redundant

(ri-dun´d&nt) (adj.) Used to describe a component of a computer or network system that is used to guard the primary system from failure by acting as a back up system. Redundant components can include both hardware elements of a system — such as disk drives, peripherals, servers, switches, routers — and software elements — such as operating systems, applications and databases.

Redundancy is the quality of systems or elements of a system that are backed up with secondary resources. For example, “The network has redundancy.”

application topology mapping

A subset of network topology and network mapping software, application topology mapping software tools are designed to map or diagram the layout of mission-critical applications in an enterprise, how different apps are connected to each other, how they can be accessed by various computers and networks, and how they are currently performing in terms of efficiency and availability.  The applications mapped by these tools can range from non-connected applications to Web-enabled applications, streaming apps and even cloud applications.

Application topology mapping tools also typically include application discovery and dependency mapping capabilities as well as application performance management (APM) features for alerting IT staff to disruptions in availability and/or quality to end users.  Many application topology mapping software tools also combine sophisticated network mapping to provide real-time views and performance monitoring of all network devices, services, applications, connections and traffic patterns on one or more networks.

Application topology mapping may also be called application dependency mapping.

LAN network administrator

The LAN network administrator is responsible for maintaining an organization’s local area network. The local area network connects computers and other equipment that shares a common communications line or network server. In most cases, the LAN spans a single geographical site, such as a corporate office.

Typical Job Duties and Responsibilities

The LAN network administrator’s job responsibilities typically include the following tasks:

• Installing LAN network components
• Tracking and renewing licenses for software and equipment
• Monitoring LAN performance
• Upgrading network software
• Upgrading network hardware
• Creating network redundancy and backups
• Ensure continuity in the event of network failure
• Install and manage network security software and hardware

Education and Certification Requirements

An information technology degree is required for LAN network administrator jobs. The standard qualification is a bachelor’s degree in IT, computer science, network administration, or management information systems. Professional IT certifications such as the Certified Wireless Network Administrator (CWNA) program offer access to broader job opportunities.

The Bureau of Labor Statistics identifies network administrators among the fastest-growing occupations in the U.S., with 30 percent job growth predicted through the 2008 to 2018 decade.

HiperLAN

Short for high performance radio local area network. Developed by the European Telecommunications Standards Institute, HiperLAN is a set of WLAN communication standards used chiefly in European countries. HiperLAN is similar to the IEEE 802.11 WLAN standards used in the U.S.

There are two types of HiperLAN:

• HiperLAN/1: provides communications at up to 20 Mbps in the 5 GHz band.
• HiperLAN/2: provides communications at up to 54 Mbps in the 5 GHz band.

Like 802.11, HiperLAN serves to ensure the possible interoperability of different manufacturers’ wireless communications equipment that operate in this spectrum.

Also see the Wireless LAN Standards chart in the Quick Reference section of Webopedia.

topology

 

 

)The shape of a local-area network (LAN) or other communications system. Topologies are either physical or logical.

There are four principal topologies used in LANs.

bus topology: All devices are connected to a central cable, called the bus or backbone. Bus networks are relatively inexpensive and easy to install for small networks. Ethernet systemsuse a bus topology.

ring topology :All devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it. Ring topologies are relatively expensive and difficult to install, but they offer high bandwidth and can span large distances.

star topology: All devices are connected to a central hub. Star networks are relatively easy to install and manage, but bottlenecks can occur because all data must pass through the hub.

tree topology: A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable.

These topologies can also be mixed. For example, a bus-star network consists of a high-bandwidth bus, called the backbone,which connects a collections of slower-bandwidth star segments.

For network diagrams, see Network Topology Diagrams in the Quick Referencesection of Webopedia.

hot plugging – hot swapping

Hot plugging (also called hot swapping) is the ability to add and remove devices to a computer system while the computer is running and have the operating system automatically recognize the change.

