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Glossary
61200051L1-1D ISU 2x64 Dual Port ISDN Service Unit User Manual 141
NEXT (near-end crosstalk)
Unwanted energy transferred from one circuit to an adjoining circuit. Occurs at
the end of the transmission link where the signal source is located. The absorbed
energy is usually propagated in the direction opposite to the absorbing channel’s
normal current flow. Caused by high-frequency or unbalanced signals and insuf-
ficient shielding.
non-ISDN line
Any connection from a CPE to a SPCS that is not served by D-channel signalling.
non-ISDN trunk
Any trunk not served by either SS7 or D-channel signalling.
NT1
Network Termination 1. A unit that provides physical and electromagnetic termi-
nation of the U-interface 2-wire transmission line, converts between Layer 1 for-
mats used at the U- and T- reference points, and performs some maintenance
functions.
packet mode
Refers to switching of packets of information for different users by statistically
multiplexing them over the same transmission facilities. ISDN packet mode capa-
bilities are based on CCITT Recommendation X.25 procedures.
point-to-point
Describing a circuit connecting two points directly with no intermediate process-
ing nodes or computers (although switching facilities could exist). A type of con-
nection that links two logical entities (i.e., phone-line circuit).
S-interface
S-reference point. The interface that connects an ISDN terminal (TE1) or Terminal
Adapter (TA) to the NT2 reference point as defined in the I.411 Recommendation.
SPCS
stored program controlled switch. A digital switch that supports call control, rout-
ing, and supplementary services provision under software control. All ISDN
switches are SPCSs
SDLC
synchronous data link control. A data communications line protocol associated
with the IBM System Network Architecture. SDLC is a bit-oriented protocol (not
a character-oriented protocol) that includes multiple block error checking and full
duplex line operation.
sync bits
Framing or synchronizing bits in synchronous transmission.