User`s guide

Glossary G-9
scramblerÑA device or software program that encodes data for encryption.
It distorts a voice or data conversation so that only another like device can Þg-
ure out the content of the message.
SD (Send Data)ÑA signal from DTE to DSU/CSU.
secondary channelÑA subchannel derived from the main channel. It does not
carry data messages and is used for diagnostic or supervisory purposes.
serial interfaceÑData channel that transfers digital data in a serial fashion:
one bit after the other. Communications lines are generally serial, thus
modems are connected to the computer via a serial port. So are mice and
scanners. Serial interfaces have multiple lines, but only one is used for data.
Contrast with parallel interface. See
RS232.
serial portÑI/O connector used to attach a modem, mouse, scanner or other
serial interface device to the computer. The typical serial port uses a DB25 or
DC9 connector, which on the back of a PC is a 25-pin male or 9-pin male
connector. Contrast with parallel port. See RS232.
serial transmissionÑA sequential transmission of bits constituting an entity
of data over a data circuit.
SG (Signal Ground)ÑA signal from DTE to DSU/CSU.
simplex currentÑOne way transmission used by Telco to provide power to
repeaters.
SLIP (Serial Line IP)ÑA TCP/IP protocol that allows IP packets to be trans-
mitted over a serial link, such as a dial-up or private telephone line.
SMDS (Switched Multimegabit Data Service)ÑA fast-packet technology
based on the connection-less data networking capability described in the
IEEE
802.6
specification. The data format for SMDS is Òcell oriented.Ó SMDS does
not support voice.
smooth clockÑA clock that eliminates gaps created during frame bit
removal.
SNMP (Simple Network Management Protocol)ÑA widely-used network
monitoring and control protocol. Data is passed from
SNMP agents (hardware
and/or software processes reporting activity in each network deviceÑhub,
router, bridge, an so on.) to the workstation console used to oversee the net-
work. The agents return information contained in a
MIB (Management Infor-
mation Base), which is a structure that deÞnes what is obtainable from the
device and what can be controlled.