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Black Box Explains...RS-232.

RS-232, also known as RS-232C and TIA/EIA-232-E, is a group of electrical, functional, and mechanical specifications for serial interfaces between computers, terminals, and peripherals. The RS-232 standard was developed by... more/see it nowthe Electrical Industries Association (EIA), and defines requirements for connecting data communications equipment (DCE)—modems, converters, etc.—and data terminal equipment (DTE)—computers, controllers, etc.) devices. RS-232 transmits data at speeds up to 115 Kbps and over distances up to 50 feet (15.2 m).

The standard, which is functionally equivalent to ITU V.24/V.28, specifies the workings of the interface, circuitry, and connector pinning. Both sync and async binary data transmission fall under RS-232. Although RS-232 is sometimes still used to transmit data from PCs to peripheral devices, the most common uses today are for network console ports and for industrial devices.

Even though RS-232 is a “standard,” you can’t necessarily expect seamless communication between two RS-232 devices. Why? Because different devices have different circuitry or pinning, and different wires may be designated to perform different functions.

The typical RS-232 connector is DB25, but some PCs and other data communication devices have DB9 connectors and many newer devices have RJ-45 RS-232 ports. To connect 9-pin PC ports or RJ-45 to devices with 25-pin connectors, you will require a simple adapter cable. collapse


Black Box Explains...DIN rail usage.

DIN rail is an industry-standard metal rail, usually installed inside an electrical enclosure, which serves as a mount for small electrical devices specially designed for use with DIN rails. These... more/see it nowdevices snap right onto the rails, sometimes requiring a set screw, and are then wired together.

Many different devices are available for mounting on DIN rails: terminal blocks, interface converters, media converter switches, repeaters, surge protectors, PLCs, fuses, or power supplies, just to name a few.

DIN rails are a space-saving way to accommodate components. And because DIN rail devices are so easy to install, replace, maintain, and inspect, this is an exceptionally convenient system that has become very popular in recent years.

A standard DIN rail is 35 mm wide with raised-lip edges, its dimensions outlined by the Deutsche Institut für Normung, a German standardization body. Rails are generally available in aluminum or steel and may be cut for installation. Depending on the requirements of the mounted components, the rail may need to be grounded. collapse


Black Box Explains...How fiber is insulated for use in harsh environments.

Fiber optic cable not only gives you immunity to interference and greater signal security, but it’s also constructed to insulate the fiber’s core from the stress associated with use in... more/see it nowharsh environments.

The core is a very delicate channel that’s used to transport data signals from an optical transmitter to an optical receiver. To help reinforce the core, absorb shock, and provide extra protection against cable bends, fiber cable contains a coating of acrylate plastic.

In an environment free from the stress of external forces such as temperature, bends, and splices, fiber optic cable can transmit light pulses with minimal attenuation. And although there will always be some attenuation from external forces and other conditions, there are two methods of cable construction to help isolate the core: loose-tube and tight-buffer construction.

In a loose-tube construction, the fiber core literally floats within a plastic gel-filled sleeve. Surrounded by this protective layer, the core is insulated from temperature extremes, as well as from damaging external forces such as cutting and crushing.

In a tight-core construction, the plastic extrusion method is used to apply a protective coating directly over the fiber coating. This helps the cable withstand even greater crushing forces. But while the tight-buffer design offers greater protection from core breakage, it’s more susceptible to stress from temperature variations. Conversely, while it’s more flexible than loose-tube cable, the tight-buffer design offers less protection from sharp bends or twists. collapse


Black Box Explains...Power over Ethernet (PoE).

What is PoE?
The seemingly universal network connection, twisted-pair Ethernet cable, has another role to play, providing electrical power to low-wattage electrical devices. Power over Ethernet (PoE) was ratified by the... more/see it nowInstitute of Electrical and Electronic Engineers (IEEE) in June 2000 as the 802.3af-2003 standard. It defines the specifications for low-level power delivery—roughly 13 watts at 48 VDC—over twisted-pair Ethernet cable to PoE-enabled devices such as IP telephones, wireless access points, Web cameras, and audio speakers.

