Glossary: glossary

100BaseTX

IEEE physical layer specification for 100 Mbps over two pairs of Category 5 UTP or STP wire.

10BaseT

An Ethernet standard that uses twisted wire pairs.

802.11b

One of the IEEE standards for wireless networking hardware. Products that adhere to a specific IEEE standard will work with each other, even if different companies manufacture them. The 802.11b standard specifies a maximum data transfer rate of 11Mbps, an operating frequency of 2.4GHz, and WEP encryption for security. 802.11b networks are also referred to as WiFi networks.

802.1g

A proposed, but as yet not ratified, extension of the IEEE 802.11 standard for wireless networking hardware. The draft 802.11g specifications used by Xwire specify a maximum data transfer rate of 54Mbps using OFDM modulation, an operating frequency of 2.4GHz, backward compatibility with IEEE 802.11b devices, and WEP encryption for security.

A record

The answer (IP address) that a DNS server returns response to a name resolution request. The A record contains a variety of information, including one or more IP addresses that resolve to the requested domain name.

Access Point

A server where subscribers can access the wireless network and register for service. Also referred to as a gateway.

activate new content

In the publishing process, activating new content means moving content that has just been delivered to a subscriber from its temporary location to its permanent location on the subscriber, and making it available to the viewer. See also controlled activation and independent activation.

active unit

In a redundant system, an active unit is a controller that currently load balances connections. If the active unit in the redundant system fails, the standby unit assumes control and begins to load balance connections.

ad-hoc

A wireless network composed solely of stations within mutual communication range of each other (no Access Point).

ad-hoc network

An ad-hoc network is a group of computers, each with a wireless adapter, connected as an independent 802.11 wireless LAN. Ad-hoc wireless computers operate on a peer-to-peer basis, communicating directly with each other without the use of an access point. Ad-hoc mode is also referred to as an Independent Basic Service Set (IBSS) or as peer-to-peer mode, and is useful at a departmental scale or SOHO operation.

adapter

Printed circuit board that plugs into a PC to add to capabilities or connectivity to a PC. In a networked environment, a network interface card (NIC) is the typical adapter that allows the PC or server to connect to the intranet and/or Internet.

administrator account

A type of user account that allows you access to all features and functions supported in the Network Manager.

AES

Advance Encryption Standard is the U.S. government's next-generation cryptography algorithm, which will replace DES and 3DES. This encryption key protocol is applied in 802.1i standard to improve WLAN security. AES will require new hardware, in contrast with TKIP that can be used on existing wireless devices.

AP

A networking device that seamlessly connects wired and wireless networks. Access Points combined with a distributed system support the creation of multiple radio cells that enable roaming throughout a facility.

ARP cache

A store of information containing address translations that relate host server IP addresses to their corresponding Ethernet addresses.

ARP request

A packet sent to a remote server by a network host. The packet requests that the remote server send a return packet, containing its Ethernet address, back to network host. The network host uses ARP requests to generate miscellaneous traffic on an interface in an attempt to verify that the interface is operating normally.

attribute

A variable that the cache statement uses to direct requests. Attributes can be either required or optional.

authentication

A method of confirming the identity of a user or client attempting to gain access to your system. There are different methods of authentication including the confirmation of passwords, certificates, or information stored on an ID card.

authentication server

A server that provides the management and services of authentication.

auto-MDI/MDIX

On a network hub or switch, an auto-MDI/MDIX port automatically senses if it needs to act as a MDI or MDIX port. The auto-MDI/MDIX capability eliminates the need for crossover cables.

auto-negotiate

Toautomatically determine the correct settings. The term is often used with communications and networking. For example, Ethernet 10/100 cards, hubs, and switches can determine the highest speed of the node they are connected to and adjust their transmission rate accordingly.

automatic fall-back

A feature provided by some wireless products to increase connection reliability. Automatic fall-back enables a device to dynamically shift between various data transfer rates. It works by decreasing the data transfer rate when interference increases, distance increases, and other factors undermine signal strength and quality.

back-end database

The database where the Network Manager stores all of the data it collects, as well as settings such as alert definitions and user accounts. The back-end database can be an Access database, or an SQL Server database.

backbone

The part of a network that connects most of the systems and networks together and handles the most data.

bandwidth

The transmission capacity of a given facility, in terms of how much data the facility can transmit in a fixed amount of time; expressed in bits per second (bps).

Basic Service Area (BSS)

A set of stations controlled by a single coordination function.

beacon interval

A beacon is a packet broadcast by the access point to keep the network synchronized. A beacon includes the wireless LAN service area, the AP address, the broadcast destination addresses, and a time stamp.

BIND

Berkley Internet Name Domain is the most common implementation of DNS, which provides a system for matching domain names to IP addresses.

bit

A binary digit. The value 0 or 1 used in the binary numbering system. Also, the smallest form of data.

bitmask

A pattern of binary values with the result that bits in the value in positions where the mask is zero are also set to zero.

boot

To cause the computer to start executing instructions. Personal computers contain built-in instructions in a ROM chip that are automatically executed on startup. These instructions search for the operating system, load it, and pass control to it.

bottleneck

A traffic slowdown that results when too many network nodes try to access a single node, often a server node, at once

bridge

A device that interconnects different networks together..

broadband

A data-transmission scheme in which multiple signals share the bandwidth of a medium. This allows the transmission of voice, data, and video signals over a single medium. Cable television uses broadband techniques to deliver dozens of channels over one cable.

browser

An application program that provides a way to look at and interact with all the information on the World Wide Web or PC. The word "browser" seems to have originated prior to the Web as a generic term for user interfaces that let you browse text files online.

buffer

A shared or assigned memory area used by hardware devices or program processes that operate at different speeds or with different sets of priorities. The buffer allows each device or process to operate without being held up by the other. In order for a buffer to be effective, the size of the buffer and the algorithms for moving data into and out of the buffer need to be considered by the buffer designer. Like a cache, a buffer is a "midpoint holding place" but exists not so much to accelerate the speed of an activity as to support the coordination of separate activities.

cable modem

A device that connects a computer to the cable television network, which in turn connects to the Internet. Once connected, cable modem users have a continuous connection to the Internet. Cable modems feature asymmetric transfer rates: around 36 Mbps downstream (from the Internet to the computer), and from 200 Kbps to 2 Mbps upstream (from the computer to the Internet).

cacheable content determination

Determines the type of content you cache on the basis of any combination of elements in the HTTP header.

cacheable content expression

An expression that determines, based on evaluating variables in the HTTP header of the request. Any content that does not meet the criteria in the cacheable content is not cached.

CAT 5

ANSI/EIA (American National Standards Institute/Electronic Industries Association) Standard 568 is one of several standards that specify "categories" (the singular is commonly referred to as "CAT") of twisted pair cabling systems (wires, junctions, and connectors) in terms of the data rates that they can sustain. CAT 5 cable has a maximum throughput of 100 Mbps and is usually utilized for 100BaseTX networks.

certificate

A file containing information about what server issued it, a unique serial number or other unique identification, valid dates, and an encrypted fingerprint that can be used to verify the contents of the certificate. In order for a client to establish an SSL connection with the server, both the client and the server must have matching valid security certificates.

chain

A series of filtering criteria used to restrict access to an IP address. The order of the criteria in the chain determines how the filter is applied, from the general first to the more detailed criteria at the end of the chain.

channel

An instance of medium use for the purpose of passing protocol data units that may be used simultaneously, in the same volume of space, with other instances of medium use (on other channels) by other instances of the same physical layer, with an acceptably low frame error ratio due to mutual interference.

client

The desktop or mobile PC that is connected to your network.

client accelerator

A configuration where caching is used in the network data path to the Internet or an enterprise intranet. In this configuration, the cache is configured for a finite number of users, but can cache content from any Web site.

