- the IEEE standard for bridging; a MAC layer standard for transparently connecting two or more LANs (often called subnetworks) that are running the same protocols and cabling. This arrangement creates an extended network, in which any two workstations on the linked LANs can share data.

- the IEEE standard for Ethernet; a physical-layer standard that uses the CSMA/CD access method on a bus-topology LAN.

- the IEEE physical-layer standard that uses the token-passing access method on a ring-topology LAN.

- the AAL divides the user information into segments suitable for packaging into a series of ATM cells. There are several types of AALs in use. FORE Sys- tems currently supports AAL 5 and AAL 3/4. AAL 3/4 supports connection-oriented VBR data transfer and connectionless VBR data transfer, respectively. AAL 5 is defined as Simple and Efficient Adaptation Layer (SEAL).

- an association established by the AAL between two or more next higher layer entities.

- a type of traffic for which the ATM network attempts to meet that traffic's bandwidth requirements. It does not guarantee a specific amount of bandwidth and the end station must retransmit any information that did not reach the far end. ACR (Allowable Cell Rate) - parameter defined by the ATM Forum for ATM traffic manage- ment. ACR varies between the MCR and the PCR, and is dynamically controlled using con- gestion control mechanisms.

- a bit mask used to identify which bits in an address (usually an IP address) are network significant, subnet significant, and host significant portions of the complete address. This mask is also known as the subnet mask because the subnetwork portion of the address can be determined by comparing the binary version of the mask to an IP address in that subnet. The mask holds the same number of bits as the protocol address it references. Agent (SNMP) - a component of network- and desktop-management software, such as SNMP, that gathers information from MIBs.

- a line AIS is asserted when a 111 binary pattern is detected in bits 6, 7, 8 of the K2 byte for five consecutive frames. A line AIS is removed when any pattern other than 111 is detected in these bits for five consecutive frames.

- an unsolicited message from a device, typically indicating a problem with the system that requires attention.

- the user interface to FORE Systems’ ForeThought switch control software (SCS). AMI lets users monitor and change various operating configurations of FORE Systems switches and network module hardware and software, IP connectivity, and SNMP network management.

- a private organization that coordinates the setting and approval of some U.S. standards. It also represents the United States to the Inter- national Standards Organization.

- a language format that defines how a program can be made to interact with another program, service, or other software; it allows users to develop custom interfaces with FORE products.

- a complete, self-contained program that performs a specific function directly for the user.

- a networking protocol developed by Apple Computer for communication between Apple’s products and other computers. Independent of the network layer, AppleTalk runs on LocalTalk, EtherTalk and TokenTalk.

- a method used to resolve higher level protocol addressing (such as IP) into the appropriate header data required for ATM; i.e., port, VPI, and VCI; also defines the AAL type to be used.

- a standard character set that (typically) assigns a 7-bit sequence to each letter, number, and selected control characters.

- a cell that provides a service to an upper layer entity or ATM Layer Manage- ment entity (ATMM-entity).

- a FORE program that repeatedly displays the state of the switch and of all its active ports.

- a method of sending information that resembles normal TDM, except that time slots are allocated as needed rather than preassigned to specific transmitters.

- a transfer mode in which the information is organized into cells. It is asynchronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic.

- an international non-profit organization formed with the objective of accelerat- ing the use of ATM products and services through a rapid convergence of interoperability specifications. In addition, the Forum promotes industry cooperation and awareness.

- a section of an ATM Layer connection between two adjacent active ATM Layer entities (ATM-entities).

- a virtual path link (VPL) or a virtual channel link (VCL).

- a virtual channel connection (VCC) or a virtual path connec- tion (VPC) directly established, such as workstation-to-workstation. This setup is not com- monly used in networks.

- a generic list of parameters that can be used to capture the intrinsic traffic characteristics of a requested ATM connection.

- an association established by the ATM Layer to support communication between two or more ATM service users (i.e., between two or more next higher layer entities or between two or more ATM entities). The communication over an ATM Layer connection may be either bidirectional or unidirectional. The same Virtual Channel Identifier (VCI) is used for both directions of a connection at an interface.

- a FORE program that shows and manipulates ATM ARP entries maintained by the given device driver. This is also used to establish PVC connections.

- a FORE program used to enable or disable SPANS signalling.

- a FORE program that shows statistics gathered about a given adapter card by the device driver. These statistics include ATM layer and ATM adaptation layer cell and error counts. This can also be used to query other hosts via SNMP.

- IEEE 802.3 interface between a media attachment unit (MAU) and a network interface card (NIC). The term AUI can also refer to the rear panel port to which an AUI cable might attach.

- a feature that automatically logs out a user if there has been no user interface activity for a specified length of time.

- a line coding technique used to accommodate the ones density requirements of T1 facilities.

- the main connectivity device of a distributed system. All systems that have con- nectivity to the backbone connect to each other. This does not stop systems from setting up private arrangements with each other to bypass the backbone for cost, performance, or secu- rity.

- usually identifies the capacity or amount of data that can be sent through a given circuit; may be user-specified in a PVC.

- unit of signalling speed. The speed in baud is the number of discrete conditions or sig- nal events per second. If each signal event represents only one bit, the baud rate is the same as bps; if each signal event represents more than one bit (such as a dibit), the baud rate is smaller than bps.

- bit set by a Frame Relay network in frames traveling in the opposite direction of frames encountering a congested path. Data ter- minal equipment (DTE) receiving frames with the BECN bit set can request that higher-level protocols take flow control action as appropriate. Compare with FECN.

- a BES contains more than 1 and fewer than 320 path coding violation error events, and no severely errored frame or AIS defects. Controlled slips are not included in determining BESs.

- used by gateways in an internet connecting autonomous networks. It is derived from experiences learned using the EGP.

- an error-detection technique in which character bit patterns are forced into parity, so that the total number of one bits is always odd or always even. This is accomplished by the addition of a one or zero bit to each byte, as the byte is transmitted; at the other end of the transmission, the receiving device verifies the parity (odd or even) and the accuracy of the transmission.

- a common digital network suitable for voice, video, and high-speed data services running at rates beginning at 155 Mbps.

- a bayonet-locking connector for miniature coax.

- Spanning-tree Protocol hello packet that is sent out at configurable intervals to exchange information among bridges in the network.

- a measure of speed or data rate. Often combined with metric prefixes in kbps for thousands of bits per second (k fir kilo-) and in Mbps for millions of bits per sec- ond (M for mega-).

- an error event on a line in which the normal pattern of alternating high (one) and low (zero) signals is disrupted. A bipolar violation is noted when two high sig- nals occur without an intervening low signal, or vice versa.

