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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


SHDSL, VDSL, VDSL2, ADSL, and SDSL.

xDSL, a term that encompasses the broad range of digital subscriber line (DSL) services, offers a low-cost, high-speed data transport option for both individuals and businesses, particularly in areas without... more/see it nowaccess to cable Internet.

xDSL provides data transmission over copper lines, using the local loop, the existing outside-plant telephone cable network that runs right to your home or office. DSL technology is relatively cheap and reliable.

SHDSL can be used effectively in enterprise LAN applications. When interconnecting sites on a corporate campus, buildings and network devices often lie beyond the reach of a standard Ethernet segment. Now you can use existing copper network infrastructure to connect remote LANS across longer distances and at higher speeds than previously thought possible.

There are various forms of DSL technologies, all of which face distance issues. The quality of the signals goes down with increasing distance. The most common will be examined here, including SHDSL, ADSL, and SDSL.

SHDSL (also known as G.SHDSL) (Single-Pair, High-Speed Digital Subscriber Line) transmits data at much higher speeds than older versions of DSL. It enables faster transmission and connections to the Internet over regular copper telephone lines than traditional voice modems can provide. Support of symmetrical data rates makes SHDSL a popular choice for businesses for PBXs, private networks, web hosting, and other services.

Ratified as a standard in 2001, SHDSL combines ADSL and SDSL features for communications over two or four (multiplexed) copper wires. SHDSL provides symmetrical upstream and downstream transmission with rates ranging from 192 kbps to 2.3 Mbps. As a departure from older DSL services designed to provide higher downstream speeds, SHDSL specified higher upstream rates, too. Higher transmission rates of 384 kbps to 4.6 Mbps can be achieved using two to four copper pairs. The distance varies according to the loop rate and noise conditions.

For higher-bandwidth symmetric links, newer G.SHDSL devices for 4-wire applications support 10-Mbps rates at distances up to 1.3 miles (2 km). Equipment for 2-wire deployments can transmit up to 5.7 Mbps at the same distance.

SHDSL (G.SHDSL) is the first DSL standard to be developed from the ground up and to be approved by the International Telecommunication Union (ITU) as a standard for symmetrical digital subscriber lines. It incorporates features of other DSL technologies, such as ADSL and SDS, and is specified in the ITU recommendation G.991.2.

Also approved in 2001, VDSL (Very High Bitrate DSL) as a DSL service allows for downstream/upstream rates up to 52 Mbps/16 Mbps. Extenders for local networks boast 100-Mbps/60-Mbps speeds when communicating at distances up to 500 feet (152.4 m) over a single voice-grade twisted pair. As a broadband solution, VDSL enables the simultaneous transmission of voice, data, and video, including HDTV, video on demand, and high-quality videoconferencing. Depending on the application, you can set VDSL to run symmetrically or asymmetrically.

VDSL2 (Very High Bitrate DSL 2), standardized in 2006, provides a higher bandwidth (up to 30 MHz) and higher symmetrical speeds than VDSL, enabling its use for Triple Play services (data, video, voice) at longer distances. While VDSL2 supports upstream/downstream rates similar to VDSL, at longer distances, the speeds don’t fall off as much as those transmitted with ordinary VDSL equipment.

ADSL (Asymmetric DSL) provides transmission speeds ranging from downstream/upstream rates of 9 Mbps/640 kbps over a relatively short distance to 1.544 Mbps/16 kbps as far away as 18,000 feet. The former speeds are more suited to a business, the latter more to the computing needs of a residential customer.

More bandwidth is usually required for downstream transmissions, such as receiving data from a host computer or downloading multimedia files. ADSL’s asymmetrical nature provides more than sufficient bandwidth for these applications.

The lopsided nature of ADSL is what makes it most likely to be used for high-speed Internet access. And the various speed/distance options available within this range are one more point in ADSL’s favor. Like most DSL services standardized by ANSI as T1.413, ADSL enables you to lease and pay for only the bandwidth you need.

SDSL (Symmetric DSL) represents the two-wire version of HDSL—which is actually symmetric DSL, albeit a four-wire version. SDSL is also known within ANSI as HDSL2.

