A term used generally, but not exclusively, to describe the routing of Internet traffic between an IP network and the public Internet. It is a service sold by ISPs to other ISPs, corporates and home users. This service is also called Upstream Transit, Internet Connectivity, Internet Access and, particularly in the home user market, Dial-up Access where the connection to the ISP is often made by a modem dialing the ISP over a standard telephone line. See also Upstream Transit and Downstream Transit. A unit of measurement of height used mainly in relation to computer and related equipment and the racks in which they are fitted. 1u is 1.75 inches, or 4.445 centimetres.