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10/5/2009
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Abstract syntax notation, number 1
An international OSI standard language (ITU-T X680 - 699) that describes the protocols and programming for the data interchanged between two communicating applications independent of their operating systems and programming languages. It is a formal notation supported by a range of tools.
Invariably used with another word in telecommunications (e.g. access control, access protection, access protocols, access network, wireless access, network access) but sometimes confusingly used on its own as a short-form way of referring to one of the many meanings better defined by the associated word. The variations generally hinge around the common dictionary usage meaning how a user is able to get into a computing or telecommunications system or application.
The most specific reference is usually to the part of the telecommunications network known as the access network.
Methods used to control the way access is gained to applications, software, systems etc.
The access network is the fundamental link between the customer and the serving node in the network.
The term has traditionally been used for the fixed access network that uses copper pairs in cables going from the familiar telephone exchange building to the customer, sometimes called the local network or the local loop. It is also sometimes known as the 'last mile' or even the 'first mile' (the mile is a measure still used in the U.S.A. and is just over 1.6km). As the traditional circuit-switched telephone switching equipment is located further and further away from customers the access network is complemented by concentrators, multiplexers or routers. As a result the building terminating the local cables is sometimes referred to as a wire-centre as it may no longer contain telephone switching equipment. The traditional access network is usually regarded as a part of the fixed network and frequently thought of as just the network of copper pairs, although fibres to businesses are common and the possibility of fibre to the home (FTTH) is constantly under review.
Of course a wide variety of other techniques meet the classification of providing a link between a customer and the serving node: these include many wireless systems including satellites, wireless LANs, wireless MANs, cellular radio systems and broadband fixed wireless systems, sometimes collectively known the wireless local loop (WLL).
Adaptive differential pulse code modulation
A form of pulse code modulation where the resulting digital signal is of a lower rate than simple PCM due to the encoding taking account of the change between consecutive speech samples. A typical PCM coding stream would be at 64kbit/s whereas a comparable ADPCM coding stream might be 32kbit/s.
A system by which information streams in a digital transmission system are taken out (= dropped) at an intermediate multiplexing point and different information streams inserted (= added).
An address defines a location and addressing is the set of schemes used to define locations at various physical and logical levels in the network as well as of the networks' users. Intuitively we understand addresses if we consider the name and address we place on a postal envelope. The address contains information about place and location in a hierarchy.
Addressing in a network is an important construct because it can determine:
- How the network is built.
- How the users perceive the network. (Think of telephone numbers and IP addresses).
- Regulatory regimes or operating constraints. (Think of telephone numbers and the IPv4 address shortage).
- Network limitations. (Think of the size of Internet routing tables).
Networks formed by users or devices wishing to communicate, without necessity for the help of, or existence of, any infrastructure or centralised administration. Each node has a wireless access interface such as Bluetooth, infra-red, UWB or WLAN, and is free to enter or leave the network at any time. Due to the limited range of a node's wireless interface, multiple hops may be needed for communication. Ad-hoc networks can function as standalone networks meeting the direct communication needs of their users, or as an addition to infrastructure based networks to extend or enhance their coverage. Applications of ad-hoc communications include sensor networks, commercial and educational use, emergency cases and military communications. See also symbiotic networks.
The reciprocal of impedance.
Advanced Communications Technology and Services - a European initiative
Advanced Communications Technology and Services, known simply as ACTS, was one of the specific programmes of the Fourth Framework Programme of European Community activities in the field of research and technological development and demonstration (1994 to 1998). ACTS built on the work of the earlier RACE programmes (Research into Advanced Communications for Europe, 1985-1995), and evolved into the European Union 5th, 6th and subsequent framework programmes.
Advanced encryption standard (AES)
A standard secret key cryptography method that uses 128, 192 and 256-bit keys. Officially adopted by the US government in 2001 to replace the Triple Data Encryption Standard (3DES) method which in turn replaced the more basic Data encryption Standard (DES). AES uses the Rijndael algorithm developed by Joan Daemen and Vincent Rijmen of Belgium and was selected from many submissions after testing. AES can be encrypted in one pass instead of three, and its key size is greater than Triple DES's 168 bits.
