A command-line symbol used for redirection that is supported by all versions of Microsoft Windows. Redirection allows you to direct the output of a Windows command to something other than the screen. The > symbol is generally referred to as the redirection symbol.
How It Works
Normally, Windows sends the output of a command to the screen. For example, suppose you open a command prompt on a machine running Windows 2000 Server with Windows Internet Name Service (WINS) installed on it and you type
dir c:\winnt\system32\wins
Graphic 0-1.The screen output of a command such as dir can be redirected to a text file.
The typical output displayed on the screen after executing such a command might be a directory listing such as the one shown in the screen capture. With the redirection symbol, however, such a command output can be redirected to a text file or to a printer. For example, if you enter the command
dir c:\winnt\system32\wins > stuff.txt
the command creates a text file called stuff.txt and sends its output to the file. If the file stuff.txt already exists, it will be overwritten. The contents of the file will look exactly like the output on the screen shown in the illustration. You can then print out the file, send it as an e-mail attachment, or archive it for documentation purposes.
TIP
To prevent the output of a command from being displayed on the screen (for example, when running a batch file), redirect the command to nul. For example, in a logon script that synchronizes the clocks of servers with server7, use
net time \\server7 /set /yes > nul
If you want to redirect the output of a series of commands to the same file cumulatively, use the >> symbol to append redirected output to an existing file instead of overwriting it.
|
A command-line symbol used for piping that is supported by all versions of Microsoft Windows. Piping allows you to make the output of one Windows command the input for another command. The | symbol is generally referred to as the pipe symbol.
How It Works
Normally, Windows sends the output of a command to the screen. For example, suppose you open a command prompt on a machine running Windows 2000 Server and you type the command
tree c:\
The screen will display the entire directory tree of your C drive, starting with the root. Because there is more than one screen of information, the screen will scroll. To view the information more conveniently, pipe the output of the above command into the more command. The more command is a filter command that displays one screen of information at a time, waiting for you to press any key to view the next screen. You would thus type the following command
tree c:\ | more
%SystemRoot%
The directory where the core Microsoft Windows NT and Windows 2000 operating system files are stored. In a default installation of Windows NT and Windows 2000, the operating system files are located in C:\Winnt. You can specify different locations for these files when you set up Windows NT or Windows 2000.
The symbol %SystemRoot% is an environment variable that can be used in Windows commands at the command line or in batch scripts such as logon scripts. (Windows NT and Windows 2000 are case insensitive: %SYSTEMROOT%, %SystemRoot%, and %systemroot% are identical.) For example, if your current directory during a command-line session on a machine running Windows NT is
C:\Inetpub\wwwroot
and you want to change to the directory where the Windows NT operating system files are located, you can type
cd %systemroot%
3.1 kHz bearer service
A service provided by some telephone companies (telcos) for transmitting data over voice trunk lines. This service is sometimes called data-over-voice (DOV). When supporting 3.1 kHz bearer service communications, telco switches must have their trunk-line echo cancellators turned off because echo cancellation will corrupt data transmission when sent over voice lines. This service is a legacy telecommunications technology that is no longer widely implemented.
5-4-3 rule
A specification describing limitations for constructing certain kinds of Ethernet networks. The 5-4-3 rule applies specifically to Ethernet networks based on either the thinnet or thicknet cabling option.
Graphic 0-2.Five segments, four repeaters, and three populated segments.
How It Works
According to the Ethernet specifications, thinnet (or thicknet) Ethernet network segments can be joined using repeaters to form larger networks, but there are limitations on how you can do this. The maximum number of segments you can join is five. To join these segments, you need to use four repeaters because Ethernet typically uses a bus topology in which all segments are joined linearly. However, in this configuration, no more than three of the segments can actually have computers attached to them, leaving two segments that are used only for extending distances rather than hosting computers. These two unpopulated segments are called inter-repeater links. You should not violate this rule when implementing Ethernet networks; otherwise, unreliable network communications might result.
8.3 filename
The file naming convention used by the legacy MS-DOS and Microsoft Windows 3. x operating systems. 8.3 filenames use the following naming convention for file and directory names:
Up to eight characters can be used for the actual name of the file.