- a device that expands a Local Area Network by forwarding frames between data link layers associated with two separate cables, usually carrying a common protocol. Bridges can usually be made to filter certain packets (to forward only certain traffic).

- a service or system requiring transmission channels capable of supporting rates greater than the Integrated Services Digital Network (ISDN) primary rate.

- an ISDN access capable of supporting one or more broadband services. Brouter (bridging/router) - a device that routes some protocols and bridges others based on configuration information.

- a second during which there were at least the set number of BES threshold event errors but fewer than the set number of SES threshold event errors.

- in an emulated LAN, the BUS is responsible for accepting broadcast, multicast, and unknown unicast packets from the LECs to the broadcast MAC address (FFFFFFFFFFFF) via dedicated point-to-point connections, and forwarding the packets to all of the members of the ELAN using a single point-to-multipoint connection.

- the procedure used to decide if a request for an ATM connection can be accepted based on the attributes of both the requested connection and the existing connections.

- an association between two or more users or between a user and a network entity that is established by the use of network capabilities. This association may have zero or more connec- tions.

- a company, such as any of the “baby Bell” companies, that provide network communications services, either within a local area or between local areas.

- a type of traffic that requires a continuous, specific amount of bandwidth over the ATM network (e.g., digital information such as video and digitized voice).

- a port on the CellPath 300 for transmitting and receiving CBR traffic. cchan - a FORE program used to manage virtual channels on a FORE Systems ATM switch running asxd.

- an international consultative committee that sets international communications recommendations, which are frequently adopted as standards; develops interface, modem, and data network recommendations. Membership includes PTTs, scientific and trade associations, and private companies. CCITT is part of the International Communications Union (a United nations treaty organization in Geneva).

- a quantification of cell clumping for a connection. The cell clumping CDV (yk) is defined as the difference between a cell’s expected reference arrival time (ck) and its actual arrival time (ak). The expected reference arrival time (ck) of cell k of a specific connection is max . T is the reciprocal of the negotiated peak cell rate.

- a terminator at one end of a layer connection within a SAP.

- an identifier of a CE that can be used to identify the connection at a SAP.

- an ATM Layer protocol data unit (PDU). The basic unit of information transported in ATM technology, each 53-byte cell contains a 5-byte header and a 48-byte payload.

- the protocol for recognizing the beginning and end of ATM cells within the raw serial bit stream.

- ATM Layer protocol control information.

- a port on the CellPath 300 that transmits and receives traffic in cell format.

- a function performed by a protocol module in which empty cells (known as unassigned cells) are added to the output stream. This is because there always must be a fixed number of cells in the output direction; when there are not enough cells to transmit, unassigned cells are added to the output data stream.

- the transit delay of an ATM cell successfully passed between two desig- nated boundaries.

- The CellPath 90 supports Circuit Emulation Services (CES) for applications requiring a fixed delay, lossless end-to-end connection through the net- work. In essence, CES provides a virtual private line service to the connecting application. Channelization - capability of transmitting independent signals together over a cable while still maintaining their separate identity for later separation.

- the last bit of byte four in an ATM cell header; indicates the eligibil- ity of the cell for discard by the network under congested conditions. If the bit is set to 1, the cell may be discarded by the network depending on traffic conditions.

- a CellPath 300 SNMP trap which is sent when the unit has been power- cycled (see trap).

- the front panel DCE port that allows access to the CellPath 300 user interface via a connected terminal.

- a communications device that offers the ability to concentrate many lower- speed channels into and out of one or more high-speed channels.

- a CellPath 300 feature that helps ensure reasonable service for VBR connections in an ATM network. For each connection, the CellPath 300 maintains a prior- ity, sustained cell rate (SCR), and peak cell rate (PCR). During times of congestion, the CellPath 300 reduces the bandwidth to the SCR, based on the priority of the connection.

- the concatenation of ATM Layer links in order to provide an end-to-end infor- mation transfer capability to access points.

- a type of service in which no pre-determined path or link has been established for transfer of information, supported by AAL 4.

- a type of service in which information always traverses the same pre-established path or link between two points, supported by AAL 3.

- a situation in which one frame’s worth of data is either lost or replicated. A controlled slip typically occurs when the sending device and receiving device are not using the same clock.

- peer entities with a lower layer connection among them

- a FORE program used to manage virtual paths on a FORE Systems ATM switch running asxd.

- equipment that is on the customer side of the point of demarcation, as opposed to equipment that is on a carrier side. See also point of demarcation. cport - a FORE program used to monitor and change the state of ports on a FORE Systems ATM switch running asxd.

- an error detection scheme in which a number is derived from the data that will be transmitted. By recalculating the CRC at the remote end and com- paring it to the value originally transmitted, the receiving node can detect errors. Cross Connection - a mapping between two channels or paths at a network device such as the CellPath 300.

- a situation in which one frame’s worth of data is either lost or repli- cated. A controlled slip typically occurs when the sending device and receiving device are not using the same clock.

- a portion of the AAL. Data is passed first to the CS where it is divided into rational, fixed-length packets or PDUs (Protocol Data Units). For example, AAL 4 processes user data into blocks that are a maximum of 64 kbytes long. CTS (Clear To Send) - and RS-232 modem interface control signal (sent from the modem to the DTE on pin 5) which indicates that the attached DTE may begin transmitting; issuance in response to the DTE’s RTS.

- See SF)

- the US government agency that funded the ARPANET.

- a packet of information used in a connectionless network service that is routed to its destination using an address included in the datagram’s header. DCE (Data Communications Equipment) - a definition in the RS232C standard that describes the functions of the signals and the physical characteristics of an interface for a com- munication device such as a modem.

- an electronic patch panel used to route digital signals in a central office.

- a function performed by a layer entity that identifies and separates SDUs from a single connection to more than one connection (see multiplexing). DFA (DXI Frame Address) - a connection identifier associated with ATM DXI packets that serves the same functions as, and translates directly to, the VPI/VCI on an ATM cell.

- a device that has two parallel rows of contacts that let the user switch electrical current through a pair of those contacts to on or off. They are used to reconfigure components and peripherals. DLCI (Data Link Connection Identifier) - a connection identifier associated with frame relay packets that serves the same functions as, and translates directly to, the VPI/VCI on an ATM cell.

- a computer that converts names to their corresponding Internet num- bers. It allows users to telnet or FTP to the name instead of the number.

- the distributed name and address mechanism used in the Internet.

