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Black Box Explains...What to consider when choosing a rack.

Why racks?
There are several things you should consider when choosing a rack.

What kind of equipment will you be putting in it? If you need frequent access to all sides of... more/see it nowthe equipment, an open rack is more convenient than a cabinet. If your equipment needs ventilation, a rack poses no air circulation limitations. And don’t neglect aesthetics. Will customers or clients see your installation? A rack with cable management looks much neater.

Finally, consider security. Because a rack is open, you need to take steps to secure your equipment. Set up your rack in a locked room so prying fingers can’t access your network equipment.

Racks come in various sizes and installation styles. Some are freestanding; some are designed to be wallmounted. Some can be a combination of both styles, sitting on the floor but attaching to the wall for more stability.

Understanding rack measurements.
The main component of a rack is a set of vertical rails with mounting holes to which you attach your equipment or shelves.

The first measurement you need to know is the width between the two rails. It’s commonly given in inches, measured from one mounting hole to the corresponding hole on the opposing rail. The most common rail width is 19"; 23" rails and racks are also available. Most rackmount equipment is designed to fit 19" rails but can be adapted for wider racks.

The next important specification is the number of rack units, which is abbreviated as “U.” This is a measurement of the vertical space available on the rails. Cabinets and racks and rackmount equipment are all measured in rack units. One rack unit (1U) is equal to 1.75" of usable vertical space. So, for example, a device that’s 2U high takes up 3.5" of rack space. A rack that’s 20U high has 35" of usable space.

Because the widths are standard, the amount of vertical space is what determines how much equipment you can actually install. Remember this measurement of usable vertical space is smaller than the external height of the rack.

Getting power to your equipment.
Unless you want to have a tangle of extension cords, you’ll need to get one or more power strips for your rack. Consider which kind would be best for your installation. Rackmount power strips come in versions that mount either vertically or horizontally. Some have outlets that are spaced widely to accommodate transformer blocks—a useful feature if most of your equipment uses bulky power transformers.

Surge protection is another important issue. Some power strips have built-in surge protection; some don’t. With the money you have invested in rackmount equipment, you’ll certainly want to make sure it’s protected.

Any mission-critical equipment should also be connected to an uninterruptible power supply (UPS). A UPS prevents your equipment from crashing during a brief blackout or brownout and allows enough time to shut everything down properly in the event of an extended power outage. Choose a rackmount UPS for the most critical equipment or plug the whole rack into a standalone UPS.

Managing cables.
Your equipment may look very tidy when it’s all mounted. But unless you’re very careful with your cables, you can create a tangle you’ll never be able to unravel.

Plotting your connections in advance helps you to decide the most efficient way to organize the cables. Knowing where the connections are tells you whether it’s better to run cables horizontally or vertically. Most network problems are in the cabling, so if you let your cables get away from you now, you’re sure to pay for it down the road.

There are many cable management accessories that can simplify your racks. collapse


Cold aisle containment.

Cold aisle containment (CAC) is a cooling method that increases cooling efficiency and reduces energy costs in data centers.

This cooling method relies on the fact that most network equipment... more/see it nowand servers are designed to cool themselves by drawing air in through the front and exhausting it out the rear. To implement cold aisle containment, rows of cabinets or racks are arranged facing each other to form aisles, and cool air is routed between the rows. Equipment takes the cool air in at the front of the cabinet and exhausts it out the back into the room.

To keep cool air from mixing with warm air, row ends are closed off with an air-flow barrier. This barrier can range from makeshift arrangements of plastic strips to doors made expressly for this purpose.

Because cold aisle containment concentrates cool air at the front of equipment where it’s most needed, it’s an exceptionally effective cooling method. Cold aisle containment significantly reduces energy costs, lowering power bills as well as reducing data centers’ carbon footprints. collapse


Black Box Explains... Crosstalk.

One of the most important cable measurements is Near-End Crosstalk (NEXT). It’s signal interference from one pair that adversely affects another pair on the same end.

