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Black Box Explains...Multi-user ServSwitch products vs. multipoint access ServSwitch products.

A multi-user ServSwitch, such as the Matrix ServSwitch, enables two or more users to access different servers at the same time. So, for instance, one user can access “Server A”... more/see it nowwhile another user accesses “Server B.” This is considered a “true two-channel” architecture because two users have independent access to CPUs. It should be pointed out that multiple users cannot access the same server at the same time.

A multipoint access ServSwitch, such as the ServSwitch Duo, provides two access points for control stations but requires that both users view the same server at the same time. So, if one user is accessing “Server A” on his screen, the other user is also seeing “Server A” on his screen. If the second user switches to “Server B,“ the first user will also switch to “Server B.” Only one of these users is actually in control. The user in control stays in control until his workstation is inactive for a period of time (selectable). Then the other station can take control.

A multipoint access ServSwitch is useful when simultaneous, independent access is not required—just the ability to access CPUs from more than one place.


Black Box Explains...Upgrading from VGA to DVI video.

Many new PCs no longer have traditional Cathode Ray Tube (CRT) computer monitors with a VGA interface. The latest high-end computers have Digital Flat Panels (DFPs) with a Digital Visual... more/see it nowInterface (DVI). Although most computers still have traditional monitors, the newer DFPs are coming on strong because flat-panel displays are not only slimmer and more attractive on the desktop, but they’re also capable of providing a much sharper, clearer image than a traditional CRT monitor.

The VGA interface was developed to support traditional CRT monitors. The DVI interface, on the other hand, is designed specifically for digital displays and supports the high resolution, the sharper image detail, and the brighter and truer colors achieved with DFPs.

Most flat-panel displays can be connected to a VGA interface, even though using this interface results in inferior video quality. VGA simply can’t support the image quality offered by a high-end digital monitor. Sadly, because a VGA connection is possible, many computer users connect their DFPs to VGA and never experience the stunning clarity their flat-panel monitors can provide.

It’s important to remember that for your new DFP display to work at its best, it must be connected to a DVI video interface. You should upgrade the video card in your PC when you buy your new video monitor. Your KVM switches should also support DVI if you plan to use them with DFPs. collapse

Black Box Explains... RJ-48

An RJ-48 plug is often mistaken for RJ-45. On the outside, the two look identical—both are housed in a miniature 8-position jack. The difference is in the pairing of the... more/see it nowwires.

In RJ-48, two of the wires are for transmit, two are for receive, and two are for the drain. The last two wires are reserved for future use.

There are three subsets within RJ-48: RJ-48C, RJ-48X, and RJ-48S.

RJ-48C and RJ-48X are very similar. Both use lines 1, 2, 4, and 5 and connect T1 lines. The RJ-48C is more common. The difference is that RJ-48X connectors have shorting bars.

RJ-48S uses lines 1, 2, 7, and 8. It connects 56K DDS lines. 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...The difference between the SurgeArrest and power strips.

It says UL® listed, so it must be okay, right? Don’t be fooled. The $5.99 surge suppressor you picked up for your home PC may be nothing more than a... more/see it nowmultiple outlet extension cord.

UL® listed means that a product has been submitted to Underwriter’s Laboratories® for safety testing in certain categories. The strip protector you just bought is probably listed in the extension cord category. It won’t stop harmful surges from destroying equipment data.

The UL® listing for surge suppressors is UL® 1449. APC® SurgeArrest® products received the best UL® 1449 rating. Some vendors rate surge protection on the basis of joule energy. But let-through should be compared.

Basically, let-through is a measure of how much of a spike or surge each protector will let though to your electronic equipment. The lower the let-through rating, the better the suppression. And the SurgeArrest is guaranteed forever—even if it takes a catastrophic hit. It may be the last surge protector you buy. collapse

Black Box Explains...Advanced printer switches.

Matrix—A matrix switch is a switch with a keypad for selecting one of many input ports to connect to any one of many output ports.

