Glossary

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4B/5B

The physical layer (PHY) coding scheme for FDDI.

802.1 IEEE

A set of standards for governing the OSI Data Link layer and the OSI physical layer. For example, 802.1d is the standard for bridging between the LAN standards

802.2 IEEE

Standards that govern the Logical Link Control (LLC) within the Data Link layer of the OSI model. LLC frames carry user infobetween two stations. These standards are common across the various lower level standards within the Data Link and the Physical layers.

A
adapter

A device, usually in the form of a user interface card, that physically connects an endstation to the network medium; for example, twisted pair, coaxial, fiber.

ANSI (American National Standards Institute)

Organization which coordinates, develops, and publishes standards used in the United States.

Application layer

The seventh layer in the OSI model for data communications. It defines protocols for user or application programs.

ARP (Address Resolution Protocol)

A TCP/IP protocol used to dynamically translate the IP address of a network host to its LAN hardware (MAC) address. This action is limited to LANs that support hardware broadcasts.

Assert

A signal is asserted by driving it to a logical true state. For positive-true signals this state is high logic voltage, and for negative-true signals this state is the low logic voltage.

attenuation

Signal power lost in a transmission medium as the signal travels from sender to receiver.

B
backbone

A network configuration that connects LANs into an integrated network.

bandwidth

Bandwidth typically indicates the data transmission capacity of a network through a given circuit. Generally, the greater the bandwidth, the more information can be sent through a circuit during a given amount of time.

baud

Measurement of signaling speed indicating line changes per second, where line changes can represent one or more bits. The baud is equal to bits-per-second only for line changes representing a single bit.

beacon

A special frame used by media access control to announce to the other stations that the ring is broken. The resulting action attempts to restructure the network to account for the probable fault.

bridge

An internetworking device used to connect two or more computer networks and to forward packets among the networks. Bridges operate at the Link layer of the OSI model.

Bus Latency

Elapsed time from bus master request until bus master is given control of the bus.

bypass

The ability of a station to be optically or electronically isolated from the network while maintaining the integrity of the ring.

C
CFM (Configuration Management)

That portion of the Connection Management (CMT) within the Station Management (SMT) function of an FDDI station that provides for the configuration of PHY and MAC entities within a node.

claim process

A technique used to determine which station will initialize the FDDI ring.

CMT (Connection Management)

That portion of the Station Management (SMT) function within an FDDI station that controls the insertion, removal, and connection of the PHY and MAC entities within that station.

concentrator

An FDDI node that provides attachment points (through M ports) for stations that are not connected directly to the dual ring. The concentrator is the focal point of the dual ring of trees topology.

counter-rotating ring

An arrangement where two signal paths, whose directions are opposite, exist in a ring topology.

CPU (Central Processing Unit)

A computer's main microprocessor chip.

CRC (Cyclic Redundancy Check)

An error checking procedure in which bytes at the end of a frame are used by the receiving node to detect a transmission problem.

D
DAC (Dual Attachment Concentrator

A concentrator that offers two connections to the FDDI network capable of accommodating the FDDI dual (counter-rotating) ring, and additional ports for the connection of other concentrators or FDDI stations.

DAS (Dual Attachment Station)

An FDDI station that offers two connections to the FDDI dual counter-rotating ring.

Differential Manchester encoding

A signaling method that encodes clock and data information into bit symbols. Each bit symbol is divided into two halves, where the second half is the inverse of the first half. A zero is represented by a polarity change at the start of the bit time; a one is represented by no polarity change at the start of the bit time.

DMA (Direct Memory Access)

A fast method of moving data between two processor subsystems without processor intervention.

DMA Controller

Provides control of the larger part of the system's DMA (Direct Memory Access) facility. The DMA controller responds to requests from the DMA device and provides address and control signals to the memory slaves and DMA device.

DMA Device

The DMA device is typically located on a peripheral board on the EISA or ISA bus. The DMA device initiates DMA transfers, which are controlled by signals generated by the system DMA controller. The DMA device either presents or receives data during a DMA transfer and uses several signals to inform the DMA controller of the staus of the transfer.

downstream

A term that refers to the relative position of two stations in a ring. A station is downstream of its neighbor if it receives the token after its neighbor receives the token.

dual homing

A method of cabling concentrators and stations that permits an alternate or backup path to the dual ring in case the primary connection fails. Can be used in a tree or dual ring of trees configuration.

dual ring

An FDDI network topology that uses two redundant rings to overcome fiber-optic failures between two nodes.

dual ring of trees

A topology of concentrators and nodes that cascade from concentrators on a dual ring.