CNAME

A canonical name (CNAME) record acts as an alias to another domain name, the canonical name. The canonical name and its alias can belong to different zones so the CNAME record must always be entered as a fully qualified domain name. CNAME records are useful for setting up logical names for network services so that they can be easily relocated to a different physical host.

COFDM

Signal power alone is not enough to maintain 802.11b-like distances in an 802.11a/g environment. To compensate, a new physical-layer encoding technology was designed that departs from the traditional direct-sequence technology being deployed today. This technology is called COFDM (coded OFDM). COFDM was developed specifically for indoor wireless use and offers performance much superior to that of spread-spectrum solutions. COFDM works by breaking one high-speed data carrier into several lower-speed subcarriers, which are then transmitted in parallel. Each high-speed carrier is 20 MHz wide and is broken up into 52 subchannels, each approximately 300 KHz wide. COFDM uses 48 of these subchannels for data, while the remaining four are used for error correction. COFDM delivers higher data rates and a high degree of multipath reflection recovery, thanks to its encoding scheme and error correction. Each subchannel in the COFDM implementation is about 300 KHz wide. At the low end of the speed gradient, BPSK (binary phase shift keying) is used to encode 125 Kbps of data per channel, resulting in a 6,000-Kbps, or 6 Mbps, data rate. Using quadrature phase shift keying, you can double the amount of data encoded to 250 Kbps per channel, yielding a 12-Mbps data rate. And by using 16-level quadrature amplitude modulation encoding 4 bits per hertz, you can achieve a data rate of 24 Mbps. The 802.11a/g standard specifies that all 802.11a/g-compliant products must support these basic data rates. The standard also lets the vendor extend the modulation scheme beyond 24 Mbps. Remember, the more bits per cycle (hertz) that are encoded, the more susceptible the signal will be to interference and fading, and ultimately, the shorter the range, unless power output is increased.

commit

To move files from a temporary to a permanent directory on a subscriber (target server). See activate new content.

community string

A password that allows access to an SNMP agent running on a network device.

compress task

A database maintenance task that you can run to help remove unnecessary data from the back-end database. A compress task removes redundant data points, but keeps important high and low data points that reflect relevant spikes and low performance levels.

content affinity

Ensures that a given subset of content remains associated with a given cache server to the maximum extent possible, even when cache servers become unavailable, or are added or removed. This feature also maximizes efficient use of cache memory.

content demand status

A measure of the frequency with which content in a given hot content subset is requested over a given hit_period. Content demand status is either hot, in which case the number of requests for content in the hot content subset during the most recent hit_period has exceeded the hot_threshold, or cool, in which case the number of requests during the most recent hit period is less then the cool_threshold.

content hash size

Specifies the number of units, or hot content subsets, into which the content is divided when determining whether content is hot or cool. The requests for all content in a given subset are summed, and a state (hot or cool) is assigned to each subset. The content_hash_size should be within the same order of magnitude as the actual number of requests possible. For example, if the entire site is composed of 500,000 pieces of content, a content_hash_size of 100,000 is typical. If you specify a value for hot_pool, but do not specify a value for this variable, the cache statement uses a default hash size of 10 subsets. See also cool, hot, and content subset.

controlled activation

In controlled activation, the publishing process moves all content together through a series of phases for a collection of subscribers. For instance, before the content for any one section can be activated on one or more subscribers, all content for all sections is copied to all subscribers. Compare to independent activation.

cookie persistence

Cookie persistence is a mode of persistence you can configure on a traffic manager where the traffic manager stores persistent connection information as a cookie.

CPU

Central Processing Unit is the computing part of the computer. Also called the "processor," it is made up of the control unit and ALU.

CSMA/CD

Carrier Sense Multiple Access/Collision Detection is the LAN access method used in Ethernet. When a device wants to gain access to the network, it checks to see if the network is quiet (senses the carrier). If it is not, it waits a random amount of time before retrying. If the network is quiet and two devices access the line at exactly the same time, their signals collide. When the collision is detected, they both back off and each waits a random amount of time before retrying.

CTS

Clear To Send is an RS-232 signal sent from the receiving station to the transmitting station that indicates it is ready to accept data.

data averaging

Reduces the size of a database by taking old data, separating it into time-based intervals, and storing all of the data points contained in an interval as a single data point. The single data points are time-weighted averages and represent the average value of the data collected during a given time period.

data center

A physical location that houses one or more host machines and provides access to the Internet.

data packet

One frame in a packet-switched message. Most data communications are based on dividing the transmitted message into packets. For example, an Ethernet packet can be from 64 to 1518 bytes in length.

data source

Stores information about how to connect to a specific ODBC database, such as the back-end database you use with the Network Manager. A data source stores the database name, the required database driver, and the login ID and password required to connect the database. You configure data sources in the ODBC Administrator tool, available in the Windows Control Panel.

database

A collection of data that is organized so that its contents can easily be accessed, managed, and updated.

DDNS

Dynamic Domain Name System allows a network device with a dynamic Internet IP address to have a fixed host and domain name, such as myhostname.mydomainname.com. It is useful when you are hosting your own Web site, FTP server, or other server behind a router, so people can find your site no matter how often the Internet IP address changes. Using DDNS requires registering with a DDNS service provider on the Internet.

default gateway

The routing device used to forward all traffic that is not addressed to a station within the local subnet.

default VLAN

The VLAN instance which, by default, is the sole VLAN initially existing on a 802.1q-compliant switch. All ports are initially assigned to VLAN 1 (have a PVID of 0x001), otherwise known as the default VLAN value.

default wildcard virtual server

A virtual server that has an IP address and port number of 0.0.0.0:0. This virtual server accepts all traffic, which does not match any other virtual server defined in the configuration.

destination processing

The interface rewrites the destination address of an incoming packet.

destination translation

Included in destination processing, destination translation means that the interface rewrites the destination address of and incoming packet.

device name

Also known as DHCP client ID or network name. Sometimes provided by an ISP when using DHCP to assign addresses.

DHCP

Dynamic Host Configuration Protocol is a protocol that lets network administrators centrally manage and automate the assignment of Internet Protocol (IP) addresses in an organization's network. Using the Internet's set of protocol (TCP/IP), each machine that can connect to the Internet needs a unique IP address. When an organization sets up its computer users with a connection to the Internet, an IP address must be assigned to each machine. Without DHCP, the IP address must be entered manually at each computer and, if computers move to another location in another part of the network, a new IP address must be entered. DHCP lets a network administrator supervise and distribute IP addresses from a central point and automatically sends a new IP address when a computer is plugged into a different place in the network. DHCP uses the concept of a "lease" or amount of time that a given IP address will be valid for a computer. The lease time can vary depending on how long a user is likely to require the Internet connection at a particular location. It's especially useful in education and other environments where users change frequently. Using very short leases, DHCP can dynamically reconfigure networks in which there are more computers than there are available IP addresses. DHCP supports static addresses for computers containing Web servers that need a permanent IP address.

disk mirroring

Process that writes duplicate data to two or more disks, allowing you to use half of your disk space, but providing error recovery in case either of the two disks should fail.

DMZ (Demilitarized Zone)

Allows one IP address (or computer) to be exposed to the Internet. Some applications require multiple TCP/IP ports to be open. It is recommended that you set your computer with a static IP address if you want to use DMZ Hosting.

DNS

Domain Name System is the way that Internet domain names are located and translated into Internet Protocol (IP) addresses. A domain name is a meaningful and easy-to-remember "handle" for an Internet address.

DNS Server Address

Keeps a database of host computers and their respective domain names and IP addresses, so that when a user enters a domain name into the Internet browser, the user is sent to the proper IP address. The DNS server address used by the computers on your home network is the location of the DNS server your ISP has assigned.

domain

A subnetwork comprised of a group of clients and servers under the control of one security database. Dividing LANs into domains improves performance and security.

domain name

The unique name that identifies an Internet site, such as domain.com. A given computer may have more than one domain name, but a given domain name points to only one computer.

download

To receive a file transmitted over a network. In a communications session, download means receive, and upload means transmit.

driver

A workstation or server software module that provides an interface between a network interface card and the upper-layer protocol software running in the computer; it is designed for a specific NIC, and is installed during the initial installation of a network-compatible client or server operating system.

