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Glossary

Adjusted Ring Length (ARL)

Calculated to ensure that if there is a ring failure, the longest ring path is still within specifications. Generally associated with token ring, Adjusted Ring Length ensures that the secondary ring can still function properly in the event of a failure on t

Agent

A person whose job is to answer calls, make calls to provide and receive information, or to sell a product or service. Sometimes also known as customer service representative or telephone advisor.

AHT

See “Average Holding Time”

American National Standards Institute (ANSI)

A U.S. standards body. ANSI is a member of the International Organization for Standardization (ISO)

Application Programming Interface (API)

A set of routines, protocols, and tools for building software applications. A good API makes it easier to develop a program by providing all the building blocks. A programmer puts the blocks together. Most operating environments, such as MS-Windows, provide an API so programmers can write applications consistent with the operating environment. Although APIs are designed for programmers, they are ultimately good for users because they guarantee that all programs using a common API will have similar interfaces. This makes it easier for users to learn new programs.

Asymmetric Digital Subscriber Line (ADSL)

A new technology that allows more data to be sent over existing copper telephone lines (POTS). ADSL supports data rates of from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate). In spite of the fact that ADSL requires a special ADSL modem, it is enjoying great success not only as a solution for remote small business sites, but also with higher-end consumer users. The ITU is currently defining an xDSL standard based on ADSL, called G.dmt.

Asynchronous

A method of transmitting data whereby each byte is clocked separately. One start bit is added to the beginning, and one or more stop bits to the end, of each character. Asynchronous transmission is the most rudimentary form of data communication, as the originating and recipient machines do not have to be in sync. It is commonly used for low-speed transmission, as with a PC’s serial port.

Asynchronous Transfer Mode (ATM)

A network technology based on transferring data in cells or packets of a fixed size. The cell used with ATM is relatively small compared to units used with older technologies. The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data dominates the line to itself. Current implementations of ATM support data transfer rates of from 25 to 622 Mbps and higher. This compares to a maximum of 100 Mbps for Ethernet, the current technology used for most LANs. ATM creates a fixed channel, or route, between two points whenever data transfer begins. This differs from TCP/IP, in which messages are divided into packets and each packet can take a different route from source to destination. This difference makes easier to track and bill data usage across an ATM network.

ATM

See "Asynchronous Transfer Mode"

ATM Adaptation Layer (AAL)

Provides a conversion function to and from ATM for various types of information, including voice, video, and data. There are several versions of AAL, each applicable to a given information type. All of them convert elements of an information stream (such as voice frames and data packets) into cells, giving ATM the versatility to carry many different types of data, from constant-rate voice data to highly bursty messages generated by LANs, all within the same cell format.

Attenuation

The progressive weakening of a signal as it travels away from its point of origin.

Audiotex

Replaying selected stored information to a caller.

Automated Attendant (AA)

Answering incoming calls with an automatic message, and routing the call on the basis of additional input from the caller.

Automated Call Distributor (ACD)

A system that distributes calls to agents, according to a predetermined set of rules.

Automatic Call Sequencer

In an ACD, a device lines up calls when all agent lines are busy.

Automatic Number Identification (ANI)

Term used in USA. Number presented to an operator or application that confirms the caller's number.

Automatic Repeat Request (ARQ)

A type of error correction ensuring that a transmitting device automaticAally resends any data containing errors.

Average Holding Time (AHT)

The sum of the lengths (in minutes or seconds) of all phone calls during the busiest hour of the day divided by the number of calls.

Bandwidth

(1) The range of signal frequencies that can be carried on a communications channel. The capacity of a channel is measured in cycles per second, or hertz (Hz), between the highest and lowest frequencies. (2) Commonly, the carrying capacity of a digital translation facility, measured in bits per seconds (BPS).

Broadband

WAN term used to describe a transmission facility providing bandwidth greater than 45 Mbps (T3). Broadband can multiplex multiple, independent carrier signals onto a single cable. This is usually accomplished through frequency division multiplexing. Broadband technology allows several signals to coexist on a single cable; traffic from one signal does not interfere with traffic from another, since data is transmitted on a different frequency. Cable television uses broadband.

Call Control

Signals used to setup, monitor, and clear down a call.

Call Vectoring

An alternative name used by some suppliers to describe Intelligent Dynamic Routing. See "Intelligent Dynamic Routing."

