Loading


Content Type (x) > Black Box Explains (x)

Results 101-110 of 210 << < 11 12 13 14 15 > >> 

Black Box Explains...Choosing a wireless antenna.


Ride the wave.

One of the most critical components to operating a successful wireless network is having the right antennas. Antennas come in many different shapes and sizes,... more/see it noweach designed for a specific function. Selecting the right antennas for your network is crucial to achieving optimum network performance. In addition, using the right antennas can decrease your networking costs since you’ll need fewer antennas and access points.


Basically, a wireless network consists of data, voice, and video information packets being transmitted over low-frequency radio waves instead of electrically over copper cable or via light over fiber lines. The antenna acts as a radiator and transmits waves through the air, just like radio and TV stations. Antennas also receive the waves from the air and transport them to the receiver, which is a radio, TV, or in the case of wireless networking, a router or an access point.


Type cast.

The type of antennas you use depends on what type of network you’re setting up and the coverage you need. How large is your network? Is it for a home, single office, campus, or larger? Is it point-to-point or multipoint?


The physical design-walls, floors, etc.- of the building(s) you’re working in also affects the type and number of antennas you need. In addition, physical terrain affects your antenna choices. Obviously, a clear line of sight works best, but you need to consider obstructions such as trees, buildings, hills, and water. (Radio waves travel faster over land than water.) You even need to consider traffic noise in urban settings.


The ideal shape.

Let’s take a look at the different types of antennas.


Isotropic Antenna. First, think of the introduction to the old RKO movies. A huge tower sits on top of the world and emanates circular waves in all directions. If you could actually see the waves, they would form a perfect sphere around the tower. This type of antenna is called an isotropic antenna, and does not exist in the real world. It is theoretical and is used as a base point for measuring actual antennas.


Go in the right direction.

Now let’s turn to real-world antennas. There are many types of antennas that emit radio waves in different directions, shapes, and on different planes. Think of the spherical isotropic antenna. If squeezed from the sides, it will become shaped like a wheel and will concentrate waves on a vertical plane. If squeezed from the top, it will flatten out like a pancake and radiate waves on a horizontal plane. Thus, there are two basic types of antennas: directional and omnidirectional.


Directional antennas.

Directional antennas, primarily used in point-to-point networks, concentrate the waves in one direction much like a flashlight concentrates light in a narrow beam. Directional antennas include backfire, Yagi, dish, panel, and sector.


Backfire. This small directional antenna looks like a cake pan with a tin can in the middle. It’s designed to be compact, often under 11" in diameter, making it unobtrusive and practical for outdoor use. These antennas also offer excellent gain, and can be used in both point-to-point or point-to-multipoint systems.


Yagi. The Yagi-Uda (or Yagi) antenna is named for its Japanese inventors. The antenna was originally intended for radio use and is now frequently used in 802.11 wireless systems.


A Yagi antenna is highly directional. It looks like a long fishbone with a central spine and perpendicular rods or discs at specified intervals. Yagi antennas offer superior gain and highly vertical directionality. The longer the Yagi, the more focused its radiation is. Many outdoor Yagi antennas are covered in PVC so you can’t see the inner structure.


Yagi antennas are good for making point-to-point links in long narrow areas (for instance, connecting to a distant point in a valley) or for point-to-point links between buildings. They can also be used to extend the range of a point-to-multipoint network.


Parabolic or Dish. These antennas look like a circular or rectangular concave bowl or "dish". The backboard can be solid or a grid design. Parabolic grid designs are excellent for outdoor use since the wind blows right through them. The concave nature of this dish design focuses energy into a narrow beam that can travel long distances, even up to several miles. This makes parabolic antennas ideal for point-to-point network connections. Since they generate a narrow beam in both the horizontal and vertical planes, offer excellent gain, and minimize interference, they’re ideal for long-distance point-to-point networks.


Panel or Patch. These antennas are often square or rectangular, and they’re frequently hung on walls. They’re designed to radiate horizontally forward and to the side, but not behind them. Sometimes they’re called "picture-frame" antennas.


Panel antennas are ideal in applications where the access point is at one end of a building. They’re good for penetrating a single floor of a building, and for small and medium-size homes and offices. Since they might not have much vertical radiation, they might not be a good choice for multifloor applications.


