S/N Ratio (Signal to Noise Ratio)
- A measurement of the signal strength differential
between the wanted signal level and the noise level within the same
frequency band. Given in Decibels (Db). Also called 'SNR'. The
performance of modems is generally given with
(Bit Error Rates) with reference to certain S/N Ratios.
SDSL (Single pair Digital
Subscriber Line) -- A single pair
(2wire), symmetric version of 4Wire
Certificate-A special piece of
information that is used to establish a secure connection. Security
Certificates contain information about the owner and issuer, and
contains a unique identification tag, valid dates, and an encrypted
"fingerprint" that can be used to verify the contents of the
certificate. Used in conjunction with the term "keys" for access
A device normally for communication egress and
access which has facilities for connection to several modems on one
side, and a connection to a LAN (or host) on the other. Servers
typically answer the incoming calls and pass the connections on to the
appropriate node. Most servers can provide
services if connected to the Internet.
SLC (Subscriber Loop Carrier)
-- Similar to a Digital Loop Carrier (DLC):
A Mux that splits out a number of
DS0's from a
Common SLC's are SLC96 and SLC2000. The SLC96 breaks out 96
from a CO switch and a SLC2000 breaks out 2000 T1's from a CO switch.
SLIC (Subscriber Line
Interface Circuits) - In general, every
analog telephone line requires its own SLIC. SLICs are found either in
conventional telephone line cards, where they provide the last link
between the DCO (Distributed Central Office) and the copper pair leading
to the customer's home, and in ISDN terminal or network adapters, where
they allow connection of analog telephones. In addition to matching the
telephone network's four- wire connection to the telephone's ring and
tip wires, SLICs provide what the telephone industry calls
BORSHT functions: Battery feed, Overvoltage
protection, Ringing, Supervision, Hybrid, and Test. (Not to be confused
SLIP (Serial Line Internet
Protocol) -- A standard for using a
regular telephone line (a serial line) and a modem to connect a computer
as a real Internet site.
will gradually replace SLIP.
SMDS (Switched Multi-megabit
Data Service) -- A new standard for very
high-speed data transfer.
SNMP (Simple Network
Management Protocol) -- A set of
standards for communication with devices connected to a
network. Examples of these devices include routers, hubs, and switches.
SNMP "compatible" products can be monitored and/or controlled using SNMP
messages called "PDU" messages (Protocol Data Units). Software for
managing devices via SNMP are available for every kind of commonly used
computer and are often bundled along with the device they are designed
to manage. Some SNMP software is designed to handle a wide variety of
devices. See: Router,
SNR - see S/N Ratio
SONET (Synchronous Optical
NETworks) -- A standard that defines
optical carrier (OC) levels and electrically equivalent synchronous
transport signals (STSs) for the fiber-optic based transmission
hierarchy. SONET is the U.S. (ANSI) standard for synchronous data
transmission on optical media. The international equivalent of SONET is
synchronous digital hierarchy (SDH). Together, they ensure standards so
that digital networks can interconnect internationally and existing
conventional transmission systems can take advantage of optical media
through tributary attachments.
SONET provides standards for a number of line
rates up to the maximum line rate of 9.953 gigabits per second (Gbps).
Actual line rates approaching 20 gigabits per second are possible. SONET
is considered to be the foundation for the physical layer of the
ATM runs as a layer on top of SONET as well as
on top of other technologies.
SONET defines a base rate of 51.84 Mbps and a
set of multiples of the base rate known as "Optical Carrier levels." An
OC-1 runs at 51.84Mbps
STS-1 (Synchronous Transport
Signal 1) - A
standard for signal definition over
fiber at 51.84Mbps.
Switched Network -
The telephone network is considered a switched network because it
electrically switches the wires that connect one telephone (modem, fax,
etc.) to another. Also referred to as
Interface - In serial data transmission
interfaces, refers to data that requires an associated clock on other
pins that tells the computing device when to look at the voltage level
on the received and transmitted data. Synchronous data is block framed
data and therefore more efficient than
Asynchronous Interface data in that each
character does not need a start and stop bit to frame each character.
V.35 is a
type of synchronous serial interface.