This is useful when a system component fails as it enables a new device to be installed without system downtime. Two external bus standards — Universal Serial Bus (USB ) and IEEE 1394 — support hot plugging. This is also a feature of PCMCIA.

Hot Plug Versus Hot Swap

While the terms hot plugging and swapping are used interchangeably, hot-pluggable devices typically require administrative tasks to complete the switch (i.e. mounting the hard drive after the new drive has been installed). Hot-swappable devices do not require any additional tasks to install, such as swapping a power supply in the system.

full-duplex

(adj.) Refers to the transmission of data in two directions simultaneously. For example, a telephone is a full-duplex device because both parties can talk at once. In contrast, a walkie-talkie is a half-duplex device because only one party can transmit at a time.

Most modems have a switch that lets you choose between full-duplex and half-duplex modes. The choice depends on which communications program you are running.

In full-duplex mode, data you transmit does not appear on your screen until it has been received and sent back by the other party. This enables you to validate that the data has been accurately transmitted. If your display screen shows two of each character, it probably means that your modem is set to half-duplex mode when it should be in full-duplex mode.

interface

(n.)A boundary across which two independent systems meet and act on or communicate with each other. In computer technology, there are several types of interfaces.

• user interface – the keyboard, mouse, menus of a computer system. The user interface allows the user to communicate with the operating system. Also see GUI.
• software interface – the languages and codes that the applications use to communicate with each other and with the hardware.
• hardware interface – the wires, plugs and sockets that hardware devices use to communicate with each other.

(v.) To connect with or interact with by means of an interface.

SCSI – Small Computer System Interface

The Small Computer System Interface (SCSI) is a set of parallel interface standards developed by the American National Standards Institute (ANSI) for attaching printers, disk drives, scanners and other peripherals to computers. SCSI (pronounced “skuzzy”) is supported by all major operating systems.

SCSI Versions

The first version (SCSI-1), adopted by ANSI in 1986, was an 8-bit version with a 5 MBps transfer speed that allowed up to eight devices to be connected with a maximum cable length of six meters. The latest version, 16-bit Ultra-640 (Fast-320) SCSI, was introduced in 2003 and has a 640 MBps transfer speed, connecting up to 16 devices with a 12 meter cable length. Other versions include:

• SCSI-2: 8-bit bus, six meter cable length, 5-10 MBps; connects 8 or 16 devices. 50-pin connector.
• Wide SCSI-2: Received its name from the wider 168 line cable with 68-pin connectors to accommodate the 16-bit bus. 3 meter cable; 20 MBps transfer rate; connected 16 devices.
• Fast SCSI-2: 8-bit bus, but double the clock speed of SCSI-2 allowing transfers of 10-20 MBps. 3 meter cable; connects 8 devices.
• Fast Wide SCSI-2: 6-bit bus; 3 meter cable; 20 MBps; 16 devices.
• Ultra SCSI-3: 8-bit and 16-bit versions, both with 1.5 meter cable length. The 8-bit version supports data rates of 20 MBps and connects 8 devices. The 16-bit version doubled the transfer rate and number of devices.
• Ultra-2 SCSI: 8-bit bus; 12 meters; 40 MBps; 8 devices.
• Wide Ultra-2 SCSI: 16-bit bus; 12 meters; 80 MBps; 16 devices.

Traditional SCSI has been superseded by later attachment protocols such as Serial Attached SCSI (SAS) and iSCSI, which build on the earlier SCSI command structure.

SCSI History and Uses

SCSI grew out of the Shugart Associates System Interface (SASI), developed by a team led by Larry Boucher at floppy disk drive manufacturer Shugart Associates. Boucher later went on to found host bus adapter manufacturer Adaptec.