Not only can crosstalk... more/see it nowoccur between adjacent wire pairs (“pair-to-pair NEXT“), but all other pairs in a UTP cable can also contribute their own levels of both near-end and far-end crosstalk, multiplying the adverse effects of this interference onto a transmitting or receiving wire pair.

Because such compounded levels of interference can prove crippling in high-speed networks, some cable manufacturers have begun listing Power Sum NEXT (PS-NEXT), FEXT, ELFEXT, and PS-ELFEXT ratings for their CAT5e and CAT6 cables. Here are explanations of the different types of measurements:

NEXT measures an unwanted signal transmitted from one pair to another on the near end.

PS-NEXT (Power Sum crosstalk) is a more rigorous crosstalk measurement that includes the total sum of all interference that can possibly occur between one pair and all the adjacent pairs in the same cable sheath. It measures the unwanted signals from multiple pairs at the near end onto another pair at the near end.

FEXT (Far-End crosstalk) measures an unwanted signal from a pair transmitting on the near end onto a pair at the far end. This measurement takes full-duplex operation into account where signals are generated simultaneously on both ends.

ELFEXT (Equal-Level Far-End Crosstalk) measures the FEXT in relation to the received signal level measured on that same pair. It basically measures interference without the effects of attenuation—the equal level.

PS-ELFEXT (Power Sum Equal-Level Far-End Crosstalk), an increasingly common measurement, measures the total sum of all intereference from pairs on the far end to a pair on the near end without the effects of attenuation. collapse


Black Box Explains...How to maximize your wireless range.

There are four simple rules that enable you to transmit wireless communications up to their maximum range:
• Try to keep a direct line between the transmitter and receiver.
• Minimize... more/see it nowthe number of walls and ceilings between the transmitter and receiver. Such obstructions reduce the range.
• If there are obstructions, be sure the wireless signal passes through drywall or open doorways and not other materials.
• Keep the transmitter and receiver at least 3 to 6 feet (0.9 to 1.8 m) away from electrical devices or appliances, especially those that generate extreme RF noise. collapse


Black Box Explains…Cooling blade servers.

Blade servers are hot. Really hot. These slim, high-powered CPUs generate heat like nothing you’ve ever installed in your data center before—a rack of blade servers can generate more heat... more/see it nowthan an electric oven! And as temperatures rise, servers may fail, leading to downtime and even data loss.

Needless to say, blade servers present a cooling challenge. If you plan to install them, you need to make sure you can accommodate their cooling needs.

Computer rooms have special equipment such as raised-floor cooling systems to meet their high cooling requirements, but it’s also important to ensure that cabinets used to house blade servers provide adequate ventilation—even in a cool room, hot spots can develop inside cabinets if air distribution is inadequate.

If you’re planning to install blade servers or other high-density components in cabinets, look for a cabinet with fully perforated doors in the front and rear— the greater the amount of perforation, the more cool air can be delivered to the components.

Don’t overload the cabinet by trying to fit in too many servers—75% to 80% of capacity is about right. Leave at least 1U of space between rows of servers for front-to-back ventilation. And finally, ensure all unused rack space is closed off with blank panels to prevent recirculation of warm air back to the front of the cabinet.

If you need help calculating your system’s cooling needs, contact our FREE Tech Support.
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Black Box Explains...Fiber.


Fiber versus copper.

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... more/see it nowto 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:



The advantages of fiber.

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 or single-mode, duplex or simplex?

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.


50- vs. 62.5-micron cable.

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.




The ferrules: ceramic or composite?

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.


Testing and certifying fiber optic cable.

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.


Fiber precautions.

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.

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Black Box Explains...IRQs, COM Ports, and Windows

Windows® 95 normally requires each serial port to have its own unique Interrupt Request Line (IRQ). However, if you use a third-party communications driver that supports IRQ sharing, you can... more/see it nowshare interrupts. Unfortunately, data throughput will not be as high as with single interrupt port configurations.

With Windows NT®, you can share interrupts across multiple ports as long as the serial ports have an Interrupt Status Port (ISP) built into the card.

