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
Octet - Another term for byte, which is a string of 8 bits.
Off Network Access Line (ONAL) - (1) Connection from a private switched network to the public switched network. (2) Connection provided by a carrier and used in common by subscribers to enter and/or exit from the switched network.
Off Premises Extension (OPX) - Also called a loop extender. Add on device / adapter for abnormally long loops or twisted pair for a PBX switch or central office switch. Allows operation for distances over 12,000 feet for central office, and over 1,500 feet for PBX.
One Way Trunk - Used in PBX applications; a reference to a Direct Inward Dial or Direct Outward Dial trunk.
Open Shortest Path First (OSPF) - Traffic control program used by routers; one of the original routing protocols.
Open Systems Interconnection (OSI) - Communications protocol guideline - seven layer / step process consisting of an Applications Layer (seventh & highest layer for connecting an applications file or program to a communications protocol), a Presentation Layer (sixth layer - encodes & decodes data to be transmitted), Session Layer (fifth layer - establishes and maintains the connection to the communications process of the lower layers, and direction of data transfer), Transport Layer (fourth layer - error correction and direction of data flow), Network Layer (third layer - switching & routing of data over physical media), Data-Link Layer (second layer - receives & transmits data over physical layer media), and Physical layer (bottom layer; the actual media of the communications transmission - twisted pair, fiber, coax, air, etc.)
Optical Carrier (OC) - SONET carrier hierarchy prefix followed by a number, such as OC-1.
Optical Carrier 1 (OC-1) - Beginning of SONET-level transmission speed; OC-1's are capable of carrying one DS-3 as payload at 51.840 Mbps. OC-1 can also be converted into an electrical signal called STS-1.
Optical Carrier 12 (OC-12) - Capable of transporting 3 DS-3 signals at 622.080 Mbps.
Optical Carrier 192 (OC-192) - Capable of transporting 3 DS-3 signals at 9.953 Gbps.
Optical Carrier 3 (OC-3) - Capable of transporting 3 DS-3 signals at 255.520 Mbps.
Optical Carrier 48 (OC-48) - Capable of transporting 3 DS-3 signals at 2.488 Gbps.
Optical Network Unit - Access node for converting optical signals transmitted via fiber, into electrical signals. Used in local markets, ONU's allow mass amounts of bandwidth to be delivered to areas beyond electrical transmission range of a central office. A hybrid fiber/coax/twisted pair network.
OSI Standards - Architecture, set up by the International Standards Organization (ISO), setting broad standards for communications to help manufactures make universally compatible equipment.
Other Common Carriers (OCC) - Long distance providers, other than AT&T. Today all carriers, including AT&T, are referred to as interexchange carriers (IXCs).
Outage - (1) Any disruption of service. (2) Point at which a customer releases a circuit for repair, lasting until the circuit is returned to the customer in working condition.
Out of Band Signaling - Signals, such as digits dialed, dial tone, phone off-hook, ringing, etc., used in PBX applications and data transfer applications, where these signals are carried on the 24th channel of a DS1 line, leaving the other 23 channels for voice/data transmission - cutting traffic over in-band signaling due to increased ability to carry data over in-band signaling.
Outside Plant - Communication utility's twisted pair/coax network that goes through towns & neighborhoods, including terminals, pedestals, cross boxes and vaults.
Outsource - Subcontracting work to other companies.
Overhead - The part of the transmission containing information/signal controlling the operation of the transmission.
Packet - Block of data handled by a network in a well-defined format, including both data and control elements; transmitted and switched independently.
Packet Interleaving - Placing many data packets, from many packet sources, on one transmission channel.
Packet Layer - X.25 Protocol layer, equivalent to an OSI network layer, handling multiplexing of data via an address system embedded in its control signaling with the packet layer on the other end.
Packet Level - In X.25 protocol where network layer functions are performed - including addressing, multiplexing, and demultiplexing.
Parallel Circuit - Circuit with more than one path for current, through multiple devices or loads (as opposed to a series circuit, which has only one path through multiple loads).
Parallel Data - Transmission of data with multiple bits transferred at one time, such as a whole byte (as opposed to series data, which sends data one bit at a time).
Parallel Port - DB25 connector used to connect computer printers, with a communication speed of 1.5 Mbps.
Parity - Bit-stream check method, used for error corrections - the number of logic 1's is counted in a bit stream - an odd count results in "odd parity, an even count results in "even parity". In odd parity, the parity bit is set to "1" if the number of 1's is odd; even parity, the parity bit is set to "1" if the number of 1's is even.
Parity Bit - Added into a bit stream, usually after every seven bits. Used in error correction - also refer to Parity.
Patch Panel - Panel using plugs, rather than terminals, for connecting fiber optics or wires; used to terminate installed wire, or used with communications circuits as a plug in test access point. DS0 and DS3 patch panels are commonly used in central offices for testing purposes, while Cat 5 patch panels are used in LAN environments to ease connection of computers to a network with pre-installed wire.