DSL Modem (Digital Subscriber Line)

Uses your existing phone lines to transmit data at high speeds.

DSSS

Spread spectrum (broadband) uses a narrowband signal to spread the transmission over a segment of the radio frequency band or spectrum. Direct sequence is a spread spectrum technique where the transmitted signal is spread over a particular frequency range. Direct-sequence systems communicate by continuously transmitting a redundant pattern of bits called a chipping sequence. Each bit of transmitted data is mapped into chips and rearranged into a pseudorandom spreading code to form the chipping sequence. The chipping sequence is combined with a transmitted data stream to produce the output signal. Wireless mobile clients receiving a direct-sequence transmission use the spreading code to map the chips within the chipping sequence back into bits to recreate the original data transmitted by the wireless device. Intercepting and decoding a direct-sequence transmission requires a predefined algorithm to associate the spreading code used by the transmitting wireless device to the receiving wireless mobile client. This algorithm is established by IEEE 802.11b specifications. The bit redundancy within the chipping sequence enables the receiving wireless mobile client to recreate the original data pattern, even if bits in the chipping sequence are corrupted by interference. The ratio of chips per bit is called the spreading ratio. A high spreading ratio increases the resistance of the signal to interference. A low spreading ratio increases the bandwidth available to the user. The wireless device uses a constant chip rate of 11Mchips/s for all data rates, but uses different modulation schemes to encode more bits per chip at the higher data rates. The wireless device is capable of an 11 Mbps data transmission rate, but the coverage area is less than a 1 or 2 Mbps wireless device since coverage area decreases as bandwidth increases.

DTIM

A Delivery Traffic Indication Message field is a countdown field informing clients of the next window for listening to broadcast and multicast messages. When the AP has buffered broadcast or multicast messages for associated clients, it sends the next DTIM with a DTIM Interval value. AP clients hear the beacons and awaken to receive the broadcast and multicast messages.

dynamic IP address

An IP address that is automatically assigned to a client station in a TCP/IP network, typically by a DHCP server. Network devices that serve multiple users, such as servers and printers, are usually assigned static IP addresses.

dynamic load balancing

Method of using current performance information from each node to determine which node should receive each new connection. The different dynamic load balancing modes incorporate different performance factors.

dynamic load balancing modes

Modes that base connection distribution on live data, such as current server performance and current connection load.

dynamic routing

The ability for a router to forward data via a different route based on the current conditions of the communications circuits. For example, it can adjust for overloaded traffic or failing lines and is much more flexible than static routing, which uses a fixed forwarding path.

dynamic site content

A type of site content, which is automatically generated each time a user accesses the site. Examples are current stock quotes or weather satellite images.

egress

The concept of a frame's transmission from a port (exit from a switch).

egress list

The set of ports permitted to forward traffic out to the network, on behalf of any given VID. Exclusion from this list for a particular VID/port will result in the outgoing frame being dropped. The egress list is primarily consulted during the egress process; but a port may be configured to potentially reject incoming traffic during the ingress process, if the traffic's VID does not match this list.

encryption

A security method that applies a specific algorithm to data in order to alter the data's appearance and prevent other devices from reading the information. This provides wireless data transmissions with a level of security.

ESSID

Extended Service Set Identifier is the most widely used LAN access method, which is defined by the IEEE 802.3 standard. Ethernet is normally a shared media LAN meaning all devices on the network segment share total bandwidth. Ethernet networks operate at 10Mbps using CSMA/CD to run over 10-BaseT cables. You must have the same ESSID entered into the gateway and each of its wireless clients. The ESSID is a unique identifier for your wireless network.

Ethernet

IEEE standard network protocol that specifies how data is placed on and retrieved from a common transmission medium. Has a transfer rate of 10 Mbps. Forms the underlying transport vehicle used by several upper-level protocols, including TCP/IP and XNS.

event

A notification for an administrator specific to the performance and status of the Network Manager and not the AP that the Network Manager monitors. The Network Manager logs its events in its own event log, and also in the NT event log. Events fall into one of the following severity categories: Critical, Error, Warning, Information, and Debug.

exception

A directory, located within the path of a section that is to be excluded from the section when creating a section version. To exclude a directory from a section, you must specify the absolute path of the directory to be excluded. You can only exclude directories, not files.

Extended Service Set (ESS)

A set of one or more interconnected basic service set (BSSs) and integrated local area networks (LANs) can be configured as an Extended Service Set.

external interface

A network interface that receives connection requests.

Fast Ethernet

A 100 Mbps technology based on the 10Base-T Ethernet CSMA/CD network access method.

FDDI

Fiber Distributed Data Interface is a multi-mode protocol for transmitting data on optical-fiber cables up to 100 Mbps.

FHSS

Frequency Hopping Spread Spectrum continuously changes (hops) the carrier frequency of a conventional carrier several times per second according to a pseudo-random set of channels. Because a fixed frequency is not used, and only the transmitter and receiver know the hop patterns, interception of FHSS is extremely difficult.

filter

Filters control network traffic by deciding whether routed packets are forwarded or blocked at the network interface based on a set of user-defined criteria. Filters can also control the rate of traffic by setting a limit on the bits per second allowed through an interface.

filtering

Discarding unwanted network traffic based on its originating address or range of addresses or its type (for example, e-mail or file transfer).

firewall

A set of related programs, located at a network gateway server, that protects the resources of a network from users from other networks. A firewall determines which information passes in and out of a network. A firewall prevents anyone outside of your network from accessing your computer and possibly damaging or viewing your files. Basically, a firewall, working closely with a router, examines each network packet to determine whether to forward it toward its destination.

firmware

Code that is written onto read-only memory (ROM) or programmable read-only memory (PROM). Once firmware has been written onto the ROM or PROM, it is retained even when the device is turned off.

forward proxy

A caching mode that forwards requests from a set of browsers to content hosts.

forward proxy caching

A configuration in which a traffic manager redundant system uses content-aware traffic direction to enhance the efficiency of an array of cache servers storing Internet content for internal users.

forwarding list

See egress list.

fragmentation

Breaking a packet into smaller units when transmitting over a network medium that cannot support the original size of the packet.

freshness

The degree to which cached documents are consistent with the original document located at the origin server. A response is fresh if its age has not exceeded its freshness lifetime.

FTP

File Transfer Protocol is a protocol used to transfer files over a TCP/IP network (Internet, UNIX, etc.). FTP includes functions to log onto the network, list directories, and copy files. It can also convert between the ASCII and EBCDIC character codes. Unlike e-mail programs in which graphics and program files have to be "attached," FTP is designed to handle binary files directly and does not add the overhead of encoding and decoding the data.

full duplex

The ability of a device or line to transmit data simultaneously in both directions.

gateway

A device that interconnects networks with different, incompatible communications protocols. A network point that manages all the data traffic of your network, as well as to the Internet and connects one network to another.

graph

An element of a report. In a report screen, the graph is shown in the Graph tab, and it shows the status or performance of the device over time.

half duplex

Data transmission that can occur in two directions over a single line, but only one direction at a time.

hardware

Hardware is the physical aspect of computers, telecommunications, and other information technology devices. The term arose as a way to distinguish the "box" and the electronic circuitry and components of a computer from the program you put in it to make it do things. The program came to be known as the software.

hit

A content request that can be satisfied by a cache, without having to obtain it from the original server.

hit rate

A measurement based on the amount of requested content in a cache divided by the total requested content. An Internet cache instantly serves hits, without using bandwidth back to the original server, meaning bandwidth and seconds in time are consumed.

host

A network server that manages one or more virtual servers

HTTP

HyperText Transport Protocol is the communications protocol used to connect to servers on the World Wide Web. Its primary function is to establish a connection with a Web server and transmit HTML pages to the client browser.

hub

The device that serves as the central location for attaching wires from workstations. Can be passive, where there is no amplification of the signals; or active, where the hubs are used like repeaters to provide an extension of the cable that connects to a workstation.

