| P-NNI | Also known as a Private Network-to-Node Interface. The interface between ATM switches or ATM switches and an entire switching system in a private network. The PNNI exchanges much more topological and complex quality of service (Q0S) routing information than the UNI. |
| PAD | Packet Assembler and Disassembler |
| PBX | Private Branch eXchange |
| PC | Priority Control. A congestion control function that uses the CLP bit to perform priority queueing and scheduling actions. |
| PC | Protocol Control |
| PCM | Pulse Code Modulation |
| PCO | Point of Control and Observation |
| PCR | Peak Cell Rate. A traffic parameter that characterizes the source and gives the
maximum rate at which cells can be transmitted. It is calculated as the reciprocal of the
minimum intercell interval (time between two cells) over a given virtual connection (VC). Field in the RM cell header indicating the maximum acceptable ER. |
| PCR | Program Clock Reference |
| PCVS | Point to Point Switched Virtual Connections |
| PD | Packetization Delay |
| PDH | Plesiochronous Digital Hierarchy. A hierarchy that refers to the DS-0, DS-1, DS-2 and DS-3 interfaces for digital transmission. Originally developed to efficiently carry digitized voice over twisted pair. |
| PDU | Packet Data Unit |
| PDU | Protocol Data Unit. Term originally used in the OSI model, also known as message, to describe the primitive passed across different layers and contains header, data and trailer information. |
| PHY | Physical Layer of the OSI model |
| PHY | Physical Layer. The bottom layer of the ATM protocol reference model, it is subdivided into two sublayers, the Transmission Convergence ( TC) and the Physical Medium (PM). It provides the ATM cells transmission over the physical interfaces that interconnect the ATM devices. |
| PICS | Protocol Implementation Conformance Statement |
| PID | Protocol Identifier Governing Connection Types |
| PIXIT | Protocol Implementation eXtra Information for Testing |
| PL | Physical Layer. See PHY. |
| PLL | Phase Locked Loop |
| PLPC | Physical Layer Convergence Protocol. A protocol that specifies a TC mapping of ATM cells to DS-3 frames. |
| PM | Physical Medium. One of the two PHY sublayers that provides the bit timing and performs the actual transmission of the bits over the physical medium. |
| PMD | Physical Medium Dependent. Same as PM. |
| POH | Path Overhead |
| POI | Path Overhead Indicator |
| PT | Payload Type. See PTI. |
| PTI | Payload Type Identifier. A 3-bit cell header field for encoding information regarding the AAL and EFCI. |
| PVC | Permanent (or Provisioned ) Virtual Connection. A virtual connection ( VPC/ VCC)
provisioned for indefinite use in an ATM network, established by the network management
system (NMS) (see also SVC). Permanent Virtual Circuit A virtual connection established by the network management between an origin and a destination that can be left up permanently ( used in X.25 and FR protocols). |
| PVCC | Permanent Virtual Channel Connection |
| PVPC | Permanent Virtual Path Connection |
| Q.93B | Currently called Q.2931. |
| Q.931 | ITU-T Recommendation for specifying the UNI signaling protocol in N-ISDN. |
| Q.933 | ITU-T Recommendation for specifying the UNI signaling protocol in Frame Relay. |
| Q.2110 | ITU-T Recommendation for specifying the UNI SSCOP. |
| Q.2130 | ITU-T Recommendation for specifying the UNI SSCF. |
| Q.2931 | ITU-T Recommendation derived from both Q.931 and Q.933 to provide SVC specifications and standards. |
| QD | Queuing Delay |
| QOS/QoS | Quality of Service. A term which refers to the set of ATM performance parameters that characterize the traffic over a given virtual connection ( VC). These parameters include the CLR, CER, CMR, CDV, CTD and the average cell transfer delay. |
| QPSX | Queue Packet and Synchronous Circuit Exchange |
| RAI | Remote Alarm Indication |
| RBOC | Regional Bell Operating Company. Local service telephone companies that resulted from the break-up of AT&T. |
| RC | Routing Control |
| RD | Route Descriptor |
| RDF | Rate Decrease Factor. A factor by which a source should decrease its transmission rate if there is congestion (see also RIF). |
| RDI | Remote Defect Identification |
| RDI | Remote Defect Indication. One of the OAM function types used for fault management (see also AIS, CC). |
| REL | Release Message |
| RFC | Request for Comment. Draft documents that contain proposed standards and specifications. RFCs can then be approved or just archived as historical recommendations. |
| RFI | Radio Frequency Interference |
| RI | Routing Information |
| RII | Routing Information Indicator |
| RIP | Routing Information Protocol |
| RISC | Reduced Instruction Set Computing |
| RLC | Release Complete |
| RM | Resource Management The management of critical network resources, such as bandwidth and buffers, at the node level. A value of 6 is reserved in the PTI to indicate an RM cell. |
| ROLC | Routing Over Large Clouds |
| RSVP | ReSerVation Protocol. A protocol developed for supporting different QoS classes in IP applications (such as videoconference, multimedia). |
