Telecom Glossary edited by Erin Malone Chris Janson 1st edition Publisher Acknowledgement: This is the first edition of this book. Please notify us of any acronyms we may have missed by submitting them via the form at www.ciena.com/glossary. We will be happy to in- clude them in further editions of “The Acronyms Guide”. For additional information on Ciena’s Carrier Ethernet or Optical Communications Certification programs please contact [email protected]. Table of Contents A .......................................1 B .......................................2 C .......................................3 D .......................................5 E .......................................6 F........................................6 G .......................................7 H .......................................8 I .........................................8 J ........................................9 K .......................................9 L ........................................9 M ....................................10 N .....................................11 O.....................................12 P .....................................13 Q.....................................14 R .....................................15 S......................................16 T .....................................17 U .....................................18 V .....................................18 W ....................................19 X .....................................19 A Add/Drop Allows optical wavelengths to be added or dropped at any line amplifier location. Add/Drop Multiplexer (ADM) A device that enables data to enter and leave a SONET bit stream without having to demultiplex the stream. ADSL (Full Rate Asymmetrical DSL) ADSL offers differing upload and download speeds and can be configured to deliver up to six megabits of data per second (6000K), from the network to the customer, that is up to 120 times faster than dial-up service and 100 times faster than ISDN. ADSL enables voice and high-speed data to be sent simul- taneously over the existing telephone line. This type of DSL is the most predominant in commercial use for business and residential customers around the world. Good for general Internet access and for applications where downstream speed is most important, such as video-on-demand. ITU-T Recommendation G.992.1 and ANSI Standard T1.413- 1998 specify full rate ADSL. ITU Recommendation G.992.3 specifies ADSL2 which pro- vides advanced diagnostics, power saving functions, PSD shaping, and slightly better performance than G.992.1. ITU Recommendation G.992.5 specifies ADSL2Plus, which provides the benefits of ADSL2Plus twice the bandwidth so that bit rates as high as 20 Mb/s downstream can be achieved on relatively short lines. AIS (Alarm Indication Signal) A signal, transmitted by a system within a communica- tions link, which lets the receiver know that some part of the link has failed. Two types of AIS signals are Alarm Indication Signal Path (AIS-P) and Alarm Indication Signal Line (AIS-L). American National Standards Institute (ANSI) The coordinating body for voluntary standards groups within the United States. ANSI is a member of the International Stan- dards Organization for Standardization (ISO). Amplifier Any device that uses a small amount of energy to control a source of a larger amount of energy. Amplitude Modulation (AM) A form of modulation in which the amplitude of a carrier wave is varied in direct proportion to that of a modulating signal. Asynchronous Replication A replication technique in which data must be committed to storage at only the primary site and not the secondary site before the write is ac- knowledged to the host. Data is then forwarded to the secondary site as the network capabilities permit. Asynchronous Serial Interface (ASI) A serial data transmission method for MPEG-2 that allows packet-based transmission of compressed video in DTV transmission. Asynchronous Transmission A method of data transmission which allows data bits to be sent at irregular intervals by preceding each with a start bit, and following it with a stop bit. Asynchronous Transfer Mode (ATM) A cell relay network protocol which encodes data traffic into small fixed-sized (53 byte: 48 bytes of data and 5 bytes of header information) cells instead of variable-sized packets, as found in packet-switched networks such as the Internet Protocol or Ethernet. It is a connection-oriented technology, in which a connec- tion is established between the two endpoints before the actual data exchange begins. ATM Adaptation Layer (AAL) A process that converts data between higher level pro- tocols such as IP and ATM. At the originating end of an ATM connection, AAL segments the higher level bundles of data into ATM cells. At the destination end of the connec- 1 tion, ATM reassembles the cells into the higher level bundles. AAL is divided into types, which in turn support specific types of data traffic. ATM Adaptation Layer 1 Circuit Emulation (AAL1) AAL that supports constant bit rate traffic that cannot tolerate delays, such as uncompressed voice and video transmission. ATM Adaptation Layer 2 Transport (AAL2) AAL that supports variable bit rate traffic such as compressed voice and video. ATM Adaptation Layer 5 (AAL5) AAL that supports variable bit rate traffic that can be delayed. ATM Service Access Multiplexer (ATM SAM) An ATM switch used by a service provider to aggregate various forms of subscriber traffic (such as T1 or Ethernet) for transmission over an ATM backbone. Attenuation (1) Limited Operation (1) The condition in a fiber optic link where op- eration is limited by the power of the received signal, rather than by bandwidth or by distortion. (2) The decrease in magnitude of power of a signal in transmission between points. A term used for expressing the total losses on an optical fiber consisting of the ratio of light output to light input. Attenuation is usually measured in decibels per kilometer (dB/km) at a specific wavelength. Typical multi-mode wavelengths are 850 and 1300 nanometers (nm); singlemode, at 1300 and 1500 nm. NOTE: When specifying attenuation, it is important to note if it is nominal or average, room temperature, value or maximum over operating range. Automatically Switched Optical Network (ASON) A network enabling the automatic delivery of transport services, not only leased-line connections but also other transport services, such as soft permanent and switched optical connections. Automatically Switched Transport Network (ASTN) A network that allows traffic paths to be set up automatically through a switched network. The term ASTN is often used interchangeably with GMPLS (Generalized MPLS). Availability The amount of time that a system is available during time periods when it is expected to be available. Availability is often measured as a percentage of an elapsed year. For example, 99.95% availability equates to 4.38 hours of downtime in a year (0.0005 * 365 * 24=4.38) for a system that is expected to be available all the time. (Provided by SNIA) B Backup A collection of data stored on (usually removable) non-volatile storage media for purposes of recovery in case the original copy of data is lost or becomes inaccessible. Also called backup copy. To be useful for recovery, a backup must be made by copying the source data image when it is in a consistent state. Backup Window An interval of time during which a set of data can be backed up without seriously affecting applications that use the data. For example, if an applica- tion accesses data from 8AM until midnight, then the window between midnight and 8AM is available for making backup copies. Offline backups require that applications not update data during the backup. Online backups typically use point-in-time copy technology to create consistent images of data for backup. Backbone (1) The part of a network used as the primary path for transporting traffic between network segments. (2) A high-speed line, or a series of connections, that forms a major pathway within a network. 2 Bandwidth (1) Measure of the information capacity of a transmission channel. (2) The difference between the highest and lowest frequencies of a band that can be passed by a transmission medium without undue distortion, such as the AM band - 535 to 1705 kilohertz. (3) Information carrying capacity of a communication channel. Analog bandwidth is the range of signal frequencies that can be transmitted by a communi- cation channel or network. (4) A term used to indicate the amount of transmission or processing capacity possessed by a system or a specific location in a system (usually a network system). Best Effort A class of service which does not guarantee delivery of packets, frames, or datagrams, but for which the network, fabric, or interconnect makes every reasonable delivery effort. Bit Error Rate (BER) (1) Percentage of bits in a transmittal received in error. (2) The number of coding violations detected in a unit of time, usually one second. (3) Specifies expected frequency of errors and compares the ratio of incorrectly transmitted bits to correctly transmitted bits. Also known as Bit Error Ratio. Bits Per Second (b/ps) (1) The number of bits passing a point every second. The trans- mission rate for digital information. (2) A measurement of how fast data is moved from one place to another (i.e., a 28.8 modem can move 28,800 b/s). Block The unit in which data is stored and retrieved on disk and tape devices. Blocks are the atomic unit of data recognition (through