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When planning a new or upgraded cabling infrastructure, you have two basic choices: fiber or copper. Both offer superior data transmission. The decision on which one to use may be difficult. It will often depend on your current network, your future networking needs, and your particular application, including bandwidth, distances, environment, cost, and more. In some cases, copper may be a better choice; in other situations, fiber offers advantages.
Although copper cable is currently more popular and much more predominant in structured cabling systems and networks, fiber is quickly gaining fans.
Fiber optic cable is becoming one of the fastest-growing transmission mediums for both new cabling installations and upgrades, including backbone, horizontal, and even desktop applications. Fiber optic cable is favored for applications that need high bandwidth, long distances, and complete immunity to electrical interference. It’s ideal for high data-rate systems such as Gigabit Ethernet, FDDI, multimedia, ATM, SONET, Fibre Channel, or any other network that requires the transfer of large, bandwidth-consuming data files, particularly over long distances. A common application for fiber optic cable is as a network backbone, where huge amounts of data are transmitted. To help you decide if fiber is right for your new network or if you want to migrate to fiber, take a look at the following:
Greater bandwidth-Because fiber provides far greater bandwidth than copper and has proven performance at rates up to 10 Gbps, it gives network designers future-proofing capabilities as network speeds and requirements increase. Also, fiber optic cable can carry more information with greater fidelity than copper wire. That’s why the telephone networks use fiber, and many CATV companies are converting to fiber.
Low attenuation and greater distance-Because the fiber optic signal is made of light, very little signal loss occurs during transmission so data can move at higher speeds and greater distances. Fiber does not have the 100-meter (304.8-ft.) distance limitation of unshielded twisted-pair copper (without a booster). Fiber distances can range from 300 meters to 40 kilometers, depending on the style of cable, wavelength, and network. (Fiber distances are typically measured in metric units.) Because fiber signals need less boosting than copper ones do, the cable performs better.
Fiber networks also enable you to put all your electronics and hardware in one central location, instead of having wiring closets with equipment throughout the building.
Security-Your data is safe with fiber cable. It does not radiate signals and is extremely difficult to tap. If the cable is tapped, it’s very easy to monitor because the cable leaks light, causing the entire system to fail. If an attempt is made to break the security of your fiber system, you’ll know it.
Immunity and reliability-Fiber provides extremely reliable data transmission. It’s completely immune to many environmental factors that affect copper cable. The fiber is made of glass, which is an insulator, so no electric current can flow through. It is immune to electromagnetic interference and radio-frequency interference (EMI/RFI), crosstalk, impedance problems, and more. You can run fiber cable next to industrial equipment without worry. Fiber is also less susceptible to temperature fluctuations than copper is and can be submerged in water.
Design-Fiber is lightweight, thin, and more durable than copper cable. And, contrary to what you might think, fiber optic cable has pulling specifications that are up to ten times greater than copper cable’s. Its small size makes it easier to handle, and it takes up much less space in cabling ducts. Although fiber is still more difficult to terminate than copper is, advancements in connectors are making temination easier. In addition, fiber is actually easier to test than copper cable.
Migration-The proliferation and lower costs of media converters are making copper to fiber migration much easier. The converters provide seamless links and enable the use of existing hardware. Fiber can be incorporated into networks in planned upgrades.
Standards-New TIA/EIA standards are bringing fiber closer to the desktop. TIA/EIA-785, ratified in 2001, provides a cost-effective migration path from 10-Mbps Ethernet to 100-Mbps Fast Ethernet over fiber (100BASE-SX). A recent addendum to the standard eliminates limitations in transceiver designs. In addition, in June 2002, the IEEE approved a 10-Gigabit Ethernet standard.
Costs-The cost for fiber cable, components, and hardware is steadily decreasing. Installation costs for fiber are higher than copper because of the skill needed for terminations. Overall, fiber is more expensive than copper in the short run, but it may actually be less expensive in the long run. Fiber typically costs less to maintain, has much less downtime, and requires less networking hardware. And fiber eliminates the need to recable for higher network performance.
Multimode-Multimode fiber optic cable can be used for most general fiber applications. Use multimode fiber for bringing fiber to the desktop, for adding segments to your existing network, or in smaller applications such as alarm systems. Multimode cable comes with two different core sizes: 50 micron or 62.5 micron.
Single-mode-Single-mode is used over distances longer than a few miles. Telcos use it for connections between switching offices. Single-mode cable features an 8.5-micron glass core.
Duplex-Use duplex multimode or single-mode fiber optic cable for applications that require simultaneous, bidirectional data transfer. Workstations, fiber switches and servers, fiber modems, and similar hardware require duplex cable. Duplex is available in single- and multimode.
Simplex-Because simplex fiber optic cable consists of only one fiber link, you should use it for applications that only require one-way data transfer. For instance, an interstate trucking scale that sends the weight of the truck to a monitoring station or an oil line monitor that sends data about oil flow to a central location. Simplex fiber comes in single- and multimode types.