Up to three characters can be used for a filename extension (optional).
A period separates the filename from the extension (if there is one).
The reason for the file naming limitation on these platforms has to do with the way the FAT file system was designed. The file allocation table (FAT) allocates only enough space for an eight-character name followed by a three-character extension. The extension identifies the type of program that can open or run the file. For example, the file resume.doc would be identified to the operating system as a file that can be opened using Microsoft Word, since the .doc extension is registered by the operating system as the extension for Word documents.
More recent versions of Windows such as Windows 95, Windows 98, Windows NT, and Windows 2000 use long filenames (LFNs), which are more descriptive than the shorter ones.
10Base2
A type of standard for implementing Ethernet networks. 10Base2 is sometimes referred to as thinnet (or “thin coax”) because it uses thin coaxial cabling for connecting stations to form a network. 10Base2 supports a maximum bandwidth of 10 Mbps, but in actual networks, the presence of collisions reduces this to more like 4 to 6 Mbps. 10Base2 is based on the 802.3 specifications of Project 802 developed by the Institute of Electrical and Electronic Engineers (IEEE).
Graphic 0-3.A 10Base2 network.
How It Works
10Base2 networks are wired together in a bus topology, in which individual stations (computers) are connected directly to one long cable. The maximum length of any particular segment of a 10Base2 network is 185 meters. If distances longer than this are required, two or more segments must be connected using repeaters. Altogether, there can be a total of five segments connected using four repeaters, as long as only three of the segments have stations attached to them. This is referred to as the 5-4-3 rule.
A 10Base2 segment should have no more than 30 stations wired to it. The minimum distance between these stations must be 0.5 meters. Stations are attached to the cable using BNC connectors, and the ends of the thinnet cabling have BNC cable connectors soldered or crimped to them.
The designation 10Base2 comes from the speed of the network (10 Mbps), the signal transmission method (baseband transmission), and the maximum segment length (185 meters, rounded off to 200 with the zeros removed).
NOTE
10Base2 networks are not implemented much anymore for two reasons. First, because their speed is limited to 10 Mbps, the networks perform poorly in today’s bandwidth-hungry, Internet-connected world. Second, 10Base2 networks have a single point of failure—the long, linear bus cable used to connect the stations. A single break or loose connection brings down the entire network, and every cable segment and station connection must be checked to determine the problem. If you are wiring an office for a small LAN with low bandwidth requirements, use 10BaseT instead. For moderate to high bandwidth requirements, try using Fast Ethernet instead.
TIP
The two ends of a 10Base2 bus must be properly terminated. If they are not, signals will bounce and network communications will be impossible.
See also 10Base5, 10BaseF, 10BaseT, Ethernet
10Base5
A type of standard for implementing Ethernet networks. 10Base5 is sometimes referred to as thicknet because it uses thick coaxial cabling for connecting stations to form a network. Another name for 10Base5 is Standard Ethernet because it was the first type of Ethernet to be implemented. 10Base5 supports a maximum bandwidth of 10 Mbps, but in actual networks, the presence of collisions reduces this to more like 4 to 6 Mbps. 10Base5 is based on the 802.3 specifications of Project 802 developed by the Institute of Electrical and Electronic Engineers (IEEE).
How It Works
10Base5 networks are wired together in a bus topology—that is, in a linear fashion using one long cable. The maximum length of any particular segment of a 10Base5 network is 500 meters, hence the 5 in 10Base5. If distances longer than this are required, two or more segments must be connected using repeaters. Altogether, there can be a total of five segments connected using four repeaters, as long as only three of the segments have stations (computers) attached to them. This is referred to as the 5-4-3 rule.
A 10Base5 segment should have no more than 100 stations wired to it. These stations are not connected directly to the thicknet cable as in 10Base2 networks. Instead, a transceiver is attached to the thicknet cable, usually using a cable-piercing connector called a vampire tap. From the transceiver, a drop cable is attached, which then connects to the network interface card (NIC) in the computer. The minimum distance between transceivers attached to the thicknet cable is 2.5 meters, and the maximum length for a drop cable is 50 meters. Thicknet cable ends have N-series connectors soldered or crimped on them for connecting segments together.