Since SCSI uses a low-voltage differential (LVD) bus, a method where data is transmitted by comparing the difference in voltage between a pair of wires, its speed and cable lengths are limited. As a result, SCSI is now largely implemented via serial communications like Serial Attached SCSI (SAS), which offers significantly higher performance. Other types of peripheral connections include the following:

• Universal Serial Bus (USB)
• Serial Attached SCSI (SAS)
• Internet Small computer System Interface (iSCSI)
• USB Attached SCSI (UAS)
• Ethernet
• Fibre Channel (FC)
• Fibre Channel over IP (FC/IP)
• Fibre Channel over Ethernet (FCoE)
• Advanced Technology Attachment (ATA)
• Serial ATA (SATA)
• eSATA

SCSI implementation

SCSI required the use of an adapter card, unlike ATA, where the adapter is built into the device. SCSI is also the foundation of SAS and iSCSI, two common uses of SCSI technology in enterprise storage environments.

SCSI Vendors

The following vendors are part of INCITS Technical Committee 10, which sets protocols for SCSI and related technologies. These suppliers provide everything from cable connectors to complete computers and storage systems.

• 3M Company
• Agilent Technologies
• Amphenol Interconnect
• Applied Micro Circuits Corporation
• BDT Media Automation GmbH
• Brocade
• Cadence Design Systems
• Cinch Connectors
• Crossroads Systems Inc
• Data Direct Networks Inc
• Dell
• Dot Hill Systems Corporation
• EMC Corporation
• ENDL Texas
• Emulex
• FCI Electronics
• Foxconn Electronics
• Fujitsu America
• Fusion-io
• Futurewei Technologies
• General Dynamics
• Google
• HCL Technologies
• HGST
• Ham
• Hewlett-Packard Company
• IBM
• ISO/IEC JTC 1/SC25
• Integrated Device Technology (IDT)
• Intel
• Intersil
• JDS Uniphase Corporation
• Kawasaki Microelectronics America
• KnowledgeTekInc
• LSI
• LeCroy
• Lexar Media
• Link-A-Media Devices
• Lorom Group East
• Marvell Semiconductor
• Maxim Integrated Products
• Microsoft
• Molex
• NVidia
• NXP Semiconductors
• NetApp
• Newisys Data Storage
• Nexenta Systems
• Nexsan Technologies
• NordigitInc
• OCZ Technology Group
• Oracle
• PMC-Sierra
• Pegatron Corporation
• Pericom Semiconductor Corporation
• QLogic
• QNAP Systems
• Quantum
• SMART Modular Technologies
• STEC
• Samsung Information Systems
• SamtecInc
• SanDisk
• Seagate Technology
• SerialTek
• TE Connectivity
• Toshiba America Information Systems
• Unisys Corporation
• VMware
• Violin Memory
• Virident Systems
• Volex
• Western Digital Corporation
• Xyratex

SCSI technology

The InterNational Committee for Information Technology Standards (INCITS), which is accredited by ANSI, has three committees covering storage interfaces. T10 Technical Committee on SCSI Storage Interfaces covers the SCSI architecture, command sets, protocols and physical layers for parallel SCSI and SAS. T11 covers Fibre Channel Interfaces (Fibre Channel, HIPPI, and IPI), and T13 covers ATA storage interfaces (ATA, ATAPI and Serial ATA).

Per the T10 Committee website (www.t10.org); “is responsible for T10 is responsible for SCSI architecture standards (SAM-n), which are used by parallel SCSI, SAS, iSCSI, SCSI Express, USB Attached SCSI, Fibre Channel, SSA, ADI, and IEEE 1394. T10 is also responsible for most SCSI command set standards (e.g., SPC-4, SBC-3, SSC-4, MMC-6, SMC-3, OSD-2, SES-3, ADC-3, RBC). These standards are used by almost all modern I/O interfaces.”

The standards ISO/IEC 14776 series) can be purchased from ANSI. The working draft documents, including Command Standards, protocols and physical layers for SCSI, SAS, Fibre Channel, SCSI Over PCIe Architecture and others can be found here. A standardized set of commands used to communicate requests and responses between the initiator and target are found here.

gigabyte

2 to the 30th power (1,073,741,824) bytes. One gigabyte is equal to 1,024 megabytes. Gigabyte is often abbreviated as G or GB.