Technology fundamentals

Glossary and definitions of commonly used telecommunications terms

Index | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

This glossary is intended to provide brief explanations and introductions to terminology commonly used in the telecommunications, networking, and information technology arenas. The definitions listed, in large part, are abbreviated and edited from the full, detailed definitions found in the 18th edition (2002) of Newton's Telecom Dictionary. Considered one of the best resources for the telecommunications industry, this dictionary defines more than 20,000 terms.

A

Active directory service

A feature of the Windows NT server and first introduced in Windows 2000, is similar to a real-time, super-fast directory information service (such as 411 or 555-1212 in North America) that requests phone numbers and addresses by sending instant messages back to a PC workstation.

Alias

Alternative identification strings for an IP address.

Analog

Derived from "analogous" which means "similar to." In telecommunications industry, the signal being transmitted (voice, video, or image) is analogous to the original signal. That is, the acoustical compression waves transmitting voice in its native form, for example, looks essentially the same as a corresponding electrical signal on an oscilloscope as the voice information is transmitted via a phone line. Outside the telecom industry, analog is often called linear and refers to the physical world of time, temperature, pressure, and sound which are represented by time-variant electrical characteristics such as frequency and voltage.

Asynchronous transfer mode (ATM)

ATM is the technology selected in 1998 by the Consultative Committee on International Telephone & Telegraph (CCITT), an international standards organization, to realize a broadband integrated services digital network (B-ISDN). It is a fast-cell-switched technology based on a fixed-length 53-byte cell. All broadband transmissions (audio, date, imaging, or video) are divided into a series of cells and routed across an ATN network consisting of links connected by ATM switches. The most significant benefit of ATM is its uniform handling of services, allowing one network to meet the needs of many broadband services.

Audio conferencing

Audio conferencing is a telephone conferencing service that uses regular telephone lines and a digital conference bridge to provide an inexpensive, flexible, and convenient method of communication. Using this service, individuals or groups at multiple locations can meet conveniently and economically for business or administrative meetings, saving travel expenses and time. Audio conferencing can also offer an alternative method of communication for some or all instruction in a distance education course.

Automatic location identification (ALI)

Utilizing ANI, ALI uses database to associate a physical location with a telephone number.

Automatic number identification (ANI)

Being able to recognize the telephone number of an individual caller utilizing technology such as caller ID, CLASS, ISDN, or system signaling.

B

Broadband integrated services digital network (B-ISDN)

B-ISDN enables telecommunications and video conferencing data to be transmitted over optical fiber at high speeds. Basically, it is a service or system requiring channels capable of supporting transmission rates greater than DS1. It supports switched, semi-permanent, and permanent point-to-point and point-to-multipoint connections and provides on-demand, reserved, and permanent services. It also contains intelligent capabilities for providing advanced service characteristics, supporting powerful operation and maintenance tools, network control, and management.

Basic rate interface (BRI)

One of two standard interfaces in ISDN. BRI is intended for consumer, small offices, home offices, and small business applications. It supports a total signaling rate of 144 Kbps, which is divided into two B (bearer) channels which run at 64 Kbps and a D (delta or data) channel which runs at 16 Kbps. The B channels "bear" the actual data payload, i.e., carry the actual information being sent.

C

Caching

Caching (pronounced "cashing") is a process by which information is stored in memory or on a server in anticipation of the next request for information. In the context of computer systems and networks, information is cached by placing it closer to the user or user application in order to make it more readily and speedily accessible.

Central office exchange (Centrex) service

Centrex is a business telephone service offered by a local telephone company from a local central office (also called a public exchange). Centrex is basically single-line telephone service with additional features, such as call forwarding, call transfer, toll restrict, call hold, least-cost routing, etc., provided by the local phone company's central office. A substitute for buying or leasing an on-premises system such as a PBX, centrex offers benefits including cost, multiple locations, growth, reliability, ability to self-manage, among others, that make it attractive for some organizations.

Circuit switching

The temporary connection of two or more communications channels. There are three types of switching, circuit, packet, and message. Users have full use of the circuit to transmit voice, data, and video until the connection is terminated. ISDN is a circuit-switched network.

Class of service (CoS)

As it relates to telephony, CoS is a collection of restricted and unrestricted privileges and features assigned to telephone systems or users of that system, such as long-distance access, ability to place international or 1-900 calls, local calls, etc. CoS also relates to service issues on a packet switched network, such as delivery time, traffic congestion, and competition for bandwidth. It allows lower priority traffic to be dropped in times of congestion on a router so that higher priority traffic can get through.

Coder/decoder (Codec)

Originally referring to the coder/decoder function in a microprocessor chip, a codec may also refer to compression/decompression in the PC industry (i.e., an overall term for technology used in digital video and stereo audio). In the telephony industry, codecs convert voice signals from their analog form to digital signals acceptable to modern digital transmission systems.