Callback

Calling a caller, either at their request or through use of CTI on an abandoned call.

Called Line Identification (CLI)

Number presented to an operator, agent, or application that confirms the caller's number.

Caller Identification

Caller identification on ISDN.

Cell

A fixed-length transmission unit that forms the basis of ATM. Each cell is 53 bytes in length, divided into a 48-byte payload and a 5-byte header.

Central Office (CO)

American term for a public telephone exchange.

Centralized Attendant Service (CAS)

One group of switchboard operators answers all the incoming calls for several telephone system located throughout the city. CAS is used by customers with several locations in the same geographic area. E.g. retail stores, banks.

Computer Telephony Integration (CTI)

Refers to systems that enable a computer to act as a call centre, accepting incoming calls and routing them to the appropriate device or person. Today's CTI systems are quite sophisticated and can handle all types of incoming and outgoing communications, including phone calls, faxes, and Internet messages.

Conditional Routing

An alternative name for intelligent dynamic routing.

Convergence

Convergence is the bringing together of disparate voice and data communications systems, creating a single unified communications solution, providing the foundation for business-enhancing multimedia applications.

Customer Service Unit (CSU)

A device used at the customer premise to connect a device, such as a PBX, to a public digital network facility, such as a T1 line. Provides repeater and control functions.

Cut-Through

1) A form of switching, typically LAN switching, in which the switch begins to forward the initial portion of a packet to its destination while the remainder of the packet is still being received. This was useful when the throughput of LAN protocols was highly degraded by latency in the data path. It is uncommon today. (2) A form of switching, typically in an ATM network, in which a routing process is used to set up a connection between two devices, but the data subsequently flows directly between the two devices, without passing through the routing process. MPOA is one important example.

Dial Tone

The sound you hear when you pick up a telephone. Dial tone in North America is an unbroken signal between 350 Hz and 440 Hz that is generated by your local telephone company. By hearing the dial tone, you know that your phone company is alive and ready to receive the number you dial. If you have a PBX, the PBX will typically provide dial tone.

Digital Number Identification System (DNIS)

Caller identification system used in the USA.

Digital Service Unit (DSU)

A device used at the customer premise to connect a data device, such as a computer, to a public digital network facility, such as a T1 line. Provides electrical translation and line coding. Technically, this is generally a DSU/CSU, combining both functions.

Digital Speech Interpolation (DSI)

In digital speech transmission, the use of periods of inactivity or constant signal level to increase the transmission efficiency by insertion of additional signals.

Direct Dial Inwards (DDI)

(1) Originally the facility to dial a person connected to a PBX directly without operator intervention. (2) A service offered by network providers where the caller dials a published service number, and the call is switched by the PBX or ACD to an extension determined by last 4 or 6 digits of the number dialled.

Directory Services

A network service that identifies all resources on a network and makes them accessible to users and applications. Resources include e-mail addresses, computers, and peripheral devices such as printers. Ideally, the directory service should make the physical network topology and protocols transparent so that a user on a network can access any resource without knowing where or how it is physically connected. There are a number of directory services that are used widely. Two of the most important ones are LDAP, which is often used for e-mail addresses, and Netware Directory Service (NDS), which is used on Novell Netware networks. Virtually all directory services are based on the X.500 ITU standard, although the standard is so large and complex than no vendor complies with it fully.

Dynamic Routing

A procedure for sending messages across a network by which line failure or overload results in message rerouting.

Encryption

The process of converting information from an easily understandable format (plain text) into apparent random gibberish (ciphertext) by the use of well-defined rules and calculations known as algorithms or cipher. A process used to ensure the privacy and confidentiality of information. The reverse process is decryption.

Extensible Markup Language (XML)

A new specification being developed by the W3C. XML is a pared-down version of SGML, designed especially for Web documents. It enables designers to create their own customized tags to provide functionality not available with HTML. For example, XML supports links that point to multiple documents, as opposed to HTML links, which can reference just one destination each. Whether XML eventually supplants HTML as the standard Web formatting specification depends a lot on whether it is supported by future Web browsers. So far, the only major browser vendor to endorse XML is Microsoft, which has stated that XML will be supported in a future version of Internet Explorer.

Fibre Channel

A form of high-speed fibre optic transmission designed primarily for communications between mainframe computers, and between mainframe computers and high-speed peripherals such as disk drives. Sometimes used for general-purpose networking.

