather just the bit-throughput rate.

Longer Maximum Distances

Typical copper data-transmission media are subject to distance limitations of maximum segment lengths no longer than 100 meters. Because they don't suffer from the EMI problems of traditional copper cabling and because they don't use electrical signals that can degrade substantially over long distances, single-mode fiber-optic cables can span distances up to 75 kilometers (about 46.6 miles) without using signal-boosting repeaters.

Better Security

Copper-cable transmission media are susceptible to eavesdropping through taps. A tap (short for wiretap) is a device that punctures through the outer jacket of a copper cable and touches the inner conductor. The tap intercepts signals sent on a LAN and sends them to another (unwanted) location. Electromagnetic (EM) taps are similar devices, but rather than puncturing the cable, they use the cable's magnetic fields, which are similar to the pattern of electrical signals. If you'll remember, simply placing a conductor next to a copper conductor with an electrical signal in it will produce a duplicate (albeit lower-power) version of the same signal. The EM tap then simply amplifies that signal and sends it on to the person who initiated the tap.

Because fiber-optic cabling uses light instead of electrical signals, it is immune to most types of eavesdropping. Traditional taps won't work because any intrusion on the cable will cause the light to be blocked and the connection simply won't function. EM taps won't work because no magnetic field is generated. Because of its immunity to traditional eavesdropping tactics, fiber-optic cabling is used in networks that must remain secure, such as government and research networks.