• Codec ID—This name can be descriptive such as a course title, room name, BL-123, a location, the Accounting Department, or an individual’s name.

Click to Meet (CTM)

Click to Meet is an application developed by First Virtual Communications (FVC), Inc. that combines a directory service for H.320, H.321, and H.323 endpoints in a multimedia environment. FVC is now owned by Radvision.

D

Default extension

Any endpoint on the network defined as an alternative destination on the network for incoming calls routed by the gateway.

Differential services code point (DSCP)

DSCP is a service that helps classify or differentiate traffic by setting the three most significant bits (MSBs) of the type of service byte in the IP header. The router then prioritizes the packet according to how the precedence bit is set.

Digital

In display units, digital refers to the use of digits for direct readout. In telecommunications, recording, or computing, digital refers to the use of a binary code to represent information. Analog signals like voice or music are encoded digitally by sampling the voice or music analog signal many times a second and assigning a number to each sample. Recording or transmitting information digitally has two major benefits: the signal can be reproduced precisely and the electronic circuitry to handle digital continues to grow more powerful and less expensive.

Digitizing

The process of converting analog or continuous signal into a series of ones and zeros, i.e., into a digital format.

Direct inward dialing (DID)

DID is the ability for a caller outside a company to call an internal extension without having to pass through an operator or attendant. Often proposed as centrex's major feature or benefit.

Domain name system/server (DNS)

The domain name system is the way Internet domain names are located and translated into IP addresses. A domain name is a meaningful, easy-to-remember "handle" for an Internet address. A domain name server (DNS) is a computer which contains programs and files composing a domain's name database. Using a DNS is like placing a call to a 1-800 phone number; it requires a "dip" into a database on the server to translate a name (i.e., sally@ihets.org) into a phone number (IP address) which is then used to connect to the host computer. In other words, a DNS translates an alphanumeric address into an IP address.

Dual tone multi-frequency (DTMF)

A way of signaling consisting of a push button or touchtone dial that sends out a sound which consists of two discrete tones picked up and interpreted by telephone switches.

E

E.164

An International Telecommunication Union (ITU) recommendation for global switched telephone numbers (GSTN) numbering. It is a 16-digit numbering scheme that provides a unique telephone number for every subscriber in the world.

Encoding

The process of converting analog voice and video into a digital format or signal.

Endpoint

A network element (component) at the end of the network; in other words, a transmitter, receiver, originating, or terminating device.

Extranet

An Internet-like network which a company runs to conduct business with its employees, customers, and or suppliers. Typically includes Web sites providing information to internal employees and features secure areas to provide information to customers and partners. An IP network through which companies run Web applications for external use by customers for electronic commerce.

F

Firewall

A combination of hardware and software which limits the exposure of a computer or group of computers to an attack from outside their network. The most common use of a firewall is on a LAN connected to the Internet; without a firewall LANs are vulnerable. Firewalls are systems or combination of systems that enforce a boundary between two or more networks. There are several types of firewalls, including: packet filter, circuit gateway, application gateway, or trusted gateway.

• Certified firewall—Since H.323-compliant applications use dynamically allocated sockets for audio, video and data channels, a firewall must be able to allow H.323 traffic through on an intelligent basis. The firewall must be either H.323-enabled with an H.323 proxy, or able to "snoop" to control channel to determine which dynamic sockets are in use for H.323 sessions, and allow traffic as long as the control channel is active. Both the Cisco PIX Firewall and Checkpoint Firewall-1 firewalls feature Set allow H.323 traffic through on an as-needed basis by "snooping" the control channel.
  

Full duplex (FDX)

Full duplex (FDX) is a transmission mode which supports transmission in two directions simultaneously or, more technically, bidirectional simultaneous two-way communications. Most speakerphones are half-duplex (i.e., supports transmission in both directions but only one direction at a time), although newer models are full duplex, which are the best and highest quality for video conferencing purposes. Can be contrasted with symmetrical or asymmetrical transmission; symmetric means the same bandwidth or speed is supported in both directions; asymmetric means more bandwidth or speed in one direction than in the other.

G

Gatekeeper

A gatekeeper (or network administrator) identifies, controls, counts, and supervises the flow of traffic through a network and maintains a registry of devices in a multimedia network. Gatekeepers perform two important functions which help maintain the robustness of the network: address translation and bandwidth management. They may exercise call control functions to limit the number of H.323 connections and the total bandwidth used by these connections in an H.323 zone.

Some gatekeeping terms include:

Admission confirm (ACF)

An authorization by a gatekeeper to admit the call. The message contains the IP address of the terminating gateway or gatekeeper and enables the originating gateway to initiate call control signaling procedures.

