Glossary
Glossary-8 Express 4100/4110 User Manual 61200176L2-1
4-wire. A 4-wire circuit delivers better reception, but also costs more. All local loop
circuits (those coming from a Class 5 central office to the subscriber’s phone system)
are 2-wire, unless a 4-wire circuit is requested.
U-interface
A twisted pair subscriber loop that connects the NT1 reference point to the ISDN net-
work, as defined in the I.411 Recommendation. This interface provides Basic Rate Ac-
cess with an operating frequency of 160 kbps and an information rate of 144 kbps.
Under U.S. regulations, this also marks the line of demarcation between customer-
owned equipment and the public network.
ZIP Zone Information Protocol. The AppleTalk session-layer protocol used to maintain
and discover the internet-wide mapping of network number ranges to zone names.
Zombie Rout es
Routes that have been identified by the router to be deleted. They remain in the router’s
route table for a specified amount of time with an infinite metric so that all other routers
will learn o f this router’s intention to delete them.