- a method defining the rate and format of digital hierarchy, with asynchronous data rates defined as follows:

1. DS0 64kbps 1 voice channel
2. DS1 1.544Mbps 24 DS0s
3. DS1C 3.152 Mbps 2 DS1s
4. DS2 6.312 Mbps 4 DS1s
5. DS3 44.736 Mbps 28 DS1s

  Synchronous data rates (SONET) are defined as:
- STS-1/OC-1 51.84 Mbps 28 DS1s or 1 DS3
- STS-3/OC-3 155.52 Mbps 3 STS-1s byte interleaved
- STS-3c/OC-3c 155.52 Mbps Concatenated, indivisible payload
- STS-12/OC-12 622.08 Mbps 12 STS-1s, 4 STS-3cs, or any mixture
- STS-12c/OC-12c 622.08 Mbps Concatenated, indivisible payload
- STS-48/OC-48 2488.32 Mbps 48 STS-1s, 16 STS-3cs, or any mixture

- an RS-232 modem interface control signal (sent from the modem to the DTE on pin 6) which indicates that the modem is connected to the telephone circuit. Usually a prerequisite to the DTE issuing RTS.

- generally user devices, such as terminals and computers, that connect to data circuit-terminating equipment. They either generate or receive the data carried by the network.

- an RS232 modem interface control signal (sent from the DTE to the modem on pin 20) which indicates that the DTE is ready for data transmission and which requests that the modem be connected to the telephone circuit.

- a generic phrase used in the full names of several protocols, all commonly used to allow a pair of DCE and DTE devices to share the implementation of a particular WAN protocol. The protocols all define the packet formats used to transport data packets between DCE and DTE devices.

- Wide-area digital transmission scheme used predominantly in Europe that carries data at a rate of 2.048 Mbps. E1 lines can be leased for private use from common carriers.

- Wide-area digital transmission scheme used predominantly in Europe that carries data at a rate of 34.368 Mbps. E3 lines can be leased for private use from common carriers.

- an EPROM that can be cleared with electrical signals rather than the traditional ultraviolet light.

- the second bit of the payload type field in the header of an ATM cell, the EFCI bit indicates network congestion to receiving hosts. On a congested switch, the EFCI bit is set to “1” by the transmitting network module when a certain number of cells have accumulated in the network module’s shared memory buffer. When a cell is received that has its EFCI bit set to “1,” the receiving host notifies the sending host, which should then reduce its transmission rate.

- used by gateways in an internet, connecting autonomous networks.

- a USA trade organization that issues its own standards and contributes to ANSI; developed RS-232. Membership includes USA manufac- turers.

- a bus architecture for desktop computers that provides a 32-bit data passage while maintaining compatibility with the ISA or AT archi- tecture.

- a FORE program that shows and manipulates MAC and ATM address mappings for LAN Emulation Clients (LECs).

- a FORE program that shows and modifies LEC configuration. Allows the user to set the NSAP address of the LAN Emulation Configuration Server (LECS), display the list of Emulated LANs (ELANs) configured in the LECS for this host, display the list of ELANs locally configured along with the membership state of each, and locally administer ELAN membership.

- the CellPath 300 extension module; paired with the system controller and supporting an optional PCMCIA card.

- an SNMP agent can come in two forms: embedded or proxy. An embedded SNMP agent is integrated into the physical hardware and software of the unit. The CellPath 300 has an internal, integrated SNMP agent.

- signals generated and radiated by an electronic device that cause interference with radio communications, among other effects. End-to-End Connection - when used in reference to an ATM network, a connection that trav- els through an ATM network, passing through various ATM devices and with endpoints at the termination of the ATM network.

- Erasable Programmable Read Only Memory (see PROM).

- the process of compensating for line distortions.

- a system in which an ATM connection is terminated or initiated. An origi- nating end system initiates the ATM connection, and a terminating end system terminates the ATM connection. OAM cells may be generated and received.

- a second during which at least one code violation occurred.

- T1 framing standard that provides frame synchronization, cyclic redundancy, and data link bits.

- a 10-Mbps, coaxial standard for LANs in which all nodes connect to the cable where they contend for access.

- as related to Generic Flow Control (GFC), fairness is defined as meeting all of the agreed quality of service (QoS) requirements by controlling the order of service for all active connections.

- in a relationship between two devices in a circuit, the far-end device is the one that is remote.

- a board of commissioners appointed by the President under the Communications Act of 1934, with the authority to regulate all interstate telecommunications originating in the United States, including transmission over phone lines.

- high-speed data network that uses fiber-optic as the physical medium. Operates in similar manner to Ethernet or Token Ring, only faster.

- a method of dividing an available frequency range into parts with each having enough bandwidth to carry one channel.

- an error detected by extracting the 4-bit FEBE field from the path status byte (G1). The legal range for the 4-bit field is between 0000 and 1000, representing zero to eight errors. Any other value is interpreted as zero errors.

- bit set by a Frame Relay network to inform data terminal equipment (DTE) receiving the frame that congestion was experienced in the path from source to destination. DTE receiving frames with the FECN bit set can request that higher-level protocols take flow control action as appropriate. Compare with BECN.

- a line error asserted when a 110 binary pattern is detected in bits 6, 7, 8 of the K2 byte for five consecutive frames. A line FERF is removed when any pattern other than 110 is detected in these bits for five consecutive frames.

- a method of coordinating the sequential flow of data through a buffer.

- a specific bit pattern used to identify the beginning or end of a frame. Frame - a variable length group of data bits with a specific format containing flags at the beginning and end to provide demarcation.

- a fast packet switching protocol based on the LAPD protocol of ISDN that per- forms routing and transfer with less overhead processing than X.25.

- an error in which one or more time slot framing bits are in error.

- a protocol that separates incoming bits into identifiable groups so that the receiving multiplexer recognizes the grouping.

- a FORE Systems routing and signalling protocol that uses private ATM (NSAP) addresses; a precursor to ATM Forum PNNI (see PNNI).

- a TCP/IP protocol that lets a user on one computer access, and transfer data to and from, another computer over a network. ftp is usually the name of the program the user invokes to accomplish this task.

- an algorithm which is employed in traffic policing and is part of the user/network service contract. The GCRA is a scheduling algorithm which ensures that cells are marked as conforming when they arrive when expected or later than expected and non-conforming when they arrive sooner than expected.

- the first four bits of the first byte in an ATM cell header. Used to control the flow of traffic across the User-to-Network Interface (UNI), and thus into the net- work. Exact mechanisms for flow control are still under investigation and no explicit defini- tion for this field exists at this time. (This field is used only at the UNI; for NNI-NNI use (between network nodes), these four bits provide additional network address capacity, and are appended to the VPI field.)

- a proprietary bus architecture used in certain Silicon Graphics, Inc. workstations.

- protocol control information located at the beginning of a protocol data unit.