Recently, the basic 802.3af standard was joined by the IEEE 802.3at PoE standard (also called PoE+ or PoE plus), ratified on September 11, 2009, which supplies up to 25 watts to larger, more power-hungry devices. 802.3at is backwards compatible with 802.3af.

How does PoE work?
The way it works is simple. Ethernet cable that meets CAT5 (or better) standards consists of four twisted pairs of cable, and PoE sends power over these pairs to PoE-enabled devices. In one method, two wire pairs are used to transmit data, and the remaining two pairs are used for power. In the other method, power and data are sent over the same pair.

When the same pair is used for both power and data, the power and data transmissions don’t interfere with each other. Because electricity and data function at opposite ends of the frequency spectrum, they can travel over the same cable. Electricity has a low frequency of 60 Hz or less, and data transmissions have frequencies that can range from 10 million to 100 million Hz.

Basic structure.
There are two types of devices involved in PoE configurations: Power Sourcing Equipment (PSE) and Powered Devices (PD).

PSEs, which include end-span and mid-span devices, provide power to PDs over the Ethernet cable. An end-span device is often a PoE-enabled network switch that’s designed to supply power directly to the cable from each port. The setup would look something like this:

End-span device → Ethernet with power

A mid-span device is inserted between a non-PoE device and the network, and it supplies power from that juncture. Here is a rough schematic of that setup:

Non-PoE switch → Ethernet without PoE → Mid-span device → Ethernet with power

Power injectors, a third type of PSE, supply power to a specific point on the network while the other network segments remain without power.

PDs are pieces of equipment like surveillance cameras, sensors, wireless access points, and any other devices that operate on PoE.

PoE applications and benefits.
• Use one set of twisted-pair wires for both data and low-wattage appliances.
• In addition to the applications noted above, PoE also works well for video surveillance, building management, retail video kiosks, smart signs, vending machines, and retail point-of-information systems.
• Save money by eliminating the need to run electrical wiring.
• Easily move an appliance with minimal disruption.
• If your LAN is protected from power failure by a UPS, the PoE devices connected to your LAN are also protected from power failure.
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Black Box Explains...Link loss.

Media converters solve the problem of connecting different media types in mixed-media networks. In order to comply with IEEE standards, they implement IEEE data-encoding rules and the Link Integrity Test.

For... more/see it nowa twisted-pair segment, a link is a signal sent by the converters when the cable is in use. If no Link Integrity Test signal is received, the connected device assumes that the link is lost.

With fiber cable, a connected device checks a line by monitoring the Link Integrity Test signal from the converter and the power of the light being received. If the light’s power drops below a certain threshold, the link is lost. In either case, link loss usually results from a broken cable, which is the cause of approximately 70% of all LAN problems.

Link loss is often indicated by an LED on a connected network device. You can also monitor a link with network-management software, such as SNMP, which sends a TRAP (alert) to the management workstation when the link is lost.

Media converters actually function as two separate Multistation Access Units (MAUs). For example, one monitor is a twisted-pair segment and one monitor is a fiber segment. If a fiber cable is broken and the link is lost, a network manager on the twisted-pair end won’t know there’s a problem until users on the fiber side report it.

To solve this problem, Black Box® Modular Media Converters feature a unique Link-Loss capability. This enables the link status on one segment to reflect the link status of the other segment. So if the link is lost on the fiber side, the link is disabled on the UTP segment as well. And the converters will send an SNMP TRAP indicating the loss of link to the management workstation. collapse


Black Box Explains... How Autocross conversion can work for you.

When using media converters with 10BASE-T or 100BASE-TX cable, you may need to connect your converter to a non-hub device such as a PC or printer.

