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10/5/2009
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eCommerce involves dealing with the customer (business to customer - B2C) via the web to support online transactions for products. It comprises the following features:
A shorter form of electronic mail which, as one of the first and popular uses of the contraction, also gave rise to e-everything (e.g. e-learning, e-commerce) as the impact of the Internet entered general awareness. e-mail was originally taken to be a predominantly text-based communication between desktop computers but the extension to allow attached files of almost any form, including speech and video, has extended the concept. It is not, however, normally associated with voice-mail or with text messages to or from mobile phones even though these are messages in electronic form. However, the use of handheld mobile devices (PDA and proprietary) for e-mail, using radio communication to a central server, is now common and growing.
Echo/echo-suppression/echo-cancellation
Most people are familiar with an echo of a sound, where the sound waves are reflected back and repeated at a lower level and with a time delay. The same applies with electromagnetic waves. The effects can be good or bad. Radar is based on the detection and resolution of reflected waves.
Telecommunications using speech would be much more difficult if the normal telephone handset did not allow for some feedback of the outgoing sound to the speaker's ear, where it is known as sidetone. Where it becomes a problem to both speech and data transmission is when the return signal is intrusive because of its level or its delay or both. It can arise due to the imperfections of transmission systems over long distances, particularly transcontinental links, transoceanic cables and satellite systems where the path length transit-time becomes noticeable in terms of the speed of light. Fortunately any problems that arise can be dealt with electronically to suppress them by turning off the return channel or to cancel them by deriving and applying an equal and opposite signal to the echo to cancel out the original. In the early days of very long-distance transmission it was a problem and a challenge especially to maintain full duplex data transmission but nowadays it is fully taken into account in the design of transmission systems and modems.
At its simplest the term means the inter-relationship of electricity and magnetism. At a more complex level the descriptions and characteristics of changing electric and magnetic fields and the way they propagate led to an understanding of the fundamental aspects of telecommunications and of much else. The basic laws of electromagnetism were first determined by James Maxwell based on work by Ampere and Faraday. Showing that electromagnetic waves moved at the speed of light subsequently led to the discovery of radio waves, developed by Hertz, and to the development of the theory of relativity by Einstein. Maxwell's original work was refined by Oliver Heaviside into four equations known as Maxwell's equations or laws.
Electromagnetic waves and spectrum
Electromagnetic waves include radio waves and extend through infra-red, visible and ultraviolet light to X-rays and Gamma-rays. They are usually defined by their frequency or wavelength in free space (a vacuum), which is virtually the same as in air. Their speed in free-space is the speed of light. However, free-space is not the only medium for electromagnetic propagation: transmission lines, including copper pairs, co-axial cables and waveguides, all convey electromagnetic waves of various frequencies, including those below radio frquencies. Transmission lines introduce speed variations compared to the speed of light which introduces delay.
Frequency, wavelength and speed of light are related (see wavelength and also the electromagnetic frequency spectrum in Units and Symbols). The longest radio waves exceed 10km and the shortest gamma rays are less than 10 pico-metres. The radio spectrum is regulated by governments through the ITU-R.
Electromagnetic emissions can take the form of particles as well as waves. An electron behaves as both a wave and a particle but the best known example of a particle is the photon. Here the relationship is between the energy of the particle and the frequency of the wave, given by E=fh where E is the energy of the photon, f is the frequency of the wave and h is a constant named after Max Planck (i.e. Planck's Constant) also forming the basis for quantum mechanics/quantum physics.
It is worth noting that at the low-end of the electromagnetic spectrum the frequencies of very low frequency radio (e.g. 16kHz) are sometimes confused with audio frequencies. Whilst the wavelength is the same there is no other similarity between sound waves travelling at approximately 344 metres/sec and radio waves travelling at 300,000,000 metres/sec: ears cannot resolve electromagnetic emissions.
An encoding process, such as in Pulse Code Modulation, finds a quantised level which is nearest to that of the signal sample. The quantised level can then be described by a suitable code, such a binary.
A process of converting a signal into a form where the authorised recipient can recover the original but an unauthorised recipient cannot.
The whole range of computing resources employed by a (usually large) company.
The network used by a (usually large) company. The term embraces the company's own resources for data and voice (e.g. LANs and PBX) and also includes the wide area communications between sites, such as leased-lines but not the PSTN.
Enterprise Resource Management (ERM)
Enterprise Resource Management (ERM) is concerned with the management of the resources of the company, primarily finances, people and materials. ERM systems embrace the following aspects:
- Financial management software that includes functionality such as General Ledger, Fixed Assets, etc., from which the company’s financial accounts are produced, as well as managing financial transactions with suppliers (Accounts Payable) and customers (Accounts Receivable).
- Human Resource management software that tracks the relationship of each employee with the company, including recruitment, training, attendance, etc., in addition to payroll, expenses management and pension.
- Supply Chain Management software that automates the ordering of goods from suppliers, transportation routing, warehouse management, etc. One significant aspect is the planning of replenishment of warehouses, which can obviously have a sizeable impact upon the company costs and cash flow. The necessary sophistication of this component has sometimes put it outside the scope of the standard ERM application.