File Transfer Protocol (FTP)

The protocol within the TCP/IP protocol suite that is used to transfer files between computers. FTP uses the reliable end-to-end transfer protocol TCP to assure the integrity of the transmitted data.

File Transfer Protocol (FTP)

Abbreviation of File Transfer Protocol, the protocol used on the Internet for sending files.

Firewall

A security mechanism that protects a server, a subnet, or an entire end user location from unauthorized access. Firewalls can be standalone devices, or they can be incorporated into routers and switches.

Handset

The part of a phone held in the hand to speak and listen that contains a transmitter and receiver.

Head End

A central point in a broadband network that receives signals on one set of frequency bands and retransmits them on another set of frequencies. The head end is viewed as a central hub.

Hub

Connection point for devices in a network. Hubs are used to connect segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets. A passive hub serves simply as a conduit for the data, enabling it to go from one device (or segment) to another. So-called intelligent hubs include additional features enabling an administrator to monitor the traffic passing through the hub and to configure each port in the hub. Intelligent hubs are also called manageable hubs. A third type of hub, called a switching hub, actually reads the destination address of each packet and then forwards the packet to the correct port. Intelligent switches and layer 3 routers have largely replaced hubs in most networks.

Hybrid Network

A LAN consisting of a number of topologies and access methods. For example, a network that includes both token ring and Ethernet.

Hybrid Switch

Can handle both voice and data traffic for next generation multiservice networks.

HyperText Transfer Protocol (HTTP)

The underlying protocol used by the World Wide Web. HTTP defines how messages are formatted and transmitted, and what action Web servers and browsers should take in response to various commands. For example, when you enter a URL in your browser, this actually sends an HTTP command to the Web server directing it to fetch and transmit the requested Web page. The other main standard that controls how the World Wide Web works is HTML, which covers how Web pages are formatted and displayed. HTTP is called a stateless protocol because each command is executed independently, without any knowledge of the commands that came before it. This is the main reason that it is difficult to implement Web sites that react intelligently to user input. This shortcoming of HTTP is being addressed in a number of new technologies, including ActiveX, Java, JavaScript and cookies. Currently, most Web browsers and servers support HTTP 1.1. One of the main features of HTTP 1.1 is that it supports persistent connections. This means that once a browser connects to a Web server, it can receive multiple files through the same connection. This should improve performance by as much as 20%.

Institute of Electrical and Electronics Engineers (IEEE)

Pronounced I-triple-E. Founded in 1884, the IEEE is an organization composed of engineers, scientists, and students. The IEEE is best known for developing standards for the computer and electronics industry. In particular, the IEEE 802 standards for local-area networks are widely followed.

Integrated Messaging

Voice messaging system that provides message interchange with fax and or e-mail in a single cell.

Integrated Services Digital Network (ISDN)

An international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires. ISDN supports data transfer rates of 64 Kbps (64,000 bits per second). Most ISDN lines offered by telephone companies give you two lines at once, called B channels. You can use one line for voice and the other for data, or you can use both lines for data to give you data rates of 128 Kbps, three times the data rate provided by today's fastest modems. The original version of ISDN employs baseband transmission. Another version, called B-ISDN, uses broadband transmission and is able to support transmission rates of 1.5 Mbps. B-ISDN requires fibre optic cables and is not widely available.

Intelligent Call Routing

An alternative name used by some suppliers to describe Intelligent Dynamic Routing.

Intelligent Dynamic Routing

Routing of a call based on, call characterization, the current status of the system and resources available.

Intelligent Hub

A hub that adds network management capabilities, such as maintaining port statistics, determining port status, and automatically segmenting faulty ports. Also known as a second-generation hub.

Interactive Voice Response (IVR)

Voice response combined with user input (touch tone or voice) to select required options for access to data, held either on the system or in a separate computer database.

International Organization for Standardization (ISO)

Note that ISO is not an acronym; instead, the name derives from the Greek word iso, which means equal. Founded in 1946, ISO is an international organization composed of national standards bodies from over 75 countries. For example, ANSI (American National Standards Institute) is a member of ISO. ISO has defined a number of important computer standards, the most significant of which is perhaps OSI (Open Systems Interconnection), a standardized architecture for designing networks.