According to IEEE 802.3 Ethernet... more/see it nowstandards, media converters originally needed a specially pinned crossover cable to connect to PCs. The crossover cable matches the devices’ transmit and receive pins. Now there are media converters that use straight-pinned 10BASE-T patch cable but incorporate an uplink or crossover connection—a switch on the converter that’s set to support the PC-to-converter connection. By setting the uplink switch to “cross,” the converter’s internal mechanism crosses the pins on the RJ-45 connector to simulate a crossover cable.

Autocross conversion eliminates both the need to crosspin cables and set an uplink switch. It adapts to the pin assignment of the twisted-pair cable whether it’s crossed or uncrossed. And because it senses the pin configuration of any cable pinned to Ethernet specifications, it adjusts automatically without user configuration. collapse


Black Box Explains...Gigabit Ethernet.

As workstations and servers migrated from ordinary 10-Mbps Ethernet to 100-Mbps speeds, it became clear that even greater speeds were needed. Gigabit Ethernet was developed for an even faster Ethernet... more/see it nowstandard to handle the network traffic generated on the server and backbone level by Fast Ethernet. Gigabit Ethernet delivers an incredible 1000 Mbps (or 1 Gbps), 100 times faster than 10BASE-T. At that speed, Gigabit Ethernet can handle even the traffic generated by campus network backbones. Plus it provides a smooth upgrade path from 10-Mbps Ethernet and 100-Mbps Fast Ethernet at a reasonable cost.

Compatibility
Gigabit Ethernet is a true Ethernet standard. Because it uses the same frame formats and flow control as earlier Ethernet versions, networks readily recognize it, and it’s compatible with older Ethernet standards. Other high-speed technologies (ATM, for instance) present compatibility problems such as different frame formats or different hardware requirements.

The primary difference between Gigabit Ethernet and earlier implementations of Ethernet is that Gigabit Ethernet almost always runs in full-duplex mode, rather than the half-duplex mode commonly found in 10- and 100-Mbps Ethernet.

One significant feature of Gigabit Ethernet is the improvement to the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) function. In half-duplex mode, all Ethernet speeds use the CSMA/CD access method to resolve contention for shared media. For Gigabit Ethernet, CSMA/CD has been enhanced to maintain the 200-meter (656.1-ft.) collision diameter.

Affordability and adaptability
You can incorporate Gigabit Ethernet into any standard Ethernet network at a reasonable cost without having to invest in additional training, cabling, management tools, or end stations. Because Gigabit Ethernet blends so well with your other Ethernet applications, you have the flexibility to give each Ethernet segment exactly as much speed as it needs—and if your needs change, Ethernet is easily adaptable to new network requirements.

Gigabit Ethernet is the ideal high-speed technology to use between 10-/100-Mbps Ethernet switches or for connection to high-speed servers with the assurance of total compatibility with your Ethernet network.

When Gigabit Ethernet first appeared, fiber was crucial to running Gigabit Ethernet effectively. Since then, the IEEE802.3ab standard for Gigabit over Category 5 cable has been approved, enabling short stretches of Gigabit speed over existing copper cable. Today, you have many choices when implementing Gigabit Ethernet:

1000BASE-X
1000BASE-X refers collectively to the IEEE802.3z standards: 1000BASE-SX, 1000BASE-LX, and 1000BASE-CX.

1000BASE-SX
The “S“ in 1000BASE-SX stands for “short.“ It uses short wavelength lasers, operating in the 770- to 860-nanometer range, to transmit data over multimode fiber. It’s less expensive than 1000BASE-LX, but has a much shorter range of 220 meters over typical 62.5-µm multimode cable.

1000BASE-LX
The “L“ stands for “long.“ It uses long wavelength lasers operating in the wavelength range of 1270 to 1355 nanometers to transmit data over single-mode fiber optic cable. 1000BASE-LX supports up to 550 meters over multimode fiber or up to 10 kilometers over single-mode fiber.

1000BASE-CX
The “C“ stands for “copper.“ It operates over special twinax cable at distances of up to 25 meters. This standard never really caught on.