Admission reject (ARJ)

Denies the endpoint's request to gain access to the network for this particular call.

Admission request (ARQ)

An attempt by an endpoint to initiate a call.

Bandwidth confirm (BCF)

Sent by gatekeeper confirming acceptance of bandwidth change request.

Bandwidth reject (BRJ)

Sent by endpoint to gatekeeper rejecting bandwidth change request.

Bandwidth request (BRQ)

Sent by endpoint to gatekeeper requesting an increase or decrease in call bandwidth.

Gatekeeper confirm (GCF)

Reply from gatekeeper to endpoint indicating the transport address of the gatekeeper RAS channel.

Gatekeeper reject (GRJ)

Reply from the gatekeeper to endpoint rejecting the endpoints request for registration, usually due to gateway or gatekeeper configuration error.

Gatekeeper request (GRQ)

Message sent by endpoint to gatekeeper.

Information request (IRQ)

Sent from the gatekeeper to endpoint requesting status.

Information request acknowledge (IACK)

Used by gatekeepers to respond to IRR

Information request negative acknowledge (INAK)

Used by gatekeepers to respond to IRR

Information request response (IRR)

Sent from the endpoint to gatekeeper in response to an IRQ. This message is also sent from endpoint to gatekeeper if the gatekeeper requests periodic status updates. The IRR is used by gateways to inform the gatekeeper about active calls.

Location confirm (LCF)

Sent by the gatekeeper and contains call signaling channel or RAS channel address of itself or the requested endpoint. It uses its own address when GKRCS is used. It also uses the requested endpoint address when directed endpoint call signaling is used.

Location reject (LRJ)

Sent by gatekeepers that received an LRQ for which the requested endpoint is not registered or has unavailable resources.

Location request (LRQ)

Sent to request the gatekeeper contact information for one or more E.164 addresses.

Registration_confirm (RCF)

Reply from gatekeeper confirming endpoint registration.

Registration_reject (RRJ)

Reply from gatekeeper rejecting endpoint registration.

Registration_request (RRQ)

Sent from an endpoint to a gatekeeper RAS channel address.

Resource availability confirm (RAC)

Notification from gatekeepers to gateway acknowledging receipt of RAI message.

Resource availability indicator (RAI)

Used by gateways to inform the gatekeeper if resources are available to take on additional calls.

Unregister_confirm (UCF)

Sent from an endpoint or gatekeeper to confirm an unregistration.

Unregister_reject (URJ)

Indicates the endpoint was not preregistered with the gatekeeper.

Unregister_request (URQ)

Sent from endpoint or gatekeeper to cancel registration.

Gateway

A gateway is an entrance and exit into a large or small communications network. Technically, a gateway is an electronic repeater device that intercepts and steers electrical signals from one network to another. Generally, the gateway includes a signal conditioner which filters out unwanted noise and controls characters. In data networks, gateways are typically a node on both of two networks connecting two otherwise incompatible networks. A gateway is also an optional element in an H.323 conference, bridging the conferences to other networks, communications protocols, and multimedia formats. Gateways are not required if connections to other networks or non-H.323 compliant terminals are not needed.

H

H.320 protocol

The most common family of International Telecommunication Union (ITU) video conferencing standards allowing ISDN BRI video conferencing systems and videophones to communicate with each other.

H.321 protocol

The ITU standard for adaptation to the ATM environment of H.320 video conferencing standards.

H.323 protocol

H.323 is a standard from the ITU which serves as the "umbrella" for a set of standards defining real-time multimedia communications for packet-based networks—or what is now called IP telephony. Much of the excitement surrounding the H.323 standards involves the use of H.323 entities to communicate over the Internet or managed IP networks. The standards under the H.323 umbrella define how components that are built in compliance with H.323 can set up calls, exchange compressed audio and/or video, participate in conferences, and interoperate with non-H.323 endpoints. It defines a set of call control, channel setup, and codec specifications for transmitting real-time voice and video over networks that don't offer guaranteed service or QoS, especially for packet networks, the Internet, and LANs, WANS, and intranets.

• H.323 ID (see codec ID)—A descriptive name of a meeting room, whether the room is the name of a course like ENGL101, a location like BL 123, the Accounting Department, or an individual's name.

Half-duplex

A half-duplex circuit designed for data transmission in both directions but not at the same time. Telex is an example of a half-duplex system, as is speaking on most speakerphones. The best speakerphones are full duplex.

Hub

A hub is the point on a network where circuits are connected. In LANs, a hub is the core of a physical "star" configuration, as in Ethernet or ARCNET. Hub hardware can be active or passive. They comprise a physical "bus" with numerous "ports" to which are connected wires which are connected to individual terminal devices. Hubs are protocol-specific (e.g., Ethernet) and are generally fast and inexpensive. Hubs can be interconnected through switches or routers with the traffic being forwarded from the originating hub if the destination address of the data packet indicates it should do so. They reduce network congestion through controlling interhub traffic.