International Telecommunications Union (ITU)

An international body of member countries whose task is to define recommendations and standards relating to the international telecommunications industry. The fundamental standards for ATM have been defined and published by the ITU (previously CCITT).

Internet Control Message Protocol (ICMP)

An extension to the Internet Protocol (IP) defined by RFC 792. ICMP supports packets containing error, control, and informational messages. The PING and TRACEROUTE commands, for example, use ICMP to test an Internet connection.

Internet Engineering Task Force (IETF)

The main standards organization for the Internet. The IETF is a large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet. It is open to any interested individual.

Internet Message Access Protocol (IMAP)

A protocol for retrieving e-mail messages. The latest version, IMAP4, is similar to POP3 but supports some additional features. For example, with IMAP4, you can search through your e-mail messages for keywords while the messages are still on mail server. You can then choose which messages to download to your machine. Like POP, IMAP uses SMTP for communication between the e-mail client and server. IMAP was developed at Stanford University in 1986.

Internet Protocol (IP)

The layer 3 protocol used in the TCP/IP set of protocols which support the Internet and many private networks. IP provides a connectionless datagram delivery service for transport-layer protocols such as TCP and UDP.

Internet Telephony

A category of hardware and software that enables people to use the Internet as the transmission medium for telephone calls. For users who have free, or fixed-price Internet access, Internet telephony software essentially provides free telephone calls anywhere in the world. To date, however, Internet telephony does not offer the same quality of telephone service as direct telephone connections. There are many Internet telephony applications available. Some, like CoolTalk and NetMeeting, come bundled with popular Web browsers. Others are stand-alone products. Internet telephony products are sometimes called IP telephony, Voice over the Internet (VoI) or Voice over IP (VoIP) products.

IP Address

The Layer 3 address of a host computer attached to a TCP/IP network. Every host must have a unique IP address. IP addresses are 32-bit values written as four sets of decimal numbers separated by periods; for example, 125.6.65.7. Each decimal number (0-255) represents 8 bits of the complete 32-bit value. This is commonly referred to as "dotted decimal" notation. The TCP/IP packet uses 32 bits to contain the IP address, which consists of a network address (netid) and a host address (hostid). The 32 bits are divided in different ways according to the class of the address, which determines the number of hosts that can be attached to the network. If more bits are used for the host addresses (such as in Class A), fewer bits are available for the network address. This process uses a subnet mask to determine what part of the address is the network portion, and which part is the host portion. This is also known as Classless Inter-domain Routing (CIDR). Network addresses are supplied to organizations by the InterNIC Registration Service. A new standard for IP addresses has been created that uses 128 bit addresses. See "IPv6".

IP Security (IPSec)

A set of protocols being developed by the IETF to support secure exchange of packets at the IP layer. Once it's completed, IPsec is expected to be deployed widely to implement Virtual Private Networks (VPNs). IPsec supports two encryption modes: Transport and Tunnel. Transport mode encrypts only the data portion (payload) of each packet, but leaves the header untouched. The more secure Tunnel mode encrypts both the header and the payload. On the receiving side, an IPSec-compliant device decrypts each packet. For IPsec to work, the sending and receiving devices must share a public key. This is accomplished through a protocol known as Internet Security Association and Key Management Protocol/Oakley (ISAKMP/Oakley), which allows the receiver to obtain a public key and authenticate the sender using digital certificates.

IP Switching

A form of layer 3 cut-through switching pioneered by Ipsilon Corporation, which is now a division of Nokia. In IP Switching, the first packet, or packets, of each information flow is routed as in a traditional router-based network. However, if the routers detect that the flow is likely to be long-lived (as, for example, an FTP connection), then a cut-through path is set up between the end stations.

Leased Line

A transmission facility which is leased by an end user from a public carrier, and which is dedicated to that user's traffic. Typically, frequency synchronization is maintained from one end of the circuit to the other. Leased line circuits are generally used less in recent times, while public data networks are more common.

Least Cost Routing (LCR)

LCR is a mechanism that allows the use of the cheapest path inside a network and the cheapest operator for a call. It is done by the PABX and according to the direction called (country, city,…) by analyzing the number called it brings the call to the cheapest trunk-group according to the called destination.

Local Loop

The physical connection from the subscriber's premise to the carrier's POP (Point of Presence). The local loop can be provided over any suitable transmission medium, including twisted pair, fibre optic, coax, or microwave.