Essentially offering the same capabilities as HDSL, SDSL offers T1 rates (1.544 Mbps) at ranges up to 10,000 feet and is primarily designed for business applications.

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Black Box Explains... TEMPEST standard and Common Criteria (EAL4+)

Common Criteria (EAL4+) defines a common set of tests regarding the process of the design, testing, verification, and shipping of new security products. Common Criteria enables customers to assess a... more/see it nowlevel of trust in how a product has been designed, tested, built, and shipped.

TEMPEST testing, while classified, is regarded as a process that assesses the threat of data linking by various covert electromagnetic eavesdropping mechanisms. The TEMPEST designation is often required by military organizations. TEMPEST, as a security standard, pertains to technical security countermeasures, standards, and instrumentation that prevent or minimize the exploitation of vulnerable data communications equipment by technical surveillance or eavesdropping.

Both testing standards are important, they just test for different things.

TEMPEST-Secure KVM Switches
For 2 or 4 ports, with USB, and DVI-I or VGA the ServSwitch Secure KVM Switch with USB (page 382) provides control and separation of up to four PCs connected to secure and unsecure networks through just one keyboard, monitor, and mouse.

  • High port-to-port electrical isolation, which facilitates data separation (RED/BLACK).
  • NSA tested and TEMPEST approved for and by the U.S. Air Force.
  • The low radiated emissions profile meets the appropriate national requirements for conducted/radiated electromagnetic emissions.
  • Switches are permanently hard wired, preventing access from one CPU to the others or access from one network to others.
  • External tamper-evident seals make it easy to spot attempted tampering.
  • Channel-to-channel 60-dB crosstalk isolation protects against signal snooping, so software tools and applications cannot be used to access any connected computer from another connected computer.
  • Users can safely switch among as many as four computers operating at different classification levels.

  • Common Criteria Evaluation Assurance to Level 4+
    A newly developed switch, the ServSwitch Secure with USB and DVI, or VGA, or VGA and a Card Reader (pages 384–385), is being evaluated for Common Criteria Evaluation Assurance to Level 4+ (EAL4+). Common Criteria is an international standardized process for information technology security evaluation, validation, and certification. The Common Criteria scheme is supported by the National Security Agency through the National Information Assurance Program (NIAP). The ServSwitch Secure KVM Switch with USB surpasses the security profiles of most other KVM switches. Along with the tamper-evident seals and other security features already mentioned, ServSwitch Secure KVM Switch with USB models feature these security measures:

  • The flow of keyboard and mouse data is unidirectional, so it’s not possible for the computer to send data along the keyboard and mouse signaling channels.
  • Keyboard and mouse devices can only be enumerated at the keyboard and mouse ports. Any other USB peripherals connected to these ports will be prohibited from operating, preventing, for example, a USB thumb drive from uploading or downloading unauthorized data.
  • At each channel switchover, the USB host controller circuit, which controls shared peripherals, erases its entire RAM. This prevents residual data from remaining in the channel after a channel change and being transferred to another computer.
  • Every time the channel is changed, shared USB peripherals are powered down, reset, and re-enumerated.
  • Every time the channel is changed, the USB host controller is also powered down and reset, further ensuring no transfer of residual data.
  • Dedicated DDC bus and EDID memory emulation at each port prevent the shared monitor link from being used as a covert attack channel.
  • With only one selection button per channel, the ServSwitch Secure models enable direct and unambiguous channel selection.
  • Hotkey and mouse switching are excluded, preventing remote control of the switch.
  • Ports are powered through the computer’s USB ports, while the shared keyboard, mouse, and monitor are powered by the switch’s power supply. The lack of a common power supply minimizes electronic signaling.
  • The switches with card readers have additional features, including active authentication verification and active tamper detection.
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    Black Box Explains...Optical isolation and ground loops.

