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Black Box Explains... Spread Spectrum wireless technology.

Frequency-Hopping Spread Spectrum wireless communication provides error-free transmission, top security, and high levels of throughput without the need for an FCC site license. The key to Spread Spectrum is a... more/see it nowfrequency-hopping transceiver.

Narrow-band frequency hoppers use a predefined algorithm to maintain synchronization and high throughput between master and remote modems. They achieve this by continually switching or “hopping” from one transmission frequency to another throughout the Spread Spectrum band. The sequence of frequencies is very difficult to predict and thus nearly impossible to eavesdrop on or jam. If interference is encountered at any particular frequency, the built-in error correction detects it and resends the data packet at the next frequency hop. Because EMI/RFI interference rarely affects the entire available bandwidth, and each frequency hop is at least 6 MHz, the radio transmitter has access to as many as 100 frequencies within the spectrum to avoid interference and ensure that data gets through. 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...Dry Contacts

A dry contact, also called a volt-free contact, is a relay contact that does not supply voltage. The relay energizes or de-energizes when a change to its input has occurred.... more/see it nowIn other words, a dry contact simply detects whether or not an input switch is open or closed.

The dry contacts in the ServSensor Contact provide a simple two-wire interface that can be easily adapted to third-party sensors and devices. Because you define what the open or closed condition means, dry contacts are infinitely adaptable.

Use dry contacts to monitor alarms such as fire alarms, burglar alarms, and alarms on power systems such as UPSs. A very common use for dry contacts is to detect whether a cabinet door is open or closed. collapse


Black Box Explains...Solid vs. stranded cable.

Solid-conductor cable is designed for backbone and horizontal cable runs. Use it for runs between two wiring closets or from the wiring closet to a wallplate. Solid cable shouldn’t be... more/see it nowbent, flexed, or twisted repeatedly. Its attenuation is lower than that of stranded-conductor cable.

Stranded cable is for use in shorter runs between network interface cards (NICs) and wallplates or between concentrators and patch panels, hubs, and other rackmounted equipment. Stranded-conductor cable is much more flexible than solid-core cable. However, attenuation is higher in stranded-conductor cable, so the total length of stranded cable in your system should be kept to a minimum to reduce signal degradation. collapse


Black Box Explains...UARTs at a glance.

Universal Asynchronous Receiver/Transmitters (UARTs) are integrated circuits that convert bytes from the computer bus into serial bits for transmission. By providing surplus memory in a buffer, UARTs help applications overcome... more/see it nowthe factors that can hinder system performance, providing maximum throughput to high-performance peripherals without slowing down CPUs.

Early UARTs such as 8250 and 16450 did not include buffering (RAM or memory). With the advent of higher-speed devices, the need for UARTs that could handle more data became critical. The first buffered UART was the 16550, which incorporates a 16-byte First In First Out (FIFO) buffer and provides greater throughput than its predecessors.

Manufacturers have been developing enhanced UARTs that continue to increase performance standards. These faster chips provide improvements such as larger buffers and increased speeds. Here are the rates of today’s common UARTs:

UART FIFO Buffer Rate Supported
16550 16-byte 115.2 kbps
16554 16-byte 115.2 kbps
16650 32-byte 460.8 kbps (burst rate)
16654 64-byte 460.8 kbps (burst rate)
16750 64-byte 460.8 kbps (burst rate)
16850 128-byte 460.8 kbps (sustained rate)
16854 128-byte 460.8 kbps (sustained rate) collapse


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


Black Box Explains...FDDI

Fiber Distributed Data Interface (FDDI) is a networking standard for operating at speeds of up to 100 Mbps. The standard FDDI network is set up in a ring topology with... more/see it nowtwo rings that transmit signals in opposite directions to a series of nodes. FDDI accommodates up to 500 nodes per dual-ring network with spacing up to 2 kilometers between adjacent nodes. FDDI uses the same token-passing scheme as the IEEE 802.5 Token Ring network to control transmission around the loop. collapse


Black Box Explains...Category 6.

Category 6 (CAT6)–Class E has a specified frequency of 250 MHz, significantly improved bandwidth capacity over CAT5e, and easily handles Gigabit Ethernet transmissions. In recent years, it has been the... more/see it nowcable of choice for new structured cabling systems. CAT6 supports 1000BASE-T and, depending on the installation, 10GBASE-T (10-GbE).

10-GbE over CAT6 introduces the problem of Alien Crosstalk (ANEXT), the unwanted coupling of signals between adjacent pairs and cables. Because ANEXT in CAT6 10-GbE networks is so dependent on installation practices, TSB-155 qualifies 10-GbE over CAT6 up to 55 meters and requires it to be 100% tested. To mitigate ANEXT in CAT6, it is recommended that you unbundle the cables and increase the separation between the cables.

You can always contact Black Box Tech Support to answer your cabling questions. Our techs can recommend cable testers and steer you in the right direction when you’re installing new cabling. And the advice is FREE! collapse


Black Box Explains...Thermocouples

A thermocouple is a device that measures temperature by using the fact that a junction between two different metals produces a varying voltage related to their temperature. Two common types... more/see it nowof thermocouple are Type J and Type K.

Type J thermocouples use iron paired with a nickel-copper alloy. Type J thermocouples may cover a temperature range of up to -40 to +1382° F (-40 to +750°C), and offer high sensitivity.

Type K, the most common type of thermocouple, uses nickel-chromium and nickel-aluminum alloys. Because Type K is an early specification, its characteristics vary widely; individual thermocouples may cover a range of up to -328 to +2462 °F (-200 to +1350 °C). collapse


Black Box Explains…Fiber Ethernet adapters vs. media converters.

When running fiber to the desktop, you have two choices for making the connection from the fiber to a PC: a fiber Ethernet adapter or a media converter like our... more/see it nowMicro Mini Media Converter.

Fiber Ethernet adapters:

  • Less expensive.
  • Create no desktop clutter, but the PC must be opened.
  • Powered from the PC—require no separate power provision.
  • Require an open PCI or PCI-E slot in the PC.
  • Can create driver issues that must be resolved.
  • May be required in high-security installations that require a 100% fiber link to the desktop.

  • Media converters:
  • More expensive.
  • No need to open the PC but can create a cluttered look.
  • Powered from an AC outlet or a PC’s USB port.
  • Don’t require an open slot in the PC.
  • Plug-and-play installation—totally transparent to data, so there are no driver problems; install in seconds.
  • The short copper link from media converter to PC may be a security vulnerability.
  • collapse

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