10Base5 networks were often used as backbones for large networks. In a typical configuration, transceivers on the thicknet backbone would attach to repeaters, which would join smaller thinnet segments to the thicknet backbone. In this way, a combination of 10Base5 and 10Base2 standards could support sufficient numbers of stations for a moderately large company.
NOTE
10Base5 networks are legacy networks that are no longer implemented, although some companies might choose to maintain them for cost reasons. The complexity and bandwidth limitations of 10Base5 networks render them obsolete. If you are wiring an office for a small LAN with low bandwidth requirements, use 10BaseT instead. For moderate to high bandwidth requirements, try using Fast Ethernet. If you are implementing a backbone for today’s high-speed enterprise networks, try using Gigabit Ethernet, Fiber Distributed Data Interface (FDDI), or some other advanced technology.
TIP
The two ends of a 10Base5 bus must be properly terminated. If they are not, signals will bounce and network communications will be impossible.
See also 10Base2, 10BaseF, 10BaseT, Ethernet
10BaseF
A type of standard for implementing Ethernet networks. 10BaseF is different from other 10-Mbps Ethernet technologies because it uses fiber-optic cabling instead of copper unshielded twisted-pair (UTP) cabling. 10BaseF is based on the 802.3 specifications of Project 802 developed by the Institute of Electrical and Electronic Engineers (IEEE).
How It Works
10BaseF is similar to 10BaseT in that each station is wired into a fiber-optic hub in a star topology to form the network. The maximum length of any segment of 10BaseF fiber-optic cabling is 2 kilometers. The recommended cabling type for 10BaseF networks is 62.5-micron diameter fiber-optic cabling. This cable can be terminated with either ST connectors or SMA connectors, depending on the vendor and the hub configuration. Two-strand multimode fiber-optic cabling is used, with one strand allotted for transmitting data and the other for receiving data.
The 10BaseF standard actually consists of three separate standards describing different media specifications:
10BaseFB: Defines how the synchronous data transmission occurs over the fiber-optic cabling. Using 10BaseFB segments, you can cascade or link synchronous fiber-optic hubs in configurations that are longer than traditional 10BaseT Ethernet networks and contain up to 1024 stations. This standard is more expensive and is not as widely implemented as 10BaseFL.
10BaseFL: Defines the characteristics of the fiber-optic link between the nodes and the hub or concentrator. 10BaseFL replaces the older standard for fiber-optic link segments, Fiber-Optic Inter-Repeater Link (FOIRL) segments, which was developed in the 1980s. 10BaseFL is the most commonly implemented version of 10BaseF.
10BaseFP: Defines the implementation of a star topology that does not use repeaters. 10BaseFP stands for Fiber Passive, and its segments can be only 500 meters in length with a maximum of 33 stations connected. This standard is rarely used today.
TIP
Use 10BaseF instead of 10BaseT in environments that are electrically noisy, such as in industrial areas, near elevator shafts, or around other motors or generators.
TIP
Use fiber-optic cabling when running cables between buildings. Differences in ground potential between the ends of copper cabling can induce voltages that can damage networking equipment if the ends are not grounded properly. Fiber-optic cabling also supports faster speeds than copper UTP cabling and provides a more suitable upgrade option to Fast Ethernet and beyond.
TIP
The maximum signal loss or attenuation on a given segment should be no more than 12.5 decibels. Using too many connectors in a segment of fiber-optic cabling can cause the attenuation to exceed this figure, which can lead to signal loss.
See also 10Base2, 10Base5, 10BaseT, SC and ST connectors
10BaseT
A type of standard for implementing Ethernet networks. 10BaseT is the most popular form of 10-Mbps Ethernet, using unshielded twisted-pair (UTP) cabling for connecting stations, and using hubs to form a network. 10BaseT supports a maximum bandwidth of 10 Mbps, but in actual networks, the presence of collisions reduces this to more like 4 to 6 Mbps. 10BaseT is based on the 802.3 specifications of Project 802 developed by the Institute of Electrical and Electronic Engineers (IEEE).
Graphic 0-4.A 10BaseT network.
