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Black Box Explains...Fiber optic cable construction.

Fiber optic cable consists of a core, cladding, coating, strengthening fibers, and cable jacket.

Core
This is the physical medium that transports optical data signals from an attached light source to... more/see it nowa receiving device. The core is a single continuous strand of glass or plastic that’s measured (in microns) by the size of its outer diameter. The larger the core, the more light the cable can carry.

All fiber optic cable is sized according to its core’s outer diameter.

The three multimode sizes most commonly available are 50, 62.5, and 100 microns. Single-mode cores are generally less than 9 microns.

Cladding
This is a thin layer that surrounds the fiber core and serves as a boundary that contains the light waves and causes the refraction, enabling data to travel throughout the length of the fiber segment.

Coating
This is a layer of plastic that surrounds the core and cladding to reinforce the fiber core, help absorb shocks, and provide extra protection against excessive cable bends. These buffer coatings are measured in microns (µ) and can range from 250 to 900 microns.

Strengthening fibers
These components help protect the core against crushing forces and excessive tension during installation.

The materials can range from Kevlar® to wire strands to gel-filled sleeves.

Cable jacket
This is the outer layer of any cable. Most fiber optic cables have an orange jacket, although some types can have black or yellow jackets. collapse


Black Box Explains... SCSI termination

Passive termination
This is the oldest method of termination. A passive terminator sits on the bus to minimize reflections at the end of the cable. Passive terminators simply provide impedance close... more/see it nowto that of the cable. The terminator is “passive” because it doesn’t do any work to regulate power for termination; it relies on the interface card to provide steady power.

Active termination
This is a more stable form of terminating SCSI cables. Active terminators control the impedance at the end of the SCSI bus by using a voltage regulator, not just the power supplied by the interface card.

Forced-perfect termination
Of all SCSI terminators, this is the most complex. A cable with a forced-perfect terminator can actually change its impedance to compensate for variations along the bus. Forced-perfect terminators force the impedance of the cable to match each device through diode switching and biasing. collapse


Black Box Explains…VoIP

Voice over Internet Protocol (VoIP) is a recently developed, cost-saving alternative to traditional telephone service that enables voice data to be transported over IP networks, like the Internet, instead of... more/see it nowthe public switched telephone network (PSTN) or a cellular network.

VoIP, which operates strictly over IP networks, can connect to other VoIP nodes or traditional phone lines. The IP network used may be the Internet or a private network.

In either instance, the actual data-transport portion of this network can still be made up of the full gamut of network services: high-speed leased lines, Frame Relay, ATM, DSL, copper, fiber, wireless, satellite, and microwave signals. VoIP simply digitizes voice data and adds it to other information traveling along the same network.

With this flexible technology, a phone call can be placed between two PCs, between a PC and a standard telephone, between a PC and an IP phone, between an IP phone and a standard telephone, or between two IP phones. It will take a long time for the PSTN to support this technology seamlessly, but this seems to be the direction in which phone systems are headed.

Benefits of VoIP
Because VoIP is inexpensive, has a worldwide reach, and operates on a few simple principles, it’s exploded in popularity in recent years—especially among both small and large businesses that incur significant long-distance telephone expenses.

Savings
Without question, the primary benefit of a VoIP system is decreasing or eliminating long-distance telephone charges. Organizations with a high volume of long-distance voice traffic stand to save quite a lot of money by implementing a VoIP system. However, this factor alone may not warrant a full commitment to VoIP for some companies.

Setup fees for VoIP are usually quite low so your organization can generally start saving money after only a month or two of service. And with the wide variety of VoIP products and services on the market, it’s easier than ever to set up a VoIP phone system over your network.

Convenience
VoIP can be set up in a way that enables you to use phone numbers in exactly the same way as you did before VoIP. Most of the services you get with traditional phone service—Voice Mail, Call Waiting, and Call Routing, for instance—are also available with VoIP.

VoIP doesn’t interfere with other network services either, so you can surf the Web while making a VoIP call.