E
ECM (Entity Coordination Management)

That portion of the Connection Management (CMT) within the Station Management (SMT) function of an FDDI station that provides for controlling bypass relays, signaling to PCM (Physical Connection Management) that the medium is available, and coordinating trace functions.

encapsulating bridge

A proprietary hardware device that encapsulates packets into specialized frames, usually by adding a header and a trailer to the frame.

encode

The act of changing data into a series of electrical or optical pulses that can travel efficiently over a medium.

extended LAN

A collection of local area networks (similar or dissimilar) interconnected with a bridge.

F
FDDI (Fiber Distributed Data Interface)

An ANSI standard (X3T9.5) for 100 Mbps LANs based on the token-passing access method. It is often used to bridge several Ethernet segments at high speed.

fiber optic cable

A transmission medium designed to transmit digital signals in the form of pulses of light.

fiber optics

The technique of using fiber optic transmitters, receivers, and cables for the transmission of data.

Float

Signal is placed in the high impedance state.

fragment

In FDDI, pieces of a frame left on the ring; caused by a station stripping a frame from the ring.

fragmentation

A process in which large frames from one network are broken up into smaller frames that are compatible with the frame size requirements of the network to which they will be forwarded.

frame

A Protocol Data Unit (PDU) transmitted between cooperating MAC entities on an FDDI ring, consisting of a variable number of bytes and control symbols.

G
graded index

A characteristic of fiber optic cable in which the core refraction index is varied so that it is high at the center and matches the refractive index of the cladding at the core-cladding boundary.

H
header

Control information added at the data source to allow data to reach its destination. At the destination, layers corresponding to those at the source that created the header read and remove it, so that only the data reaches the final destination.

host

Generally, any computer on a network.

Host CPU

The main system processor. The host CPU typically has its own local bus allowing the CPU to access cache or local memory without using the EISA bus. The host CPU accesses the EISA bus like any other bus master, with the exception of a few special features. The data size of the host CPU does not determine the EISA bus size; the CPU can have an 8-, 16-, or 32-bit data bus and still access the 16- or 32-bit EISA bus.

host name

A unique name that identifies each host machine on a network.

I
ICMP (Internet Control Message Protocol)

An integral part of the Internet Protocol (IP) that handles error and control messages. Specifically, gateways and hosts use ICMP to send reports of problems with datagrams back to the original source of the datagram. ICMP includes an echo request/reply used to test whether a destination is reachable or responding.

IEEE (Institute of Electrical and Electronic Engineers)

An information exchange organization. As part of its various functions, it coordinates, develops, and publishes network standards for use in the United States, following ANSI rules.

Inter-frame gap

The interval between frames on the network media. It is defined by FDDI standards to prevent one frame from becoming confused with the next.

IP (Internet Protocol)

A network layer protocol that contains addressing and control information to allow packets to be routed over dissimilar networks.

ISO (International Standards Organization)

An international body that creates networking standards, including the Open Systems Interconnection (OSI) model.

K
KB

Kilobytes. 1024 bytes.

L
LAN (Local Area Network)

A data communications network that spans a limited geographical area. The network provides high bandwidth communication over coaxial cable, twisted pair, fiber, or microwave media. It is usually owned by the user.

local

Local refers to files and devices, such as disk drives, that are attached to or on your machine.

logical ring

The circular path a token follows in an FDDI network made up of all the connected MAC sublayers. The physical topology can be a dual ring of trees, a tree, or a ring.

M
MAC (Media Access Control)

The Data Link layer in the ISO model that describes how devices share access to a network. Ethernet, token-ring, and FDDI are MAC layer specifications. Wiring hubs deal primarily with MAC layer equipment.

Manchester encoding

A signaling method by which clock and data bit information can be combined into a single, self-synchronizable data stream. A transition takes place in the middle of each bit time. A low-to-high transition represents a one; a high-to-low transition represents a zero.

Mbps

Megabits (1,048,576 bits) per second.

MIB (Management Information Base)

A set of variables that describe how data is stored, monitored, and managed. MIB-I and MIB-II are revisions of the database used in a TCP/IP network. The original MIB was renamed to MIB-I when the MIB-II was defined.