Hypertext markup language (HTML)

This is the authoring software language used on the World Wide Web and is used for creating Web pages. HTML is basically ASCII text surrounded by HTML commands in angle brackets which is interpreted by a browser(s). The term "hypertext" was first developed in 1965 as a nonsequential writing tool which allowed textual elements in documents to be linked. Today, hypertext not only links text documents but also visual and audio information.

I

Integrated services digital network (ISDN)

ISDN is a set of international standards set by the International Telecommunications Union Telecom Standardization (ITU-T) for a circuit-switched digital network that supports access to any type of service (e.g., voice, data, and video) over a single, integrated local loop from the customer premises to the network edge. It requires that all network elements be in place throughout the inter network and specified BRI and PRI as two standard interfaces. A highly sophisticated enhancement of the traditional circuit-switched PSTN, ISDN is flexible, fast, powerful and offers a number of considerable capabilities.

Interactive voice response (IVR)

Where a computer has a keyboard for entering information and a screen for displaying that information, an IVR uses remote touchtone telephones and snippets of recordings (human or computerized). Recordings are used for repetitive messages and/or distributing calls to direct callers to specific information, thus enabling more intelligent and informed call processing (by humans or automated systems). IVR can be used to distribute information and allow individuals to access information from an organization's database and to receive that information using an ordinary touch-tone phone or a PC via the Internet. In addition, IVR systems enable users to execute certain transactions online without the intervention of customer service personnel.

Internet2

Internet2 is a high-speed network connecting universities, research networks, and advanced educational networks with the goal of developing and deploying advanced network applications and technology. It provides a connection for educators and researchers to virtually every research network across the globe, opening the door for increased collaboration and enhanced communication. Through IHETS’ membership as a Sponsored Education Group Participant (SEGP), Indiana's higher education institutions can utilize the newest and most advanced educational technologies—networking tools, applications, middleware, and content. They can also share these technologies with their partners across in other educational sectors throughout the U.S. SEGP status provides all IHETS members with an Internet2 connection, thereby offering them educational and research opportunities previously available only to large public research institutions. In addition to content resources, Hoosier educators can collaborate with one another or other Internet2/SEGP participants utilizing advanced applications such as multicast, digital video, H.323 video, and future interactive video and multimedia technologies

Internet protocol (IP) address

An IP address is the unique address of a computer attached to a TCP/IP network. IP addresses are 32 bits long, where each octet is represented in decimal and is separated by dots. They are usually expressed as four groups of numerals (dotted quad notation) separated by dots, i.e., 128.127.50.224. There are three classes of IP addresses: A, B, and C. The most common is a class C address where 128.127.50.224 would represent a network. network. network.local address.

IP telephony

Largely interchanged with voice over IP (VoIP), IP telephony involves software and hardware to provide the end user with a feature-rich experience when making a phone call with an IP-based device.

Telephone networks are made up of key systems, PBXs (private branch exchanges), and large class associated switches located at a central office. A traditional telephone network is a circuit-switched network—in other words, when a user goes off-hook and dials, the central office connects that user to another port if the party being called is available. At that point, the circuits being used can not be used by another resource at that time. If the line is busy, the call will not complete, in turn the calling party will get a busy signal.

Although that scenario has been corrected by call-waiting, voice technology in general has not progressed the same way a lot of other technologies, such as PCs and networking, have. IP telephony is a major advancement in changing the way telephone networks communicate.

With IP telephony, a LAN or WAN can be used not only for voice transmission over IP, but also to replace the “traditional PBX” with an IP PBX. IP telephones connect directly to a data network. Once connected, the telephone is given an IP address and configured to be an endpoint on the network in the same fashion as a PC. Some IP phones will also give the functionality of a Web browser on the display. Users will be able to check stocks or the weather or access just about anything else they may want. This technology will allow a user to move his or her phone to any place on the network, making it easier and more convenient for the user.

IP video

IP video is the ability to transmit video and audio over a data communications network. Video signals are transmitted using an IP packet or IP data network. A packet is piece of a message transmitted over a packet-switching network. One of the key features of a packet is that it contains the destination address in addition to the data. In IP networks, packets are often called datagrams. IP specifies the format of datagrams, and the addressing scheme. Most networks combine IP with a higher-level protocol called transmission control protocol (TCP), which establishes a virtual (conceptual, not real) connection between a destination and an origination. IP by itself is something like the postal system. It allows you to address a package and drop it in the system, but there’s no direct link between you and the recipient. TCP/IP, on the other hand, establishes a connection between two hosts so that they can send messages back and forth for a period of time.

