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10/5/2009
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X
See Home Networks
An early interface used between data terminal equipment and data circuit-terminating equipment to link to a packet-switched network. It uses the bottom three layers of the OSI basic reference model - the physical, data link and network layers. The physical layer uses the X21 protocol through the physical manifestation of the RS232 socket. The data link layer uses link access protocol B (LAPB) which is a sub-set of high-level data link control (HDLC) and provides error-free transport between packet switching exchanges on a link-by-link basis. The X25 packet-layer protocol (PLP) in the network layer is used to provide error and flow control.
As transmission networks improved in reliability and availability layer 1 transmission became virtually error free and this led to a lighter weight protocol which was based on X25. The layer three protocol is eliminated and the layer 2 protocol reduced to a minimal core LAPB, effectively shifting the added functionality of the X25 PLP and LAPB into the higher layers of the protocol stack at the end points of the network path. This layer 2 protocol is called frame relay.
See directories.
Denoting one of many forms of digital subscriber line (DSL). Typical examples are ADSL (A for asynchronous) and VDSL (V for very high speed).
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. XML Along with the hyper-text transfer protocol (HTTP) and the hyper-text mark-up language (HTML), is almost a ubiquitous technology across the software world, and is therefore of key importance to the telecommunications industry.
Also see web services.
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