B-51
Appendix B: Glossary
to detect suspicious activity and to drop packets prohibited by an
organization’s policies. Many network security experts recommend stateful-
inspection as the most trusted firewall technology.
S/T Interface A common way of referring to either S or T Interfaces, which are often
combined in ISDN connections. This interface connects TE1 or a TA directly
to a PRI ISDN NT2 device or a BRI ISDN NT1 device. ISDN devices outside of
North America usually provide an S/T interface to communicate with the
service provider, which supplies the NT2 and/or NT1.
STM STatistical Multiplexing. A method that service providers use to multiplex
packets and send the datagrams FIFO. Statistical multiplexing is similar to
time-division multiplexing (TDM), except that rather than arbitrarily assigning
a time slot to each signal, each signal is assigned a slot according to priority
and need. Statistical multiplexing ensures that timeslots will not be wasted,
but it consumes time and processes.
STP Shielded Twisted Pair. A kind of copper wiring where each twisted pair is
covered in an insulating tube. The covering is designed to protect the wire
from electromagnetic interference and functions as a ground. This extra
protection, however, limits the wire’s flexibility.
Straight-through
Cable
A cable that has each internal twisted pair of wires connected to the same pin
number at each end.
SVC Switched Virtual Circuit. A temporary physical circuit that is created when a
connection is established and that is relinquished after the connection is
terminated. The connection path is different each time the subscriber con-
nects. This connection is most often used for dial-up WAN access like ISDN
lines.
SYN Synchronize. One of the TCP flags, used when initiating a session to set the
first sequence number for the packets that will be transmitted during the
session. A circuit-level gateway monitors packets with SYN-flags to determine
whether a requested session is legitimate.
Synchronous
Transmission
A method of data transmission that allows bits to be sent in a continuous
stream; the beginning of one character is contiguous with the end of the
preceding one. The separation of characters requires the receiver to maintain
synchronization with a master timing source.
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