- line-code type standard for T1 where each block of three zeros is replaced by 00V or B0V, where B represents an inserted pulse conforming to the AMI rule (ITU-T G.701, item 9004) and V represents an AMI violation (ITU-T G.701, item 9007). The choice of 00V or B0V is made so that the number of B pulses between consecutive V pulses is odd (successive V pulses are of alternate polarity so that no d.c. component is introduced). Compare with AMI.

- Bit-oriented synchronous data link layer protocol developed by the ISO. Derived from SDLC, HDLC specifies a data encapsulation method on synchronous serial links using frame characters and checksums. See also SDLC.

- a CRC code located in the last byte of an ATM cell header that is used for checking cell integrity only.

- ANSI standard that extends the computer bus over fairly short distances at speeds of 800 and 1600 Mbps.

- the Hewlett-Packard version of UNIX.

- a serial communications connection that operates at speeds of up to 1.544 Mbps.

- a device that connects several other devices, usually in a star topology.

- FORE’s interface cards for the LAX-20 LAN Access Switch, designed to connect Ethernet, Token Ring, and FDDI LANs to ForeRunner ATM networks.

- the protocol that handles errors and control messages at the IP layer. ICMP is actually a part of the IP protocol layer. It can generate error messages, test packets, and informational messages related to IP.

- the world’s largest technical pro- fessional society. Based in the U.S., the IEEE sponsors technical conferences, symposia & local meetings worldwide, publishes nearly 25% of the world’s technical papers in electrical, elec- tronics & computer engineering, provides educational programs for members, and promotes standardization.

IETF (Internet Engineering Task Force) - a large, open, international community of network designers, operators, vendors and researchers whose purpose is to coordinate the operation, management and evolution of the Internet to resolve short- and mid-range protocol and architectural issues.

- the standard that specifies the use of the Simple Network Management Protocol (SNMP) and an ATM management information base (MIB) to provide network status and configuration information.

- the unit of information transferred to/from the upper layer in a single inter- action across a SAP. Each Interface Data Unit (IDU) controls interface information and may also contain the whole or part of the SDU.

- while an internet is a network, the term “internet” is usually used to refer to a collec- tion of networks interconnected with routers.

- (note the capital “I”) the largest internet in the world including large national back- bone nets and many regional and local networks worldwide. The Internet uses the TCP/IP suite. Networks with only e-mail connectivity are not considered on the Internet.

- the numbers used to identify hosts on an internet network.

Internet host numbers are divided into two parts; the first is the network number and the second, or local, part is a host number on that particular network. There are also three classes of networks in the Internet, based on the number of hosts on a given network. Large networks are classified as Class A, having addresses in the range 1-126 and having a maximum of 16,387,064 hosts. Medium networks are classified as Class B, with addresses in the range 128-191 and with a maximum of 64,516 hosts. Small networks are classified as Class C, having addresses in the range 192-254 with a maximum of 254 hosts. Addresses are given as dotted decimal numbers in the following format:

nnn.nnn.nnn.nnn

In a Class A network, the first of the numbers is the network number, the last three numbers are the local host address.

In a Class B network, the first two numbers are the network, the last two are the local host address.

In a Class C network, the first three numbers are the network address, the last number is the local host address.

The following table summarizes the classes and sizes:

Network mask values are used to identify the network portion and the host portion of the address. For:

1. Class A - the default mask is 255.0.0.0
2. Class B - the default mask is 255.255.0.0
3. Class C - the default mask is 255.255.255.0

Subnet masking is used when a portion of the host ID is used to identify a subnetwork. For example, if a portion of a Class B network address is used for a subnetwork, the mask could be set as 255.255.255.0. This would allow the third byte to be used as a subnetwork address. All hosts on the network would still use the IP address to get on the Internet. IP (Internet Protocol) - a connectionless, best-effort packet switching protocol that offers a common layer over dissimilar networks. IP Address - a unique 32-bit integer used to identify a device in an IP network. You will most commonly see IP addresses written in “dot” notation; for instance, 192.228.32.14 (see IP net- mask).

- a pattern of 32 bits that is combined with an IP address to determine which bits of an IP address denote the network number and which denote the host number. Netmasks are useful for sub-dividing IP networks. IP netmasks are written in “dot” notation; for instance, 255.255.255.0 (see IP address).

(Internetwork Packet Exchange) - a NetWare protocol similar to the Xerox Network Systems (XNS) protocol that provides datagram delivery of messages.

- a system that provides forwarding functions or relaying functions or both for a specific ATM connection. OAM cells may be generated and received.

- a bus standard developed by IBM for expansion cards in the first IBM PC. The orig- inal bus supported a data path only 8 bits wide. IBM subsequently developed a 16-bit version for its AT class computers. The 16-bit AT ISA bus supports both 8- and 16-bit cards. The 8-bit bus is commonly called the PC/XT bus, and the 16-bit bus is called the AT bus.

- an emerging technology that is beginning to be offered by the telephone carriers of the world. ISDN combines voice and digital network ser- vices into a single medium or wire.

- a voluntary, non treaty organization founded in 1946 that is responsible for creating international standards in many areas, including com- puters and communications.

- signals carrying embedded timing information or signals that are dependent on uniform timing; usually associated with voice and/or video transmission.

- the telecommunications agency of the United Nations, established to provide standardized communications procedures and practices, including frequency allocation and radio regulations, on a worldwide basis.

- Wide-area digital transmission scheme used predominantly in Japan that carries data at a rate of 6.312 Mbps.

- analog communication line distortion caused by variations of a signal from its refer- ence timing position.

- a patch cable or wire used to establish a circuit, often temporarily, for testing or diag- nostics; also, the devices, shorting blocks, used to connect adjacent exposed pins on a printed circuit board that control the functionality of the card.

- a data network intended to serve an area of only a few square kilometers or less. Because the network is known to cover only a small area, optimizations can be made in the network signal protocols that permit higher data rates.

- a program that provides control over the execution of the LAN Emulation Server (LES), Broadcast/Unknown Server (BUS), and LAN Emulation Configuration Server (LECS) on the local host.

- a LAN access device that allows a shared transmission medium to accommodate more data sources than there are channels currently available within the transmission medium.

(Link Access Procedure, Balanced) - Data link protocol in the X.25 protocol stack.

LAPB is a bit-oriented protocol derived from HDLC. See also HDLC and X.25.

- a FORE Systems LAN Access Switch, designed to connect Ethernet, Token Ring, and FDDI LANs to ForeRunner ATM networks. The LAX-20 is a multiport, multiprotocol internet- working switch that combines the advantages of a high-performance LAN switch and a full- featured ATM interface capable of carrying LAN traffic.

- an active layer within an element.

- a part of the activity of the layer entities.

- a capability of a layer and the layers beneath it that is provided to the upper layer entities at the boundary between that layer and the next higher layer.

