ADTRAN L768 - Manual (Page 133)

Glosssary
61202192L1-1 Express L768/L1.5 User Manual 117
2B+D
The Basic Rate Interface (BRI) in ISDN. A single ISDN circuit divided into two
64 kbps digital channels for voice or data and one 16 kbps channel for low
speed data (up to 9,600 baud) and signalling. 2B+D is carried on one or two
pairs of wires depending on the interface, the same wire pairs that today bring
a single voice circuit into your home or office. See ISDN.
23B+D
In ISDN, also known as the Primary Rate Interface. A circuit with a wide
range of frequencies that is divided in twenty-three 64 kbps paths for carrying
voice, data, video, or other information simultaneously. It bears a remarkable
similarity to today’s T1 link, except that T1 carries 24 voice channels. In ISDN,
23B+D gives twenty-three channels and one D channel for out-of-band signal-
ling. However, in T1, signalling is handled in-band. See ISDN.
two-wire circuit
A transmission circuit composed of two wires, signal and ground, used to both
send and receive information. In contrast, a 4-wire circuit consists of two
pairs. One pair is used to send and one pair is used to receive. All trunk cir-
cuits (long distance) are 4-wire. A 4-wire circuit delivers better reception, but
also costs more. All local loop circuits (those coming from a Class 5 central of-
fice to the subscriber’s phone system) are 2-wire, unless a 4-wire circuit is re-
quested.
U-interface
A twisted pair subscriber loop that connects the NT1 reference point to the
ISDN network, as defined in the I.411 Recommendation. This interface pro-
vides Basic Rate Access with an operating frequency of 160 kbps and an infor-
mation 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.