Advanced intelligent network (AIN)
The term Intelligent Network originated in about 1986 and grew out of the initial implementation of calling-card services in the USA in 1981. It was initially service dependent and the concept arose of "an evolving service-independent network architecture that provides important new capabilities for the rapid creation of customisable telecommunications services" which became known as the Advanced Intelligent Network. With the passage of time it has become largely synonymous with IN. See also Intelligent networks, standards and services, BTTJ Vol 13, No 2.
Advanced Mobile Phone Service (AMPS)
A name for first generation analogue cellular service in the USA.
An agent has several meanings within telecommunications. Whilst it can mean the person answering calls at a call-centre the principal meaning here is for a software agent which performs some information gathering and/or processing task. The concept has been around for a long time allied to developments in artificial intelligence but it is now being adopted for a wide range of applications including Internet searching, management systems and fraud detection systems. See also artificial intelligence.
There is a long history with telecommunications equipment and systems that when something goes wrong it raises an alarm so that an intervention can be made to put it right. In a Strowger exchange a fault would trigger a sequence of events that set an alarm bell ringing to get the attention of a maintenance engineer. The fault would be identified and localised through a set of lights identifying (by their physical location) the floor, rack, equipment bay and then right down to the faulty item. An unattended exchange directed the first main alarm to an attended exchange so that someone could be despatched to follow a similar procedure on site.
As electro-mechanical switching systems were phased out, and the complexity of electronic systems of all types increased, the fault rates of electronic systems became much lower requiring far fewer maintenance people. This resulted in most locations being unattended requiring more centralised alarm reporting together with more detailed fault analysis. Paradoxically the alarm systems to do this became much more complex needing detailed interface specifications to facilitate integration. Nowadays alarm handling and management is mainly a branch of operational support system (OSS) design covering the management of alarms generated by network elements from many different vendors, associating them with the affected services and customers, displaying them to the appropriate personnel and using filtration and correlation tools to facilitate handling and restoration.
Sending a call over another route by a switching system in real-time when the first choice is busy or faulty.
It can also be used to mean the separate physical routing of cables or wireless systems such that the infrastrucure for two alternative routings do not have common physical proximity, more properly known as physical diversity. Physical diversity is used by network operators to provide resilience in the event of major failures. Sometimes physical diversity is specified for parts of private networks.
A form of modulation in which the amplitude of a carrier wave is made to vary in sympathy with the frequency of a signal to be transmitted. One of three basic forms of modulation, the others being frequency modulation and phase modulation. The simplest form af varying the amplitude is to switch the wave on and off and this led to Morse code (and other telegraphic codes). However, for telephony the audio component is used to vary the amplitude of the carrier wave. AM is still used widely for commercial broadcast radio at LF, MF and HF (long wave, medium wave and short wave).
American National Standards Institute (ANSI)
A USA national standards organisation. The American National Standards Institute is a private, non-profit organization that administers and coordinates the U.S. voluntary standardization and conformity assessment system. The Institute's mission is to enhance both the global competitiveness of U.S. business and the U.S. quality of life by promoting and facilitating voluntary consensus standards and conformity assessment systems, and safeguarding their integrity.
American standard code for information interchange (ASCII)
ASCII is the common code for computer equipment. The standard ASCII character set consists of 128 decimal numbers ranging from zero through 127 assigned to letters, numbers, punctuation marks, and the most common special characters. The Extended ASCII character set also consists of 128 decimal numbers and ranges from 128 through 255 representing additional special, mathematical, graphic, and foreign characters - see units and symbols section.
A direct representation of a phenomenon in another form. Often used to indicate human functions such as hearing, speech and vision.
An analogue signal is an electrical signal which represents another form. For example the representation of sound waves as an audio signal or the the representation of an audio signal as a radio frequency signal. For transmission over telecommunications systems analogue signals are now almost always converted to digital form.
The conversion from analogue to digital and from digital to analogue is usually referred to as A/D conversion (the re-conversion may sometimes, but not always, be referred to as D/A).
Analogue display service interface (ADSI)
A USA standard protocol for transferring information between a network or service element and a customer located terminal, typically used for telephones with a limited display capability.
Not isochronous. A signal where the time interval separating any two significant instants in sequential signals is not related to the time interval separating any other two significant instants. See also asynchronous, heterochronous, isochronous, mesochronous, plesiochronous, and synchronous.