Portability
VoIP doesn’t tie you to one phone or to a single location. Anywhere you find high-speed reliable Internet access, you can use VoIP. Your phone number stays the same wherever you are—office, home, hotel, or even traveling overseas.

Standards
Although the ITU standards for VoIP have evolved significantly in the last few years, VoIP is still suffering from a lack of generally accepted interoperability standards.

H.323, a standard for real-time audio, video, and data communications across IP-based networks (including the Internet), is almost universally accepted as the primary standard for VoIP call setup and signaling. It’s actually a collection of standards that works together for sending multimedia and data over networks that don’t provide guaranteed Quality of Service (QoS).

The H.323 standard includes:
- Real-Time Transport Protocol (RTP) specifies end-to-end network transport functions for applications transmitting real-time data such as video. RTP provides services like payload type identification, sequence numbering, time stamping, and delivery monitoring to real-time applications. Plus, it works with RTCP.
- Real-time Transport Control Protocol (RTCP) works with RTP to provide a feedback mechanism, providing QoS status and control information to the streaming server.
- Registration, Admission, Status (RAS) is a gateway protocol that manages functions such as signaling, registration, admissions, bandwidth changes, status, and disengage procedures.
- Q.931 manages call setup and termination.
- H.245 negotiates channel usage and capabilities.
- H.235 provides security and authentication.

As VoIP product manufacturers began conducting interoperability tests for more complex operations, they recognized that they needed a simpler and more adaptable standard for call handling and signaling protocol.

To this end, the IETF developed the Session Initiation Protocol (SIP). SIP is built with less computer code than H.323 is, so it’s less cumbersome. Because SIP is similar in nature to HTML—it uses ASCII text for configuration—users can adapt it more easily for specific VoIP systems. In contrast, modifying H.323 for VoIP applications requires a knowledgeable computer programmer.

Both H.323 and SIP are considered “thick clients,” where intelligence is maintained in the end devices such as IP telephones. In this respect, H.323 has a head start, although most VoIP systems today support both H.323 and SIP.

Providers
Despite the fact that VoIP standards are still developing, providers are already flooding the market with products and services while forming partnerships and matching expertise to strengthen their position in this new market. The biggest of these players and alliances—the ones who have the size and experience to grasp technical issues and quickly build infrastructures over which to offer VoIP services—are able to keep up with (and often influence) the continual changes in this market and keep rolling out new services.

Components
A VoIP system depends on devices that connect your traditional phone or phone system to an IP network. Components that you’ll see in a VoIP system include:
- End-user devices
- Gateways or gatekeepers
- IPBXs
- IP Networks

End-user devices are usually VoIP telephones or PCs running VoIP software. End-user devices have their own IP address and make a direct connection to the IP network.

A gateway is a device that converts circuit-switched analog voice calls from a traditional PBX into VoIP packets and transmits them over an IP network either to another gateway or directly to an end-user device.

A gateway can have additional features such as voice compression, echo cancellation, and packet prioritization.

Because VoIP-enabled end-user devices can communicate directly with each other over an IP network, a gateway is not a required component of a VoIP system as long as the VoIP devices are connected directly to the IP network.

An IPBX is a PBX with a built-in gateway. IPBX systems are equipped for hundreds of telephone ports, with WAN support for trunk connections to the PSTN, and with high-speed IP WAN links. In addition to VoIP features, these systems usually include other features typical of traditional PBX systems such as music on hold, auto-attendant, and call management. Often, they include Ethernet ports to support VoIP telephones.

VoIP can be set up with or without a connection to standard PSTN phone service. You can, of course, place calls over the Internet directly from your PC or IP phone to another VoIP-enabled device. But what makes VoIP so versatile is that, through the use of a gateway service, it can also be used to call the numbers of phones connected to standard land-line or cellular phone services. They can also receive calls from standard telephones.

Not all fun and free calls
There are still things to consider when you’re deciding whether or not to invest in VoIP.