Because panel antennas can be easily concealed, they’re a good choice when aesthetics are important.


Sector. A sector antenna can be any type of antenna that directs the radio waves in a specific area. They are often large, outdoor flat-panel or dish-type antennas mounted up high and tilted downward toward the ground. These antennas are often used in sprawling campus settings to cover large areas.


Omnidirectional antennas.

Omnidirectional antennas provide the widest coverage possible and are generally used in point-to-multipoint networks. Their range can be extended by overlapping circles of coverage from multiple access points. Most omnidirectional antennas emanate waves in a fan-shaped pattern on a horizontal plane. Overall, omnidirectional antennas have lower gain than directional antennas. Examples of omnidirectional antennas include: integrated, blade, and ceiling.


Integrated. Integrated antennas are antennas that are built into wireless networking devices. They may be embedded in PC card client adapters or in the covers or body of laptops or other devices, such as access points. Integrated antennas often do not offer the same reception as external antennas and might not pick up weak signals. Access points with integral antennas must often be moved or tilted to get the best reception.


Blade. These small, omnidirectional antennas are often housed in long, thin envelopes of plastic. They are most often used to pick up a signal in a low-signal or no-signal spot. You usually will see them on the walls of cubicles, mounted on desktops, or even hung above cubicles to catch signals. They’re basically an inexpensive signal booster.


Ceiling Dome. These are sometimes also called ceiling blister antennas. They look somewhat like a smoke detector and are designed for unobtrusive use in ceilings, particularly drop ceilings. Ceiling dome antennas often have a pigtail for easy connection to access points. They’re excellent for use in corporate environments where wide coverage over a cube farm is needed.


Wave basics.

To better understand wireless antennas and networking, there are some basic measurements and terms that need to be discussed.


Gain. One of the primary measurements of antennas is gain. Gain is measured as dBi, which is how much the antenna increases the transmitter’s power compared to the theoretical isotropic antenna, which has a gain of 0 dBi. dBi is the true gain the antenna provides to the transmitter’s output. Gain is also reciprocal-it’s the same transmitting and receiving. Higher gain means stronger sent and received signals. An easy way to remember gain basics is that every 3 dB of gain added doubles the effective power output of an antenna. The more an antenna concentrates a signal, the higher the gain it will have.


You can actually calculate the gains and losses of a system by adding up the gains and losses of its parts in decibels.


Frequency and Wavelength. Electromagnetic waves are comprised of two components: frequency and wavelength.


Frequency is how many waves occur each second. Wavelength is the distance between one peak of a wave and the next peak. Lower frequencies have longer wavelengths; higher frequencies have shorter wavelengths. For example, the frequency of AM radio is 1 MHz with a wavelength of about 1000 feet. FM radios operate at a much higher frequency of 100 MHz and have a wavelength of about 100 feet.


The two most common frequencies for wireless networking are 2.4-GHz and 5-GHz. Both are very high frequencies with very short wavelengths in the microwave band. The 2.4-GHz frequency has a wavelength of about 5 inches.


Beamwidth. Consider an antenna to be like a flashlight or spotlight. It reflects and directs the light (or radio waves) in a particular direction. Beamwidth actually measures how energy is focused or concentrated.


Polarization. This is the direction in which the antenna radiates wavelengths, either vertically, horizontally, or circularly. Vertical antennas have vertical polarization and are the most common. For optimum performance, it is important that the sending and receiving antennas have the same polarization.


VSWR and Return Loss. Voltage Standing Wave Ratio (VSWR) measures how well the antenna is matched to the network at the operating frequency being used. It indicates how much of the received signal won’t reach either the transceiver or receiver. Return loss measures how well matched an antenna is to the network. Typical VSWR numbers are 1:1.2 or 1:1.5. A typical return loss number is 20.

collapse


Black Box Explains...Type 1 vs. Type 6 Cable

Type 1 Cable is made of solid wire, typically 22 AWG bare copper. It has braided shielding around each pair. It’s recommended for long runs in walls, conduits, etc.