Locator Services

Use of a code such as IP or telephone area code to locate local information from a database.

Logical Agent

Agent who is independent of the terminal at which he or she logs on.

Message

A unit of data that is transmitted from one correspondent to another. Auditory data placed in a voice mailbox is one type of message. Voice messages may be left by callers, subscribers, systems, or system administrators. Data messages are exchanged over a network. A variety of protocols and network transmission mechanisms are defined to facilitate this message exchange.

Messaging Application Programming Interface (MAPI)

A system built into Microsoft Windows that enables different e-mail applications to work together to distribute mail. As long as both applications are MAPI-enabled, they can share mail messages with each other.

Multiplex

To transmit two or more messages or message streams on a single channel, typically through the use of frequency-division multiplexing, time division multiplexing, or statistical time division multiplexing.

Multiplexor (MUX)

A communications device that multiplexes (combines several signals for transmission over a single medium. A demultiplexor completes the process by separating multiplexed signals from a transmission line. Frequently a multiplexor and demultiplexor are combined into a single device capable of processing both outgoing and incoming signals. A multiplexor is sometimes called a MUX.

Multi-Protocol Label Switching (MPLS)

An IETF initiative that integrates Layer 2 information about network links (bandwidth, latency, utilization) into Layer 3 (IP) within a particular autonomous system-or ISP - in order to simplify and improve IP -packet exchange. MPLS gives network operators a great deal of flexibility to divert and route traffic around link failures, congestion, and bottlenecks. From a QoS standpoint, ISPs will better be able to manage different kinds of data streams based on priority and service plan. For instance, those who subscribe to a premium service plan or those who receive a lot of streaming media or high-bandwidth content can see minimal latency and packet loss. When packets enter a MPLS-based network, label edge routers (LERs) give them a label (identifier). These labels not only contain information based on the routing table entry (e.g., destination, bandwidth, delay, and other metrics), but also refer to the IP header field (source IP address), Layer 4 socket number information, and differentiated service. Once this classification is complete and mapped, different packets are assigned to corresponding labelled switch paths (LSPs), where label switch routers (LSRs) place outgoing labels on the packets. With these LSPs, network operators can divert and route traffic based on data-stream type and Internet-access customer.

Network File System (NFS)

An open operating system designed by Sun Microsystems that allows all network users to access shared files stored on computers of different types. NFS provides access to shared files through an interface called the Virtual File System (VFS) that runs on top of TCP/IP. Users can manipulate shared files as if they were stored locally on the users' own hard disk. With NFS, computers connected to a network operate as clients while accessing remote files, and as servers while providing remote users access to local shared files. The NFS standards are publicly available and widely used.

Node

In networks, a processing location. A node can be a computer or some other device, such as a printer. Every node has a unique network address, sometimes called a Data Link Control (DLC) address or Media Access Control (MAC) address.

Point-to-Point Protocol (PPP)

The successor to SLIP, PPP is a layer 2 protocol that provides router-to-router and computer-to-network connections across a wide area circuit, generally in a TCP/IP network.

Point-to-Point Tunnelling Protocol (PPTP)

A new technology for creating Virtual Private Networks (VPNs), developed jointly by Microsoft Corporation, U.S. Robotics, and several remote access vendor companies, known collectively as the PPTP Forum. A VPN is a private network of computers that uses the public Internet to connect some nodes. Because the Internet is essentially an open network, the Point-to-Point Tunnelling Protocol (PPTP) is used to ensure that messages transmitted from one VPN node to another are secure. With PPTP, users can dial in to their corporate network via the Internet. Although PPTP has been submitted to the IETF for standardization, it is currently available only on networks served by a Windows NT 4.0 server and Linux.

Private Branch Exchange (PBX or PABX)

A private telephone network used within an enterprise. Users of the PBX share a certain number of outside lines for making telephone calls external to the PBX. Most medium-sized and larger companies use a PBX because it's much less expensive than connecting an external telephone line to every telephone in the organization. In addition, it's easier to call someone within a PBX because the number you need to dial is typically just 3 or 4 digits. A variation on the PBX theme is the Centrex, which is a PBX with all switching occurring at a local telephone office instead of at the company's premises. See also "Private Communications Exchange."