How It Works
10BaseT networks are wired together in a star topology to a central hub. The UTP cabling used for wiring should be category 3 cabling, category 4 cabling, or category 5 cabling, terminated with RJ-45 connectors. Patch panels can be used to organize wiring and provide termination points for cables running to wall plates in work areas. Patch cables then connect each port on the patch panel to the hub. Usually, most of the wiring is hidden in a wiring cabinet and arranged on a rack for easy access.
The maximum length of any particular segment of a 10BaseT network is 100 meters. If distances longer than this are required, two or more segments must be connected using repeaters. The minimum length of a segment should be 2.5 meters. By using stackable hubs or by cascading regular hubs into a cascaded star topology, you can network large numbers of computers using 10BaseT cable. Although they support up to 1024 nodes, collision domains supporting no more than 200 or 300 nodes will yield the best performance.
NOTE
The maximum length of a 10BaseT cable segment is not a result of the specifications for round-trip communications on an Ethernet network, but rather a limitation caused by the relatively low signal strength of 10BaseT systems. With enhanced category 5 cabling, you might be able to sustain network communications effectively with cable lengths up to about 150 meters, although this is not normally recommended.
TIP
When wiring a 10BaseT network, use enhanced category 5 cabling. This will make it unnecessary to rewire your network should you decide to upgrade to Fast Ethernet.
See also 10Base2, 10Base5, 10BaseF
24 x 7
A standard for uninterrupted running of network services. A 24 x 7 network is a network whose services and resources are available 24 hours a day, seven days a week, with virtually no downtime. A further extension is the goal of 24 x 7 x 365 availability. In today’s emerging e-business economy, availability of the network and its resources and applications can make the difference between business success and failure.
A variety of technologies can be used to approach the goal of 24 x 7 availability. One of the most successful is clustering, a technology in which an application runs redundantly on multiple servers. When one of the nodes in a cluster fails, the other nodes take on the workload of the failed node so that there is no interruption in service while the failed node is being repaired or replaced. Microsoft Cluster Server (MSCS), included in Microsoft Windows NT Server, Enterprise Edition, offers clustering services for high-availability line-of-business applications.
Other technologies important to the 24 x 7 goal include fault tolerant hardware technologies. Examples are hot-swappable components, such as power supplies and hard disks that can be removed and replaced without the system having to power down or reboot. RAID 5 disk systems guard against data loss from disk failure. Cellular phones and pagers also play a role in attaining the 24 x 7 goal, as they allow businesses to keep in touch with administrators and technical support staff around the clock.
TIP
Pay your network administrators and support staff well—they deserve it in a 24 x 7 networking environment. Forget about alternative forms of compensation and shell out the big bucks. If you lose these people, they will be hard to replace!
100BaseFX
A type of standard for implementing Fast Ethernet networks. 100BaseFX is a version of Fast Ethernet that is often used for wiring campus backbones. 100BaseFX is based on 802.3u, which is an extension of the 802.3 specifications of Project 802 developed by the IEEE. 100BaseFX and a related standard, 100BaseTX, are sometimes collectively referred to as 100BaseX.
How It Works
100BaseFX networks are wired together in a star topology using fiber-optic cabling and 100-Mbps fiber-optic hubs or Ethernet switches. The maximum length of any segment of fiber-optic cabling connecting a station (computer) to a hub is 412 meters. The grade of fiber-optic cabling used is usually two-strand multimode fiber-optic cabling, with one strand carrying transmitted data and the other strand receiving data. However, you can also use two-strand single-mode fiber-optic cabling. If multimode fiber-optic cabling is used, the variety used is typically a grade with a 62.5-micron core diameter. Repeaters can be used to extend the length of cabling and for interfacing between 100BaseFX/TX and 100BaseT4 segments. The maximum allowable distances with repeaters are 2 kilometers using multimode fiber-optic cabling and 10 kilometers using single-mode fiber-optic cabling. Only one or two repeaters can be used per collision domain, depending on whether Class I or Class II repeaters are used.
TIP
When using 100BaseFX with repeaters for backbone cabling runs, Ethernet switches cannot be more than 412 meters apart when running in half-duplex mode and 2 kilometers apart when running in full-duplex mode.
