A group of bits, including data and control signals, arranged in a specific format and transmitted as a whole. The structure of a packet depends on the protocol. In general, a packet includes three principal elements: control information (such as destination, origin, length of packet), data to be transmitted, and error detection and correction bits. An information block identified by a label at layer 3 of the OSI reference model.
A router-based utility used for capturing packets on a given interface, supporting various router platforms and media types.
The determination of whether to forward or drop a packet according to a prescribed set of criteria, such as source or destination or packet length. Helps to control network traffic.
A communications network that uses packet switching technology.
A communications paradigm in which packets (messages) are individually routed between hosts, with no previously established communication path. See also circuit switching, connection-oriented, connectionless.
A transfer mode in which the transmission and switching functions are achieved by packet-oriented techniques, so as to dynamically share network transmission and switching resources between a multiplicity of connections.
Packet assembler/disassembler. A software module that receives characters from terminals, assembles them into packets, and sends them. The receiving end disassembles the packets and sends the characters to a terminal.
Password Authentication Protocol. A method of establishing security on PPP links where the caller must provide a password in order to establish the link.
A form of collapsed backbone in which multiple segments are distributed to each wiring closet, providing access to all segments from each wiring closet.
(1) Electronic isolation of an Ethernet device from network communications. Bay Networks products support automatic partitioning of ports on fault or error conditions.
(2) A reserved or isolated segment of memory or disk storage on a computer or network device.
Central connecting device in a network that joins wires from several stations but does not provide signal processing or regeneration. See also active hub, intelligent hub.
PassThru ports provide a direct connection from the StackProbe port to the monitored server or switch, without using hub capacity. See also StackProbeTM.
Length of wire or optical fiber cable used to connect the concentrator ports to locations on a patch panel. The type of patch cable to use is determined by
(1) the cable type (single-mode fiber, multimode fiber, STP, or UTP) and
(2) the type of patch panel and wall outlet to which the cable is connected.
An array of jacks through which a number of circuits can be connected or interconnected by patch cables.
The data portion of an ATM cell or packet. The cell consists of a 5-octet header and a 48-octet payload.
Part (3 bits) of an ATM cell header that indicates the type of information that the cell is carrying; for example, user data or management information.
Private branch exchange. A private telephone exchange, such as a company switchboard, typically used and operated by a business, that provides internal communication and access to the public network. Most PBX systems are automated to allow users to dial a specified digit to obtain an outside line.
Peripheral component interconnect (bus). A local bus designed by Intel Corporation that provides a high-speed data path between the CPU and up to 10 peripherals. Can coexist within a computer with the ISA or EISA bus.
Physical Connection Management. Part of the station management specification of an FDDI network. Resides in the physical sublayer and is responsible for the initialization of connections and signaling between ports.
Pulse code modulation. The most common method of encoding an analog voice signal into a digital bit stream.
Personal Computer Memory Card International Association.
Physical Coding Sublayer. A part of the physical layer of the OSI model (layer 1). See also OSI reference model, PMA, PMD.
Plesiochronous Digital Hierarchy. The multiplexing hierarchy used in T-Carrier and E-Carrier voice communication networks. Plesiochronous means "almost synchronous," referring to the process of adding extra bits to multiple 2 Mb/s channels to achieve the same bit rate. See also SDH.
Public Data Network (X.25). A packet switched wide area network under government control. Packet data networking technology, level 3 of X.25, defines how user messages are broken into packets, how calls are established and cleared, and how data flows across the entire PDN.
Protocol data unit. The unit of data in the OSI reference model containing both protocol-control information and user data from the layer above. The block of information is exchanged between two processes within communicating machines.
Path delay value. The time it takes an Ethernet packet to travel the longest path across the network.
Packet Exchange Protocol. A Xerox protocol used internally by Novell NetWare to transport internal NCP (NetWare Core Protocol) commands.
One of the five network management application areas defined by ISO; concerned with evaluating the behavior and effectiveness of network communications. See also network management, ISO.
The ability to associate a workstation connected to a specific port with any token ring supported within a hub. Also known as per-port switching and configuration switching.
The ability to associate a workstation connected to a specific port with any Ethernet segment supported within a hub. Also known as per-port switching and configuration switching.
A circuit derived from two pairs of wires called side circuits, arranged so that each pair of wires is a circuit in itself while also acting as one conductor of the phantom. Used in token ring networks to insert and deinsert a station in the ring based on station power.
Physical layer. The sublayer of the various physical layer protocols that provides the clock speed, data-encoding scheme, and control symbols used in the network.
Layer 1 of the OSI reference model. Provides the means to activate and use physical connections for bit transmission. Defines protocols governing transmission media and electrical or optical signals. In plain terms, the physical layer provides the procedures for transferring data across a network physical medium.
Any means in the physical world for transferring signals between OSI systems. Considered to be outside the OSI reference model and, therefore, sometimes referred to as layer 0. The physical connector to the medium can be considered as the bottom interface of the physical layer (layer 1 of the OSI reference model).
A component of an SNA (Systems Network Architecture) node that controls the resources of the node and reports errors. The access method in the node.
Primary in. In an FDDI network, one of the ports associated with a dual attached device.
Packet Internet Groper. A program useful for testing and debugging networks. PING sends an echo packet to the specified host, waits for a response, and reports success or failure and statistics about its operation.
Packet Level Protocol. A protocol that defines the means of packet transfer between an X.25 DTE and an X.25 DCE. It supports packet sequencing, flow control, and error detection and recovery.
A termination on the end of a cable, designed to provide contact with a socket, receptacle, or jack.
Physical Medium Attachment (sublayer). A part of the physical layer of the OSI model (layer 1). See also OSI reference model, PCS, PMD.