- the information transferred between corresponding entities on behalf of the upper layer or layer management entities for which they are providing services.

- a FORE program that implements both the LAN Emulation Server (LES) and the Broad- cast/Unknown Server (BUS).

- the component in an end system that performs data forwarding, address resolution, and other control functions when communicating with other components within an ELAN.

- a FORE program that implements the assignment of individual LECs to different emulated LANs.

- the LECS is responsible for the initial configuration of LECs. It provides information about available ELANs that a LEC may join, together with the addresses of the LES and BUS associated with each ELAN.

- a FORE program that provides information about an ELAN. This information is obtained from the LES, and includes MAC addresses registered on the ELAN together with their corre- sponding ATM addresses.

- the LES implements the control coordination function for an ELAN. The LES provides the service of registering and resolving MAC addresses to ATM addresses.

Link Down Trap - a CellPath 300 SNMP trap that signifies that the Ethernet interface has tran- sitioned from a normal state to an error state, or has been disconnected. Link Up Trap - a CellPath 300 SNMP trap that signifies that the Ethernet interface has transi- tioned from an error condition to a normal state. Glossary - 16 ForeRunner HE/200E/LE ATM Adapters for the PC User’s Manual Glossary LLC (Logical Link Control) - a protocol developed by the IEEE 802 committee for data-link- layer transmission control; the upper sublayer of the IEEE Layer 2 (OSI) protocol that comple- ments the MAC protocol; IEEE standard 802.2; includes end-system addressing and error checking. LOF (Loss Of Frame) - a type of transmission error that may occur in wide-area carrier lines. Loopback - a troubleshooting technique that returns a transmitted signal to its source so that the signal can be analyzed for errors. Typically, a loopback is set at various points in a line until the section of the line that is causing the problem is discovered. looptest - a program that tests the interface for basic cell reception and transmission function- ality. It is usually used for diagnostic purposes to determine if an interface is functioning prop- erly. LOP (Loss Of Pointer) - a type of transmission error that may occur in wide-area carrier lines. LOS (Loss Of Signal) - a type of transmission error that may occur in wide-area carrier lines. MAC (Media Access Control) - a media-specific access control protocol within IEEE 802 spec- ifications; currently includes variations for Token Ring, token bus, and CSMA/CD; the lower sublayer of the IEEE's link layer (OSI), which complements the Logical Link Control (LLC). MAU (Media Attachment Unit) - device used in Ethernet and IEEE 802.3 networks that pro- vides the interface between the AUI port of a station and the common medium of the Ether- net. The MAU, which can be built into a station or can be a separate device, performs physical layer functions including conversion of the digital data from the Ethernet interface, collision detection, and injection of bits onto the network. Maximum Burst Tolerance - the largest burst of data that a network device is guaranteed to handle without discarding cells or packets. Bursts of data larger than the maximum burst size may be subject to discard. MCR (Minimum Cell Rate) - parameter defined by the ATM Forum for ATM traffic manage- ment. MCR is defined only for ABR transmissions, and specifies the minimum value for the ACR. Metasignalling - an ATM Layer Management (LM) process that manages different types of signalling and possibly semipermanent virtual channels (VCs), including the assignment, removal, and checking of VCs. Metasignalling VCs - the standardized VCs that convey metasignalling information across a User-to-Network Interface (UNI). MIB (Management Information Base) - the set of parameters that an SNMP management sta- tion can query or set in the SNMP agent of a networked device (e.g., router). MIC (Media Interface Connector) - the optical fiber connector that joins the fiber to the FDDI controller. ForeRunner HE/200E/LE ATM Adapters for the PC User’s Manual Glossary - 17 Glossary Glossary MicroChannel - a proprietary 16- or 32-bit bus developed by IBM for its PS/2 computers’ internal expansion cards; also offered by others. MTU (Maximum Transmission Unit) - the largest unit of data that can be sent over a type of physical medium. Multi-homed - a device that has both an ATM and another network connection, typically Ethernet. Multiplexing - a function within a layer that interleaves the information from multiple con- nections into one connection (see demultiplexing). Multipoint Access - user access in which more than one terminal equipment (TE) is sup- ported by a single network termination. Multipoint-to-Point Connection - a Point-to-Multipoint Connection may have zero band- width from the Root Node to the Leaf Nodes, and non-zero return bandwidth from the Leaf Nodes to the Root Node. Such a connection is also known as a Multipoint-to-Point Connec- tion. Multipoint-to-Multipoint Connection - a collection of associated ATM VC or VP links, and their associated endpoint nodes, with the following properties: 1. All N nodes in the connection, called Endpoints, serve as a Root Node in a Point-to-Multi- point connection to all of the (N-1) remaining endpoints. 2. Each of the endpoints can send information directly to any other endpoint, but the receiving endpoint cannot distinguish which of the endpoints is sending information without addi- tional (e.g., higher layer) information. Near-End - in a relationship between two devices in a circuit, the near-end device is the one that is local. Network Module - ATM port interface cards which may be individually added or removed from any ForeRunner ATM switch to provide a diverse choice of connection alternatives. Each network module provides between one and six full-duplex ATM physical connections to the ForeRunner switch. NMS (Network Management Station) - the system responsible for managing a network or a portion of a network. The NMS talks to network management agents, which reside in the managed nodes. NNI (Network-to-Network Interface or Network Node Interface) - the interface between two public network pieces of equipment. nonvolatile - a term used to describe a data storage device (memory) that retains its contents when power is lost. Glossary - 18 ForeRunner HE/200E/LE ATM Adapters for the PC User’s Manual Glossary NuBus - a high-speed bus used in the Macintosh family of computers, structured so that users can put a card into any slot on the board without creating conflict over the priority between those cards OAM (Operation and Maintenance) Cell - a cell that contains ATM LM information. It does not form part of the upper layer information transfer. octet - a grouping of 8 bits; similar, but not identical, to a byte. OID (Object Identifier) - the address of a MIB variable. OOF (Out-of-Frame) - a signal condition and alarm in which some or all framing bits are lost. OpenView - Hewlett-Packard’s network management software. OSI (Open Systems Interconnection) - the 7-layer suite of protocols designed by ISO com- mittees to be the international standard computer network architecture. OSPF (Open Shortest Path First) Protocol - a routing algorithm for IP that incorporates least-cost, equal-cost, and load balancing. Out-of-Band Management - refers to switch configuration via the serial port or over Ether- net, not ATM. packet - a group of bits - including information bits and overhead bits - transmitted as a com- plete package on a network. Usually smaller than a transmission block. Packet Port - a port on the CellPath 300 that transmits and receives packet traffic. Packet Switching - a communications paradigm in which packets (messages) are individu- ally routed between hosts with no previously established communications path. Payload Scrambling - a technique that eliminates certain bit patterns that may occur within an ATM cell payload that could be misinterpreted by certain sensitive transmission equipment as an alarm condition. PBX (Private Branch Exchange) - a private phone system (switch) that connects to the pub- lic telephone network and offers in-house connectivity. To reach an outside line, the user must dial a digit like 8 or 9. PCI (Peripheral Component Interconnect) - a local-bus standard created by Intel. PCM (Pulse Code Modulation) - a modulation scheme that samples the information signals and transmits a series of coded pulses to represent the data. PCR (Peak Cell Rate) - parameter defined by the ATM Forum for ATM traffic management. In CBR transmissions, PCR determines how often data samples are sent. In ABR transmis- sions, PCR determines the maximum value of the ACR. PDN (Public Data Network) - a network designed primarily for data transmission and intended for sharing by many users from many organizations.