MIC (Media Interface Connector)

An optical fiber connector pair that links the fiber media to the FDDI node or another cable. The MIC consists of two halves. The MIC plug terminates an optical fiber cable. The MIC receptacle is associated with the FDDI node.

multicast

A technique that allows copies of a single packet or cell to be passed to a selected subset of all possible destinations.

multimode

A large-core (62.5 micron) optical fiber through which multiple modes will propagate.

N
network

An interconnection of multiple stations or systems that are able to send messages to or receive messages from one another.

Network layer

Layer 3 in the OSI model; permits communications between network nodes in an open network.

NIF (Neighborhood Information Frame)

Special frames used by the SMT Frame Services within the Station Management (SMT) function of an FDDI station that periodically announce their addresses to downstream neighbors. Each station in the ring makes such an announcement every 30 seconds by sending a NIF that uses Next Station Addressing (NSA), a special addressing mode that permits a station to send a frame to the next station on the token path without knowing the address of that station. This information can be used to create a logical ring map for the order in which each station appears within the ring.

NMS (Network Management Station)

The system responsible for managing a network or a portion of a network. The NMS communicates to network management agents which reside in the managed node using a network management protocol.

node

A device, such as a station or concentrator, connected to a network.

NRZ (Nonreturn to Zero)

A data transmission technique where a polarity level, high or low, represents a logical 1 or 0.

NRZI (Nonreturn to Zero Invert on Ones)

A data transmission technique where a polarity transition from low to high, or high to low, represents a logical 1. The absence of a polarity transition represents a 0.

NSA (Next Station Addressing)

A special addressing mode in FDDI networks that permits a station to send a frame to the next station on the token path without knowing that station's address.

O
optical receiver

An opto-electronic circuit that converts an incoming optical signal to an electrical signal, typically a photodetector.

optical transmitter

An opto-electronic circuit that converts an electrical signal to an optical signal, typically a light emitting diode or a laser diode.

OSI Model (Open Systems Interconnection)

The 7-layer protocol model defined by the International Standards Organization (ISO) for data communications.

P
packet

Data information that is grouped and transmitted together, such as messages, commands, and control codes.

PCM (Physical Connection Management)

That portion of the Connection Management (CMT) within the Station Management (SMT) function of an FDDI station that manages the physical connect between adjacent PHYs. This includes the signaling of the connection type, link confidence testing, and the enforcement of connection rules.

PDU (Protocol Data Unit)

The unit of data transfer between peer layer entities. It may contain control information, address information, and/or data (for example, a Service Data Unit from a higher layer entity). A valid PDU is at least 24 bits in length. The FDDI MAC PDUs are tokens and frames.

peer-to-peer

Assigning of communications tasks so that data transmission between logical groups or layers in a network architecture is accomplished between entities in the same sublayer of the OSI model.

PHY (Physical Layer Protocol)

A standard protocol that defines symbols, line states, clocking requirements, and the encoding of data for transmission.

Physical layer

Layer 1 in the OSI model; defines and handles the electrical and physical connections between systems. The physical layer can also encode data into a form that is compatible with the medium (coaxial, twisted pair, fiber, and so on).

PING (Packet Internet Groper)

A TCP/IP protocol facility used to test the reachability of destinations by sending an ICMP (Internet Control Message Protocol) echo request and waiting for a reply.

PMD (Physical Layer Medium Dependent)

A standard that defines the medium and protocols to transfer symbols between PHYs.

point-to-point

Transmission of data between two nodes where one node is the sender and the other node is the receiver.

Presentation layer

Layer 6 in the OSI model; details protocols governing data formats and conversions.

propagation delay

The time it takes for a signal to travel across the network.

protocol

A set of rules and conventions that govern the exchange of information between communicating parties on a network.

R
reconfiguration

The operation by which a station determines the location of a fault and isolates it by utilizing the redundancy of the dual FDDI ring.

repeat frame

The operation of repeating a group of symbols on the network in exactly the same manner they were received by the station.

repeater

A level 1 hardware device that performs the basic actions of restoring signal amplitude, waveform, and timing of signals, before transmission onto another network segment.

ring

Connections between two or more stations that form a circular topology.

RMT (Ring Management)

That portion of the Station Management (SMT) function within an FDDI station that receives status information from the Media Access Control (MAC) and the Connection Management (CMT). The RMT then reports this status to the SMT and higher-level processes.

router

A level 3 hardware device that uses layer 3 protocols to control network communication between stations and forwards messages to endstations or other routers.

S
SAC (Single Attachment Concentrator)

A concentrator that offers one S port for attachment to the FDDI network and M ports for the attachment of stations or other concentrators.