The Interrupt Service Routine, a software routine that services interrupts and requests processor time, reads the ISP and is immmediately directed to the port that has an interrupt pending. Compared to the polling method used if the serial ports don’t have an ISP, this feature can determine which port generated the interrupt up to four times more efficiently—and it almost eliminates the risk of lost data. Windows NT supports the ISP by enabling the user to configure the registry to match the card’s settings. Black Box models IC102C-R3, IC058C, and IC112C-R3 all have ISPs and come with a Windows NT setup utility to simplify installation and configuration.

If your serial port doesn’t have an ISP, the Interrupt Service Routine has to poll each port separately to determine which port generated the interrupt. collapse


Black Box Explains...Virtual LANs (VLANs).

True to their name, VLANs are literally “virtual“ LANs—mini subLANs that, once configured, can exist and function logically as single, secure network segments, even though they may be part of... more/see it nowa much larger physical LAN.

VLAN technology is ideal for enterprises with far-reaching networks. Instead of having to make expensive, time-consuming service calls, system administrators can configure or reconfigure workstations easily or set up secure network segments using simple point-and-click, drag-and-drop management utilities. VLANs provide a way to define dynamic new LAN pathways and create innovative virtual network segments that can range far beyond the traditional limits of geographically isolated workstation groups radiating from centralized hubs.

For instance, using VLAN switches, you can establish a secure VLAN made up of select devices located throughout your enterprise (managers’ workstations, for example) or any other device that you decide requires full access to the VLAN you’ve created.

According to Cisco, a VLAN is a switched network logically segmented by functions, project teams, or applications regardless of the physical location of users. You can assign each switch port to a different VLAN. Ports configured in the same VLAN share broadcasts; ports that don’t belong to the VLAN don’t share the data.

VLAN switches group users and ports logically across the enterprise—they don’t impose physical constraints like in a shared-hub architecture. In replacing shared hubs, VLAN switches remove the physical barriers imposed by each wiring closet.

To learn more about smart networking with VLANs, call the experts in our Local Area Network Support group at 724-746-5500, press 1, 2, 4. collapse


Black Box Explains... KVM IP gateways

Just as a gate serves as an entry or exit point to a property, a gateway serves the same purpose in the networking world. It’s the device that acts as... more/see it nowa network entrance or go-between for two or more networks.

There are different types of gateways, depending on the network.

An application gateway converts data or commands from one format to another. A VoIP gateway converts analog voice calls into VoIP packets. An IP gateway is like a media gateway, translating data from one telecommunications device to another.

Gateways often include other features and devices, such as protocol converters, routers, firewalls, encryption, voice compression, etc. Although a gateway is an essential feature of most routers, other devices, such as a PC or server, can also function as a gateway.

A KVMoIP switch contains an IP gateway, which is the pathway the KVM signals use to travel from the IP network to an existing non-IP KVM switch. It converts and directs the KVM signals, giving a user access to and control of an existing non-IP KVM switch over the Internet. collapse


Black Box Explains...Low-profile PCI serial adapters.

Ever notice that newer computers are getting smaller and slimmer? That means regular PCI boards won’t fit into these computers’ low-profile PCI slots. But because miniaturization is the rage in... more/see it nowall matters of technology, it was only a short matter of time before low-profile PCI serial adapters became available—and Black Box has them.

Low-profile cards meet the PCI Special Interest Group (PCI-SIG) Low-Profile PCI specifications, the form-factor definitions for input/output expansion. Low-Profile PCI has two card lengths defined for 32-bit bus cards: MD1 and MD2. MD1 is the smaller of the two, with cards no larger than 4.721 inches long and 2.536 inches high. MD2 cards are a maximum of 6.6 inches long and 2.536 inches high.

BLACK BOX® Low-Profile Serial PCI cards comply with the MD1 low-profile specification and are compatible with the universal bus. Universal bus is a PCI card that can operate in either a 5-V or 3.3-V signaling level system. collapse

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