Private Communications Exchange (PCX)

This is a client/server, open standards system that is now replacing PBXs. It brings together an organization's networking and information technology systems with the Internet, aligning voice communications more tightly with computer applications.

Private Network-to-Node Interface (PNNI)

An advanced, dynamic routing protocol that operates between ATM switches. It is based on link-state protocols, such as OSPF, with extensions that enable switches to advertise their own capabilities, such as capacity and delay.

Protocol

An agreed-upon format for transmitting data between two devices. The protocol determines the type of error checking to be used, the data compression method if used, how the sending device will indicate that it has finished sending a message, and how the receiving device will indicate that it has received a message. There are a variety of standard protocols from which programmers can choose. Each has particular advantages and disadvantages; for example, some are simpler than others are, some are more reliable, and some are faster. From a user's point of view, the only interesting aspect about protocols is that your computer or device must support the right ones if you want to communicate with other computers. Protocols are implemented either in hardware or software.

Public Switched Telephone Network (PSTN)

Refers to the international telephone system based on copper wires carrying analogue voice data. This is in contrast to newer telephone networks base on digital technologies, such as ISDN and FDDI. Telephone service carried by the PSTN is often called plain old telephone service (POTS).

Pulse Code Modulation (PCM)

A sampling technique for digitizing analogue signals, especially audio signals. PCM samples the signal 8000 times a second; each sample is represented by 8 bits for a total of 64 Kbps. There are two standards for coding the sample level. The Mu-Law standard is used in North America and Japan while the A-Law standard is use in most other countries. PCM is used with T-1 and T-3 carrier systems. These carrier systems combine the PCM signals from many lines and transmit them over a single cable or other medium.

Pulse Dialling

A signalling method between a phone and switch, where each digit sent by the phone is represented by a series of pulses.

QSIG

QSIG is a protocol standardized by ITU. This protocol has been designed to run on PRA/PRI accesses and to become the standard protocol between PABXs. It has been implemented by most manufacturers of PABXs to build digital heterogeneous networking. It is a feature-rich protocol if used in its Generic-Function and Supplementary Services version.

RADIUS

See "Remote Access Dial-In User Service".

Redundant Array of Inexpensive Disks (RAID)

A category of disk drives that employs two or more drives in combination for fault tolerance and performance. RAID disk drives are used frequently on servers but aren't generally necessary for personal computers.

Ringback Signal

The tone heard by a calling device when, at the called-device's end, the telephone is ringing or the system is otherwise being alerted of the incoming call.

Ringing Signal

Any AC or DC signal transmitted over a line or trunk for the purpose of alerting someone or something at the distant end of an incoming call.

Route

The path network traffic takes from its source to its destination.

Router

A layer-three device responsible for making decisions regarding which of several paths network traffic will follow. To do this, it uses a routing protocol to gain information about the network, and algorithms to choose the best route based on several criteria (known as routing metrics). Routers interconnect subnets.

Routing

The process of delivering a message across a network or networks via the most appropriate path.

Secure Sockets Layer (SSL)

A protocol developed by Netscape for transmitting private documents via the Internet. SSL works by using a private key to encrypt data that's transferred over the SSL connection. Both Netscape Navigator and Internet Explorer support SSL, and many Web sites use the protocol to obtain confidential user information, such as credit card numbers. By convention, Web pages that require an SSL connection start with https: instead of http:. Another protocol for transmitting data securely over the World Wide Web is Secure HTTP (S-HTTP). Whereas SSL creates a secure connection between a client and a server, over which any amount of data can be sent securely, S-HTTP is designed to transmit individual messages securely. SSL and S-HTTP, therefore, can be seen as complementary rather than competing technologies. Both protocols have been approved by the Internet Engineering Task Force (IETF) as a standard.

Session Initiation Protocol (SIP)

The Session Initiation Protocol (SIP) is a signalling protocol, widely used for setting up and tearing down multimedia communication sessions such as voice and video calls over the Internet. Other feasible application examples include video conferencing, streaming multimedia distribution, instant messaging, presence information and online games.

S-HTTP

An extension to the HTTP protocol to support sending data securely over the World Wide Web. Not all Web browsers and servers support S-HTTP. Another technology for transmitting secure communications over the World Wide Web —Secure Sockets Layer (SSL) — is more prevalent. However, SSL and S-HTTP have very different designs and goals so it is possible to use the two protocols together. Whereas SSL is designed to establish a secure connection between two computers, S-HTTP is designed to send individual messages securely. Both protocols have been submitted to the Internet Engineering Task Force (IETF) for approval as a standard. S-HTTP was developed by Enterprise Integration Technologies (EIT), which was acquired by Verifone, Inc. in 1995.