ICMP

Internet Control Message Protocol is an Internet communications protocol used to determine information about routes to destination addresses.

IEEE

The Institute of Electrical and Electronics Engineers. The IEEE describes itself as the world's largest technical professional society - promoting the development and application of electrotechnology and allied sciences for the benefit of humanity, the advancement of the profession, and the well-being of our members. The IEEE fosters the development of standards that often become national and international standards. The organization publishes a number of journals, has many local chapters, and has several large societies in special areas, such as the IEEE Computer Society.

IEEE 802.11

IEEE 802.xx is a set of specifications for LANs from the Institute of Electrical and Electronic Engineers (IEEE). Most wired networks conform to 802.3, the specification for CSMA/CD based Ethernet networks or 802.5, the specification for token ring networks. 802.11 defines the standard for wireless LANs encompassing three incompatible (non-interoperable) technologies: Frequency Hopping Spread Spectrum (FHSS), Direct Sequence Spread Spectrum (DSSS), and Infrared. 802.11 specifies a carrier sense media access control and physical layer specifications for 1 and 2 Mbps wireless LANs.

IEEE 802.11a

The 802.11b standard was designed to operate in the 2.4-GHz ISM (Industrial, Scientific and Medical) band using direct-sequence spread-spectrum technology. The 802.11a standard, on the other hand, was designed to operate in the more recently allocated 5-GHz UNII (Unlicensed National Information Infrastructure) band. And unlike 802.11b, the 802.11a standard departs from the traditional spread-spectrum technology, instead using a frequency division multiplexing scheme that's intended to be friendlier to office environments. The 802.11a standard, which supports data rates of up to 54 Mbps, is the Fast Ethernet analog to 802.11b, which supports data rates of up to 11 Mbps. Like Ethernet and Fast Ethernet, 802.11b and 802.11a use an identical MAC (Media Access Control). However, while Fast Ethernet uses the same physical-layer encoding scheme as Ethernet (only faster), 802.11a uses an entirely different encoding scheme, called OFDM (orthogonal frequency division multiplexing). The 802.11b spectrum is plagued by saturation from wireless phones, microwave ovens and other emerging wireless technologies, such as Bluetooth. In contrast, 802.11a spectrum is relatively free of interference. The 802.11a standard gains some of its performance from the higher frequencies at which it operates. The laws of information theory tie frequency, radiated power and distance together in an inverse relationship. Thus, moving up to the 5-GHz spectrum from 2.4 GHz will lead to shorter distances, given the same radiated power and encoding scheme. Compared with 802.11g: 802.11a is a standard for access points and radio NICs that is ahead of 802.11g in the market by about six months. 802.11a operates in the 5GHz frequency band with twelve separate non-overlapping channels. As a result, you can have up to twelve access points set to different channels in the same area without them interfering with each other. This makes access point channel assignment much easier and significantly increases the throughput the wireless LAN can deliver within a given area. In addition, RF interference is much less likely because of the less-crowded 5 GHz band.

IEEE 802.11b

In 1997, the Institute of Electrical and Electronics Engineers (IEEE) adopted the 802.11 standard for wireless devices operating in the 2.4 GHz frequency band. This standard includes provisions for three radio technologies: direct sequence spread spectrum, frequency hopping spread spectrum, and infrared. Devices that comply with the 802.11 standard operate at a data rate of either 1 or 2 Mbps. In 1999, the IEEE created the 802.11b standard. 802.11b is essentially identical to the 802.11 standard except 802.11b provides for data rates of up to 11 Mbps for direct sequence spread spectrum devices. Under 802.11b, direct sequence devices can operate at 11 Mbps, 5.5 Mbps, 2 Mbps, or 1 Mbps. This provides interoperability with existing 802.11 direct sequence devices that operate only at 2 Mbps. Direct sequence spread spectrum devices spread a radio signal over a range of frequencies. The IEEE 802.11b specification allocates the 2.4 GHz frequency band into 14 overlapping operating Channels. Each Channel corresponds to a different set of frequencies.

IEEE 802.11g

802.11g is a proposed (to be finalized) new extension to 802.11b (used in majority of wireless LANs today) that broadens 802.11b's data rates to 54 Mbps within the 2.4 GHz band using OFDM (orthogonal frequency division multiplexing) technology. 802.11g allows backward compatibility with 802.11b devices but only at 11 Mbps or lower, depending on the range and presence of obstructions.

if-modified-since (ims)

A request sent by a cache to the origin server, used to check the freshness of a cached web object that appears stale, for example, if the object has an explicit expiration date. The cache sends the request to the origin server, then the server examines the time and date stamp of the object, then compares that to information provided by the cache. If the time and date stamps are the same, then the object is considered fresh and can be served from the cache. If the time and date stamps differ, then the object is considered stale and the server sends a new version of the content to the cache, which then forwards it to the client.

infrastructure

A wireless network centered about an access point. In this environment, the access point not only provides communication with the wired network but also mediates wireless network traffic in the immediate neighborhood.

infrastructure network

A group of computers or other devices, each with a wireless adapter, connected as an 802.11 wireless LAN. In infrastructure mode, the wireless devices communicate with each other and to a wired network by first going through an access point. An infrastructure wireless network connected to a wired network is referred to as a Basic Service Set (BSS). A set of two or more BSS in a single network is referred to as an Extended Service Set (ESS). Infrastructure mode is useful at a corporation scale, or when it is necessary to connect the wired and wireless networks.

ingress

The concept of a frame's receipt into a port (entry into a switch).

intelligent cache population

Allows caches to retrieve content from other caches in addition to the origin web server. This feature is useful only when working with non-transparent cache servers, which can receive requests that are destined for the cache servers themselves, as opposed to transparent cache servers, which can intercept requests destined for a web server but cannot themselves receive requests. Intelligent cache population minimizes the load on the origin Web server and speeds cache population.

internal interface

A network interface on a network server configured to process source requests. In a basic configuration, this interface has the administration ports open. In a normal configuration, this is typically a network interface, which handles connections from internal servers.

internet caching protocol

A protocol that allows network caches to request content from other ICP-compliant web caches when it is employed in cache clusters.

IP

A protocol that allows packets to be exchanged between computers. The TCP/IP standard protocol that defines the IP datagram as the unit of information passed across an Internet and provides the basis for connectionless packet delivery service. IP includes the ICMP control and error message protocol as an integral part. It provides the functional equivalent of ISO OSI Network Services.

IP address

An address assigned to a host or interface for the purpose of routing packets. An IP address is a 32-bit number that identifies each sender or receiver of information that is sent across the Internet. An IP address has two parts: the identifier of a particular network on the Internet and an identifier of the particular device (which can be a server or a workstation) within that network. In the most widely installed level of the Internet Protocol (IP) today, an IP address is a 32-binary digit number that identifies each sender or receiver of information that is sent in packets across the Internet. When you request an HTML page or send e-mail, the Internet Protocol part of TCP/IP includes your IP address in the message (actually, in each of the packets if more than one is required) and sends it to the IP address that is obtained by looking up the domain name in the Uniform Resource Locator you requested or in the e-mail address you're sending a note to. At the other end, the recipient can see the IP address of the Web page requestor or the e-mail sender and can respond by sending another message using the IP address it received.gateway

ipconfig

A utility that provides for querying, defining, and managing IP addresses within a network. A commonly used utility, under Windows NT and 2000, for configuring networks with static IP addresses.