- Project management software that is used for estimating and optimising tasks and resources required to plan and complete a project.
- Maintenance management software that automates the many aspects of maintenance operations (eg machinery and equipment, buildings or grounds). The software generally includes functionality for planning, organising, and implementing maintenance activities.
This is neither an acronym nor an abbreviation. However, it can be thought of as e-numbering as it brings together the world of telephony and the Internet, especially with the use of voice over IP (VoIP).
With telephone and IP networks converging, there was a need to make the best use of the telephony numbering system and the data-related naming and addressing systems to bring benefit to customers. The ENUM protocol is the result of work of the Internet Engineering Task Force's (IETF's) Telephone Number Mapping working group. The charter of this working group was to define a DNS-based architecture and protocols for mapping a telephone number to a Uniform Resource Identifier (URI) which can be used to resolve E.164 telephone numbers into other resources or services on the Internet.
An electronic form of smoothing out inequalities of a signal, usually in the frequency domain but also sometimes in the time domain. Examples include audio equalisation to improve the frequency response of circuits over audio cables and equalisation to overcome group delay.
The Erlang is the unit of telephone traffic. At its simplest, a circuit fully occupied over the period of measurement is carrying 1 Erlang. The period of measurement, stemming from the history of the busy-hour, is usually 1 hour. However, whilst this simple definition relates occupancy to the traffic carried it does not take into account the traffic offered. The full application of Erlang's work relates the proportion of lost calls (i.e. grade of service) with the average traffic offered and the number of circuits available.
A K Erlang was a Danish engineer who developed mathematical solutions to issues of switching system design. Other solutions were developed by Grinsted, Lely, Molina, Lubberger and many others but the assumptions of Erlang most nearly met the practical conditions of the then British Post Office (now BT) and were adopted by them and became Internationally accepted.
In a digital system an error occurs when a received symbol is not the in the same state as when it was transmitted, when a symbol is omitted completely, or when a symbol is spuriously added.
The monitoring, detection and correction of errors were key developments in the early days of digital transmission. High-speed digital systems became possible through the design of systems to minimise error rate. Errors can have different effects - they can result in no impairment of a signal if corrected or they may result in loss of information and/or synchronisation failure. There is therefore a concept of the magnitude of errors. Errors apply to symbols and also to groups of symbols such as words, blocks, packets and frames. Errors can occur singly (random) or in groups (bursts).
Error detection identifies that a symbol, word, block, packet or frame has an error as received. Error detection takes many forms and will depend on the coding system employed. For instance, some codes have a parity bit which allows the checking of received patterns for consistency but the parity bit adds an overhead or redundancy. All forms of error detection incur an overhead and add redundancy and the various forms of detection are often called redundancy checks. These come in various forms: parity checks are called vertical redundancy checking (VRC), blocks can be checked with longitudinal redundancy checking (LRC) but the more common form for blocks, packets and frames is cyclic redundancy checking (CRC).
CRC makes use of a frame check sequence (FCS) or block check character (BCC) to derive a polynomial. This is coded and sent. At the receiving end it is divided by a polynomial derived at that end. If there is no remainder then that signal was error free. There are different forms of CRC depending on the mathematical derivation of the polynomial.
Error correction corrects a detected error. The simplest form of error correction is repetition of the whole or part of the message on request - known as automatic repeat request (ARQ). This obviously requires a return (feedback) channel to be in place. With a poor channel the repetition rate could reach the state that the information transfer is zero so throughput and efficiency must be taken into account as well. The other main form is forward-acting error correction (FEC) which uses special codes designed to allow error correction at the receiving end.
Error performance is a key aspect of quality of service.
Ethernet is a technology that allows a variety of computing devices to be connected together by the use of a low-cost and flexible network design. Ethernet is widely regarded as today's dominant network technology in the Internet (which is actually a network of networks) and around 95% of business data traffic originates on an Ethernet. More and more people are installing networks in their homes and most of these will use Ethernet as well.
Extensible mark-up language (XML)
XML is a standard specification for defining the contents of a computer message. If a software application writes its output in XML and another application is capable of interpreting XML, then it can read the output and act on it. The way XML does this is via the use of tags.
External plant (outside plant)
External plant, known as outside plant in the USA, covers the range of ducts (conduits in USA), cables, poles and street furniture used in telecommunications networks. Sometimes affectionately known as "poles and holes", and also as overhead (the poles etc) and underground (the holes etc). The majority of external plant is to be found in the local-loop otherwise known as the access network providing the communications path between the telephone switching equipment and the customer but important elements are to be found in the inner-core (main) and outer-core (junction) networks providing inter-node transmission systems.
Safety issues for the telephone company employees, contractors and members of the public are extremely important in this area and are given high priority by designers and managers.
An term generally assumed to mean an extension of a company Intranet to allow use by employees and/or trusted customers/suppliers to some parts of the Intranet without allowing access to all-comers from the Internet.
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