PDU (Protocol Data Unit) - a unit of data specified in a layer protocol and consisting of proto- col control information and layer user data. Peak Cell Rate - at the PHY Layer SAP of a point-to-point VCC, the Peak Cell Rate Rpis the inverse of the minimum inter-arrival time T0 of the request to send an ATM-SDU. Peer Entities - entities within the same layer. PHY (Physical Layer) - the actual cards, wires, and/or fiber-optic cabling used to connect computers, routers, and switches. Physical Layer (PHY) Connection - an association established by the PHY between two or more ATM-entities. A PHY connection consists of the concatenation of PHY links in order to provide an end-to-end transfer capability to PHY SAPs. PLCP (Physical Layer Convergence Protocol) - a framing protocol that runs on top of the T1 or E1 framing protocol. PLM (Physical Layer Module) - interface card in the CellPath 300 that provides the logic to support the physical layer of the network link. A PLM has the actual physical port mounted on it. Various PLMs support various physical layers, such as OC-3c/STM1 or DS3. PLP (Packet Level Protocol) - Network layer protocol in the X.25 protocol stack. Sometimes called X.25 Level 3 or X.25 Protocol. See also X.25. PM (Protocol Module) - interface card in the CellPath 300 that provides the logic supporting the protocol layer of the network link. Various PMs support various protocols, such as ATM cell, Frame Relay, or CBR traffic. PMD (Physical Medium Dependent) - a sublayer concerned with the bit transfer between two network nodes. It deals with wave shapes, timing recovery, line coding, and electro-optic conversions for fiber based links. PNNI (Private Network Node Interface or Private Network-to-Network Interface) - a proto- col that defines the interaction of private ATM switches or groups of private ATM switches ping (Packet Internet Groper) - a program used to test reachability of destinations by send- ing them an ICMP echo request and waiting for a reply. Point-to-Multipoint Connection - a collection of associated ATM VC or VP links, with associ- ated endpoint nodes, with the following properties: 1. One ATM link, called the Root Link, serves as the root in a simple tree topology. When the Root node sends information, all of the remaining nodes on the connection, called Leaf nodes, receive copies of the information. 2. Each of the Leaf Nodes on the connection can send information directly to the Root Node. The Root Node cannot distinguish which Leaf is sending information without additional (higher layer) information. (See the following note for Phase 1.) 3. The Leaf Nodes cannot communicate directly to each other with this connection type. Glossary - 20 ForeRunner HE/200E/LE ATM Adapters for the PC User’s Manual Glossary Note: Phase 1 signalling does not support traffic sent from a Leaf to the Root. Point-to-Point Connection - a connection with only two endpoints. Point of Demarcation - the dividing line between a carrier and the customer premise that is governed by strict standards that define the characteristics of the equipment on each side of the demarcation. Equipment on one side of the point of demarcation is the responsibility of the customer. Equipment on the other side of the point of demarcation is the responsibility of the carrier. Policing - the function that ensures that a network device does not accept traffic that exceeds the configured bandwidth of a connection. Primitive - an abstract, implementation-independent interaction between a layer service user and a layer service provider. Priority - the parameter of ATM connections that determines the order in which they are reduced from the peak cell rate to the sustained cell rate in times of congestion. Connections with lower priority (4 is low, 1 is high) are reduced first. PROM (Programmable Read-Only Memory) - a chip-based information storage area that can be recorded by an operator but erased only through a physical process. Protocol - a set of rules and formats (semantic and syntactic) that determines the communica- tion behavior of layer entities in the performance of the layer functions. Protocol Control Information - the information exchanged between corresponding entities using a lower layer connection to coordinate their joint operation. Proxy - the process in which one system acts for another system to answer protocol requests. Proxy Agent - an agent that queries on behalf of the manager, used to monitor objects that are not directly manageable. PSN (Packet Switched Network) - a network designed to carry data in the form of packets. The packet and its format is internal to that network. PT (Payload Type) - bits 2…4 in the fourth byte of an ATM cell header. The PT indicates the type of information carried by the cell. At this time, values 0…3 are used to identify various types of user data, values 4 and 5 indicate management information, and values 6 and 7 are reserved for future use. PVC (Permanent Virtual Circuit (or Channel)) - a circuit or channel through an ATM net- work provisioned by a carrier between two endpoints; used for dedicated long-term informa- tion transport between locations. Q.2931 - Derived from Q.93B, the narrowband ISDN signalling protocol, an ITU standard describing the signalling protocol to be used by switched virtual circuits on ATM LANs. Real-Time Clock - a clock that maintains the time of day, in contrast to a clock that is used to time the electrical pulses on a circuit. ForeRunner HE/200E/LE ATM Adapters for the PC User’s Manual Glossary - 21 Glossary Glossary Relaying - a function of a layer by means of which a layer entity receives data from a corre- sponding entity and transmits it to another corresponding entity. RFCs (Requests For Comment) - IETF documents suggesting protocols and policies of the Internet, inviting comments as to the quality and validity of those policies. These comments are collected and analyzed by the IETF in order to finalize Internet standards. RFI (Radio Frequency Interference) - the unintentional transmission of radio signals. Com- puter equipment and wiring can both generate and receive RFI. RIP (Routing Information Protocol) - a distance vector-based protocol that provides a mea- sure of distance, or hops, from a transmitting workstation to a receiving workstation. RISC (Reduced Instruction Set Computer) - a generic name for CPUs that use a simpler instruction set than more traditional designs. Router - a device that forwards traffic between networks or subnetworks based on network layer information. RTS (Request To Send) - an RS-232 modem interface signal (sent from the DTE to the modem on pin 4) which indicates that the DTE has data to transmit. SBus - hardware interface for add-in boards in later-version Sun 3 workstations. SAP (Service Access Point) - the point at which an entity of a layer provides services to its LM entity or to an entity of the next higher layer. SAR (Segmentation And Reassembly) - the SAR accepts PDUs from the CS and divides them into very small segments (44 bytes long). If the CS-PDU is less than 44 bytes, it is padded to 44 with zeroes. A two-byte header and trailer are added to this basic segment. The header identifies the message type (beginning, end, continuation, or single) and contains sequence numbering and message identification. The trailer gives the SAR-PDU payload length, exclu- sive of pad, and contains a CRC check to ensure the SAR-PDU