IPSec

Internet Protocol Security is a suite of protocols used to implement secure exchange of packets at the IP layer. IPSec supports two basic modes: Transport and Tunnel. Transport encrypts the payload of each packet, leaving the header untouched, while Tunnel mode encrypts both the header and the payload and is therefore more secure. IPSec must be supported on both transmitter and receiver and must share a public key. Tunnel mode is widely deployed in VPNs (Virtual Private Networks).

IRQ

Interrupt ReQuest is a hardware interrupt on a PC. There are 16 IRQ lines used to signal the CPU that a peripheral event has started or terminated. Except for PCI devices, two devices cannot use the same line.

ISM band

The FCC and their counterparts outside of the U.S. have set aside bandwidth for unlicensed use in the ISM (Industrial, Scientific, and Medical) band. Spectrum in the vicinity of 2.4 GHz, in particular, is being made available worldwide. This presents a truly revolutionary opportunity to place convenient high-speed wireless capabilities in the hands of users around the globe.

ISM Bands

Industrial, Scientific, and Medicine Bands are radio frequency bands that the Federal Communications Commission (FCC) authorized for wireless LANs. The ISM bands are located at 902 MHz, 2.400GHz, and 5.7 GHz.

ISP

An ISP (Internet service provider) is a company that provides individuals and companies access to the Internet and other related services such as Web site building and virtual hosting.

LAN

A local area network (LAN) is a group of computers and associated devices that share a common communications line and typically share the resources of a single processor or server within a small geographic area (for example, within an office building).

last hop

The previous hop a connection took to get to the network server.

latency

The time delay between when the first bit of a packet is received and the last bit is forwarded.

load balancing mode

A method of determining how to distribute connections across an array.

local DNS

A DNS server, which makes name resolution requests on behalf of a client. Local DNS servers are the source of name resolution requests. Also referred to as LDNS.

loopback adapter

A software interface that is not associated with an actual network card. The nPath routing configuration requires you to configure loopback adapters on servers.

MAC

Media Access Control is a protocol that defines the way workstations gain access to transmission media, most widely used in reference to LANs. For IEEE LANs, the MAC layer is the lower sublayer of the data link layer protocol.

MAC address

An address used to represent hardware devices on an Ethernet network.

Mbps

One million bits per second; unit of measurement for data transmission.

MD5

A type of one-way authentication method that uses passwords. MD5 authentication is not as secure as the EAP-TLS or EAP/TTLS authentication methods. MD5 authentication does not support dynamic WEP key management.

MDI

On a network hub or switch, a Medium Dependent Interface port, also known as an uplink port, connects to another hub or switch using a straight-through cable. To connect a MDI port to a computer, use a crossover cable.

MDIX

On a network hub or switch, a Medium Dependent Interface Crossed port connects to a computer using a straight-through cable. To connect a MDIX port to another hub or switch, use a crossover cable.

member

A reference to a node when it is included in a particular virtual server mapping. Virtual server mappings typically include multiple member nodes.

metrics information

Statistical data that is typically collected for paths between two servers. Metrics information is used for load balancing, and it can include statistics such as round trip time, packet rate, and packet loss.

MIB

Management Information Base is a database of network management information that is used and maintained by a network management protocol such as SNMP or CMIP. The value of a MIB object can be changed or retrieved using SNMP or CMIP commands, usually through a GUI network management system. MIB objects are organized in a tree structure that includes public (standard) and private (proprietary) branches.

mIRC

mIRC runs under Windows and provides a graphical interface for logging onto IRC servers and listing, joining, and leaving channels.

miss

A content request that cannot be satisfied by a cache. For example, if the content is stale, requiring a request from the origin server.

miss request

A miss request results from a request for content a cache does not have.

mod_dav

Mod_dav is an Apache HTTP web server module that implements WebDAV. The Apache group provides open-source HTTP web servers and enhancements. If you are already using an Apache server, you could use mod_dav to implement WebDAV.

monitor

A monitor collects status and performance information for an individual network device, and stores the data in a back-end database.

motherboard

The physical arrangement in a computer that contains the computer's basic circuitry and components.

multicasting

Sending data to a group of nodes instead of a single destination.

name resolution

The process by which a name server matches a domain name to an IP address, and sends the information to the client requesting the resolution.

name server

A server that maintains a DNS database, and resolves domain names to IP addresses using that database.

name server records

Records used to define a set of authoritative name servers for a zone. A name server is considered authoritative for some given zone when it has a complete set of data for the zone, allowing it to answer queries about the zone on its own, without needing to consult another server.

named

The name server daemon, which manages domain name server software.

nanny

A watchdog daemon used to monitor the status of the proxy server. If the proxy server quits responding, the nanny reboots the server automatically.

NAT

Network Address Translation is the translation of an Internet Protocol address (IP address) used within one network to a different IP address known within another network. One network is designated the inside network and the other is the outside.

NetBEUI

NetBIOS Extended User Interface is the transport layer for NetBIOS. NetBIOS and NetBEUI were originally part of a single protocol suite that was later separated. NetBIOS sessions can be transported over NetBEUI, TCP/IP, and IPX/SPX protocols.

NetBIOS

The native networking protocol in DOS and Windows networks. Although originally combined with its transport layer protocol (NetBEUI), NetBIOS today provides a programming interface for applications at the session layer (layer 5). NetBIOS can ride over NetBEUI, its native transport, which is not routable, or over TCP/IP and IPX/SPX, which are routable protocols. NetBIOS computers are identified by a unique 15-character name, and Windows machines (NetBIOS machines) periodically broadcast their names over the network so that Network Neighborhood can catalog them. For TCP/IP networks, NetBIOS names are turned into IP addresses via manual configuration in an LMHOSTS file or a WINS server. There are two NetBIOS modes. The Datagram mode is the fastest mode, but does not guarantee delivery. It uses a self-contained packet with send and receive name, usually limited to 512 bytes. If the recipient device is not listening for messages, the datagram is lost. The Session mode establishes a connection until broken. It guarantees delivery of messages up to 64KB long.

netmask

A 32-bit bit mask which shows how an Internet address is to be divided into network, subnet and host parts.

network

A system that transmits any combination of voice, video, and/or data between users.

Network Manager

An application that runs on a single console and allows network views of services or individual components. Reports on network status. Modifies configurations.

NIC

Network Interface Card is a board installed in a computer system, usually a PC, to provide network communication capabilities to and from that computer system. Also called an adapter.

node

A network junction or connection point, typically a computer or work station. A specific combination of an IP address and port number associated with a server in the array.

node address

The IP address associated with one or more nodes. This IP address can be the real IP address of a network server, or it can be an alias IP address on a network server.

node port

The port number or service name hosted by a specific node.

node status

Node status indicates whether a node is up and available to receive connections, or down and unavailable.

non-cacheable content

Content that is not identified in the cacheable content condition part of a cache rule statement.

non-transparent cache server

Cache servers that can receive requests that are destined for the cache servers themselves.

notebook

A battery-powered personal computer generally smaller than a briefcase that can easily be transported and conveniently used in temporary spaces such as on airplanes, in libraries, at temporary offices, and at meetings. A notebook computer, sometimes called a laptop computer, typically weighs less than five pounds and is three inches or less in thickness.

NTP

Network Time Protocol is used over the Internet to synchronize system clocks to Universal Coordinated Time. NTP provides a mechanism to set and maintain clock synchronization within milliseconds.