Path - Alignment process for microwave radio links, or the space between two microwave dishes for a microwave link.
Payload - A transmission packet/signal has two components, overhead and payload. Overhead has operational, maintenance and synchronization information that makes the protocol work, while the payload carries the customer information.
Permanent Virtual Circuit (PVC) - (1) Point to point, non-switched circuit over which only data, reset, interrupt and flow-control packets can flow. (2) Logical channel that is maintained in a data transfer state between two user devices (typically a terminal and host) at all times when the network is operational. Supports only X.25 data terminal equipment.
Peta - Prefix for 1,000,000,000,000,000. For example, a 1 PB hard drive would be equivalent to 1 million 1 GB hard drives.
Physical Colocation - Interconnection agreement and physical location where telephone companies hand off services / calls between each other, such as between a CLEC and RBOC, or between long distance and local telephone companies.
Physical Layer - Communications protocol layer, which is the actual media of the transmission (such as twisted pair wire, fiber, air, coax, etc.), as well as the connectors used and the pin-outs of the connectors. For example, the 568B wiring scheme for CAT5 wire is a physical layer function.
Plain Old Telephone Service (POTS) - Telephone line, with number. Standard subscribed services by residences and some small businesses.
Plant - Aka telephone company equipment, poles, cable, cable vaults, central offices, and transmission equipment.
Point of Presence (POP) - Physical location within a local access and transport area (LATA) where an interexchange carrier's circuits connect with the lines of the local telephone company servicing that lATA.
Point-to-Point Circuit - Private communications link between two terminations which do not connect with a public telephone system.
Point-to-Point Protocol (PPP) - Aka Dial-up IP. Provides router-to-router and host-to-host network connections over both synchronous and asynchronous circuits.
Policy Based Routing - Routing scheme, based on user configured policies, that forwards packets to specific interfaces. Policies may state that traffic from one network should be forwarded out of one interface, while any other traffic be forwarded out another interface.
Port - (1) Entrance or access point to a computer, multiplexer network or device where signals may be supplied, extracted, or observed. (2) Place where a peripheral device is connected to a computer.
Portability - Ability to take change telephone companies without changing your phone number.
Post, Telephone, and Telegraph (PTT) - General name for communications service providers in countries that are not controlled by a nongovernmental agency or corporation; usually an extension of postal services.
Predictive Dialing - Aka Auto Dialing or Progressive Dialing. Used by telemarketers, where numbers are entered into a predictive dialer, the system dials the number, and when call is answered the call with associated information is transferred to the appropriate telemarketer.
Premises Equipment - Aka Customer Premises Equipment (CPE). All equipment on the customer side of the network interface, such as wiring, telephones, answering machines, CSU/DSU's, etc.
Permanent Virtual Circuit (PVC) - Logical connection on a packet network between two end communicating devices, by using Committed Information Rates (CIR)s, as on a frame relay.
Premises Wire - Wire on the customer side of the network interface.
Presentation Layer - Communications protocol layer, that encodes/decodes data to be transmitted within the protocol.
Primary Rate Interface (PRI) - One of two ISDN circuit sizes. A PRI circuit has 23 B channels, and one D channel, where the B (Bearer) channel carries customer communications, and the D (data) channel provides control and signaling for the B channel. For information on the other ISDN circuit size - see Basic Rate Interface (BRI).
Primary Routing Point - Switch designated as the control point for a long-haul telephone call.
Private Branch Exchange (PBX) - Small, local telephone office, either manually or automatically operated, serving extensions in a business complex; provides access to the public domain.
Private Line - (1) Point-to-point telephone line for the exclusive use of one party. (2) Leased, owned, or otherwise dedicated channel. (3) Channel and channel equipment furnished to a user as a unit for exclusive use without interexchange switching arrangements.
Protocol - Rules/Organized Process that communications equipment use to transfer data. Protocols, and layers of protocols that carry other protocols (i.e. protocol stacks), including ISDN, Ethernet, token ring, DS1, ATM, frame relay, SONET, and POTS signaling.
Provisioning - The process of allocating & programming central office ports & equipment, and allocating copper pairs, before a technician installs telephone service.
Public Service Commission (PSC) - Public Utilities Commission watchdog, that regulates telecommunications companies and other utility companies. To be regulated, a telecommunications company must have a minimum number of customers; RBOC's are regulated by their area PUC's.
Public Switched Network (PSN) - Any switching system or telecom carrier network that provided circuit switching between public users.
Public Telephone Network (PTN) - Aka Public Switched Telephone Network (PSTN) or Public Switched Network (PSN).
Public Utilities Commission (PUC) - Governing body of the regulated public utility service companies as well s the PSC.