See also 100BaseT4, 100BaseTX, Fast Ethernet
100BaseT
See Fast Ethernet
100BaseT4
A type of standard for implementing Fast Ethernet networks. 100BaseT4 is based on 802.3u, which is an extension of the 802.3 specifications of Project 802 developed by the IEEE. 100BaseT4 is the most commonly used implementation of Fast Ethernet today.
Graphic 0-5.A 100BaseT4 network.
How It Works
100BaseT4 networks are wired together in a star topology using unshielded twisted-pair (UTP) cabling and 100-Mbps hubs or Ethernet switches. The UTP cabling can be category 3 cabling, category 4 cabling, or category 5 cabling—with category 5 (cat5) cabling and enhanced category 5 cabling being the most commonly used options. 100BaseT4 uses all four pairs of wire standard UTP cabling. One pair is used for transmission and another pair for reception. The other two pairs are bidirectional and can be used to transmit or receive data. In this way, three of the four wire pairs are used at any given time to provide half-duplex transmission or reception of signals. Sharing three pairs of wires for data transfer allows 100BaseT4 to make use of lower-grade cabling installed in older buildings.
The maximum length of any segment of UTP cabling connecting a station (computer) to a hub is 100 meters. This ensures that round-trip signaling specifications are met, since violating these specifications can produce late collisions that disrupt network communications. The Electronic Industries Alliance/Telecommunications Industry Association (EIA/TIA)–recommended length of cabling between the station and the wiring closet is only 90 meters, allowing up to 10 meters more of cabling for patch cables used to connect patch panels to hubs or switches. The pinning of the RJ-45 connectors used for 100BaseT4 wiring is the same as for 10BaseT wiring.
TIP
Make sure all your cabling, connectors, and patch panels are fully cat5-compliant. Make sure that when UTP cabling is connected to patch panels, wall plates, or connectors, the wires are not untwisted more than half an inch at the termination point. 100BaseT4 most benefits companies with an older, preinstalled base of category 3 or category 4 cabling. 100BaseT4 hubs and switches are typically available in an autosensing 10/100-Mbps variety for interoperability with older 10BaseT networks and to facilitate an easy upgrade from 10BaseT to 100BaseT.
See also 100BaseFX, 100BaseTX, Fast Ethernet
100BaseTX
A type of standard for implementing Fast Ethernet networks. 100BaseTX is based on 802.3u, which is an extension of the 802.3 specifications of Project 802 developed by the IEEE. 100BaseTX and a related standard, 100BaseFX, are sometimes collectively referred to as 100BaseX.
Graphic 0-6.A 100BaseTX network.
How It Works
100BaseTX networks are wired together in a star topology using unshielded twisted-pair (UTP) cabling or shielded twisted-pair (STP) cabling and 100-Mbps hubs or Ethernet switches. If UTP cabling is used (which is the most common scenario), it must be category 5 cabling (cat5 cabling) or enhanced category 5 cabling. 100BaseTX uses two pairs of wires in twisted-pair cabling, with one pair of wires used for transmission and the other used for reception. In this fashion, with appropriate equipment, 100BaseTX is capable of supporting both the normal half-duplex Ethernet and the newer full-duplex Ethernet signaling technologies. The maximum length of any segment of UTP cabling connecting a station to a hub is 100 meters. This ensures that round-trip signaling specifications are met, since violating these specifications can produce late collisions that disrupt network communications. The Electronic Industries Alliance/Telecommunications Industry Alliance (EIA/TIA) recommends only 90 meters of cabling between the station (computer) and the wiring closet, allowing up to 10 meters more of cabling for patch cables used to connect patch panels to hubs or switches. The pinning of the RJ-45 connectors used for 100BaseTX wiring is the same as for 10BaseT wiring.
TIP
Make sure all your cabling, connectors, and patch panels are fully cat5-compliant. Make sure that when UTP cabling is connected to patch panels, wall plates, or connectors, the wires are not untwisted more than half an inch at the termination point.
See also 100BaseFX, 100BaseT4, Fast Ethernet
100BaseVG
See 100VG-AnyLan
100BaseX
See 100BaseFX, 100BaseTX
100VG-AnyLan
An alternative to Fast Ethernet that provides 100-Mbps communications based on technology developed by Hewlett-Packard. 100VG-AnyLan is based on the 802.12 specifications of Project 802 developed by the IEEE. 100VG-AnyLan is informally named 100BaseVG.