Physical medium dependent or physical layer media dependent (sublayer). A part of the physical layer of the OSI model (layer 1). See also OSI reference model, PCS, PMA.
Parameter management frames. A type of station management frame in FDDI used by a station to read or write SMT MIB objects, allowing remote management of the station.
Private network-to-network interface. A hierarchical, dynamic link-state routing protocol for building large-scale ATM-based networks. PNNI defines signaling requests to establish point-to-point and point-to-multipoint connections across those networks.
Primary out. In an FDDI network, one of the ports associated with a dual attached device. Generally connects to a trunk ring.
A Bay Networks Series 1000 Ethernet web-based network monitoring device providing instant network management via RMON/RMON2 instrumentation. The probe is compatible with Optivity Network Management System applications. See also Optivity Network Management SystemTM (NMS), RMON, RMON2.
Path over head. Part of the SONET framing structure that provides the SPE with overhead information. See also SPE.
An inquiry from the CPU, central hub, or controller asking for a specific set of data (for example, statistics) from a device, device subsystem, or application (such as a specific protocol or interface).
The time (in seconds) between data requests or inquiries initiated by a CPU and received by a subordinate device or device subsystem.
Point of presence. The (local or long distance) carrier's switching central office. For an Internet service provider (ISP), a POP is a local number that a user can call to connect to the ISP.
A place where data can enter or leave a network device or computer. On a PC, the serial and parallel ports are external sockets for plugging in communications lines, modems, and printers.
Plain Old Telephone System or Plain Old Telephone Service switching circuit. The analog phone lines capable of making and receiving calls.
An allowance for attenuation in a fiber optic or broadband link, the difference between transmitter power and receiver sensitivity.
A component in a device that coverts external AC power to DC power for the device internal circuitry.
Point-to-Point Protocol. Protocol between the terminal and the router. A communications protocol that provides dial-up access to the Internet. PPP encapsulates common network-layer protocols in specialized Network Control Protocol packets; for example, IP over PPP (IPCP) and IPX over PPP (IPXCP).
Point-to-Point Tunneling Protocol. A tunneling protocol using existing Internet protocols of PPP and TCP/IP to create Virtual Private Networks (VPNs). See also tunneling, VPN.
Parallel Packet Express. The 1 Gb/s processor interconnect in Bay Networks BLN and BCN routers that distributes data to one of four 256 Mb/s data paths to maximize performance and ensure continuous operation.
Building wiring that runs from network stations to wiring closets or between wiring closets; includes the horizontal cabling on each floor and the backbone or vertical cabling between floors. Also called distribution cabling.
A modular Bay Networks concentrator, such as a System 3000 concentrator, suitable for larger networks.
Layer 6 of the OSI reference model, which determines how application information is represented (that is, encoded) while in transit between two end systems. See also OSI reference model.
Primary rate interface or primary rate ISDN (Integrated Services Digital Network). In North America, PRI consists of 23 B channels and 1 D channel for a combined capacity of 1.544 Mb/s. In Europe, 30 B channels and 1 D channel provide a combined capacity of 2.048 Mb/s. See also BRI, ISDN.
In an FDDI network, one of the ports associated with a dual attached device.
A Bay Networks network management module configured to provide retiming and intended to be active and functional.The main (online) network management module is in charge of gathering concentrator statistics and status and reporting them back to the control console adapter in the network management control console.
In an FDDI network, one of the ports associated with a dual attached device. Generally connects to a trunk ring.
One of the two logical token paths in a dual ring. It is the primary data path. See also secondary ring.
Process performed by filters to assign preference to time-sensitive or mission-critical traffic, thereby reducing the occurrence of session timeouts and improving application response time. Priorities can be assigned based on protocol, source or destination network, packet type, or protocol-specific or other identifiable fields.
Private management domain. A private domain to which message transfer agents (MTAs) send mail. Usually a corporate or government agency e-mail system connected to an administrative management domain (ADMD).
Device attached to a network that allows you to get information on the network to the packet level.
Programmable read-only memory. Read-only memory (ROM) factory-programmed for use in a specific computer.
The process by which a device, such as an NMM, monitors network performance by examining every packet transmitted on the network.
A formal set of rules developed by international standards bodies, LAN equipment vendors, or groups governing the format, control, and timing of network communications. A set of conventions dealing with transmissions between two systems. Typically defines how to implement a group of services in one or two layers of the OSI reference model. Protocols can describe low-level details of machine-to-machine interfaces or high-level exchanges between allocation programs.
Information exchanged between corresponding devices, using a lower-layer connection, to coordinate data transfer (sending and receipt) between one another. See also cell header.
An outbound filter mechanism that lets you specify priority queues of the router to use when transmitting packets. Supports WAN protocols only. See also traffic filter.
Path switching elements. An integrated circuit that provides sophisticated management functionality to FDDI products.
Packet-switch node. The name of an ARPANET packet switch.
Public-switched telephone network. The worldwide voice telephone network; the local telephone company.
Payload type. Part (3 bits) of an ATM cell header that indicates the type of information that the cell is carrying; for example, user data or management information.
Post Telephone and Telegraph. International administrations that regulate and perform telecommunications services, per ITU-T standards. See also CEPT.
Physical unit or peripheral physical unit. A component of a Systems Network Architecture (SNA) node that controls the resources of the node and reports errors. The access method in the node.
A connecting block used in telephone connections, typically consisting of an insulated base covered by four vertical columns of 50 insulation displacement or wire-wrap connectors; also called splice block, telco block, Type 66 block, or wiring block.
Permanent virtual circuit. Dedicated connection between devices manually set up to be used for a single purpose (comparable to having a "leased line"). See also SVC.
Path variability value. The amount or value of the shrinkage in the path delay value. The maximum PVV that an Ethernet network can tolerate is 49 bits.