Regulation vagaries
Much of the government regulation of VoIP is still being worked out. The U.S. government hasn’t decided whether VoIP is going to be regulated as phone service or whether to tax it. VoIP isn’t available worldwide because some governments fear the loss of tax revenue or control.

Compatibility
Although older VoIP equipment may still have some compatibility issues, current VoIP products from different vendors generally work together.

Cost
For all the popular talk about VoIP being free, it isn’t truly free. Any VoIP system has costs associated with its implementation—equipment, high-speed Internet access, and gateway service. So, although it’s inexpensive, it’s a long way from being free. For organizations with a high volume of long-distance calls, especially to international locations, VoIP almost always pays for itself quickly. However, private users or organizations with a low volume of long-distance calls primarily within the U.S., may find that a standard service is actually more economical in the short- to mid-term.

QoS
VoIP depends on having a fast, reliable network to operate. A fast network connection with guaranteed bandwidth is not a problem in a corporate intranet where you have complete control over the network. However, if you’re using the Internet for VoIP, you’re using a public network that may be subject to slowdowns that cause drop-outs and distortion. You may find that your high-speed Internet connection is faster than the actual Internet and that the quality of your connection is generally unacceptable or is unacceptable at times when Internet usage is high.

There are four common network issues that can cause problems with a VoIP system:
- Latency is a delay in data transmission. With VoIP, this usually results in people speaking over one another because neither can tell when the other is finished talking.
- Loss. Losing a small percentage of voice transmission doesn’t affect VoIP, but too much (more than 1%) compromises the quality of the call.
- Jitter—is common to congested networks with bursty traffic. Jitter can be managed to some degree with software buffers.
- Sequence errors—or changes in the order of packets when they’re recompiled at the receiving station, degrades sound quality.

Emergency services
If you subscribe to a VoIP gateway service that enables you to use your VoIP phone like a regular phone, be aware that you may not be able to call 911 for emergencies. If 911 service is important to you because you don’t have an alternative way to call 911, shop for a VoIP provider who does provide this service.

Consider, too, that VoIP needs both working Internet access and power to work. If you lose your Internet service, your phone goes, too. And, unlike regular phone service that can keep basic telephones working when the power goes out, VoIP needs power—if you lose power, you lose your phone.

Moving forward
Before VoIP technology becomes truly universal, the current worldwide PSTN will have to migrate to a packet-based IP equivalent. Industry inertia alone dictates this will not occur instantly. The current worldwide PSTN system has grown to what it is over a period of 125 years. Given the sheer complexity of the existing PSTN, the migration to an IP packet network will probably occur during several decades.

As migration from the PSTN to IP-based networks proceeds, businesses and home users will gradually discover reasons of their own to implement VoIP. It won’t happen right away, but we predict that VoIP will become a big part of telecommunications in the not-so-distant future.

Although it’s not quite as convenient as conventional phone service, VoIP can offer serious savings—particularly if you now regularly pay for multiple overseas phone calls. Keep in mind though, VoIP isn’t a one-size-fits-all solution. But with a little planning, VoIP could spell savings for you! collapse


Black Box Explains... Bridges

If you work with legacy networks, you have doubtlessly encountered bridges. Bridges perform the same function as today’s switches in that they connect multiple network segments to create one homogenous... more/see it nownetwork, while keeping each segment isolated from the others.

Bridges operate on MAC-layer addresses and are protocol independent, so they transfer data between workstations without understanding the protocol. Since they don’t have to understand the protocol, they require little or no configuration.

Once you connect the bridge to the network, it automatically learns the addresses of all connected nodes and then creates an internal address table of this information.

When the bridge sees a packet, it checks the packet’s destination address against its internal list. If the address indicates the packet needs to be forwarded, the bridge passes the packet to the appropriate segment. If a bridge doesn’t know where a packet belongs—for example, when a station is first powered on—it passes on the packet.