integrity. The result is a 48-byte PDU that fits into the payload field of an ATM cell. SC - CellPath 300 System Controller; paired with the Extension Module (EM). SCR (sustainable cell rate) - parameter defined by the ATM Forum for ATM traffic manage- ment. For VBR connections, SCR determines the long-term average cell rate that can be trans- mitted. SCSI (Small Computer Systems Interface) - a standard for a controller bus that connects disk drives and other devices to their controllers on a computer bus. It is typically used in small systems. SDLC (Synchronous Data Link Control) - IBM’s data link protocol used in SNA networks. SDU (Service Data Unit) - a unit of interface information whose identity is preserved from one end of a layer connection to the other. Glossary - 22 ForeRunner HE/200E/LE ATM Adapters for the PC User’s Manual Glossary SEAL (Simple and Efficient Adaptation Layer) - also called AAL 5, this ATM adaptation layer assumes that higher layer processes will provide error recovery, thereby simplifying the SAR portion of the adaptation layer. Using this AAL type packs all 48 bytes of an ATM cell information field with data. It also assumes that only one message is crossing the UNI at a time. That is, multiple end-users at one location cannot interleave messages on the same VC, but must queue them for sequential transmission. Segment - a single ATM link or group of interconnected ATM links of an ATM connection. Semipermanent Connection - a connection established via a service order or via network management. SES (Severely Errored Seconds) - a second during which more event errors have occurred than the SES threshold. SF (Superframe) - Common framing type used on T1 circuits. SF consists of 12 frames of 192 bits each, with the 193rd bit providing error checking and other functions. SF has been super- seded by ESF, but is still widely used. Also called D4 framing. See also ESF. SGMP (Simple Gateway Management Protocol) - the predecessor to SNMP. Shaping Descriptor - n ordered pairs of GCRA parameters (I,L) used to define the negotiated traffic shape of an APP connection. The traffic shape refers to the load-balancing of a network. In this context, load-balancing means configuring the data flows to maximize the efficiency of the network. SIR (Sustained Information Rate) - the long-term average data transmission rate across the User-to-Network Interface. SMDS (Switched Multimegabit Data Service) - a high-speed, datagram-based, public data network service expected to be widely used by telephone companies in their data networks. SMTP (Simple Mail Transfer Protocol) - the Internet electronic mail protocol used to transfer electronic mail between hosts. SNAP - SubNetwork Access Protocol SNMP (Simple Network Management Protocol) - the Internet standard protocol for manag- ing nodes on an IP network. snmpd - an SMNP agent for a given adapter card. SONET (Synchronous Optical Network) - a new and growing body of standards that defines all aspects of transporting and managing digital traffic over optical facilities in the public net- work. Source Traffic Descriptor - a set of traffic parameters belonging to the ATM Traffic Descrip- tor used during the connection set-up to capture the intrinsic traffic characteristics of the con- nection requested by the source. ForeRunner HE/200E/LE ATM Adapters for the PC User’s Manual Glossary - 23 Glossary Glossary Spanning Tree Protocol - provides loop-free topology in a network environment where there are redundant paths. SPANS (Simple Protocol for ATM Network Signalling) - FORE Systems’ proprietary signal- ling protocol used for establishing SVCs between FORE Systems equipment. SPARC (Scalable Processor Architecture Reduced instruction set Computer) - a power- ful workstation similar to a reduced-instruction-set-computing (RISC) workstation. SPE (Synchronous Payload Envelope) - the payload field plus a little overhead of a basic SONET signal. SPVC (Smart PVC) - a generic term for any communications medium which is permanently provisioned at the end points, but switched in the middle. In ATM, there are two kinds of SPVCs: smart permanent virtual path connections (SPVPCs) and smart permanent virtual channel connections (SPVCCs). Static Route - a route that is entered manually into the routing table. Statistical Multiplexing - a technique for allowing multiple channels and paths to share the same link, typified by the ability to give the bandwidth of a temporarily idle channel to another channel. STM (Synchronous Transfer Mode) - a transport and switching method that depends on information occurring in regular and fixed patterns with respect to a reference such as a frame pattern. STP (Shielded Twisted Pair) - two or more insulated wires that are twisted together and then wrapped in a cable with metallic braid or foil to prevent interference and offer noise-free transmissions. STS (Synchronous Transport Signal) - a SONET electrical signal rate. Sublayer - a logical subdivision of a layer. Super User - a login ID that allows unlimited access to the full range of a device’s functional- ity, including especially the ability to reconfigure the device and set passwords. SVC (Switched Virtual Circuit (or Channel)) - a channel established on demand by network signalling, used for information transport between two locations and lasting only for the duration of the transfer; the datacom equivalent of a dialed telephone call. Switched Connection - a connection established via signalling. Symmetric Connection - a connection with the same bandwidth value specified for both directions. Synchronous - signals that are sourced from the same timing reference and hence are identi- cal in frequency. Glossary - 24 ForeRunner HE/200E/LE ATM Adapters for the PC User’s Manual Glossary Systems Network Architecture (SNA) - a proprietary networking architecture used by IBM and IBM-compatible mainframe computers. T1 - a specification for a transmission line. The specification details the input and output char- acteristics and the bandwidth. T1 lines run at 1.544 Mbps and provide for 24 data channels. In common usage, the term “T1” is used interchangeably with “DS1.” T3 - a specification for a transmission line, the equivalent of 28 T1 lines. T3 lines run at 44.736 Mbps. In common usage, the term “T3” is used interchangeably with “DS3.” Tachometer - in ForeView, the tachometer shows the level of activity on a given port. The num- ber in the tachometer shows the value of a chosen parameter in percentage, with a colored bar providing a semi-logarithmic representation of that percentage. TAXI (Transparent Asynchronous Transmitter/Receiver Interface) - Encoding scheme used for FDDI LANs as well as for ATM; supports speeds of up to 100 Mbps over multimode fiber. TC (Transmission Convergence) - generates and receives transmission frames and is respon- sible for all overhead associated with the transmission frame. The TC sublayer packages cells into the transmission frame. TCP (Transmission Control Protocol) - a specification for software that bundles and unbun- dles sent and received data into packets, manages the transmission of packets on a network, and checks for errors. TCP/IP (Transmission Control Protocol/Internet Protocol) - a set of communications proto- cols that has evolved since the late 1970s, when it was first developed by the Department of Defense. Because programs supporting these protocols are available on