Graphic 0-7.A 100VG-AnyLan network.
How It Works
100VG-AnyLan networks are wired together in a star topology using unshielded twisted-pair (UTP) cabling, shielded twisted-pair (STP) cabling, or fiber-optic cabling with supporting 100-Mbps hubs or Ethernet switches. If UTP cabling is used, it can be category 3 cabling, category 4 cabling, or category 5 cabling—with category 5 (CAT5) cabling or enhanced category 5 cabling preferred. 100BaseVG uses all four pairs of wires in UTP cabling. When using UTP category 3 cabling, category 4 cabling, or STP cabling, the maximum length of a segment is 100 meters. With UTP category 5 cabling, the maximum length of a segment is 200 meters. When using multimode fiber-optic cabling, the maximum length is 2000 meters.
100VG-AnyLan differs from Fast Ethernet by not using the traditional Carrier Sense Multiple Access with Collision Detection (CSMA/CD) method for media access used in Ethernet and Fast Ethernet networks; instead, 100VG-AnyLan uses the demand priority method for media access, which eliminates the overhead of collisions. 100VG-AnyLan uses a special coding scheme called quartet signaling, which makes it possible to transmit data over all four pairs of wires in a UTP cable simultaneously. This means that special 100VG-AnyLan hubs are required to support demand priority media access. Otherwise, the frame format, topology, and other specifications of 100VG-AnyLan are the same as for Ethernet.
NOTE
100VG-AnyLan is also being developed to support token ring networks.
1000BaseCX
A type of standard for implementing Gigabit Ethernet networks. The CX in 1000BaseCX stands for short-haul copper, and it indicates that this version of Gigabit Ethernet is intended for short cable runs over copper cabling. Gigabit Ethernet standards are defined in the 802.3z standards of Project 802 developed by the IEEE. 1000BaseCX technologies are in the beginning stages of being widely implemented in enterprise-level networks and are primarily used for collapsed backbones and high-speed interconnects within wiring closets and equipment rooms.
Graphic 0-8.A 1000BaseCX network.
How It Works
1000BaseCX is an extension of standard Ethernet technologies to gigabit-level network speeds. 1000BaseCX is normally implemented using shielded twisted-pair (STP) cabling. Cable segments have a maximum length of only 25 meters. 1000BaseCX employs 8B/10B coding, with serial transmission rates of 1.25 Gbps. STP cabling is standard 150-ohm balanced cabling and should have a quality slightly better than IBM Type I cabling.
1000BaseCX is intended mainly for connecting high-speed hubs, Ethernet switches, and routers together in wiring closets. Common implementations for 1000BaseCX are in switch-switch and switch-server connections, with switch-server connections being the most frequently implemented use for 1000BaseCX.
1000BaseLX
A type of standard for implementing Gigabit Ethernet networks. The LX in 1000BaseLX stands for long, and it indicates that this version of Gigabit Ethernet is intended for use with long-wavelength transmissions over long cable runs of fiber-optic cabling. Gigabit Ethernet standards are defined in the 802.3z standards of Project 802 developed by the IEEE. 1000BaseLX technologies are in the beginning stages of being widely implemented in enterprise-level networks and are primarily used for long cable runs between pieces of equipment on a campus or within a building.
How It Works
1000BaseLX is an extension of standard Ethernet technologies to gigabit-level network speeds. 1000BaseLX is implemented using either single-mode fiber-optic cabling or multimode fiber-optic cabling. Cable segment lengths depend on the cable grade used, as shown in the following table.
1000BaseLX Cable Segment Lengths
Cable Grade
Maximum Segment Length
Single-mode fiber
5000 meters
50-micron multimode fiber
550 meters
62.5-micron multimode fiber
440 meters
1000BaseLX is intended mainly for connecting high-speed hubs, Ethernet switches, and routers together in different wiring closets or buildings using long cabling runs. 1000BaseLX is most commonly implemented in a switch-switch configuration.
Graphic 0-9.A 1000BaseLX network.