Bridges can also distinguish between local data and remote data, so data traveling from one workstation to another in the same network doesn’t have to cross the bridge.

Although they are no longer in general use, Black Box stocks bridges for use as replacement parts in legacy networks. Replacing bridges with bridges rather than switches is often preferable because bridges are generally available with the BNC and AUI interfaces often found in older networks. Also, some bridges are able to link to other protocols such as RS-530 and X.21, enabling you to use these media to establish Ethernet network connections. collapse


Black Box Explains...UARTs and PCI buses.

Universal Asynchronous Receiver/Transmitters UARTs are designed to convert sync data from a PC bus to an async format that external I/O devices such as printers or modems use. UARTs insert... more/see it nowor remove start bits, stop bits, and parity bits in the data stream as needed by the attached PC or peripheral. They can provide maximum throughput to your high-performance peripherals without slowing down your CPU.

In the early years of PCs and single-application operating systems, UARTs interfaced directly between the CPU bus and external RS-232 I/O devices. Early UARTs did not contain any type of buffer because PCs only performed one task at a time and both PCs and peripherals were slow.

With the advent of faster PCs, higher-speed modems, and multitasking operating systems, buffering (RAM or memory) was added so that UARTs could handle more data. The first buffered UART was the 16550 UART, which incorporates a 16-byte FIFO (First In First Out) buffer and can support sustained data-transfer rates up to 115.2 kbps.

The 16650 UART features a 32-byte FIFO and can handle sustained baud rates of 460.8 kbps. Burst data rates of up to 921.6 kbps have even been achieved in laboratory tests.

The 16750 UART has a 64-byte FIFO. It also features sustained baud rates of 460.8 kbps but delivers better performance because of its larger buffer.

Used in newer PCI cards, the 16850 UART has a 128-byte FIFO buffer for each port. It features sustained baud rates of 460.8 kbps.

The Peripheral Component Interconnect (PCI®) Bus enhances both speed and throughput. PCI Local Bus is a high-performance bus that provides a processor-independent data path between the CPU and high-speed peripherals. PCI is a robust interconnect interface designed specifically to accommodate multiple high-performance peripherals for graphics, full-motion video, SCSI, and LANs.

A Universal PCI (uPCI) card has connectors that work with both a newer 3.3-V power supply and motherboard and with older 5.5-V versions. collapse


Black Box Explains...PC, UPC, and APC fiber connectors.

Fiber optic cables have different types of mechanical connections. The type of connection determines the quality of the fiber optic lightwave transmission. The different types we’ll discuss here are the... more/see it nowflat-surface, Physical Contact (PC), Ultra Physical Contact (UPC), and Angled Physical Contact (APC).

The original fiber connector is a flat-surface connection, or a flat connector. When mated, an air gap naturally forms between the two surfaces from small imperfections in the flat surfaces. The back reflection in flat connectors is about -14 dB or roughly 4%.

As technology progresses, connections improve. The most common connection now is the PC connector. Physical Contact connectors are just that—the end faces and fibers of two cables actually touch each other when mated.

In the PC connector, the two fibers meet, as they do with the flat connector, but the end faces are polished to be slightly curved or spherical. This eliminates the air gap and forces the fibers into contact. The back reflection is about -40 dB. This connector is used in most applications.

An improvement to the PC is the UPC connector. The end faces are given an extended polishing for a better surface finish. The back reflection is reduced even more to about -55 dB. These connectors are often used in digital, CATV, and telephony systems.

The latest technology is the APC connector. The end faces are still curved but are angled at an industry-standard eight degrees. This maintains a tight connection, and it reduces back reflection to about -70 dB. These connectors are preferred for CATV and analog systems.

PC and UPC connectors have reliable, low insertion losses. But their back reflection depends on the surface finish of the fiber. The finer the fiber grain structure, the lower the back reflection. And when PC and UPC connectors are continually mated and remated, back reflection degrades at a rate of about 4 to 6 dB every 100 matings for a PC connector. APC connector back reflection does not degrade with repeated matings. collapse


Black Box Explains...USB.