J

Java

Java is a programming language developed by Sun Microsystems that allows Web applications to be played in any browser on any machine using any platform.

Java telephony application programming interface (JTAPI)

JTAPI is a set of modularly designed application programming interfaces for Java-based computer telephony applications. Its primary use is with call centers. As stated in the definition above, JTAPI allows for Web-based telephony applications to be accessed by any computer using any platform.

L

Local area network (LAN)

LAN (local area network) is a computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a wide area network (WAN). Most LANs connect workstations and personal computers. Each node (individual computer ) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data. Users can also use the LAN to communicate with each other by sending e-mail or engaging in chat sessions.

M

Master address street guide (MASG)

In the U.S. emergency services telephone network, the MASG is a database containing the mapping of street addresses to emergency service numbers within a given community; allows derivation of call routing information from a call's ALI.

Moves/adds/changes (M/A/C)

Any ancillary work performed on a PBX switch, cabinet, or peripheral item after installation. M/A/C is a process whereby personnel are assigned to phones, wires are run, and basic infrastructure is determined. The initial setup of a telephony system will incur the greatest number of M/A/Cs. As personnel change, M/A/Cs need to be completed.

Moving Picture Experts Group (MPEG)

Pronounced “EHM-peg,” the Moving Picture Experts Group is an organization that develops standards for digital video and digital audio compression. There are a number of MPEG standards, continually being developed and refined, each serving a different purpose. For example, MPEG-1 is designed for encoding video at 1.5 million bits per second and can be used for video-CD, while MPEG-2 is designed for encoding video at 4 million bits per second and is intended for digital TV broadcast and DVD.

Multicast

Communication between a single originator and multiple receivers on a network. Distribution via e-mail of a newsletter is a common example. IP multicast video on a network allows multiple users to receive high-bandwidth audio and video from a single point of origination while conserving bandwidth consumption by eliminating multiple streams. The originator provides a single stream and users "tune in" to the broadcasting server.

Multipoint conference unit (MCU)

Multipoint conference units (MCUs) are an important part of any fideo conferencing infrastructure, allowing three or more parties or persons to join in a virtual meeting room. These H.323 endpoints allow multipoint conferences to take place on a LAN.

N

Network

A network is a group of two or more computer systems linked together. There are many types of networks, including:

• Local area networks (LANs)—The computers are geographically close together (i.e., in the same building).
• Wide area networks (WANs)—The computers are farther apart and are connected by telephone lines or radio waves.
• Campus area networks (CANs)—The computers are within a limited geographic area, such as a campus or military base.
• Metropolitan area networks (MANs)—A data network designed for a town or city.
• Home area networks (HANs)—A network contained within a user’s home that connects a person’s digital devices.

Computers on a network are sometimes called nodes. Computers and devices that allocate resources for a network are called servers.

Network address translation (NAT)

The network address translation (NAT) is an Internet standard that enables a LAN to use one set of IP addresses for internal traffic and a second set of addresses for external traffic.This allows a company to shield internal addresses from the public Internet. According to Cisco, there are several NAT applications. One enables private IP internal networks that use nonregistered IP addresses to connect to the Internet. It is configured on the router at the border of a stub domain (referred to as the "inside network") and a public network such as the Internet (an "outside network"). It translates internal local addresses to globally unique IP addresses before sending packets to the outside network.

Network news feed

Network news feed is subscribing to the USEnet network. This is a large network similar to online message boards but much broader in scope.

North American numbering plan (NANP)

NANP assigns area codes and sets rules for calls to be routed across North America. NANP refers to a unique E.164 number accessible from the public switched telephone network (PSTN) using direct inward dialing (DID).

P

Packet switched networks

These networks break up messages into smaller packets before "switching" the packets to their destination. Each packet contains a destination address so all packets in a single message do not have to travel by the same path. The destination computer reassembles the packets back into their proper sequence.

Plain old telephone service (POTS)

A no frills, no added features service that provides standard single-line telephones, telephone lines, and access to the publics switched network.

Port address translation (PAT)

A feature which allows an individual to number a LAN with inside local addresses and filter them through one globally routable IP address.

Primary domain name service

The primary domain name is the primary or first name that identifies one or more IP (Internet Protocol) addresses. For example, the domain name microsoft.com represents about a dozen IP addresses. Domain names are used in URLs to identify particular Web pages. Every domain name has a suffix or extension that indicates to which top level domain (TLD) it belongs. There are only a limited number of domains, including:

• Government agencies (.gov)
• Educational institutions (.edu)
• Nonprofit organizations (.org)
• Commercial (for profit) businesses (.com)
• Network organizations (.net)
• Military organizations (.mil)

Because the Internet is based on IP addresses, not domain names, every Web server requires a domain name system (DNS) server to translate domain names into IP addresses.

