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10/5/2009
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Generally taken to cover low frequencies (less than 10 Hz) of jitter. It can cover small fractions (micro/nano) of a second up to daily and annual variations.
The technique for marking paper, including banknotes, as a sign of its quality and/or authenticity and as a hindrance to forgery has been extended to software. Small amounts of code, visible or invisible, can be incorporated into programs to make copying traceable.
Waveguides are essentially hollow copper pipes (rectangular and circular) with special dimensions for carrying specific frequency ranges of microwave signals. Waveguides are low loss and are typically used to feed an antenna from a microwave transmitter. At one stage waveguides were considered for long-distance transmission but optical-fibres overtook the concept.
Wavelength Division Multiplexing (WDM)
A way of increasing the capacity of an optical fibre by simultaneously utilising different wavelengths (frequencies) of light for the transmission of signals. The different wavelengths are determined by very pure laser light sources with each one being modulated with a different signal and the resulting wavelengths combined (i.e. multiplexed) onto a single fibre. At the receive end the signals can be separated by optical splitters and filters or by a dispersive element acting in the way that a prism does with visible colours. Athough in practice most optical communication is outside the visible spectrum the similarity with visible light, where different frequencies (i.e. wavelengths) manifest themselves as different colours, results in people referring to WDM as using different 'colours' of light.
When a large number of wavelengths (e.g. 40) are combined on to a single fibre it is usually referred to as dense wavelength division multiplexing (DWDM).
Ultra-long-haul WDM transmission systems, BTTJ, Vol 20, No 4.
The distance a wave travels in the time it takes to go through a complete cycle. This can be seen from the diagram of a sine wave (see sinusoid) where the length of a single cycle of a wave can be measured from any point on one wave to the corresponding point on the next.
The speed the wave travels needs to be known. The length of the cycle depends on the frequency, or the number of time the cycle occurs in one second. The wavelength (l) is found from the formula:
Wavelength (metres)= Velocity (metres per second)/Frequency (Hz)
Electromagnetic waves travel through space at the speed of light (approximately 300,000,000 metres/second). Thus for a frequency of 10 Mhz the wavelength is 300,000,000/10,000,000 = 30 metres.
Sound waves travel through air at approximately 344 metres/second (dependent on altitude, temperature). Thus for a frequency of 440 Hz the wavelength is 344/440 = 0.782 metres.
Broadcasting on the internet - by voice and/or vision. Refers to real-time (live) broadcasts but webcasts can then be stored for hearing/viewing anytime.
A handheld, wireless device designed for web browsing. A webpad is like a laptop computer without the fold-down screen and keyboard, which is why it is sometimes called a 'web slate' or 'tablet computer'. Using a touch screen, webpads come in all shapes and sizes but typically in 2003 are less than 2.5 cm thick and weigh less than 2 kilograms.
"Web Services" is a phrase used to describe a new approach to applications and systems integration, built around the use of technologies such as the extensible mark-up language (XML). It brings with it not only a new approach for the development of software products and services, but also new models by which businesses will trade. More detail is given in An introduction to Web Services, BTTJ Vol 22 No1 and Web Services architecture, BTTJ Vol 22, No 1.
Also see Parlay X Web services, BTTJ, Vol 22, No 1, An overview of Web Services security, BTTJ, Vol 22, No 1 and A management platform for commercial Web Services, Vol 22, No 1.
Wholesale
See Network Wholesaler.
A general description for far-reaching networks, both nationally and internationally. The term was introduced to distinguish from local area networks (LANs) which were initially used for enterprise (company) networks but now also used in the home. Where traffic on a LAN has to communicate beyond the LAN it is connected to the outside world which is described as a WAN. In practice the connection could take all sorts of forms, such as leased lines or frame relay. However, as an all embracing term it is often used as an overall term for the public network. An intermediate term, the metropolitan area network (MAN), is also used sometimes to describe a more restricted coverage area.