TIP
When you use multimode fiber-optic cabling in 1000BaseLX implementations, a condition called differential mode delay (DMD) can sometimes occur. This condition occurs only in cabling of uneven quality, and it leads to signal jitter that can disrupt network communications. To resolve this problem, newer 1000BaseLX transceivers condition the signal to distribute its power equally among all transmission modes of the cable.
1000BaseSX
A type of standard for implementing Gigabit Ethernet networks. The SX in 1000BaseSX stands for short, and it indicates that this version of Gigabit Ethernet is intended for use with short-wavelength transmissions over short cable runs of fiber-optic cabling. Gigabit Ethernet standards are defined in the 802.3z standards of Project 802 developed by the IEEE. 1000BaseSX technologies are in the beginning stages of being widely implemented in enterprise-level networks and are primarily used for shorter cable runs between pieces of equipment within a building.
How It Works
1000BaseSX is an extension of standard Ethernet technologies to gigabit-level network speeds. 1000BaseSX is implemented using only multimode fiber-optic cabling. Cable segment lengths depend on the cable grade used, as shown in the following table.
1000BaseSX Cable Segment Lengths
Cable Grade
Maximum Segment Length
50-micron multimode fiber
500 meters
62.5-micron multimode fiber
220 meters
1000BaseSX is intended mainly for connecting high-speed hubs, Ethernet switches, and routers together in different wiring closets or buildings using long cabling runs. 1000BaseSX is most commonly implemented in a switch-switch configuration.
TIP
When multimode fiber-optic cabling is used in 1000BaseSX implementations, a condition called differential mode delay (DMD) can sometimes occur. This condition occurs only in cabling of uneven quality, and it leads to signal jitter that can disrupt network communications. To resolve this problem, newer 1000BaseSX transceivers condition the signal to distribute its power equally among all transmission modes of the cable.
1000BaseT
A type of standard for implementing Gigabit Ethernet networks. The T in 1000BaseT identifies it as an extension of the traditional 10BaseT and 100BaseT Ethernet technologies for transmission over copper unshielded twisted-pair (UTP) cabling. Gigabit Ethernet standards are defined in the 802.3z and 802.3ab standards of Project 802 developed by the IEEE. 1000BaseT technologies are in the beginning stages of being widely implemented in enterprise-level networks. They are primarily used for short, high-speed interconnects within wiring closets and for connecting high-speed workstations to wiring closets.
Graphic 0-10.A 1000BaseT network.
How It Works
1000BaseT is an extension of standard Ethernet technologies to gigabit-level network speeds. 1000BaseT is normally implemented using the commonly installed category 5 cabling or enhanced category 5 cabling version of UTP cabling. 1000BaseT uses all four pairs of wires in standard UTP cabling, as opposed to the two pairs of wires used in 10BaseT and 100BaseT networks. Using all four pairs of UTP cabling has certain associated problems because of attenuation, crosstalk, and echoes arising from full-duplex transmission over single wires. The 802.3ab standards specify special filters for hybrid circuits used in full-duplex transmission over single wires, a special five-level pulse amplitude modulation (PAM) encoding mechanism instead of binary signals, forward error correction techniques, and pulse shaping technologies to make 1000BaseT a functional and reliable networking technology.
Cable segments for 1000BaseT have a maximum length of 100 meters. 1000BaseT is intended mainly for connecting high-speed hubs, Ethernet switches, and routers together in wiring closets; for switch-switch connections in backbones; for switch-server connections; and for horizontal cable runs to high-speed workstations.
TIP
1000BaseT is intended to provide the simplest upgrade path for legacy 10BaseT and 100BaseT Ethernet networks.
3270
The information display protocol for IBM mainframe computers. The 3270 protocol enables conversations to take place between mainframe hosts and other devices such as dumb terminals, printers, and controllers.
Microsoft SNA Server provides access to resources on mainframe computers by defining and assigning 3270 logical units. These logical units are defined within SNA Server and are configured to use an existing connection to the mainframe system that matches a logical unit resource allocated on the mainframe, usually specified within Virtual Telecommunications Access Method (VTAM). SNA Server client software is installed on client PCs to manage communications between a 3270 application and the SNA Server.
