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.
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 its 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 needsand 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 refers collectively to the IEEE802.3z standards: 1000BASE-SX, 1000BASE-LX, and 1000BASE-CX.
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. Its less expensive than 1000BASE-LX, but has a much shorter range of 220 meters over typical 62.5-µm multimode cable.
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.
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...Layer 2, 3, and 4 switches.
... more/see it now
E-Mail, Diagnostics, Word Processing, Database
Shells and Gateway Workstation Software
TR=Token Ring; A=ARCNET®; P=PhoneNET®
With the rapid development of computer networks over the last decade, high-end switching has become one of the most important functions on a network for moving data efficiently and quickly from one place to another.
Here’s how a switch works: As data passes through the switch, it examines addressing information attached to each data packet. From this information, the switch determines the packet’s destination on the network. It then creates a virtual link to the destination and sends the packet there.
The efficiency and speed of a switch depends on its algorithms, its switching fabric, and its processor. Its complexity is determined by the layer at which the switch operates in the OSI (Open Systems Interconnection) Reference Model (see above).
OSI is a layered network design framework that establishes a standard so that devices from different vendors work together. Network addresses are based on this OSI Model and are hierarchical. The more details that are included, the more specific the address becomes and the easier it is to find.
The Layer at which the switch operates is determined by how much addressing detail the switch reads as data passes through.
Switches can also be considered low end or high end. A low-end switch operates in Layer 2 of the OSI Model and can also operate in a combination of Layers 2 and 3. High-end switches operate in Layer 3, Layer 4, or a combination of the two.
Layer 2 Switches (The Data-Link Layer)
Layer 2 switches operate using physical network addresses. Physical addresses, also known as link-layer, hardware, or MAC-layer addresses, identify individual devices. Most hardware devices are permanently assigned this number during the manufacturing process.
Switches operating at Layer 2 are very fast because they’re just sorting physical addresses, but they usually aren’t very smart—that is, they don’t look at the data packet very closely to learn anything more about where it’s headed.
Layer 3 Switches (The Network Layer)
Layer 3 switches use network or IP addresses that identify locations on the network. They read network addresses more closely than Layer 2 switches—they identify network locations as well as the physical device. A location can be a LAN workstation, a location in a computer’s memory, or even a different packet of data traveling through a network.
Switches operating at Layer 3 are smarter than Layer 2 devices and incorporate routing functions to actively calculate the best way to send a packet to its destination. But although they’re smarter, they may not be as fast if their algorithms, fabric, and processor don’t support high speeds.
Layer 4 Switches (The Transport Layer)
Layer 4 of the OSI Model coordinates communications between systems. Layer 4 switches are capable of identifying which application protocols (HTTP, SNTP, FTP, and so forth) are included with each packet, and they use this information to hand off the packet to the appropriate higher-layer software. Layer 4 switches make packet-forwarding decisions based not only on the MAC address and IP address, but also on the application to which a packet belongs.
Because Layer 4 devices enable you to establish priorities for network traffic based on application, you can assign a high priority to packets belonging to vital in-house applications such as Peoplesoft, with different forwarding rules for low-priority packets such as generic HTTP-based Internet traffic.
Layer 4 switches also provide an effective wire-speed security shield for your network because any company- or industry-specific protocols can be confined to only authorized switched ports or users. This security feature is often reinforced with traffic filtering and forwarding features. collapse
Black Box Explains...Remote Access Servers.
Remote access servers (RASs) are high-level intelligent devices with multiple asynchronous communication ports that connect to modems and provide remote users with dial-in access to a central site network.
You... more/see it nowcan configure your RAS to operate via remote control or remote node access.
Remote control operation enables remote users to send keystroke data and receive screen output from the central site. The actual processing takes place inside the communication server. Remote node access enables the remote user to become a network node and all remote workstations to function as if they were connected locally.
A fixed-port remote access server has a network connection to your LAN and one or more asynchronous RS-232 ports that connect to external modems. It usually comes equipped with 4, 8, or 16 async ports and is easy to install, support, and maintain. These devices are ideal for traveling workers who dont have a remote office but who need connections to the corporate network for short periods of time.
For configuration flexibility, scalability, and remote wide-area connection options, choose a modular remote-access server that you can change as your network grows. Most modular RASs accept a variety of modules, including:
• High-density async RS-232 modules that connect to external modems or ISDN terminal adapters. These modules typically have eight or more ports.
• High-density modem modules that usually incorporate eight modems on a single card, enabling you to consolidate equipment costs, increase reliability, and simplify management.
• Digital modules that enable you to make direct connections to high-speed digital lines. Instead of using multiple dialup lines, you can use these devices to bring a single high-speed digital phone line—known as a channelized T1— to your equipment.
The best way to determine what type of RAS you need—or whether you need a router or a RAS—is to identify what remote solution will meet your connectivity requirements. If you’re not sure what you need, contact our FREE Tech Support. 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...DIN rail.