    Optical isolation protects your equipment from dangerous ground loops. A ground loop is a current across a conductor, created by a difference in potential between two grounded points, as in... more/see it nowequipment in two buildings connected by a run of RS-232 or other data line. When two devices are connected and their potentials are different, voltage flows from high to low by traveling through the data cable. If the voltage potential is large enough, your equipment won’t be able to handle the excess voltage and one of your ports will be damaged.

    Ground loops can also exist in industrial environments. They can be created when power is supplied to your equipment from different transformers or when someone simply turns equipment on and off. Ground loops can also occur when there is a nearby lightning strike. During an electrical storm, the ground at one location can be charged differently than the other location, causing a heavy current flow through the serial communication lines that damage components.

    You can’t test for ground loops. You don’t know you have one until a vital component fails. Only prevention works. For data communication involving copper cable, optical isolation is key.

    With optical isolation, electrical data is converted to an optical beam, then back to an electrical pulse. Because there is no electrical connection between the DTE and DCE sides, an optical isolator— unlike a surge suppressor—will not pass large sustained power surges through to your equipment. Since data only passes through the optical isolator, your equipment is protected against ground loops and other power surges. collapse


    Black Box Explains... Industrial modem benefits.

    Not all modems shuttle data in air-conditioned, climate-controlled comfort. And modems that operate in cozy environments have absolutely no business being exposed to harsh industrial conditions or to the elements.

    But... more/see it nowjust because you work in a rough-and-tumble place doesn’t mean you have to sacrifice the convenience of a good modem. Instead, you should opt for an industrial modem. There are many industrial modems built for various degrees of extremity.

    Survivability depends on reliability.
    Sure, standard modems give you access to data in remote sites or enable you to service equipment on the plant floor—and you can do all this from the convenience of your office. However, these benefits are only possible if your modem can continue to function in its environment. And since standard modems aren’t built for adverse conditions, they’re not going to be reliable.

    No penalties for interference.
    Electrical control equipment—such as motors, relays, compressors, and generators—emit electromagnetic interference (EMI) that can affect the performance and reliability of a standard telephone modem.

    EMI is emitted through power lines, the RS-232 communications cable, or through the telephone line itself. The very means of data communication, cable, is often the worst enemy of the standard modems that use it.

    An industrial modem, on the other hand, has filters and superior EMI immunity to protect itself and your data. If you build your electrical cabinets to UL® or CSA standards, remember that your modem must also conform to UL® standard 508.

    They go to extremes.
    Temperature is the biggest killer of electronic equipment in industrial environments. The heat generated by industrial equipment in sealed enclosures or where space is a premium can make the temperature as much as 50 °F higher than the surrounding environment.

    So standard modems can’t take the heat. But what about being outdoors in the other extreme, cold weather? Well, standard modems can’t take the cold either.

    If you install your equipment in remote outdoor locations, it must work on the coldest days— especially those cold days when you least want to get in the car and go to the site to repair a standard modem that froze up.

    Whether they’re placed in manufacturing environments or the great outdoors, industrial modems get the data through when you need it. They go to extremes for you.

    Heavy metal for all kinds of banging around.
    Industrial modems are built with durable metal enclosures that protect circuitry in rough conditions and ward off signal-disrupting EMI. Plus, they feature steel-bolt flanges to anchor them. In short, industrial modems can take the physical, heavy-duty punishment thrown their way.

    So where exactly can you use an industrial modem?
    • Heavy industry and manufacturing
    • Oil and gas fields
    • Refineries
    • Storage sites
    • Utility substations
    • Agricultural projects
    • Military facilities
    • Research installations
    • Water/wastewater systems

    …and another thing!
    If dedicated copper lines can’t be run through industrial environments, or if the fiber optic option is cost-prohibitive, there are also wireless industrial modems that make line-of-sight connections. If there’s a way to get the data through, industrial modems will get the job done.

    Industrial-strength assurance.
    Industrial modems remain in service for a very long time. But if you ever need a replacement that is hardware or software compatible, be assured that Black Box continues to support its products year after year—so you don’t spend your time re-engineering systems if you have to make a replacement. collapse


    Black Box Explains... Why go wireless?