Wi-Fi is a registered trademark of the Wi-Fi Alliance ( http://www.weca.net ). Referring to Wireless Fidelity, or Wi-Fi, has a comforting similarity with the long-standing familiar and consumer friendly term High Fidelity, or Hi-Fi. "Wi-Fi Certified" is a standard for interworking intended to give consumers confidence that when they purchase WLAN equipment (wireless local area network to the IEEE 802.11 standard) it will interwork and be compatible with other 802.11 WLAN equipment from other manufacturers. Initially focused on 802.11b (2.4 GHz/11 Mbit/s), compatibility becomes more complex with 802.11a (5 Ghz/54 Mbit/s) which is not compatible with 802.11b and 802.11g (2.4 GHz/54 Mbit/s) where the aim is that it will be backwards compatible to 802.11b.
WiMAX stands for Wireless interoperability of microwave access. It is a wide-area wireless access technology operating in the 2 - 11 GHz range and based on the IEEE 802.16 family of standards. The potential range can be up to 70km with aggregate bit-rates of 70 Mbit/s. As an international standard it is intended to overcome some of the limitations (particularly cost) of earlier proprietary fixed wireless point-to-multipoint access systems such as local multi-point distribution system (LMDS) and multi-channel multi-point distribution sytems (MMDS). WiMAX uses orthogonal frequency division multiplexing (OFDM).
This used to be an old-fashioned term referring to the apparatus in people's homes used to receive radio broadcasts but it has had a resurgence in use, if rather unspecific in nature. It is generally taken to be synonymous with radio but also embraces other parts of the electromagnetic spectrum such a visible and non-visible light, notably infra-red. An alternative term of tetherless is also used. The subject is covered widely in this encyclopedia and the following entries will provide more information: Cordless telephones/DECT; cellular mobile systems; Wi-Fi, WiMAX, wireless local area networks (WLANs); paging systems; satellites.
A fairly generic term that can refer to the wireless local loop (WLL) or, more usually, to the use of radio to access communications systems, including cellular radio systems and wireless LANs.
Wireless application protocol (WAP)
A standard designed to allow the content of the Internet to be viewed on the screen of a mobile device, such as a mobile phone or a personal organiser. WAP overcomes any processing limitations of such devices because the information and services available are stripped down to their basic text format.
A wireless LAN is a means for a user to connect to a fixed local area network (LAN) through a wireless (radio) link. The dominant LAN technology is Ethernet where the standards are set by the IEEE 802 series committees. The dominant WLAN technology is also Ethernet based with standards set by the IEEE 802.11 committee. There are several variants of the standards - see Wi-Fi but also HiperLAN.
Wireless Local Loop (WLL) refers to the use of wireless links to access the fixed network as a substitute for the normal local loop. These can be individual VHF/UHF links for use in remote rural areas but are more generally point-to-multipoint microwave systems. They are attractive in some locations where a fixed local-loop is not available or expensive to construct. Whilst they have been used for telephony they are especially attractive for the delivery of broadband signals, including television. Consideration has been given over the years to the use of pole-top wireless distribution to substitute for just the final drop of the local loop. See also LMDS, MMDS
See also:
Wireless Access, BTTJ, Vol 18, No 3.
An overview of satellite access networks, BTTJ, Vol 18, No 3. (under satellite in printed edition)
A small wire centre used for distribution flexibility enclosed in small housing or small room and usually serving a building or floor of a building in a block of flats (apartments) or offices (a closet is an American term for a cupboard).
The way the activities needed to accomplish a task move around an organisation until it is completed. Workflow implies that a process has been established, and once there is a process it can be automated and improved by new technologies. IT is applied to workflow to improve its velocity, accuracy and auditability. New IT technologies can provide continuous improvements so automating workflow is a journey and not a destination.
This usually means the management of the field force: people who are out and about performing tasks related to the network or to customers.
The lowest level in the hierarchy of the work of a project. All the work needed to complete a project is made up of work packages through which resources can be identified, time and costs estimated and deliverables defined. Specific people (work package managers) own the work packages and they are responsible for defining all the activities to complete them.
A software virus that replicates itself in many computers attached to a network. It is usually malicious with the intent of bringing normal operations to a halt through the excessive use of resources such as bandwidth and/or processing power.
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