Type 6... more/see it nowCable is typically made of 26 AWG stranded copper and has one shield around both pairs. It’s lighter and more flexible than Type 1 Cable and has a better “look.” It’s recommended for use in office environments. collapse


Black Box Explains...Multicasting video over a LAN: Use the right switch.

In KVM extension applications where you want to distribute HD video across a network, you need to understand how it works and what kind of networking equipment to use with... more/see it nowyour extenders.

Think of your network as a river of data with a steady current of data moving smoothly down the channel. All your network users are like tiny tributaries branching off this river, taking only as much water (bandwidth) as they need to process data. When you start to multicast video, data, and audio over the LAN, those streams suddenly become the size of the main river. Each user is then basically flooded with data and it becomes difficult or impossible to do any other tasks. This scenario of sending transmissions to every user on the network is called broadcasting, and it slows down the network to a trickle. There are network protocol methods that alleviate this problem, but it depends on the network switch you use.

Unicast vs. multicasting, and why a typical Layer 2 switch isn’t sufficient.
Unicasting is sending data from one network device to another (point to point); in a typical unicast network, Layer 2 switches easily support these types of communications. But multicasting is transmitting data from one network device to multiple users. When multicasting with Layer 2 switches, all attached devices receive the packets, whether they want them or not. Because a multicast header does NOT have a destination IP address, an average network switch (a Layer 2 switch without supported capabilities) will not know what to do with it. So the switch sends the packet out to every network port on all attached devices. When the client or network interface card (NIC) receives the packet, it analyzes it and discards it if not wanted.

The solution: a Layer 3 switch with IGMPv2 or IGMPv3 and packet forwarding.
Multicasting with Layer 3 switches is much more efficient than with Layer 2 switches because it identifies the multicast packet and sends it only to the intended receivers. A Layer 2 switch sends the multicast packets to every device and, If there are many sources, the network will slow down because of all the traffic. And, without IGMPv2 or IGMPv3 snooping support, the switch can handle only a few devices sending multicasting packets.

Layer 3 switches with IGMP support, however, “know” who wants to receive the multicast packet and who doesn’t. When a receiving device wants to tap into a multicasting stream, it responds to the multicast broadcast with an IGMP report, the equivalent of saying, “I want to connect to this stream.” The report is only sent in the first cycle, initializing the connection between the stream and receiving device. If the device was previously connected to the stream, it sends a grafting request for removing the temporary block on the unicast routing table. The switch can then send the multicast packets to newly connected members of the multicast group. Then, when a device no longer wants to receive the multicast packets, it sends a pruning request to the IGMP-supported switch, which temporarily removes the device from the multicast group and stream.

Therefore, for multicasting, use routers or Layer 3 switches that support the IGMP protocol. Without this support, your network devices will be receiving so many multicasting packets, they will not be able to communicate with other devices using different protocols, such as FTP. Plus, a feature-rich, IGMP-supported Layer 3 switch gives you the bandwidth control needed to send video from multiple sources over a LAN. collapse


Black Box Explains...Remote power control.

Simply put, remote power control is the ability to reset or reboot PC, LAN, telecom, and other computer equipment without being at the equipment’s location.

Who needs remote power control?... more/see it nowAny organization with a network that reaches remote sites. This can include branch offices, unmanned information kiosks, remote monitoring stations, alarm and control systems, and even HVAC systems.

When equipment locks up at remote sites, it is usually up to the system manager at headquarters to reset it. Often, there aren’t any technically trained personnel at the remote site who can perform maintenance and resets on equipment. So, in order to save traveling time and minimize downtime, remote power control enables the system manager to take care of things at the office without ever leaving home!

Remote power control can be done with modems or existing or special phone lines. The ideal system uses “out-of-band management,“ an alternate path over an ordinary dialup line that doesn’t interfere with network equipment.

An effective remote power control system incorporates the following:
• An existing phone line, such as a line being used for a fax, modem, or phone.
• Transparent operation. The system shouldn’t interfere with or be affected by normal calls.
• Security features. The system should prevent unauthorized access to network equipment.
• Flexibility. System managers should be able to dial in from anywhere and control mulitple devices with one call.
• Have power control devices that meet UL® and FCC requirements. collapse


Black Box Explains… Category 7/Class F.


