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10/5/2009
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Intuitively we understand naming if we consider the name and address we place on a postal envelope. The address contains information about place and location in a hierarchy. The name identifies the person. The name may or may not be unique, this depends entirely on the context the name is used.
Like addresses names can also impact:
- How the naming services are built. (Think of DNS).
- How the users perceive the network. (Think of telephone numbers and Web addresses).
- Regulatory regimes or operating constraints. (Think of telephone numbers and the Internet naming registrars).
- Application limitations. (Think of how DNS structure impacts web server design).
A term of variable meaning depending on context. Often taken to mean one voice channel or one ISDN circuit and sometimes simply 'not Broadband'. However, a voice engineer may consider a few hertz or a data channel of a few tens of bit/s for telemetry as narrowband compared to a normal voice channel and a transmission engineer dealing with 2.5 and 10 Gbit/s circuits may consider a few hundred Mbit/s as narrowband.
Another fairly imprecise term meaning not Broadband ISDN (B-ISDN). N-ISDN is generally taken to mean basic-rate ISDN (144kbit/s) although few would accept primary-rate ISDN (2Mbit/s or 1.5 Mbit/s in the USA) as being either N-ISDN or B-ISDN.
Negative impedance amplifier, converter or repeater
This is a form of amplifier, or repeater, used on medium to long audio-circuit interconnections using a pair of wires between telephone exchanges (junction circuits or short-trunks, typically in the 1970s and 1980s over paper insulated cables constructed in quads). Simply put, this device operates on the principle that if a resistor absorbs power from a circuit, so a negative resistor would put power into a circuit. An impedance is a complex form of resistance with other electrical characteristics and is exhibited by a cable pair. Thus a negative impedance placed across a pair of wires will put power into the circuit and amplify the signal in both directions. There are many constraints on the approach, including its use only with a cable pair of well defined construction so that the impedance of the amplifier can be closely matched to the impedance of the pair. With proper engineering they were inexpensive, small, low-current pieces of equipment that under failure maintained the signalling and speech path (albeit without amplification). Their use died with digitalisation.
It is possible to generate two types of negative impedance. The series type is stable when it is terminated in an open circuit and oscillates when connected to a low impedance. The shunt type (really a negative admittance) is stable when short-circuited but will oscillate when terminated in a high impedance. Series and shunt types were therefore used in combination to minimise problems from echoes and reflections due to imperfections in matching a lumped (negative) impedance to the distributed line impedance.
Network Address Translation (NAT)
Network Address Translation (NAT) is a technique increasingly found in IP networks. It has become a major topic since it destroys the end-to-end principle of the Internet and so has a detrimental effect on certain types of application. A NAT device functions by altering the addressing information within an IP packet such that the packet appears to come from, and/or will be sent to, something different to that initially set by the originating host.
Equipment that provides the functions necessary for the operation of the access protocols by the network.
A network operator that provides network capacity and services to a service provider.
A point for gaining access to a network. The term can apply at the physical level such that a wire-centre or MDF is a node. It can also apply to a device in the network, e.g. a switching centre or a device on a LAN. It will be identifiable by a node address.
Noise is an unwanted electrical signal. Examples of noise in transmission lines include white noise, impulsive noise produced by interference, power hum picked up from mains cables and cross-talk from other circuits.
Generally referring to a customer with communications needs at several fixed locations and on the move. Embraces mobile and mobility with an emphasis on fixed locations as well. Nomadic computing is an example where a laptop may be used from home, the office, airports, hotels etc.
Part of a set of means of identifying parts of a network, including ends and nodes, with an unique identity - the others being naming and addressing. Most commonly epitomised by a telephone number on a circuit-switched network. Numbering plans explain how numbers are allocated.
A means whereby a customer can retain a number when changing service provider or for some changes of service type (e.g. from voice to ISDN). Depending on whether the number concerned is geographically or non-geographically based the term can cover retaining a number after a change of fixed location. In the UK it is not possible to transfer a number between a afixed network and a cellular network. Number portability is often implemented through an Intelligent Network (IN). capability.
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