dictionary of multimedia and internet applications: a guide for developers and users. francis botto

Print ISBN 0-471-98624-0 Online ISBN 0-470-84178-8

Backbone A core high-speed transmission line which serves a number of networks. Switches and bridges provide the physical connections be-tween it and the multiple networks for which it provides bi-directional data traffic paths. A backbone is comparable to a main artery in human anatomy, which divides into smaller veins and capillaries that might be thought of as switches and networks. A backbone might comprise ATM backbone switches, which comprise a number of ports for connection to networks. Enterprise backbones that have ATM backbone switches offer scalability and fault tolerance, and are based on internationally agreed standards.

(See ATM and Frame relay)

Backbone switch A device that acts as a distribution point for data traffic flowing on a backbone. ATM backbone switches have a number of ports for connection to multiple networks and/or devices. ATM backbone switches are:

● scalable, because upsizing is possible through the replacement or addition

of switches; downsizing is also possible where switches are removed or replaced

● fault-tolerant

● based on internationally agreed standards. Specifications for ATM backbone switches include the:

● number of ports per switch

● number of calls that the switch can route per second ● speed of the backplane, or its data transfer rate in bits per second; the

number of ports per switch.

Makers of ATM backbone switches include 3Com Corporation, Cabletron Systems, DEC, Cisco, FORE systems and NEC.

Backdoor A flaw in the security defences of a system or a network. For

Backdrop

example, modem access, either inbound or outbound, may bypass the network collective security infrastructures.

(See Firewall and Security.)

Backdrop A background image or colour in a multimedia presentation or title that remains constant for a given number of frames.

Back-end application A term used to describe a server-side application,

which may drive or provide services for client applications and systems. The latter tier is the front-end, with which the user interacts. Between the back-and front-end applications is middleware or glues, which exist at a number of levels. These may bind together and coordinate application logic, data and presentation distributed across the back- and front -ends.

(See Application, Client/server, Front-end and Glue.)

Background 1. Multi-tasking operating systems, such as Windows 98, Windows NT and OS/2 Warp, are able to run applications in the back-ground of others. Background applications and tasks generally receive less processing time and run more slowly. 2. A background sound may be added to a Web page using FrontPage or other Web development tools. The sound technology used may be wave audio or MIDI.

(See FrontPage, MIDI and Wave audio.)

Background mode In Windows, background mode permits the back-ground colour to be toggled between opaque (on) and transparent (off).

Backtracking The process of retracing a user’s path of interaction. Using Windows Help systems the Back button provides a means of doing this. All fully specified authoring tools – such as Multimedia ToolBook – and Help System development tools allow the developer to integrate a backtracking feature in applications. Web browsers also feature backtracking controls.

(See Hypertext and Multimedia.)

Backward-compatible A hardware component, program object, language compiler, program or operating system that is compatible with an earlier version.

Bandwidth The rate at which data is transferred to, or from, a computer or appliance, using a medium that might be physical or wireless. Media and their bandwidths include:

● A single-speed CD-ROM has a bandwidth of 1.2 Mbps (or 150 Kbyte/s),

and generally CD-ROM drives exhibit data transfer rates which are

broadly multiples of 150 Kbyte/s.