Although 50-micron fiber cable features a smaller core, which is the light-carrying portion of the fiber, both 62.5- and 50-micron cable feature the same glass cladding diameter of 125 microns. You can use both in the same types of networks, although 50-micron cable is recommended for premise applications: backbone, horizontal, and intrabuilding connections, and should be considered especially for any new construction and installations. And both can use either LED or laser light sources.
The big difference between 50-micron and 62.5-micron cable is in bandwidth-50-micron cable features three times the bandwidth of standard 62.5-micron cable, particularly at 850 nm. The 850-nm wavelength is becoming more important as lasers are being used more frequently as a light source.
Other differences are distance and speed. 50-micron cable provides longer link lengths and/or higher speeds in the 850-nm wavelength. See the table below.
As a general rule, use ceramic ferrules for critical network connections such as backbone cables or for connections that will be changed frequently, like those in wiring closets. Ceramic ferrules are more precisely molded and fit closer to the fiber, which gives the fiber optic cables a lower optical loss.
Use composite ferrules for connections that are less critical to the network’s overall operation and less frequently changed. Like their ceramic counterparts, composite ferrules are characterized by low loss, good quality, and a long life. However, they are not as precisely molded and slightly easier to damage, so they aren’t as well-suited for critical connections.
If you’re accustomed to certifying copper cable, you’ll be pleasantly surprised at how easy it is to certify fiber optic cable because it’s immune to electrical interference. You only need to check a few measurements.
Attenuation (or decibel loss)-Measured in decibels/kilometer (dB/km), this is the decrease of signal strength as it travels through the fiber cable. Generally, attenuation problems are more common on multimode fiber optic cables.
Return loss-This is the amount of light reflected from the far end of the cable back to the source. The lower the number, the better. For example, a reading of -60 decibels is better than -20 decibels. Like attenuation, return loss is usually greater with multimode cable.
Graded refractive index-This measures how the light is sent down the fiber. This is commonly measured at wavelengths of 850 and 1300 nanometers. Compared to other operating frequencies, these two ranges yield the lowest intrinsic power loss. (NOTE: This is valid for multimode fiber only.)
Propagation delay-This is the time it takes a signal to travel from one point to another over a transmission channel.
Optical time-domain reflectometry (OTDR)-This enables you to isolate cable faults by transmitting high-frequency pulses onto a cable and examining their reflections along the cable. With OTDR, you can also determine the length of a fiber optic cable because the OTDR value includes the distance the optic signal travels.
There are many fiber optic testers on the market today. Basic fiber optic testers function by shining a light down one end of the cable. At the other end, there’s a receiver calibrated to the strength of the light source. With this test, you can measure how much light is going to the other end of the cable. Generally, these testers give you the results in dB lost, which you then compare to the loss budget. If the measured loss is less than the number calculated by your loss budget, your installation is good.
Newer fiber optic testers have a broad range of capabilities. They can test both 850- and 1300-nanometer signals at the same time and can even check your cable for compliance with specific standards.
A few properties particular to fiber optic cable can cause problems if you aren’t careful during installation.
Intrinsic power loss-As the optic signal travels through the fiber core, the signal inevitably loses some speed through absorption, reflection, and scattering. This problem is easy to manage by making sure your splices are good and your connections are clean.
Microbending-Microbends are minute deviations in fiber caused by excessive bends, pinches, and kinks. Using cable with reinforcing fibers and other special manufacturing techniques minimizes this problem.
Connector loss-Connector loss occurs when two fiber segments are misaligned. This problem is commonly caused by poor splicing. Scratches and dirt introduced during the splicing process can also cause connector loss.
Coupling loss-Similar to connector loss, coupling loss results in reduced signal power and is from poorly terminated connector couplings.
Remember to be careful and use common sense when installing fiber cable. Use clean components. Keep dirt and dust to a minimum. Don’t pull the cable excessively or bend it too sharply around any corners. That way, your fiber optic installation can serve you well for many years.
If you have an existing network, there’s a 90% chance it’s Ethernet. If you’re installing a new network, there’s a 98% chance it’s Ethernet—the Ethernet standard is the overwhelming favorite network standard today.
Ethernet was developed by Xerox®, DEC®, and Intel® in the mid-1970s as a 10-Mbps (Megabits per second) networking protocol—very fast for its day—operating over a heavy coax cable (Standard Ethernet).
Today, although many networks have migrated to Fast Ethernet (100 Mbps) or even Gigabit Ethernet (1000 Mbps), 10-Mbps Ethernet is still in widespread use and forms the basis of most networks.
Ethernet is defined by international standards, specifically IEEE 802.3. It enables the connection of up to 1024 nodes over coax, twisted-pair, or fiber optic cable. Most new installations today use economical, lightweight cables such as Category 5 unshielded twisted-pair cable and fiber optic cable.
Ethernet signals are transmitted from a station serially, one bit at a time, to every other station on the network.