OFDM

Orthogonal Frequency Division Multiplexing) was developed for wireless applications, this technology offers superior performance-increased data rates and more reliable transmissions-than previous technologies, such as DSSS. OFDM is a scheme in which numerous signals of different frequencies are combined to form a single signal for transmission on the medium. OFDM works by breaking one high-speed data stream into a number of lower speed data streams, which are then transmitted in parallel. Each lower speed stream is used to modulate a subcarrier. Essentially, this creates a multi-carrier transmission by dividing a wide frequency band or channel into a number of narrower frequency bands or sub-channels. OFDM is also used for other applications, including powerline networking.

origin pool

Specifies a pool of servers that contain original copies of all content. Requests are load balanced to this pool when any of the following are true: the requested content is not cacheable, no cache server is available, or a redundant system is redirecting a request from a cache server that did not have the requested content.

origin server

The Web server on which all original copies of your content reside.

packet

A unit of data routed between an origin and a destination in a network.

packet rate

The number of data packets processed per second by a server.

partitioning

To divide a resource or application into smaller pieces.

passphrase

A string of words and characters that you type in to authenticate yourself as a user. Passphrases are similar to passwords, but longer. Passphrases are considered to be more secure because of their greater length.

path

A logical route between a two network servers.

path probing

The collection of metrics data, such as round trip time and packet rate, for a given path between a requesting path.

PC card -

A credit card sized removable module that contains memory, I/O, or a hard disk.

PCI

A peripheral bus commonly used in PCs, Macintosh computers, and workstations. It was designed primarily by Intel and first appeared on PCs in late 1993. PCI provides a high-speed data path between the CPU and peripheral devices (video, disk, network, etc.). There are typically three or four PCI slots on the motherboard. In a Pentium PC, there is generally a mix of PCI and ISA slots or PCI and EISA slots. Early on, the PCI bus was known as a "local bus." PCI provides "plug-and-play" capability, automatically configuring the PCI cards at startup. When PCI is used with the ISA bus, the only thing that is generally required is to indicate in the CMOS memory which IRQs are already in use by ISA cards. PCI takes care of the rest. PCI allows IRQs to be shared, which helps to solve the problem of limited IRQs available on a PC. For example, if there were only one IRQ left over after ISA devices were given their required IRQs, all PCI devices could share it. In a PCI-only machine, there cannot be insufficient IRQs, as all can be shared.

PCMCIA

Personal Computer Memory Card International Association that develops standards for PC cards, formerly known as PCMCIA cards. These cards are available in three types, and are about the same length and width as credit cards. However, the different width of the cards ranges in thickness from 3.3 mm (Type I) to 5.0 mm (Type II) to 10.5 mm (Type III). These cards can be used for various functions, including memory storage, land line modems, and wireless modems.

performance report

A type of report that contains performance data such as current connections, inbound packets per second, or inbound dropped packets per second.

persistence

A series of related connections received from the same client, having the same session ID. When persistence is turned on, a controller sends all connections having the same session ID to the same node instead of load balancing the connections.

persistent session

A set of related connections. For example, a series of connections received from the same client to the same server for processing.

Ping

Packet Internet Groper is an Internet utility used to determine whether a particular IP address is online. It is used to test and debug a network by sending out a packet and waiting for a response.

Plug-and-Play

The ability of a computer system to configure expansion boards and other devices automatically without requiring the user to turn off the system during installation.

POP3

Post Office Protocol 3 is a standard mail server commonly used on the Internet. It provides a message store that holds incoming e-mail until users log on and download it. POP3 is a simple system with little selectivity. All pending messages and attachments are downloaded at the same time. POP3 uses the SMTP messaging protocol.

port

A pathway into and out of the computer or a network device such as a switch or router. For example, the serial and parallel ports on a personal computer are external sockets for plugging in communications lines, modems, and printers.

port mirroring

Port mirroring, also known as a roving analysis port, is a method of monitoring network traffic that forwards a copy of each incoming and outgoing packet from one port of a network switch to another port where the packet can be studied. A network administrator uses port mirroring as a diagnostic tool or debugging feature, especially when fending off an attack. It enables the administrator to keep close track of switch performance and alter it if necessary. Port mirroring can be managed locally or remotely.

port VLAN list

See egress list.

port-specific wildcard virtual server

A wildcard virtual server address that uses a port number other than 0.

PPP

Point-to-Point Protocol is a protocol for communication between computers using a serial interface, typically a personal computer connected by phone line to a server.

PPPoE

Point to Point Protocol over Ethernet is a method for the encapsulation of PPP packets over Ethernet frames from the user to the ISP over the Internet. One reason PPPoE is preferred by ISPs is because it provides authentication (username and password) in addition to data transport. A PPPoE session can be initiated by either a client application residing on a PC, or by client firmware residing on a modem or router.

PPTP

Point-to-Point Tunneling Protocol is a protocol that allows the Point to Point Protocol (PPP) to be tunneled through an IP network. PPTP does not specify any changes to the PPP protocol but rather describes a "tunneling service" for carrying PPP (a tunneling service is any network service enabled by tunneling protocols such as PPTP, L2F, L2TP, and IPSEC tunnel mode). One example of a tunneling service is secure access from a remote small office network to a headquarters corporate intranet via a Virtual Private Network (VPN) that traverses the Internet. However, tunneling services are not restricted to corporate environments and may also be used for personal (i.e., non-business) applications.

pragma

Web content authors insert the "Pragma: No-Cache" Hypertext Markup Language (HTML) META tag to identify a page that should not be cached. For example, the author may not want to cache a web page that dynamically displays stock quotes since these can change by the minute.

primary DNS

A server that is authoritative for handling DNS name resolution requests.

private key

One of two keys used in asymmetric cryptography. The private key can be used to encrypt data that can then be decrypted using the public key, which is shared with all involved parties.

public key

The second of two keys used in asymmetric cryptography. The public key, which is shared by all involved parties, is used to decrypt data that was encrypted with the private key.

publish

The process of identifying specific versions of sections to be included in an edition, and then delivering and activating this edition to subscribers.

purge task

Database maintenance task that removes data from the back-end database based on age.

PVID

Port VLAN Identifier is the per-port value to be used for applying VID assignments to untagged frames, during the ingress process. PVID initially reflects the default VLAN value, for all ports.

quality of service (QoS) chart

A chart that monitors the uptime of a network.

RAID

Redundant Array of Independent Drives allows you to store information in multiple hard drive locations, providing the safety of redundancy or the performance of writing data simultaneously to multiple locations. In the case of redundant disks, if one disk fails, another can immediately take over, reducing the total failure rates and providing fault-tolerance. Performance improvements result from using simultaneous operating system processes to write to multiple disks at the same time.

rate class

A rate class determines the volume of traffic allowed through a rate filter.

ratio

A parameter that assigns a weight to a virtual server for load balancing purposes.

redundant system

A pair of controllers that are configured for fail-over. In a redundant system, there are two controller units, one running as the active unit and one running as the standby unit. If the active unit fails, the standby unit takes over and manages connection requests.

regular expression

A sequence of characters that defines a pattern you want to search for.

remote administrative IP address

An IP address from which a controller allows shell connections, such as Telnet or SSH.

resolvers

TCP/IP protocol library software that formats DNS queries, which request hostname to Internet address conversion.

resource record

A record in a DNS database that stores data associated with domain names. A resource record typically includes a name, an address type, and data specific to that address type.

reverse domains

A type of DNS resolution request that matches a given IP address to a domain name. The more common type of DNS resolution request starts with a given domain name and matches that to an IP address.

reverse proxy

A caching mode in which the cache acts on the behalf of one or more content hosts.

RF

The international unit for measuring frequency is Hertz (Hz), equivalent to the older unit of cycles per second. One megahertz (MHz) is one million Hertz. One gigahertz (GHz) is one billion Hertz. The standard US electrical power frequency is 60 Hz, the AM broadcast radio frequency band is 0.55-1.6 MHz, the FM broadcast radio frequency band is 88-108 MHz, and wireless 802.11 LANs operate at 2.4 GHz.