A device for transmitting or receiving radio frequency signals. See also propagation.
A mini Java program delivered from a remote location, usually over the Internet and as part of a web page, for use by a Java-capable web-browser (i.e. it runs on a browser that runs Java Virtual Machine).
The task to which a system is applied. The programmes that make use of an underlying resource - such as a computer operatimg system or a telecommunications network.
Where an application hosting company provides the computing and network infrastructure on which companies can run their own applications. It is one way for companies to outsource the management of part of their computing and network infrastructure to another company.
A program in a computer system that performs a specific task for end users (e.g. word processing, accounting), but not concerned with controlling the computer or its operating system.
Application Programming Interface (API)
An API is the interface between a user and a service and represents an abstraction and an encapsulation of the service. An API service definition consists of three basic elements: a description of the service, a set of procedure or function calls, and definitions of the data types that are employed. The publication of APIs contributes to the ease of use, openness and longevity of the underlying resource. A network API is an open interface which can be used by application programmers to make use of specified resources within a public telecommunications network - an example of this is Parlay.
Application service provider (ASP)
A company that hosts a set of application packages on their computing and network infrastructure as a service for business users. This is directed towards companies that are not large enough to run their own instances of these packages, but want to benefit from the best of breed functionality provided by them as well as trained maintenance support. Several companies are likely to be sharing one application, and partitioning of data and its security becomes of key importance. The business model for such services continues to evolve as the balance between computing infrastructure and communications costs change over time.
The first three digits of a 10 digit public switched network telephone number in the North American numbering plan. Strictly speaking this is the numbering plan area (NPA) code, which is commonly called the area code. The North American numbering plan covers the United States and its territories, Canada, Bermuda, Anguilla, Antigua & Barbuda, the Bahamas, Barbados, the British Virgin Islands, the Cayman Islands, Dominica, the Dominican Republic, Grenada, Jamaica, Montserrat, St. Kitts and Nevis, St. Lucia, St. Vincent and the Grenadines, Trinidad and Tobago, and Turks & Caicos. The 10 digit number is of the format NXX-NXX-XXX where N is any digit from 2 to 9 and X is any digit from 0 to 9. The area code can be geographic (e.g. 307 for Wyoming) or non-geographic (e.g. 800 for toll free).
The architecture of a system is about its design and how the components inter-connect. It is not the design itself but is a framework for the design and it provides a level of abstraction which allows designers to reason about its behaviour. An agreed architecture is the key to the proper design of the component parts of end-to-end systems. A US Federal Standard defines an architecture as the design principles, physical configuration, functional organisation, operational procedures and data formats used as the basis for the design, construction, modification and operation of a communications network.
A field of research that is working towards the dream of building intelligent machines. AI encompasses many areas of investigation including knowledge-based systems, natural-language processing, speech recognition and synthesis, automated reasoning, automatic programming, machine vision, search and knowledge representation, planning and scheduling, neural networks, robotics, distributed AI and agents, soft computing and nature inspired computing. Although the dream of building a machine to simulate a human in conversation remains a dream (still based on the challenge laid down by Alan Turing in the late 1930's) there has been substantial progress in industry at large, including telecommunications. The paper What has AI done for us?, BTTJ, October 2003 illustrates the position at that time with examples from industry and BT.
Asymmetric digital subscriber line (ADSL)
A high-speed transmission technology used in the local loop, typically to provide digital transmission for data and video services over a single copper-pair whilst maintaining the original existing speech-band telephony service on the same pair.
Digital signals where the time intervals between significant instants have, at least on average, the same duration (or durations that are integer multiples) of the shortest one are called isochronous signals. Isochronous signals can be synchronous or asynchronous, therefore an asynchronous signal is one that is not synchronous. Asynchronous signals can be heterochronous, mesochronous, or plesiochronous. See also anisochronous.
Asynchronous transfer mode (ATM)
ATM is a cell switching technology. It offers low-latency transmission with guaranteed quality of service for carrying voice, data and multimedia signals at up to gigabit speeds. Its title arises because information is transferred across the network asynchronously by it being buffered as it arrives and then filling a cell. which is then transferred. If there is no information an empty (unassigned) cell is sent. A stream of information is sent in cells which arrive in the order that they were sent. Unassigned cells and sequence integrity are two of the ways in which it differs from packet switching - others are that the cells are shorter than in packet networks to achieve low-latency and overheads are minimised due to the controlled environment. The implementation of ATM in networks is closely related to the underlying fibre and SDH networks and to the relationships with IP and MPLS networks. See Asynchronous transfer mode - an overview, BTTJ, Vol 13, No 3.