Gigabit over CAT5—1000BASE-TX
The 802.3ab specification, or 1000BASE-TX, enables you to run IEEE-compliant Gigabit Ethernet over copper twisted-pair cable at distances of up to 100 meters of CAT5 or higher cable.

Gigabit Ethernet uses all four twisted pairs within the cable, unlike 10BASE-T and 100BASE-TX, which only use two of the four pairs. It works by transmitting 250 Mbps over each of the four pairs in 4-pair cable. collapse


Black Box Explains...DIN rails.

A DIN rail is an industry-standard metal rail, usually installed inside an electrical enclosure, which serves as a mount for small electrical devices specially designed for use with DIN rails.... more/see it nowThese devices snap right onto the rails, sometimes requiring a set screw, and are then wired together.

Many different devices are available for mounting on DIN rails: terminal blocks, interface converters, media converter switches, repeaters, surge protectors, PLCs, fuses, or power supplies, just to name a few.

DIN rails are a space-saving way to accommodate components. And because DIN rail devices are so easy to install, replace, maintain, and inspect, this is an exceptionally convenient system that has become very popular in recent years.

A standard DIN rail is 35-mm wide with raised-lip edges, its dimensions outlined by the Deutsche Institut für Normung, a German standardization body. Rails are generally available in aluminum or steel and may be cut for installation. Depending on the requirements of the mounted components, the rail may need to be grounded. collapse


Black Box Explains...802.3ah.

802.3ah, also called Ethernet in the First Mile (EFM), is a new Ethernet standard designed to compete with standards such as DSL and cable modem in delivering broadband access to... more/see it nowhomes.

The 802.3ah specification covers point-to-point copper, point-to-point fiber, and point-to-multipoint fiber.

Ethernet in the First Mile over Copper (EFMC)
This point-to-point specification for copper wire takes advantage of DSL technology to send Ethernet over one pair of copper wires at 10 Mbps for 750 meters or 2 Mbps for 2700 meters.

Ethernet in the First Mile over Fiber (EFMF)
This point-to-point specification for single-mode, single-strand or single-mode, duplex fiber sends Ethernet at speeds of 100 Mbps or 1 Gbps up to 10 kilometers. It includes an optional extended temperature range from -40 to 185° F (-40 to 85° C) for outdoor use.

Ethernet in the First Mile over Passive Optical Networks (EPON)
This point-to-multipoint specification for fiber uses an optical splitter to divide the Ethernet signal into separate strands that go to individual subscribers. This enables an ISP to link many subscribers to a single uplink fiber without using active components in the field.

802.3ah includes the OAM specification, which provides utilities for monitoring and troubleshooting Ethernet links remotely, a capability vital for carrier-class deployment. OAM protocols address discovery, link monitoring, remote fault signaling, and remote loopback.

OAM is managed in-band but takes up very little bandwidth so network performance is not noticeably affected. OAM itself is not affected by VLANs or port-access restrictions. collapse


Black Box Explains...Why media converters need SNMP.

The number of Ethernet switches and fiber optic segments being added to Ethernet networks keeps increasing. And as long as most Ethernet switches are only available with 10BASE-T and 100BASE-TX... more/see it nowinterfaces, media converters will remain in demand.

Until now, a failure on the network could go unnoticed. Once a failure was detected, it could take a long time to isolate it, especially if a technician had to be sent to the site. But media converters with SNMP eliminate some of the guesswork.

With SNMP, the IS manager can detect a failure, isolate it to a specific port, and determine what hardware is required to repair it. A technician can then be sent directly to the right place to fix faulty hardware or repair a broken cable.

SNMP enables you to set up alarms or traps when a link is down. You can turn features on and off from a central terminal, so there’s no need to leave your desk. You can also monitor power supplies and replace them without interrupting service. SNMP management reduces the time and money it takes to get your network up and running again. The users on your network will notice—and appreciate—the improved service and reliability. collapse

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