RIP

A simple routing protocol that is part of the TCP/IP protocol suite. It determines a route based on the smallest hop count between source and destination. Routing Information Protocol is a distance vector protocol that routinely broadcasts routing information to its neighboring routers. Routing Information Protocol(RIP1) is defined as a means by which routing equipment can find the best path for transmitting data packets from one network to another. Upgrades have been made to the RIP1 protocol, resulting in Routing Information Protocol Version 2 (RIP2). RIP2 was developed to cover some of the inefficiencies of RIP1. Metric: RIP metric is a value of distance for the network. Usually RIP increments the metric when the network information is received. Redistributed routes' default metric offset is set to 1. These rules can be used to change the metric offset only for the matched networks specified or excluded in the Route Metric Offset table. But the metric offset of other networks is still set to 1.

RJ-11

A telephone connector that holds up to six wires. The Registered Jack-11 is the common connector used to plug a telephone into a wall.

RJ-45

A connector similar to a telephone connector that holds up to eight wires, used for connecting Ethernet devices.

roaming

In an infrastructure mode wireless network, this refers to the ability to move out of one access point's range and into another and transparently reassociate and reauthenticate to the new access point. This reassociation and reauthentication should occur without user intervention and ideally without interruption to network connectivity. A typical scenario would be a location with multiple access points, where users can physically relocate from one area to another and easily maintain connectivity.

root name server

A master DNS server that maintains a complete DNS database. There are approximately 13 root name servers in the world that manage the World Wide Web.

round robin mode

A static load balancing mode that bases connection distribution on a set server order. Round robin mode sends a connection request to the next available server in the order.

router

Protocol-dependent device that connects subnetworks together. Routers are useful in breaking down a very large network into smaller subnetworks; they introduce longer delays and typically have much lower throughput rates than bridges.

RTS

Request To Send is an RS-232 signal sent from the transmitting station to the receiving station requesting permission to transmit.

RTT

Round Trip Time is a calculation of the time (in microseconds) that a server takes to respond to a ping issued by another server.

secondary DNS

A name server that retrieves DNS data from the name server that is authoritative for the DNS zone.

section

The source content retrieved via one path (server and directory) and access method (authorization and protocol). Different updates are saved as unique section versions, which may be used in different publications and publication editions.

server

Any computer whose function in a network is to provide user access to files, printing, communications, and other services.

server accelerator

A configuration where caching is used in front of the origin server, reducing the number of requests the server must handle. In this configuration, the cache is configured to serve content to any number of users, but can only cache and serve content from specified origin servers.

site content

Data, including text, images, audio, and video feeds, that is accessible to clients who connect to a given site.

SMTP

Simple Mail Transfer Protocol is the standard e-mail protocol on the Internet. It is a TCP/IP protocol that defines the message format and the message transfer agent (MTA), which stores and forwards the mail.

SNAT

A Secure Network Address Translation defines a routable alias IP address that one or more nodes can use as a source IP address when making connections to hosts on the external network.

SNMP agent

The application or daemon that runs on a network device and controls SNMP communications, including access to the SNMP MIB.

SNMP MIB

The text file that identifies and describes the different data sets available from the network device. A MIB file essentially contains one or more object IDs, each of which describes available data such as inbound packets per second processed by a controller, or pages per minute printed on a network printer.

SNMP Object ID

An identifier that represents a specific data set defined in a SNMP MIB. Also a type of monitor that tracks data based on a specific SNMP object ID.

software

Instructions for the computer. A series of instructions that performs a particular task is called a "program." The two major categories of software are "system software" and "application software." System software is made up of control programs such as the operating system and database management system (DBMS). Application software is any program that processes data for the user. A common misconception is that software is data. It is not. Software tells the hardware how to process the data.

SOHO

Small Office/Home Office is the market segment of professionals who work at home or in small offices.

source processing

Source processing means that the interface rewrites the source of an incoming packet.

spread spectrum

A wideband radio frequency technique developed by the military for use in reliable, secure, mission-critical communications systems. It is designed to trade off bandwidth efficiency for reliability, integrity, and security. In other words, more bandwidth is consumed than in the case of narrowband transmission, but the trade off produces a signal that is, in effect, louder and thus easier to detect, provided that the receiver knows the parameters of the spread-spectrum signal being broadcast. If a receiver is not tuned to the right frequency, a spread-spectrum signal looks like background noise. There are two main alternatives, Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS).

SSH

An encryption utility that allows secure shell connections to a remote system.

SSID

A group name shared by every member of a wireless network. Only client PCs with the same SSID are allowed to establish a connection.

stale

A response is stale if its age has passed its freshness lifetime. See freshness.

standby unit

A unit in a redundant system that is always prepared to become the active unit if the active unit fails.

static IP address

A permanent IP address that is assigned to a node in a TCP/IP network.

static routing

Forwarding data in a network via a fixed path. Static routing cannot adjust to changing line conditions as can dynamic routing.

static site content

A type of site content that is stored in HTML pages, and changes only when an administrator edits the HTML document itself.

station

Any device containing IEEE 802.11 wireless medium access conformity.

status report

A type of report that contains status information. Status reports have only two state options. The state options vary depending on the type of data being monitored, but they are typically defined as up or down, on or off, or true or failed.

storage

The semi-permanent or permanent holding place for digital data.

STP

hielded Twisted Pair is a telephone wire that is wrapped in a metal sheath to eliminate external interference.

stripes

In products that support caching, stripes are cacheable content subsets distributed among your cache servers.

sub-statement

A logical section within a statement that defines a particular element in the statement. A sub-statement begins with the sub-statement name followed by an open bracket and ends with the closing bracket. Everything between those brackets is part of the sub-statement

subdomain

A sub-section of a high level domain. For example, the state of Washington is a high level domain, and King county is a subdomain within the Washington state domain.

subnet mask

The method used for splitting IP networks into a series of subgroups, or subnets. The mask is a binary pattern that is matched up with the IP address to turn part of the host ID address field into a field for subnets.

subscriber

A user of a network or service.

swapping

Replacing one segment of a program in memory with another and restoring it back to the original when required.

switch

1. A data switch connects computing devices to host computers, allowing a large number of devices to share a limited number of ports. 2. A device for making, breaking, or changing the connections in an electrical circuit.

syslog

The standard UNIX system logging utility, which monitors critical system events, as well as configuration changes made on the system.

TCP

Transmission Control Protocol is a method (protocol) used along with the IP (Internet Protocol) to send data in the form of message units (datagram) between network devices over a LAN or WAN. While IP takes care of handling the actual delivery of the data (routing), TCP takes care of keeping track of the individual units of data (called packets) that a message is divided into for efficient delivery over the network. TCP is known as a "connection oriented" protocol due to requiring the receiver of a packet to return an acknowledgment of receipt to the sender of the packet resulting in transmission control.

TCP wrapper

Performs basic checking on the source IP address and try to verify that the request is legitimate.

TCP/IP

Transmission Control Protocol/Internet Protocol is the basic communication language or set of protocols for communications over a network (developed specifically for the Internet). TCP/IP defines a suite or group of protocols and not only TCP and IP.

Telnet

A terminal emulation protocol commonly used on the Internet and TCP/IP-based networks. It allows a user at a terminal or computer to log onto a remote device and run a program.

TFTP

Trivial File Transfer Protocol is a version of the TCP/IP FTP protocol that has no directory or password capability.

threshold

A threshold is a specific performance level that triggers an alert. For status reports, you can define only two thresholds: when the state reaches 0 (for down, off, failed, or other similar status), and when the state reaches 1 (for up, on, successful, or other similar status). For performance reports, you set threshold values based on the type of performance data you are working with. See also, alerts.

throughput

The amount of data moved successfully from one place to another in a given time period.

TKIP

Temporal Key Integrity Protocol is used in WPA to replace WEP with a new encryption algorithm that is stronger than the WEP algorithm but that uses the calculation facilities present on existing wireless devices to perform encryption operations.

topology

A network's topology is a logical characterization of how the devices on the network are connected and the distances between them. The most common network devices include hubs, switches, routers, and gateways. Most large networks contain several levels of interconnection, the most important of which include edge connections, backbone connections, and wide-area connections.

transparent cache server

A cache server that can intercept requests destined for a web server, but are incapable of receiving requests.

transparent proxy

A cache mode in which the router or switch intercepts requests and sends them to the cache. Unlike forward proxy, the end user's web browser does not require special configuration and the cache is transparent to the end-user. This mode is also known as transparent forward proxy.

trap

A program interrupt, usually caused by some exceptional situation in the user program. In most cases, the system performs some action, then returns control to the program.

trend

A linear calculation that shows predicted performance based on historical data.