Signalling

(1) The use of signals to control communications. (2) In a telecommunications network, the information exchange concerning the establishment and control of a connection and the management of the network, in contrast to user information transfer. (3) The sending of a signal from the transmitting end of a circuit to inform a user at the receiving end that a message is to be sent.

Simple Mail Transfer Protocol (SMTP)

A protocol for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP. In addition, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP and IMAP server and the SMTP server when you configure your e-mail application.

Single Mode

A form of fibre optic cabling in which light follows a single path as it traverses the cable. More expensive, and with a higher maximum rate and distance, than multimode fibre optic cable.

Speaker Dependent Voice Recognition

Recognition of spoken words, by a speaker which the system has been trained to recognize.

Speaker Independent Voice Recognition

Recognition of words spoken by any speaker.

Speaker Verification

Recognizing a speaker by their voice print.

Statistical Time Division Multiplexing (STDM)

Also known as statistical multiplexing. A form of time division multiplexing in which a given data stream can obtain more or less bandwidth dynamically, based on its needs and on the demands of other data streams. Widely used in devices such as routers, LAN switches, and frame relay switches.

Subscriber

A voice messaging system user who has the capability to originate and receive voice messages and to manage stored voice data. Formerly referred to as a caller.

Supervisory Signal

Supervisory signals are the means by which a telephone user initiates a request for service; or holds or releases a connection; or flashes to recall an operator or to initiate additional features, for example, 3 way calling. Supervisory signals are also used to initiate and terminate charging on a call. A signal also indicates whether or not a circuit is in use.

Switched Virtual Circuit (SVC)

A temporary virtual circuit that is set up and used only as long as data is being transmitted. Once the communication between the two hosts is complete, the SVC disappears. In contrast, a permanent virtual circuit (PVC) remains available at all times.

Synchronous

Signals that are sourced from the same timing reference and have the same frequency. For example, in high-speed wide area digital communications, the network commonly provides a reference-clocking source to which each subscriber's equipment synchronizes its transmissions.

Synchronous Optical Network (SONET)

A set of standards for data communication over fibre optic cable at speeds of 51.84 Mbps and above.

Synchronous Transfer Mode

B-ISDN communications method that transmits a group of different data streams synchronized to a single reference clock.

Telephony Application Programming Interface (TAPI)

An API for connecting a PC running Windows to telephone services. TAPI was introduced in 1993 as the result of joint development by Microsoft and Intel. The standard supports connections by individual computers as well as LAN connections serving many computers. Within each connection type, TAPI defines standards for simple call control and for manipulating call content. The Telephony Server Application Programming Interface (TSAPI) defines similar capabilities for NetWare servers.

Telnet

The protocol within the TCP/IP protocol suite that provides a terminal connection function. Telnet allows a user at one site to connect to another timesharing system over an IP network by transmitting keystrokes to the remote machine and echoing characters back to the user. The remotely connected user will have the impression that he is working on a local machine if he is using a high speed IP connection. Telnet validates access to the remote system by validating user id and password.

Tie line

A dedicated circuit linking two points without having to dial the normal phone number. A tie line may be accessed by lifting a telephone handset or by pushing one, two or three buttons.

Time Division Multiplexing (TDM)

A type of multiplexing that combines data streams by assigning each stream a different time slot in a set. TDM repeatedly transmits a fixed sequence of time slots over a single transmission channel. Within T-Carrier systems, such as T1 and T3, TDM combines Pulse Code Modulated (PCM) streams created for each conversation or data stream.

Transmission Control Protocol/Internet Protocol (TCP/IP)

The suite of communications protocols used to connect hosts on the Internet. TCP/IP uses several protocols, the two main ones being TCP and IP. TCP/IP is built into the UNIX operating system and is used by the Internet, making it the de facto standard for transmitting data over networks. Even network operating systems that have their own protocols, such as NetWare, also support TCP/IP.

Trivial File Transfer Protocol (TFTP)

A simple form of the File Transfer Protocol (FTP). TFTP uses the User Datagram Protocol (UDP) and provides no security features. It is often used by servers to boot diskless workstations, X-terminals, and routers.

