OC-1

Optical Carrier Level 1
The optical signal that results from an optical conversion of an STS-1 signal. It is this signal that will form the basis of the interface.

Open Circuit

A circuit available for use.

PSN

Public Switched Network
Common carrier network that provides circuit switching among public users

PBX

Private Branch Exchange

Private switchboard that provides onsite dial service and can provide connections to local and trunked communications networks

POTS

Plain Old Telephone Service
Handles calls that requires just basic call handling.

PSTN

Public Switched Telephone Network
A domestic telecommunications network usually accessed by telephones, key telephone systems, private branch exchange trunks, and data arrangements

PRI

Primary Rate Interface

ISDN North American standard, having 23 B + D channels, in which both channels operate at 64 kb/s.

Private Lines (Leased Lines)

Telephone line that has been leased for private use.

Usually large companies obtain private lines to interconnect geographical locations within the organization.

Private Network

A network that is designed for use exclusively by a person or organization and usually does not have points of access from users external to the company

Protocol

A format or set of rules and conventions that control the format and relative timing of message transmission between two points on a computer network