Primary rate interface (PRI)

In the U.S., a PRI line provides 23B channels and one 64 Kbps D channel (23B+D) that is equivalent to a T1 line. In Europe, a PRI line provides 30B channels and 1D channel (30B+D) equivalent to an E1 line.

Private branch exchange (PBX)

A private telephone switching system in an organization that interconnects telephone extensions to each other and the public telephone network. Users of a PBX share a certain number of outside lines for making telephone calls external to the PBX. Most medium-sized and larger organizations use a PBX because it’s much less expensive than connecting an external telephone line to every telephone in the organization. In addition, PBX and central office exchange (centrex) environments typically allow fewer digits to be dialed if you are calling within your office dial-plan.

For many organizations, a traditional PBX system meets communication needs. Current features allow for voicemail, "hunt groups" that can ring multiple extensions, and call forwarding. Phone or keyset offerings include analog and digital—and some vendors are now “IP enabling” their systems for IP telephones/keysets.

Proxy server

A proxy server intercepts all requests to a real server to see if it can fulfill the requests itself. If not, it forwards requests to the real server.

Proxy servers have two main purposes:

• Improve performance—Proxy servers can dramatically improve performance for groups of users. This is because it saves the results of all requests for a certain amount of time. The major online services such as Compuserve and America Online, for example, employ an array of proxy servers.
• Filter requests—Proxy servers can also be used to filter requests. For example, a company might use a proxy server to prevent its employees from accessing a specific set of Web sites.

Public safety answering point (PSAP)

Another name for the 911 service center where calls are answered. A PSAP may cover several ESZ, or an emergency service zone which typically refers to an area that integrates several types of emergency services. This zone will also have a list of corresponding numbers that enable PSAPs to route calls more efficiently.

Public switched telephone network (PSTN)

PSTN refers to the local, long distance, and international phone system. In the U.S., the term refers to the entire collection of telephone companies, which may number in the thousands. In other countries, there may be just one telephone company.

Q

Quality of Service (QoS)

QoS is a measure of the telephone service quality provided to a subscriber. Some states have attempted to define the quality of service they want their citizens to have by creating various standards to which they mandate phone companies perform. These standards include the longest amount of time a customer should wait after picking up the handset before receiving a dial tone (three seconds in most states). It may also refer to a networking term that specifies a guaranteed bandwidth throughput level.

R

Random early detection (RED)

A congestion avoidance mechanism for TCP/IP networks. Implemented in a router at the edge of the network, RED takes advantage of TCP's inherent congestion control mechanism. In advance of periods of high congestion, RED will drop TCP/IP packets from queues on a random basis to avoid buffer overflow.

Realtime transport protocol (RTP)

A standard for streaming realtime multimedia over IP in packets. Supports transport of real-time data, like interactive voice and video over packet switched networks. Provides support for content identification, timing reconstruction, loss detection, and security.

Registration admission status (RAS) protocol

The communication protocol used to convey registration, admission, and status messages between H.323 endpoints and the gatekeeper.

Resource reservation protocol (RSVP)

This protocol is designed to support resource (such as bandwidth) reservations through various networks and media. A user's QoS requests are propagated to all routers along the data path, allowing the network to reconfigure itself (at all levels) to meet the desired level of service.

Rich text format (RTF)

A standard formalized by Microsoft Corporation for specifying formatting of documents. RTF files are actually ASCII files with special commands to indicate formatting information, such as fonts and margins.

Room system

H.320 based legacy video conferencing stations. They are called room systems because they usually include large monitors with a wide-angle camera and serve groups of people who meet in a room and conference with other groups at remote locations.

Router

In software, a router is a system-level function that directs a call to an application. As applied to hardware, routers are the central switching offices of the Internet and corporate intranets and WANS. A router is, in the strictest sense, an interface between two networks. Routers are protocol-sensitive, typically supporting multiple protocols.

S

Secondary domain name server (DNS)

A secondary domain name server maintains backup or copies of primary domain name server records or “zone” files. This provides a redundancy (safety) feature, which ultimately provides greater reliability to a network in event of a primary failure.

Security

Security refers to techniques for ensuring that data on a network is protected from unauthorized use; these techniques can be software-based, where passwords restrict access to certain data files or directories. Data encryption is the translation of data into a form that is unintelligible without a deciphering mechanism. These kinds of security measures are usually implemented by the network operating system. Audit trails are another software-based security technique where an ongoing journal of what users do with what files is maintained. A password is a secret word or phrase that gives a user access to a particular program or system.