| RT | Routing Type |
| RTS | Residual Time Stamp |
| SA | Source MAC address |
| SA | Source Address |
| SAAL | Signaling AAL Service-specific parts of the AAL protocol responsible for signaling. Its specifications, being developed by ITU-T, were adopted from N-ISDN. |
| SAP | Service Access Point. Physical interface between the layers in the OSI model through
which lower layers provide services to the higher layers passing over the Protocol Data
Units ( PDUs). Subnetwork Attachment Point. The unique address maintained by a subnetwork for each of the DTEs attached to it. |
| SAR | Segmentation and Reassembly. The lower half of the AAL. It inserts the data from the information frames into the cell. It adds any necessary header or trailer bits to the data and passes the 48-octet to the ATM layer. Each AAL type has its own SAR format. At the destination, the cell payload is extracted and converted to the appropriate PDU (see also CS) . |
| SCCP | Signaling Connection and Control Part |
| SCP | Service Control Point |
| SCR | Sustainable Cell Rate. A traffic parameter that characterizes a bursty source and specifies the maximum average rate at which cells can be sent over a given virtual connection ( VC). It can be defined as the ratio of the MBS to the minimum burst interarrival time. |
| SDH | Synchronous Digital Hierarchy. A hierarchy that designates signal interfaces for very high-speed digital transmission over optical fiber links (see also SONET). |
| SDU | Service Data Unit |
| SE | Switching Element |
| SEAL | Simple Efficient Adaptation Layer. The original name and recommendation for AAL5. |
| SF | Switching Fabric |
| SGM | Segmentation Message |
| SID | Signaling Identifier |
| SIPP | SMDS Interface Protocol |
| SIR | Sustained Information Rate. A flow control mechanism used in SMDS. |
| SMC | Sleep Mode Connection |
| SMDS | Switched Multimegabit Digital Service. A connectionless, MAN service, based on 53-byte packets, that targeted the interconnection of different LANs into a switched public network. |
| SMF | Single Mode Fiber |
| SN | Sequence Number. Part of the header of the SAR-PDU (2 bits in AAL1, 4 bits in AAL3/4) it is used as a sequence counter for detecting lost, out-of-sequence or misinserted SAR-PDUs. |
| SNA | Systems Network Architecture. A host-based network architecture introduced by IBM, where logical channels are created between end-points. |
| SNAP | Sub Network Access Protocol |
| SNMP | Simple Network Management Protocol. An IETF-defined standard for handling management information. It is normally found as an application on top of the user datagram protocol ( UDP). |
| SOH | Section Overhead |
| SONET | Synchronous Optical Network. An ANSI-defined standard for high-speed and high-quality digital optical transmission. It has been recognized as the North American standard for SDH. |
| SPID | Service Protocol Identifier |
| SPTS | Single Program Transport Stream |
| SR | Source Routing (Bridging) |
| SRF | Specifically Routed Frame |
| SRT | Source Routing Transparent |
| SRTS | Synchronous Residual Time Stamp |
| SSCF | Service Specific Coordination Function. Part of the SSCS portion of the SAAL. Among other functions it providesa clear interface for relaying user data and providing independence from the underlying sublayers (see also SSCOP). |
| SSCOP | Service Specific Connection-Oriented Protocol. Part of the SSCS portion of the SAAL. SSCOP is an end-to-end protocol that provides error detection and correction by retransmission, status reporting between the sender and the receiver, while it guarantees delivery integrity (see also SSCF). |
| SSCS | Service Specific Convergence Sublayer. One of the two components of the Convergence Sublayer (CS) of the AAL that is particular to the traffic service class to be converted. It is developed to support certain user applications such as LAN Emulation, transport of high-quality video, database management. |
| ST | Segment Type. A 2-bit field in the SAR-PDU header that indicates whether the SAR-PDU is a BOM, COM, EOM or SSM. |
| STE | Spanning Tree Explorer |
| STM | Synchronous Transfer Mode. A packet switching approach where time is divided in time slots assigned to single channels during which users can transmit periodically. Basically, time slots denote allocated (fixed) parts of the total available bandwidth ( see also TDM ). |
| STM1 | Synchronous Transport Mode 1 -- 155mbits/sec |
| STP | Signaling Transfer Point |
| STP | Shielded Twisted Pair. Two insulated copper wires twisted together and wrapped by a protective jacket shield (see also UTP). |
| STS | Synchronous Time Stamps |
| STS-3c | Synchronous Transport System-Level 3 concatenated |
| SUT | System Under Test |
| SVC | Switched Virtual Connection. A connection that is set up and taken down dynamically
through signaling (see also PVC). Switched Virtual Circuit. A connection where control signaling is used to establish and tear it down dynamically. Examples are the telephone system, ISDN, X.25. |
| SVCI | Switched Virtual Circuit Identifier |
| SVP | Switched Virtual Path |
| SWG | Sub-Working Group |