Asynchronous transfer mode adaptation layer (AAL)
The AAL performs the necessary mapping between the ATM layer and the next highest layer of the ATM protocol model. This is usually done at the edge of the ATM network.
The decrease in power of a signal as it passes through an attenuating device or system, for example down a transmission line. The loss is expressed in decibels (db). An attenuator is a device that reduces the signal level by a given amount.
Audio frequencies are soundwaves which humans can hear and, whilst optimistic for most adults, is generally taken to be in the range 20Hz - 20kHz. For telecommunications purposes the range from 300 - 3,400 Hz is completely adequate for the transmission of speech information.
An audio amplifier is an electronic device used to increase the amplitude of an audio signal.
An audio signal is the electrical equivalent of the soundwaves. Sound waves are converted to and from electrical signals by devices such as microphones and loudspeakers.
Making sure that the person (or another system) trying to access a system is correctly authorised to do so by proving their identity. Authentication of access by a user to multiple services in the same session must be simple with no unnecessary repeats of, for instance, usernames and passwords, which is then sometimes known as single sign-on. Authentication can include various levels such as passwords, access cards and biometric data. Part of the process of making a call in a cellular system involves the authentication of the handset before the call is set up.
Authorisation, authentication and accounting (AAA)
These are the systems used to allow users to access networks and systems attached to networks. AAA systems are composed of several components.
Automatic call distribution/distributor
A method of distributing incoming calls to a business such that they are evenly allocated amongst the available operators. The technologies are associated with computer telephony integration (CTI) and the widespread adoption of call-centres.
Varying the gain in an amplifying system by electronic control to attempt to maintain a constant output level with varying input level, such as in a radio-frequency receiver or audio amplifier. Where applied wholly to an audio system it is often referred to as automatic volume control (AVC).
Automatic volume control (AVC)
In some applications using audio amplifiers it is desirable for the output level to be largely independent of the input level. This can be achieved by the use of AVC whereby a signal proportional to the output is fed back to the input stage to regulate the gain in the amplifier. By adding circuitry for controlling time constants the same techniques provide audio compression in which soft sounds are emphasised and loud sounds minimised to limit the dynamic range and its inverse, audio expansion. AVC is a specific form of AGC.
Autonomous means self-governing. An autonomous network is one where the computing components perform services collaboratively and usually without human intervention. The term is evolving and is used at one extreme to mean simple collaborative networking of people with a common interest to, at the other extreme, the most advanced research ideas for machine to machine collaboration embracing issues and technologies such as intelligent agents, task scheduling, load balancing, network access security and network management.
An autonomous system is a routing entity in the Internet. It is a connected group of one or more Internet Protocol prefixes run by one or more network operators which has a consolidated policy and procedure for exchanging traffic with others. It uses an interior gateway protocol (IGP) within the AS and an exterior gateway protocol (EGP) to route traffic to other AS's. An autonomous system number (ASN) is an unique identifier for each autonomous system. Many thousands of ASNs have been allocated. ASN1 was given to Bolt, Baranek and Newman (BBN) as a result of the part they played in ARPANET, the early stage of the development of the Internet.
Generally taken to mean the projection and sound systems required for a presentation or display.
A quality of service measure indicating the time the service or network element is available for use compared to the time it is not. It is usually stated as a percentage or decimal. Availability to the user can be translated into system requirements and is influenced by a number of areas such as the time to recover from a fault or by providing redundancy so that if one part fails another takes on the function and thus the inherent reliability of each part can be less onerous. The balance of decisions made in the system design to meet the requirement is invariably based on cost. The most common manifestation of availability is the so-called five nines, or 99.999%, of network up-time widely adopted for telecommunications systems. See also performance and quality of service.
Average revenue per user (ARPU)
A measure, first used in the cellular industry, to provide an average measure of the income derived by taking the sum of the income from all the users of a service or system divided by the number of users. Widely used by financial analysts to evaluate an operator's performance.
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