Category 7/Class F (ISO/IEC 11801:2002) specifies a frequency range of 1–600 MHz over 100 meters of fully shielded twisted-pair cabling. It encompasses four individually shielded pairs inside an overall shield,... more/see it nowcalled Shielded/Foiled Twisted Pair (S/FTP) or Foiled/ Foiled Twisted Pair (F/FTP). There is a pending class Fa, based on the use of S/FTP cable to 1000 MHz. It can support 10GBASE-T transmissions.

With both types of cable, each twisted pair is enclosed in foil. In S/FTP cable, all four pairs are encased in an overall metal braid. In F/FTP, the four pairs are encased in foil.

Category 7/Class F cable can be terminated with two interface designs as specified in IEC 6063-7-7 and IEC 61076-3-104. One is an RJ-45 compatible GG-45 connector. The other is the more common TERA connector, which was launched in 1999.

Category 7/Class F is backwards compatible with traditional CAT6 and CAT5 cable, but it has far more stringent specifications for crosstalk and system noise. The fully shielded cable virtually eliminates crosstalk between the pairs. In addition, the cable is noise resistant, which makes the Category 7/Class F systems ideal for high EMI areas, such as industrial and medical imaging facilities.
Category 7/Class F cable can also increase security by preventing the emission of data signals from the cable to nearby areas. 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...NEBS Level 3.

Network Equipment Building System (NEBS) standards set requirements for telco equipment. The standards are maintained by Telcordia Technologies, Inc., formerly Bellcore. Bellcore Special Report, SR-3580 defines three distinct functional levels... more/see it nowof NEBS compliance. The third of these levels, NEBS Level 3, is the most stringent, certifying carrier-class equipment intended for long-term use in variable environments.

NEBS Level 3 certifies that a piece of equipment can be safely used in an extreme environment. To become certified at NEBS Level 3, a device must meet strict physical, electrical, and environmental requirements to prove it will operate safely and reliably in extreme conditions. It must pass a series of tests that include extreme heat, humidity, fire, earthquakes (Zone 4), light, and noise. collapse


Black Box Explains...Ethernet.



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... more/see it nowthe 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.


How Ethernet Works

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.


Standard (Thick) Ethernet (10BASE5)


  • Uses “thick” coax cable with N-type connectors for a backbone and a transceiver cable with 9-pin connectors from the transceiver to the NIC.
  • Both ends of each segment should be terminated with a 50-ohm resistor.
  • Maximum segment length is 500 meters.
  • Maximum total length is 2500 meters.
  • Maximum length of transceiver cable is 50 meters.
  • Minimum distance between transceivers is 2.5 meters.
  • No more than 100 transceiver connections per segment are allowed.
Thin Ethernet (ThinNet) (10BASE2)


  • Uses "Thin" coax cable.
  • The maximum length of one segment is 185 meters.
  • The maximum number of segments is five.
  • The maximum total length of all segments is 925 meters.
  • The minimum distance between T-connectors is 0.5 meters.
  • No more than 30 connections per segment are allowed.
  • T-connectors must be plugged directly into each device.
Twisted-Pair Ethernet (10BASE-T)


  • Uses 22 to 26 AWG unshielded twisted-pair cable (for best results, use Category 4 or 5 unshielded twisted pair).
  • The maximum length of one segment is 100 meters.
  • Devices are connected to a 10BASE-T hub in a star configuration.
  • Devices with standard AUI connectors may be attached via a 10BASE-T transceiver.
Fiber Optic Ethernet (10BASE-FL, FOIRL)


  • Uses 50-, 62.5-, or 100-micron duplex multimode fiber optic cable (62.5 micron is recommended).
  • The maximum length of one 10BASE-FL (the new standard for fiber optic connections) segment is 2 kilometers.
  • The maximum length of one FOIRL (the standard that preceded the new 10BASE-FL) segment is 1 kilometer.
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...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

Results 101-110 of 210 << < 11 12 13 14 15 > >> 
Close

Support

Delivering superior technical support is our highest priority. Depending on the products or services we provide for you, please visit your appropriate support area.



 
Print
Black Box 1-877-877-2269 Black Box Network Services