SAS (Single Attachment Station)

An FDDI station that offers one S port for attachment to the FDDI ring.

services

A set of functions proved by one OSI/ISO layer or sublayer entity, for use by a higher layer or sublayer entity or by management entities.

Session layer

Layer 5 in the OSI model; defines protocols governing communications between applications.

SIF (Station Information Frame)

Special frames used by the SMT Frame Services within the Station Management (SMT) function of an FDDI station that contain more information about the station's configuration and characteristics than the associated Neighborhood Information Frame (NIF). This information can be used to create a physical ring map that shows the position of each station in both the token path and the network topology.

single mode

A small-core (9 micron) optical fiber through which only one mode can propagate.

Slave

A memory or I/O device that uses EISA control signals to interface to the bus.

Slot Specific Signal

Each connector has a unique variant of the signal (instead of a single signal that is bused to all connnectors).

SMT (Station Management)

An entity within a network station on an FDDI ring that monitors station activity and exercises control over station activity. The standard defines how to manage the Physical Layer Medium Dependent (PMD), the Physical Layer Protocol (PHY), and the Media Access Control (MAC) portions of FDDI.

SMT Frame Services

That portion of Station Management (SMT) that provides the means to control and observe the FDDI network. The service uses Neighborhood Information Frames (NIF) and Station Information Frames (SIF) to pass an announcement, a request, and the response to a request.

SNMP (Simple Network Management Protocol)

A high level standards-based protocol for network management, usually used in TCP/IP networks. An SNMP monitor controls and measures the activities of SNMP agents that are embedded in nodes and network devices on the network. SNMP relies on Management Information Bases (MIBs) embedded in the network resources to monitor and control the network's topology.

spanning tree

A method of creating a loop-free logical topology on an extended LAN. Formation of a spanning tree topology for transmission of messages across bridges is based on the industry standard spanning tree algorithm defined in IEEE 802.1d.

station

An addressable node on the network capable of transmitting and receiving data. In an FDDI ring, the station can repeat data. A station has at least one instance of SMT, at least one instance of PHY and PMD, and an optional MAC entity.

stuck beacon

The condition where a station is locked into sending continuous beacon frames.

T
TCP/IP (Transmission Control Protocol/Internet Protocol)

A set of communications protocols that define how different types of computers talk to each other. It is the standard architecture for internetworking multiple organizations, and the common link that ties the huge Internet together.

token

A bit pattern consisting of a unique symbol sequence that circulates around the ring following a data transmission. The token grants stations the right to transmit.

token holding timer

A timer that controls the amount of time a station may hold the token in order to transmit asynchronous frames.

token passing

A method where each node, in turn, receives and passes on the right to use the channel. The nodes are usually configured in a logical ring.

Token Ring

A network topology utilizing a token-passing media access protocol in a ring topology. 100 Mbps FDDI and ANSI 802.5 4- and 16-Mbps Token Ring are token ring technologies.

trace

A diagnostic process to recover from a stuck-beacon condition. The fault is localized to the beaconing MAC and its upstream neighbor MAC.

Transport layer

Layer 4 in the OSI model; defines protocols governing message structure and some error checking.

TRT (Token Rotation Timer)

A clock that times the period between the receipt of tokens.

TTP (Timed-Token Protocol)

The rules defining how the target token rotation time is set, the length of time a station can hold the token, and how the ring is initialized.

TTRT (Target Token Rotation Time)

The value used by the MAC receiver to time the operations of the MAC layer. The TTRT value varies, depending on whether or not the ring is operational.

TVX (Valid Transmission Timer)

A timer that times the period between valid transmissions on the ring; used to detect excessive ring noise, token loss, and other faults.

U
upstream

A term that refers to the relative position of two stations in a ring. A station is upstream of its neighbor if it receives the token before its neighbor receives the token.

UTP (Unshielded Twisted Pair)

Type 3 cable with one or more twisted pairs where the wiring is not protected from electromagnetic and radio frequency, but covered with plastic or PVC.

W
WAN (Wide Area Network)

A network spanning a large geographical area that provides communications among devices on a regional, national or international basis.

workgroup

A network configuration characterized by a small number of attached devices spread over a limited geographical area.

workstation

A networked computer typically reserved for end-user applications.

X
X3T9.5 ANSI

The standard specification for an FDDI network operating at 100 Mbps in a ring topology that can extend to hundreds of stations over tens of kilometers without degrading the system.

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