What is USB?
Universal Serial Bus (USB) is a royalty-free bus specification developed in the 1990s by leading manufacturers in the PC and telephony industries to support plug-and-play peripheral connections. USB... more/see it nowhas standardized how peripherals, such as keyboards, disk drivers, cameras, printers, and hubs) are connected to computers.

USB offers increased bandwidth, isochronous and asynchronous data transfer, and lower cost than older input/output ports. Designed to consolidate the cable clutter associated with multiple peripherals and ports, USB supports all types of computer- and telephone-related devices.

Universal Serial Bus (USB) USB detects and configures the new devices instantly.
Before USB, adding peripherals required skill. You had to open your computer to install a card, set DIP switches, and make IRQ settings. Now you can connect digital printers, recorders, backup drives, and other devices in seconds. USB detects and configures the new devices instantly.

Benefits of USB.
• USB is “universal.” Almost every device today has a USB port of some type.
• Convenient plug-and-play connections. No powering down. No rebooting.
• Power. USB supplies power so you don’t have to worry about adding power. The A socket supplies the power.
• Speed. USB is fast and getting faster. The original USB 1.0 had a data rate of 1.5 Mbps. USB 3.0 has a data rate of 4.8 Gbps.

USB Standards

USB 1.1
USB 1.1, introduced in 1995, is the original USB standard. It has two data rates: 12 Mbps (Full-Speed) for devices such as disk drives that need high-speed throughput and 1.5 Mbps (Low-Speed) for devices such as joysticks that need much lower bandwidth.

USB 2.0
In 2002, USB 2.0, (High-Speed) was introduced. This version is backward-compatible with USB 1.1. It increases the speed of the peripheral to PC connection from 12 Mbps to 480 Mbps, or 40 times faster than USB 1.1.

This increase in bandwidth enhances the use of external peripherals that require high throughput, such as printers, cameras, video equipment, and more. USB 2.0 supports demanding applications, such as Web publishing, in which multiple high-speed devices run simultaneously.

USB 3.0
USB 3.0 (SuperSpeed) (2008) provides vast improvements over USB 2.0. USB 3.0 has speeds up to 5 Gbps, nearly ten times that of USB 2.0. USB 3.0 adds a physical bus running in parallel with the existing 2.0 bus.

USB 3.0 is designed to be backward compatible with USB 2.0.

USB 3.0 Connector
USB 3.0 has a flat USB Type A plug, but inside there is an extra set of connectors and the edge of the plug is blue instead of white. The Type B plug looks different with an extra set of connectors. Type A plugs from USB 3.0 and 2.0 are designed to interoperate. USB 3.0 Type B plugs are larger than USB 2.0 plugs. USB 2.0 Type B plugs can be inserted into USB 3.0 receptacles, but the opposite is not possible.

USB 3.0 Cable
The USB 3.0 cable contains nine wires—four wire pairs plus a ground. It has two more data pairs than USB 2.0, which has one pair for data and one pair for power. The extra pairs enable USB 3.0 to support bidirectional asynchronous, full-duplex data transfer instead of USB 2.0’s half-duplex polling method.

USB 3.0 Power
USB 3.0 provides 50% more power than USB 2.0 (150 mA vs 100 mA) to unconfigured devices and up to 80% more power (900 mA vs 500 mA) to configured devices. It also conserves power too compared to USB 2.0, which uses power when the cable isn’t being used.

USB 3.1
Released in 2013, is called SuperSpeed USB 10 Gbps. There are three main differentiators to USB 3.1. It doubles the data rate from 5 Gbps to 10 Gbps. It will use the new, under-development Type C connector, which is far smaller and designed for use with everything from laptops to mobile phones. The Type C connector is being touted as a single-cable solution for audio, video, data, and power. It will also have a reversible plug orientation. Lastly, will have bidirectional power delivery of up to 100 watts and power auto-negotiation. It is backward compatible with USB 3.0 and 2.0, but an adapter is needed for the physical connection.