TTL

Time to Live is a variable that controls the number of seconds considers data to be valid for.

Tunnel Broker

Service providing IPv6 connectivity to the 6bone by tunneling over IPv4. See FreeNet6

TX Rate

Transmission Rate.

UDP

User Datagram Protocol is a method (protocol) used along with the IP (Internet Protocol) to send data in the form of message units (datagram) between network devices over a LAN or WAN. While IP takes care of handling the actual delivery of the data (routing), UDP takes care of keeping track of the individual units of data (called packets) that a message is divided into for efficient delivery over the network. UDP is known as a "connection-less" protocol due to NOT requiring the receiver of a packet to return an acknowledgment of receipt to the sender of the packet (as opposed to TCP).

UDP persistence

Forces UDP packets that have the same source address and virtual server as prior UPD packets to use the same node as used by the prior UDP packets for the specified period.

unavailable

A status used for virtual servers, and hosts.

untagged list

The set of ports which, having made the decision to forward a frame as part of the egress process, will transmit it untagged. Exclusion from this list for a particular VID/port will result in the frame being VLAN-tagged, if/when transmitted.

up

A status used for virtual servers and nodes. When a virtual server or node is up, the virtual server or node is available to receive connections.

upgrade

To replace existing software or firmware with a newer version.

upload

To send a file transmitted over a network. In a communications session, upload means transmit, and download means receive

URL

Uniform Resource Locator is the address that defines the route to a file on the Web or any other Internet facility. URLs are typed into the browser to access Web pages, and URLs are embedded within the pages themselves to provide the hypertext links to other pages.

UTP

Unshielded twisted pair is the most common kind of copper telephone wiring. Twisted pair is the ordinary copper wire that connects home and many business computers to the telephone company. To reduce crosstalk or electromagnetic induction between pairs of wires, two insulated copper wires are twisted around each other. Each signal on twisted pair requires both wires. Since some telephone sets or desktop locations require multiple connections, twisted pair is sometimes installed in two or more pairs, all within a single cable.

VID

VLAN Identifier is the 12-bit VLAN number (maximum possible decimal value is 4,096) assigned to a frame during the ingress process. A frame's VID, used in conjunction with ingress and egress rules as defined by the VLAN administrator, dictates whether individual ports are permitted to handle the frame. It is useful to think of 802.1q as 802.1d, but with a few added restrictions that tend to reduce the communication possibilities.

virtual address

An IP address associated with one or more virtual servers.

virtual port

The port number or service name associated with one or more virtual servers. A virtual port number should be the same TCP or UDP port number to which client programs expect to connect.

virtual server

A specific combination of a virtual address and virtual port, associated with a content site that is managed by a traffic manager or other type of host server.

virtual server mapping

The group of nodes across which a virtual server load balances connections for a given site.

VLAN

Virtual Local Area Network is a network structure that places restrictions on traffic flow, permitting traffic to pass among a select group of network nodes, to the exclusion of other network nodes, based on the assigned group membership of individual nodes or switch ports. 802.1q is only one of a number of VLAN schemes.

VLAN classification

The means by which optional rules may be established local to each port, to be used during the ingress process to examine each incoming untagged frame for a match to the (layer 2, 3, or 4) rules, with the goal of possibly overriding the PVID value when determining the proper VID assignment for the frame.

VLAN identifier

See VID.

VLAN number

Term used in this document for any case in which a reference to a VLAN instance must be made; and the more specific terms VID, PVID, and default VLAN are not applicable. In 802.1q, the VLAN number is used in lieu of the VLAN name, which can be entered into the switches but has no significance to 802.1q operation.

VLAN tag

A 32-bit label (ethertype x'8100') inserted into a frame, by originating station or relaying bridge, immediately following the layer 2 source address (or, if a source routed frame, immediately following the RIF), 12 bits of which identifies its VLAN association by VLAN number. Although not all frames need be tagged, sufficient tagging should be done so that there is no ambiguity regarding VLAN membership when a frame is received by a 802.1q-compliant bridge. It is also desirable to isolate non-802.1q-compliant nodes from the possibility of receiving tagged frames, as the tags would make the layer 3+ information unreadable to them and the frames would be dropped.

VPN

A technique that allows two or more LANs to be extended over public communication channels by creating private communication subchannels (tunnels). Effectively, these LANs can use a WAN as a single large "virtually private" LAN. This removes the need to use leased lines for WAN communications through secure use of a publicly available WAN (such as the Internet). Examples of VPN technology are: PPTP (Point to Point Tunneling Protocol), L2TP (Layer 2 Tunneling Protocol), and IPSec (Internet Protocol Security).

WAN

A communications network that covers a relatively large geographic area, consisting of two or more LANs. Broadband communication over the WAN is often through public networks such as the telephone (DSL) or cable systems, or through leased lines or satellites. In its most basic definition, the Internet could be considered a WAN. A system of LANs, connected together. A network that connects computers located in separate areas, (i.e., different buildings, cities, countries). The Internet is a wide area network.

WCCP

Web Cache Coordination Protocol is a protocol that enables a WCCP-enabled router, such as those available from Cisco Systems, to work with a network cache in handling web traffic.

WebDAV

Web Distributed Authoring and Versioning implements most of the advantages of a computer file system over the Web using HTTP 1.1 to transfer files between computers. WebDAV provides more efficient file transfers than FTP and enables application programmers to provide more features to users, such as setting the permissions on files delivered to a target server.

WECA

Wireless Ethernet Compatibility Alliance is an industry group that certifies cross-vender interoperability and compatibility of IEEE 802.11b wireless networking products and to promote that standard for enterprise, small business, and home environments.

WEP

The IEEE 802.11b standard specifies an optional encryption feature, known as Wired Equivalent Privacy or WEP, that is designed to provide a wireless LAN with a security level equal to what is found on a wired Ethernet network. WEP encrypts the data portion of each packet exchanged on the 802.11b network using either a 64-bit or 128-bit encryption algorithm. In addition, WEP is also used in conjunction with the optional Shared Key Authentication algorithm to prevent unauthorized devices from associating with an 802.11b network.

WiFi

Wireless Fidelity is a branding term used to signify compliance with the IEEE 802.11b standard for wireless Ethernet.

WINIPCFG

Configuration utility based on the Win32 API for querying, defining, and managing IP addresses within a network. A commonly used utility for configuring networks with static IP addresses.

WKS

Well-Known Services is a type of resource record that describes the services usually provided by a particular protocol on a specific port.

WLAN

Wireless Local Area Network is a group of computers and associated devices that communicate with each other wirelessly.

workgroup

Two or more individuals that share files and databases.

WPA

WiFi Protected Access is specification that offsets encryption and authentication improvements that are stronger than the Wireless Encryption Protocol (WEP), which it is meant to replace.

WPA-PSK

A special mode of WPA for home environment without a Remote Authentication Dial-In User Service (RADIUS). It is required to enter a password into their access point or home wireless gateway and each clients that is on the wireless network to keeps out eavesdroppers and other unauthorized users by requiring all devices to have the matching password.

XML

A format in which data is compressed and can be encrypted for security. This allows the data to be sent and received using normal server/browser technology (HTTP/HTTPS ports). Using XML, data can be transmitted in secure form through firewalls and routers that might otherwise stop the transmission of performance data.

zone file

A database set of domains with one or many domain names, designated mail servers, a list of other name servers that can answer resolution requests, and a set of zone attributes called SOA (Start Of Authority).