Trunk Line

When dealing with a PBX, trunk lines are the phone lines coming into the PBX from the telephone provider. This differentiates these incoming lines from extension lines that connect the PBX to (usually) individual phone sets. Trunking saves cost, because there are usually fewer trunk lines than extension lines, since it is unusual in most offices to have all extension lines in use for external calls at once.

Uniform Resource Locator (URL)

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. The URL contains the protocol prefix, port number, domain name, subdirectory names, and file name. Port addresses are generally defaults and are rarely specified. To access a home page on a Web site, only the protocol and domain name is required. For example, http://www.alcatel.com retrieves the home page at Alcatel's Web site. The http:// is the Web protocol, and www.alcatel.com is the domain name.

Universal Serial Bus (USB)

A new external bus standard that supports data transfer rates of 12 Mbps (12 million bits per second). A single USB port can be used to connect up to 127 peripheral devices, such as mice, modems, and keyboards. USB also supports Plug-and-Play installation and hot plugging. Starting in 1996, a few computer manufacturers started including USB support in their new machines. It wasn't until the release of the best-selling iMac in 1998 that USB became widespread. It is expected to completely replace serial and parallel ports.

Unvoiced Sounds

May be fricative or aspirated. Vocal cords do not vibrate for either. Fricative sounds such as ‘s' or ‘sh' are generated at some point in the vocal tract. As air is forced past it turbulence occurs causing a random noise. Since the points of constriction tend to occur near the front of the mouth, the resonances of the vocal tract have little effect on sound being produced. In aspirated sounds, such as ‘h' of ‘hello', turbulent airflow occurs at the glottis as the vocal cords are held slightly apart. Resonances of the vocal tract modulate the spectrum of the random noise as heard in whispered speech.

Virtual LAN (VLAN)

A network of computers that are in the same broadcast domain. Even though they may be physically located on other machines, the devices in a virtual LAN are logically associated such that they behave as one subnet. VLANs are configured through software rather than hardware, which make them extremely flexible. One of the biggest advantages of VLANs is that when a computer is physically moved to another location, it can stay on the same VLAN without any hardware reconfiguration.

Virtual Private Network (VPN)

A network that is constructed by using public wires to connect nodes. For example, there are a number of systems that enable you to create networks using the Internet as the medium for transporting data. These systems use encryption and other security mechanisms to ensure that only authorized users can access the network and that the data cannot be intercepted.

Voice Board

An interface card which handles the connection between voice input and the computer.

Voice Encoding Algorithm-ADPCM (G.721)

A standard for digitally encoding analogue voice signals.

Voice Message

A digitally recorded message, input from a telephone.

Voice over IP (VoIP)

The ability to make telephone calls and send faxes over IP-based data networks with a suitable quality of service (QoS) and superior cost/benefit. Additionally VoIP provides the foundation to allow productivity improving applications to be deployed. For example, voice messages can be prepared using a telephone and then delivered to an integrated voice/data mailbox using Internet or intranet services.

Voice Processing

A broad term encompassing several voice-linked facilities. The facilities divide into two sections; treating voice calls as messages, and using a telephone as an interactive terminal to gain access to data and other message facilities.

Voice Recognition

Recognition of spoken words. It can by speaker dependent or speaker independent.

Voice Response (VR)

Response to an incoming telephone call with synthesized speech.

Voiced Sounds

Sounds such as 'aah' or 'oh' are produced when the vocal cords are tensed together and vibrate as the air pressure builds up, forcing the glottis open, and then subsides as the air passes through. This vibration has a frequency spectrum rich in harmonics at multiples of the fundamental frequency (pitch). Speakers vary pitch with air pressure in the lungs and tension on the vocal cords.

Voicemail (VM)

A system for storing, reviewing, and distributing voice messages.

Waveform Coding

A technique whereby the waveform of a source signal (e.g. speech pattern) is approximated by mimicking the amplitudes-vs-time waveform. In this technique, the speech coding consists of sampling the amplitude of the waveform, approximating the sampled value by the quantization process, and representing, or digitally encoding, the quantized amplitude value by a number of binary bits for transmission. Upon arrival at the destination, the received digital signal is decoded to reconstruct the original waveform as faithfully as possible.