Transmission Rates
USB 3.0: 4.8 Gbps
USB 2.0: 480 Mbps
USB 1.1: 12 Mbps

Cable Length/Node
5 meters (3 meters for 3.0 devices requiring higher speeds).
Devices/bus: 127
Tier/bus: 5
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Black Box Explains...NEMA ratings for enclosures.

The National Electrical Manufacturers’ Association (NEMA) issues guidelines and ratings for an enclosure’s level of protection against contaminants that might come in contact with its enclosed equipment.

There are many numerical... more/see it nowNEMA designations; we’ll discuss NEMA enclosures relevant to our on-line catalog: NEMA 3, NEMA 3R, NEMA 4, NEMA 4X, and NEMA 12.

NEMA 3 enclosures, designed for both indoor and outdoor use, provide protection against falling dirt, windblown dust, rain, sleet, and snow, as well as ice formation.

The NEMA 3R rating is identical to NEMA 3 except that it doesn’t specify protection against windblown dust.

NEMA 4 and 4X enclosures, also designed for indoor and outdoor use, protect against windblown dust and rain, splashing and hose-directed water, and ice formation. NEMA 4X goes further than NEMA 4, specifying that the enclosure will also protect against corrosion caused by the elements.

NEMA 12 enclosures are constructed for indoor use only and are designed to provide protection against falling dirt, circulating dust, lint, fibers, and dripping or splashing noncorrosive liquids. Protection against oil and coolant seepage is also a prerequisite for NEMA 12 designation. collapse


Black Box Explains…SFP compatibility.

Standards for SFP fiber optic media are published in the SFP Multi-Source Agreement, which specifies size, connectors, and signaling for SFPs, with the idea that all SFPs are compatible with... more/see it nowdevices that have appropriate SFP slots. These standards, which also extend to SFP+ and XFP transceivers, enable users to mix and match components from different vendors to meet their own particular requirements.

However, some major manufacturers, notably Cisco®, HP®, and 3Com®, sell network devices with SFP slots that lock out transceivers from other vendors. Because the price of SFPs—especially Gigabit SFPs and 10GBASE SFP+ and XFP transceivers—can add significantly to the price of a switch, this lock-out scheme raises hardware costs and limits transceiver choices.

Many vendors don’t advertise that SFP slots on their devices don’t accept standard SFPs from other vendors. This can lead to unpleasant surprises when a device simply refuses to communicate with an SFP.

Another game that some vendors play is to build devices that accept open-standard SFPs, but refuse to support those devices when SFPs from another vendor are used with them.

The only way around this “lock-in” practice is to only buy network devices that accept standard SFPs from all vendors and to buy from vendors that support their devices no matter whose SFPs are used with them. Questions? Call our FREE Tech Support at 724-746-5500. collapse


Black Box Explains...CAT5: When more isn’t always better.

In data communications applications, using products that exceed required capacities is usually not a problem. For example, if a 28.8K modem is required, a 33.6K or 56K model will work... more/see it nowjust fine.

But sometimes, more isn’t better. Take KVM extenders designed to expect CAT5 and only CAT5 cable. You’d expect that Category 3 cable wouldn’t be effective with these products, and you would be right.

But you may also assume that if Category 5 cable works fine, Category 5e, Category 6, and other higher-capacity cables would work even better. Unfortunately, this isn’t the case, and here’s why:

KVM extenders from many manufacturers, including ServSwitch CAT5 KVM Extenders, are designed specifically for the Category 5 specs defined by the TIA/EIA standard. Higher-level cables, such as Category 5e, have different characteristics and specifications. Although differences—specifically twist ratios—might seem small, they can have a negative impact on these extenders, which are expecting a true Category 5 transmission.

So with ServSwitch CAT5 KVM Extenders, you can think big with CAT5—just don’t think bigger. collapse

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