    • It’s great for communicating in harsh climates or in areas where it’s expensive to run cable. Wireless solutions are well suited for use in military applications, farming, refineries, mining,... more/see it nowconstruction, and field research.
    • Because sometimes you just can’t run wire, like in historic buildings or hazmat areas.
    • When it’s physically or legally impossible to support conventional hard-wired RS-232 communications, wireless networking may be your only answer.
    • It gives you quick, temporary connections at trade shows, and fast reconfigurations—even troubleshooting or remote field testing.
    • It provides reliable disaster relief when all else fails! Count on wireless networks to maintain mission-critical links when disaster strikes.
    • It’s more affordable, more reliable, and faster than ever before.
    • Best of all, no FCC licensing required! collapse


    Black Box Explains... Smart Serial Interface

    Smart Serial is the Cisco router interface. It uses a space-saving 26-pin connector that automatically detects RS-232, RS-449, RS-530, X.21, and V.35 interfaces for both DTE and DCE devices based... more/see it nowon the type of cable used.

    Smart Serial connectors can be found on Smart Serial cables and on the dual-serial-port WAN interface cards used in Cisco 2600 and 1720 series routers. The cables feature a Smart Serial connector on one end and a standard cable connector (such as DB25 or V.35) on the other end. The Smart Serial connector attaches to the dual-serial-port WAN interface card.

    Each port on the WAN interface card features a Smart Serial connector. Ports can be configured independently to support two different physical interfaces. For example, you can run RS-232 cable to one port and RS-449 cable to the other port using a single WAN interface card.

    What if you need to replace that RS-232 cable with V.35 cable? Just plug a Smart Serial–V.35 cable into the port. Because any Smart Serial connector on the WAN interface card attaches to any Smart Serial cable connector, no additional interface or adapter is necessary. Changing the configuration of your network is literally a snap! collapse


    Black Box Explains...16850 UART.

    The 16850 Universal Asynchronous Receiver/Transmitter (UART) features a 128-byte First In First Out (FIFO) buffer. When implemented with the appropriate onboard drivers and receivers, it enables your onboard serial ports... more/see it nowto achieve sustained data rates of up to 460.8 kbps.

    The 16850 UART includes automatic handshaking (RTS/CTS) and automatic RS-485 line control. It also features external clocking for isochronous applications, a performance enhancement not offered by earlier UARTs. collapse


    Black Box Explains…Digital Visual Interface (DVI) connectors.

    The DVI (Digital Video Interface) technology is the standard digital transfer medium for computers while the HDMI interface is more commonly found on HDTVs, and other high-end displays.

    The Digital... more/see it nowVisual Interface (DVI) standard is based on transition-minimized differential signaling (TMDS). There are two DVI formats: Single-Link and Dual-Link. Single-link cables use one TMDS-165 MHz transmitter and dual-link cables use two. The dual-link cables double the power of the transmission. A single-link cable can transmit a resolution ?of 1920 x 1200 vs. 2560 x 1600 for a dual-link cable.

    There are several types of connectors: ?DVI-D, DVI-I, DVI-A, DFP, and EVC.

  • DVI-D is a digital-only connector for use between a digital video source and monitors. DVI-D eliminates analog conversion and improves the display. It can be used when one or both connections are DVI-D.
  • DVI-I (integrated) supports both digital and analog RGB connections. It can transmit either a digital-to-digital signals or an analog-to-analog signal. It is used by some manufacturers on products instead of separate analog and digital connectors. If both connectors are DVI-I, you can use any DVI cable, but a DVI-I is recommended.
  • DVI-A (analog) is used to carry an DVI signal from a computer to an analog VGA device, such as a display. If one or both of your connections are DVI-A, use this cable. ?If one connection is DVI and the other is ?VGA HD15, you need a cable or adapter ?with both connectors.
  • DFP (Digital Flat Panel) was an early digital-only connector used on some displays.
  • EVC (also known as P&D, for ?Plug & Display), another older connector, handles digital and analog connections.
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    Black Box Explains...Rack units.

    A Rack Unit is abbreviated as U. One Rack Unit (1U) is equal to 1.75" (4.44 cm).

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