Port-Contention—A port-contention switch is an... more/see it nowautomatic electronic switch that can be serial or parallel. It has multiple input ports but only one output port. The switch monitors all ports simultaneously. When a port receives data, it prints and all the other ports have to wait.

Scanning—A scanning switch is like a port-contention switch, but it scans ports one at a time to find one that’s sending data.

Code-Operated—Code-operated switches receive a code (data string) from a PC or terminal to select a port.

Matrix Code-Operated—This matrix version of the code-operated switch can be an any-port to any-port switch. This means than any port on the switch can attach to any other port or any two or more ports can make a simultaneous link and transfer data. collapse

Black Box Explains...Choosing SCSI cables.

1. Quality. Your system’s performance depends on the quality of your SCSI cables. Without high-quality cables specifically designed for SCSI applications, you could be jeopardizing your SCSI lifeline. Inferior cables,... more/see it nowadapters, and terminators can cause random errors, data corruption, or even a system crash! Black Box® SCSI Cables and components are the absolute best-quality products. And they’re guaranteed for life.

2. Length. For peak network performance, make sure your cables are the right length. As cable runs get longer, signals weaken and are more susceptible to noise. Always use the shortest cable for the task. And stay within the SCSI-1 and SCSI-2 standards of six meters or three meters for Fast SCSI. Remember, this is the total length of the bus, including all internal and external cables. collapse

Black Box Explains...On-screen menus.

When the ServSwitch™ brand of KVM switches was first introduced, there were only two ways to switch: from front-panel push buttons or by sending command sequences from the keyboard. While... more/see it nowthis was more convenient than having a separate keyboard, monitor, and mouse for each CPU, the operator still had to remember key combinations and which server was connected to which port—leading to many cryptic, scribbled notes attached to the switch and to the workstation.

But with the advent of on-screen menus, an operator can use easy-to-read, pop-up menus to identify and select CPUs. It’s even possible to give each CPU a name that makes sense to you—names like “MIS Server,” “Accounting Server,” and so on.

Black Box Explains... Pulling eyes and fiber cable.

Fiber optic cable can be damaged if pulled improperly. Broken or cracked fiber, for example, can result from pulling on the fiber core or jacket instead of the strength member.... more/see it nowAnd too much tension or stress on the jacket, as well as too tight of a bend radius, can damage the fiber core. If the cable’s core is harmed, the damage can be difficult to detect.

Once the cable is pulled successfully, damage can still occur during the termination phase. Field termination can be difficult and is often done incorrectly, resulting in poor transmission. One way to eliminate field termination is to pull preterminated cable. But this can damage the cable as well because the connectors can be knocked off during the pulling process. The terminated cable may also be too bulky to fit through ducts easily. To help solve all these problems, use preterminated fiber optic cable with a pulling eye. This works best for runs up to 2000 feet (609.6 m).

The pulling eye contains a connector and a flexible, multiweave mesh-fabric gripping tube. The latched connector is attached internally to the Kevlar®, which absorbs most of the pulling tension. Additionally, the pulling eye’s mesh grips the jacket over a wide surface area, distributing any remaining pulling tension and renders it harmless. The end of the gripping tube features one of three different types of pulling eyes: swivel, flexible, or breakaway.

Swivel eyes enable the cable to go around bends without getting tangled. They also prevent twists in the pull from being transferred to the cable. A flexible eye follows the line of the pull around corners and bends, but it’s less rigid. A breakaway eye offers a swivel function but breaks if the tension is too great. We recommend using the swivel-type pulling eye.

A pulling eye enables all the fibers to be preterminated to ensure better performance. The terminated fibers are staggered inside the gripping tube to minimize the diameter of the cable. This enables the cable to be pulled through the conduit more easily. collapse

Black Box Explains...Quick disconnnects.

A quick disconnect enables you to disconnect your headset without disconnecting your call or taking off your headset. This option is expecially convenient when you need to leave your desk... more/see it nowand keep your caller on the line. When you return to your desk, all you need to do is reconnect the plug and you’re talking again. The quick disconnect works well for call centers and busy offices where files aren’t at your desk or when you need to speak to a supervisor. collapse

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