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...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 wont 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 cant test for ground loops. You dont 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 suppressorwill 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... 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 cables 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 eyes 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 its 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... Using fiber optics for KVM extension.
If you‘re sending KVM signals between buildings for an extended distance, in areas supplied by different power sources, in an electrically noisy environment, or where data security is a big... more/see it nowconcern, you need to use a fiber optic-based KVM extender.
Optical fiber is an ideal transmission medium not only for backbone and horizontal connection, but also for workstation-to-backracked CPU or server links. It works very well in applications where you need to transfer large, bandwidth-consuming data files over long distances, and where you require immunity from electrical interference or data theft.
The choice for extraordinary reach.
Fiber doesn’t have the 100-meter (328-ft.) distance limitation that UTP copper without a booster does. Fiber distances can range from 300 meters (984.2 ft.) to 70 kilometers (24.8 mi.), depending on the cable, wavelength, and network. With fiber-based KVM extenders, the transmitter converts conventional data signals into a modulated light beam, then transports the beam via the fiber to a receiver, which converts the light back into electrical signals.
Many newer fiber-based KVM extenders support both analog and digital transmission. Often, they work by digitizing video output from a local CPU, then sending it across fiber link to a remote unit, which converts it back to the original analog signal. In many cases, one fiber of the fiber pair transmits monitor video serially and the second fiber sends remote mouse and keyboard information back to the local CPU.
The choice for ensuring signal integrity.
Because fiber is made of glass, which is an insulator, no electric current can flow through. It’s immune to electromagnetic interference and radio-frequency interference (EMI/RFI), crosstalk, impedance problems, and more. This is why fiber-based KVM extenders are beneficial to users in process control, engineering, utility, and factory automation applications. The users need to keep critical information safe and secure off the factory floor but be able to access that data from workstations and control consoles within the harsh environments. Plus, fiber is also less susceptible to temperature fluctuations than copper is, and it can be submerged ?in water.
The choice for greater signal fidelity.
Fiber-based KVM extenders can carry more information with greater fidelity than copper-based ones can. For this reason, they’re ideal for high-data-rate systems in which multimedia workstations are used.
Newer KVM extenders enable you to send both DVI and keyboard and mouse signals over the same fiber cable, transmitting video digitally for zero signal loss. This way, you can get HD-quality resolution even at very long distances from the source. Users in university or government R&D, broadcasting, healthcare—basically anyone who depends on detailed image rendering—can benefit from this technology.
The choice for data security.
Plus, your data is safe when using fiber to connect a workstation with a CPU or server under lock and key. It doesn’t radiate signals and is extremely difficult to tap. If the cable is tapped, it’s very easy to monitor because the cable leaks light, causing the entire system to fail. If an attempt is made to break the physical security of your fiber system, you’ll know it.
Many IT managers in military, government, finance, and healthcare choose fiber-based KVM extenders for this very reason. Plus corporations, aware of rising data privacy concerns over customer billing information and the need to protect intellectual property, use this type of extension technology in their offices, too.
Considerations for fiber-based KVM extension.
Before selecting a fiber-based KVM extender, it’s important to know the limitations of your system. You need to know where couplers, links, interconnect equipment, and other devices are going to be placed. If it’s a longer run, you have to determine whether multimode or single-mode fiber cable is needed.
The most important consideration in planning cabling for fiber-based KVM extension is the power budget specification of device connection. The receiver at the remote end has to receive the light signal at a certain level. This value, called the loss budget, tells you the amount of loss in decibels (dB) that can be present in the link between the two devices before the units fail to perform properly.
Specifically, this value takes the fiber type (multimode or single-mode) and wavelength you intend to use—and the amount of expected in-line attenuation—into consideration. This is the decrease of signal strength as it travels through the fiber cable. In the budget loss calculation, you also have to account for splices, patch panels, and connectors, where additional dBs may lost in the entire end-to-end fiber extension. If the measured loss is less than the number calculated by your loss budget, your installation is good.
Testers are available to determine if the fiber cabling supports your intended application. You can measure how much light is going to the other end of the cable. Generally, these testers give you the results in dB lost, which you then compare to the loss budget to determine your link loss margin.
Also, in some instances, particularly when using single-mode fiber to drive the signal farther, the signal may be too strong between connected devices. This causes the light signal to reflect back down the fiber cable, which can corrupt data, result in a faulty transmission, and even damage equipment. To prevent this, use fiber attenuators. They’re used with ?single-mode fiber optic devices and cable to filter the strength of the fiber optic signal from the transmitter’s LED output so it doesn’t overwhelm the receiver. Depending on the type of attenuator attached to the devices at each end of the link, you can diminish the strength of the light signal a variable amount by a certain number of decibels.
Need help calculating your budget loss? Call our FREE Tech Support. If necessary, they can even recommend a fusion splicing fiber kit, a fiber tester, or a signal attenuator for your specific requirements.