Terms used as applied to Data (and some Voice) Transmission over Copper Wire

A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z

S/N Ratio
Security Certificate
Switched Network
Synchronous Interface

























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 BER (Bit Error Rates) with reference to certain S/N Ratios.

SDSL (Single pair Digital Subscriber Line) -- A single pair (2wire), symmetric version of 4Wire HDSL

Security 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 authorization.

Server -- 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 PPP or SLIP 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 T1 link. Common SLC's are SLC96 and SLC2000. The SLC96 breaks out 96 T1's 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 with SLC)

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. PPP and TCP/IP 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 TCP/IP 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, MIB, OpenView

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 broadband ISDN (BISDN).

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 SONET standard for signal definition over OC-1 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 Dial-up network.

Synchronous 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.


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