Server

In hardware, a server is a powerful device used to store and distribute large amounts of digital data and files through a network. Most large networks have multiple servers acting as gatekeepers controlling access to e-mail, software applications, and databases, for example. In software, a server is a program that serves other "client" programs. The connection between a client and a server is networked and follows a protocol for encoding the client's requests and the server's responses. Programs can act as both client and server, changing roles based on the connection. The terms "client" and "server" refer to the role software performs during a specific connection. Servers can function as an origin server, proxy server, gateway server, or tunnel modifying its response based on the specifics of the client request.

Session initiation protocol (SIP)

A protocol for the establishment, modification, and termination of conferencing and telephony session over an IP-based network. Considered a faster, easier, and more scalable method to implement than H.323 for the use of IP telephony; SIP addressing can be based on a telephone number or a uniform resource locator (URL).

Streaming

An Internet term for linking audio recordings and video files to a Web site and, when Web visitors click the links, they hear and see the audio and video immediately rather than having to wait for the entire file to be downloaded and then playing it.

Streaming media

Streaming media is sound (audio) and graphics (video) transmitted over the Internet in a continuous or "streaming" fashion using data packets. The most effective reception of streaming media requires some form of broadband technology such as broadband, cable modem, or DSL. With streaming media, Web users do not have to wait to download a large file before seeing the video or hearing the sound. Instead, the media is sent in compressed form in a continuous stream that is played by the viewer as it arrives. The user needs a player, like Windows Media Player or Real Player, which are programs that uncompress and send video data to the display and audio data to speakers.

State universities voice network (SUVON)

SUVON is a statewide, circuit-switched telephone system connecting the campuses of Indiana’s higher educational institutions. SUVON links the telephone systems of 75 college and university campuses and learning centers throughout Indiana and is available around the clock to campus faculty and staff for educational and business use. IHETS manages SUVON and provides this service for the purpose of reducing the cost of network traffic from member campuses and learning centers to other authorized locations and into those Indiana communities available via the network. Some campuses offer “off-net,” which allows other campuses to complete long distance calls as local in their local calling area.

Switch

A mechanical, electrical, or electronic device which opens or closes circuits, completes or breaks in an electrical path, or selects paths at circuits. Switches work at the physical and data link layers, but emphasize data. A switch looks at incoming data (voice, video, audio, etc.) to determine the destination address. Based on that address, a transmission path is set up through the switching matrix between the incoming and outgoing physical communications ports and links. It then selects a path or circuit for sending the unit of data to its next destination.

Subnet mask

A subnet mask is a mechanism used to split a network into subnetworks; it can be used to reduce the traffic on each subnetwork by confining traffic to only the subnetwork(s) for which it is intended, thereby eliminating issues of associated congestion on other subnetwork(s) and reducing congestion in the network as a whole. Each subnet functions as though it were independent, keeping traffic local and forwarding traffic to another subnetwork only if the address of the data is external to the subnetwork.

T

T1 or T-1

A trunk level 1 or T1 line is a standard for digital transmission in North America and is part of a progression of digital transmission pipes or a hierarchy known generically as the digital signal level (DSL) hierarchy. This digital transmission link (usually fiber optic or copper) carries voice, video, and data up to 1.544 Mbps.

T.120

The most important transmission protocol standard for document conferencing (viewing, changing, and moving files) over transmission media ranging from analog phone lines to the Internet. T.120 is the International Telecommunications Union (ITU) standard for document conferencing via file transfer protocol (FTP).

Telephone application programming interface (TAPI)

Also called Microsoft/Intel telephony API, TAPI is a developing set of functions that allow Windows applications to program telephone-line-based devices such as single and multiline phone (both digital and analog), modems, and fax machines in a device-independent manner. TAPI essentially makes telephony devices easy to install and allows many application programs to with with various telephony devices, irrespective of manufacturer.

Telephony

The science of transmitting voice, data, video, and/or image signals. Telephony refers to the integration of the telephone into the computer workstation. Voice mail and incoming faxes can be integrated with e-mail, with all of the features of the telephone system available through their computer workstations, integrating the telephone with other desktop functions.

Terminal equipment

Terminal equipment usually refers to telephones, desktop computers, terminals, etc. at the end of a telephone line. For IHETS IP video certification and registration, however, terminal equipment refers to one of the following types of endpoints for a codec.

• Room system—This is a product designed to provide a custom video conferencing configuration in which high-quality video performance and extensive conferencing capabilities for applications such as distance learning, meetings, and multi-site conferencing is needed for an entire room, such as a board room or class room. Performance is based on IP data rates as fast as two megabits per second. Room systems typically support multiple video and audio inputs such as document cameras, computer video converters, VCRs, etc. Support for one to three video displays is also common. They may be used with large viewing monitors or projection systems and can be permanently built into a room or serve as semi-mobile units that could be used in another room if needed. Some have built-in streaming capabilities. The advantage is video quality and built-in multipoint capabilities.
  