so many different computer systems, they have become an excellent way to connect different types of computers over networks. TDM (Time Division Multiplexing) - a method of traditional digital multiplexing in which a signal occupies a fixed, repetitive time slot within a higher-rate signal. Telnet - a TCP/IP protocol that defines a client/server mechanism for emulating directly-con- nected terminal connections. Token Ring - a network access method in which the stations circulate a token. Stations with data to send must have the token to transmit their data. topology - a program that displays the topology of a FORE Systems ATM network. An updated topology can be periodically re-displayed by use of the interval command option. Traffic - the calls being sent and received over a communications network. Also, the packets that are sent on a data network. Trailer - the protocol control information located at the end of a PDU. ForeRunner HE/200E/LE ATM Adapters for the PC User’s Manual Glossary - 25 Glossary Glossary Transit Delay - the time difference between the instant at which the first bit of a PDU crosses one designated boundary, and the instant at which the last bit of the same PDU crosses a sec- ond designated boundary. trap - a program interrupt mechanism that automatically updates the state of the network to remote network management hosts. The SNMP agent on the switch supports these SNMP traps. UAS (Unavailable Seconds) - a measurement of signal quality. Unavailable seconds start accruing when ten consecutive severely errored seconds occur. UBR (Unspecified Bit Rate) - a type of traffic that is not considered time-critical (e.g., ARP messages, pure data), allocated whatever bandwidth is available at any given time. UBR traf- fic is given a “best effort” priority in an ATM network with no guarantee of successful trans- mission. UDP (User Datagram Protocol) - the TCP/IP transaction protocol used for applications such as remote network management and name-service access; this lets users assign a name, such as “RVAX*2,S,” to a physical or numbered address. Unassigned Cells - a generated cell identified by a standardized virtual path identifier (VPI) and virtual channel identifier (VCI) value, which does not carry information from an applica- tion using the ATM Layer service. UNI (User-to-Network Interface) - the physical and electrical demarcation point between the user and the public network service provider. UNI 3.0 - the User-to-Network Interface standard set forth by the ATM Forum that defines how private customer premise equipment interacts with private ATM switches. UPC (Usage Parameter Control) - the mechanism that ensures that traffic on a given connec- tion does not exceed the contracted bandwidth of the connection. UPC is responsible for polic- ing or enforcement. UPC is sometimes confused with congestion management, to which it is functionally related on the CellPath 300 (see congestion management). UTP (Unshielded Twisted Pair) - a cable that consists of two or more insulated conductors in which each pair of conductors are twisted around each other. There is no external protection and noise resistance comes solely from the twists. V.35 - ITU-T standard describing a synchronous, physical layer protocol used for communica- tions between a network access device and a packet network. V.35 is most commonly used in the United States and Europe, and is recommended for speeds up to 48 Kbps. VBR (Variable Bit Rate) - a type of traffic that, when sent over a network, is tolerant of delays and changes in the amount of bandwidth it is allocated (e.g., data applications). VC (Virtual Channel (or Circuit)) - a communications path between two nodes identified by label rather than fixed physical path. Glossary - 26 ForeRunner HE/200E/LE ATM Adapters for the PC User’s Manual Glossary VCC (Virtual Channel Connection) - a unidirectional concatenation of VCLs that extends between the points where the ATM service users access the ATM Layer. The points at which the ATM cell payload is passed to, or received from, the users of the ATM Layer (i.e., a higher layer or ATMM-entity) for processing signify the endpoints of a VCC. VCI (Virtual Channel Identifier) - the address or label of a VC; a value stored in a field in the ATM cell header that identifies an individual virtual channel to which the cell belongs. VCI values may be different for each data link hop of an ATM virtual connection. VCL (Virtual Channel Link) - a means of unidirectional transport of ATM cells between the point where a VCI value is assigned and the point where that value is translated or removed. VINES (Virtual Network Software) - Banyan’s network operating system based on UNIX and its protocols. Virtual Channel Switch - a network element that connects VCLs. It terminates VPCs and translates VCI values. The Virtual Channel Switch is directed by Control Plane functions and relays the cells of a VC. Virtual Connection - an endpoint-to-endpoint connection in an ATM network. A virtual con- nection can be either a virtual path or a virtual channel. Virtual Path Switch - a network element that connects VPLs, it translates VPI (not VCI) values and is directed by Control Plane functions. The Virtual Path Switch relays the cells of a Virtual Path. VPT (Virtual Path Terminator) - a system that unbundles the VCs of a VP for independent processing of each VC. VP (Virtual Path) - a unidirectional logical association or bundle of VCs. VPC (Virtual Path Connection) - a concatenation of VPLs between virtual path terminators (VPTs). VPCs are unidirectional. VPDN (Virtual Private Data Network) - a private data communications network built on pub- lic switching and transport facilities rather than dedicated leased facilities such as T1s. VPI (Virtual Path Identifier) - the address or label of a particular VP; a value stored in a field in the ATM cell header that identifies an individual virtual path to which the cell belongs. A virtual path may comprise multiple virtual channels. VPL (Virtual Path Link) - a means of unidirectional transport of ATM cells between the point where a VPI value is assigned and the point where that value is translated or removed. VPN (Virtual Private Network) - a private voice communications network built on public switching and transport facilities rather than dedicated leased facilities such as T1s. VT (Virtual Tributary) - a structure used to carry payloads such as DS1s that run at signifi- cantly lower rates than STS-1s. WAN (Wide-Area Network) - a network that covers a large geographic area. ForeRunner HE/200E/LE ATM Adapters for the PC User’s Manual Glossary - 27 Glossary Glossary Warm Start Trap - a CellPath 300 SNMP trap that indicates that SNMP alarm messages or agents have been enabled. Yellow Alarm - an alarm that occurs on a device when the signal from the device is not received at the far-end. X.21 - ITU-T standard for serial communications over synchronous digital lines. The X.21 pro- tocol is used primarily in Europe and Japan. X.25 - ITU-T standard that defines how connections between DTE and DCE are maintained for remote terminal access and computer communications in PDNs. X.25 specifies LAPB, a data link protocol, and PLP, a network layer protocol. Frame Relay has, to some degree, super- seded X.25. See also Frame Relay, LAPB, and PLP.

From:-

ForeRunner HE/200E/LE
ATM Adapters for the PC
User’s Manual
MANU0177-04 - Rev. A - February, 1999