Ethernet uses a broadcast access method called Carrier Sense Multiple Access/Collision Detection (CSMA/CD) in which every computer on the network hears every transmission, but each computer listens only to transmissions intended for it.
Each computer can send a message anytime it likes without having to wait for network permission. The signal it sends travels to every computer on the network. Every computer hears the message, but only the computer for which the message is intended recognizes it. This computer recognizes the message because the message contains its address. The message also contains the address of the sending computer so the message can be acknowledged.
If two computers send messages at the same moment, a collision occurs, interfering with the signals. A computer can tell if a collision has occurred when it doesn’t hear its own message within a given amount of time. When a collision occurs, each of the colliding computers waits a random amount of time before resending the message.
The process of collision detection and retransmission is handled by the Ethernet adapter itself and doesn’t involve the computer. The process of collision resolution takes only a fraction of a second under most circumstances. Collisions are normal and expected events on an Ethernet network. As more computers are added to the network and the traffic level increases, more collisions occur as part of normal operation. However, if the network gets too crowded, collisions increase to the point where they slow down the network considerably.
Setting up wireless devices that belong to the 802.11 family is relatively simple, but you do have to pay attention to a few simple factors.
The 802.11 wireless standards support two basic configurations: ad-hoc mode and infrastructure mode.
In ad-hoc mode, wireless user devices such as laptop computers and PDAs communicate directly with each other in a peer-to-peer manner without the benefit of access points.
Ad-hoc mode is generally used to form very small spontaneous networks. For instance, with ad-hoc mode, laptop users in a meeting can quickly establish a small network to share files.
Infrastructure mode uses wireless access points to enable wireless devices to communicate with each other and with your wired network. Most networks use infrastructure mode.
The basic components of infrastructure mode networks include:
Access points are standalone hardware devices that provide a central point of communication for your wireless users. How many you need in your application depends on the number of users and the amount of bandwidth required by each user. Bandwidth is shared, so if your network has many users who routinely send data-heavy multimedia files, additional access points may be required to accommodate the demand.
A small-office network with fewer than 15 users may need just 1 access point. Larger networks require multiple points. If the hardware supports it, you can overlap coverage areas to allow users to roam between cells without any break in network coverage. A user’s wireless device picks up a signal beacon from the strongest access point to maintain seamless coverage.
How many access points to use also depends on your operating environment and the required range. Radio propagation can be affected by walls and electrical interference that can cause signal reflection and fading. If you’re linking mobile users indoors-where walls and other obstructions impede the radiated signal-the typical maximum range is 150 feet. Outdoors, you can get greater WLAN range-up to 2000 feet (depending on your antenna type) where there’s a clear line of sight!
For optimal speed and range, install your wireless access point several feet above the floor or ground and away from metal equipment or large appliances that may emit interference.
In addition to sharing bandwidth, users also share a band. Most IEEE 802.11 or 802.11b devices function in the 2.4-2.4835-GHz band. But these frequencies are often congested, so you may want to use devices that take advantage of the IEEE 802.11a 5.725-5.825-GHz band.
No matter what frequency you use, you’ll want to isolate your users from outsiders using the same frequency. To do this, assign your users a network identifier, such as an Extended Service Set Identifier (ESSID), as well as distinct channels.
The access point links your wireless network to your wired network, enabling your wireless users to access shared data resources and devices across your LAN enterprise. Some access points even feature capabilities for routing traffic in one or both directions between a wired and wireless network.
For Internet access, connect a broadband router with an access point to an Internet connection over a broadband service such as DSL, cable modem, or satellite.
For connecting network printers, you can dedicate a computer to act as a print server or add a wireless print server device; this enables those on your wireless network to share printers.
If you plan to install access points, you can boost your signal considerably by adding external antennas. Various mounting configurations and high- and low-gain options are available.
You can also use add-on antennas to connect nodes where the topology doesn’t allow for a clear signal between access points. Or use them to link multiple LANs located far apart.
Additional external antennas are also useful to help overcome the effects of multipath propagation in which a signal takes different paths and confuses the receiver. It’s also helpful to deploy antennas that propagate the signal in a way that fits the environment. For instance, for a long, narrow corridor, use an antenna that focuses the RF pattern in one direction instead of one that radiates the signal in all directions.
A site survey done ahead of time to plot where the signal is the strongest can help you identify problem areas and avoid dead spots where coverage isn’t up to par or is unreliable. For this, building blueprints are helpful in revealing potential obstructions that you might not see in your physical site walkthrough.
To field test for a clear signal path, attach an antenna to an access point or laptop acting as the transmitter at one end. Attach another antenna to a wireless device acting as a receiver at the other end. Then check for interference using RF test equipment (such as a wireless spectrum analyzer) and determine whether vertical or horizontal polarization will work best.
Need help doing this? Call us. We even offer a Site Survey Kit that has a variety of antennas included. Great for installers, the kit enables you to test a variety of antennas in the field before placing a larger antenna order.
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