• Set-top system—Designed for small or medium rooms, this system can sit on a cart or on top of a monitor. It will typically perform as well as a room system at lower data rates, but does not support rates above 768K and do not have multipoint conferencing capabilities. One advantage to the set-top system is that equipment on the lower end of a pricing scale can give excellent performance if the extra options and features of the room system are not required.
  
• Desktop system—A video conferencing terminal, hardware, or software that interacts directly with desktop PC. Designed to be a one-person unit, a desktop system is not suitable for a conference or classroom environment; rather it is an office or computer lab solution. Desktop systems connect through USB ports or installed hardware cards. The PC's processor speed directly impacts performance. The advantage of this system is low cost focus on individual users who don't need multipoint conferencing. It is functional within minutes of installation.

Transcoding

A procedure for modifying a stream of data carried so that it may be carried via a different type of network. It allows H.320 video encoding, carried via circuit-switched time division multiplexer (TDM) systems to be converted to H.323 so that it can connect with and be transmitted across packet switched ethernet LANs.

U

Unified messaging

Also known as integrated messaging (IM) and unified communications (UC). Integrates e-mails, voice mails, and faxes received through a telephone system into one list, which is sortable by date, sender, or file size. Some unified messaging systems allow users to have their telephone systems "read" them their e-mail messages using text to speech functions and to "listen" to their voice mails from their desktops.

User datagram protocol (UDP)

UDP is part of the TCP/IP protocol suite, created to provide applications access to the connectionless features of IP. Provides for exchange of datagrams without acknowledgements or guaranteed delivery. Normally bundled with IP-layer software.

Universal resource locator (URL)

An Internet address that can lead users to a file on any computer connected to the Internet anywhere in the world. A URL is a string expression representing any resource on the Internet or local TC/IP system. It takes the form of http://www.xxx.com, for example, where xxx is the name of the site or file being accessed.

V

V.35

An Internet standard describing a trunk interface between a network access device and a packet network that defines signaling for data rates greater than 19.2 Kbps. It is typically used for equipment that interfaces to a high-speed digital carrier.

Video conference

A video conference is a two-way virtual meeting or conference with others using video and audio software and hardware to see, hear, communicate, and collaborate. Audio is provided through special video conferencing equipment, the telephone, or the computer. The conference takes place via a video codec at both ends that are linked by digital circuits. The amount of bandwidth required for high-quality video and audio is diminishing as technological advances continue.

Virtual local area network (VLAN)

A logical grouping of users regardless of their physical locations on the network; a LAN "extended" beyond its geographical limits by using telephone company resources and facilities, like T1 lines.

Virtual private network (VPN)

A VPN exhibits some of the characteristics of a private network even though it uses the resources of a public switched network. VPNs are lower-cost alternatives to private networks; they typically offer priority access to bandwidth and other network resources, whereas a true private network offers guaranteed access at all times. A VPN might offer relatively tight security mechanisms, whereas a private network is totally secure. There are several definitions of VPNs, but their application scenarios include remote access, intranets, and extranets.

Voice over IP (VoIP)

Voice over Internet Protocol is technology used to transmit voice conversations over a data network such as the Internet or a corporate intranet or managed networks typically used by long and local service providers. VoIP can be a lower-cost alternative to managing separate voice and data networks. For those with IP telephony, M/A/Cs will be easier and less expensive. VoIP also offers features including integrated messaging, bandwidth on demand, voice e-mails, and more.

W

Wide area network (WAN)

WANs are are a public voice or data network extending beyond the metropolitan area network (MAN). A WAN can extend beyond official city limits, perhaps even internationally.

Web sites

Web sites are any machine on the Internet that is running a Web server to respond to requests from remote Web browsers. In more common usage, it refers to individuals sets of Web pages that can be visited and viewed via browsers. The front page of a Web site is called its "home page."

Weighted random early detection (WRED)

A QoS mechanism for IP-based networks.

X

eXtensible markup language (XML)

XML is a simplified version of SGML, designed especially for Web documents. It enables designers to create their own customized tags to provide functionality not available with HTML. It supports links, for example, that point to multiple documents, as opposed to HTML links, which can reference just one destination each.

Z

Zone

A zone can refer to a telephony definition as in one of a series of specified areas, beyond the base rate area of an exchange. It can also refer to a LAN definition in which a zone is one part of a LAN defined by a router. It is also a collection of all terminals, gateways, and MCUs managed by a single gatekeeper in an H.323 context.

Zone prefix

This is a prefix that identifies the addresses to be serviced by a given gatekeeper. Zone prefixes are typically area codes and serve the same purpose as the domain names in an H.323-ID address.