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Glossary
Glossary-8 Express 4110/4120 User Manual 61200176L3-1
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 Routes
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 of this router’s intention to delete them.