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twisted pair - This refers to a transmission medium consisting of two insulated
copper wires arranged in a regular spiral pattern. The wires can be shielded or
unshielded. Twisted pair is common in telephony applications and is increasingly
common in data networks.
UNIX - UNIX is an operating system that was developed in 1969 at Bell
Laboratories.
upstream - Refers to data sent from a subscriber site to the CO.
URL - A Universal Resource Locator is an address entered in Internet browsers that
usually begins with http:// and contains a .com, .edu, .org, .net, or .gov. Every
Internet site (WWW, FTP, etc.) has a unique URL.
virtual circuits, channels, and paths - These all refer to logical circuits created to
ensure reliable communication between two network devices. In ATM, a virtual
circuit is called a virtual channel and may be identified by a VCI number. A bundle
of virtual channels is called a virtual path and may be identified by a VPI number.
VPI/VCI - The VPI (Virtual Path Identifier, an 8-bit field in an ATM header),
combined with the VCI (Virtual Channel Identifier, a 16-bit field in an ATM header),
is used to identify the next destination of a packet as it passes through a series of
ATM switches.
VPN - A Virtual Private Network allows IP traffic to travel securely over a public
TCP/IP network.
WAN - A Wide Area Network connects users in different geographical areas. The
Internet is a public WAN.
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