Network Glossary
- AAL (ATM Adaptation Layer) - A
collection of standardized protocols that adapt user traffic to the cell
format. The AAL is subdivided into the Convergence Sublayer (CS) and the
Segmentation and Reassembly (SAR) sublayer. There are several types of
AALs - AAL1, AAL2, AAL3/4 and AAL5 - to support the various AAL service
classes.
- ABR (Available Bit Rate) - One
of five ATM Forum-defined service categories. In this service type, the
network makes the best effort to pass the maximum number of cells but does
not guarantee cell delivery. Supports variable bit rate data traffic with
flow control, a minimum guaranteed data transmission rate and specified
performance parameters. In exchange for regulating user traffic flow, the
network offers minimal cell loss of accepted traffic. Traffic parameters
are PCR and MCR. QoS parameters are CLR and CER.
- Address - A coded representation
of the origin or destination of data.
- ADPCM (Adaptive Differential Pulse Code Modulation)
- An ITU standard technique for encoding analog voice signals into
a digital form at 32 kbps (half the standard PCM rate).
- Agent - In SNMP, the word agent
refers to the managed system.
- AMI (Alternate Mark Inversion) - A
bipolar coding scheme in which successive ones (marks) must alternate in
polarity.
- Analog - A continuous wave or signal
(such as human voice).
- Analog Loopback - A testing technique
that isolates faults in transmission equipment by performing a loopback
on the data at the analog (line) side of the modem.
- Analog Transmission - The
transmission of a continuously variable signal, as opposed to a discrete
(digital) one.
- ANSI - American National Standards
Institute.
- AR (Access Rate) - The data rate of
the user access channel in a Frame Relay network. The speed of the access
channel determines how fast (maximum rate) the end user can inject data
into a Frame Relay network.
- ARQ (Automatic Request for Repeat or Retransmission)
- A communications feature where the receiver asks the transmitter
to resend a block or frame because errors were detected by the receiver.
- ASCII (American Standard Code for Information
Interchange) - A seven-level code (128 possible characters)
used for data transfer.
- Asynchronous Transmission - A
transmission method that sends units of data one character at a time.
Characters are preceded by start bits and followed by stop bits, which
provide synchronization at the receive terminal. Also called start-stop
transmission.
- ATM - Asynchronous
Transfer Mode. A standard (ITU) implementation
of cell relay, which is a packet switching technique using packets (cells)
of a fixed length. It is asynchronous in the sense that the recurrence
of cells containing information from an individual user is not periodic.
- ATM-ARP (ATM Address Resolution Protocol)
- An address resolution protocol for mapping ATM and IP addresses (each
host is assigned a unique IP address). It can be used for discovering LAN
hosts attached to an ATM network or in classical IP over ATM.
- ATM Forum - A worldwide organization that
promotes and sets standards for ATM networks and equipment.
- Attenuation - Signal power loss through
equipment, lines or other transmission devices. Measured in decibels.
- AWG - The American Wire Gauge System,
which specifies wire width.
Network Glossary
- Balanced - A transmission line
in which voltages on the two conductors are equal in magnitude, but opposite
in polarity, with respect to ground.
- Bandwidth - The range of frequencies
passing through a given circuit. The greater the bandwidth, the more information
can be sent through the circuit in a given amount of time.
- Baseband - Refers to transmission
of a digital or analog signal at its original frequency, as an unmodulated
signal.
- Baud - Unit of signaling speed
equivalent to the number of discrete conditions or events per second. If
each signal event represents only one bit condition, baud rate equals bps
(bits per second).
- Bc (Committed Burst Size) - the
maximum amount of data (in bits) that the network agrees to transfer during
a time interval Tc.
- Be (Excess Burst Size) - The maximum
amount of uncommitted data (in bits) in excess of Bc that a Frame Relay
network can try to deliver during time interval Tc. The network treats
Be data as discard-eligible.
- BECN (Backward Explicit Congestion Notification)
- A bit set by a Frame Relay network to notify an interface
device (DTE) that congestion avoidance procedures should be initiated by
the sending device.
- BERT (Bit Error Rate Test/Tester) - A
device used to test the bit error rate of a communications circuit (i.e.
the ratio of received erroneous bits to received bits, usually a number
referenced to a power of 10).
- Bipolar - A signaling method (in
T1/E1 ) represents a binary "1" by alternating positive and negative
pulses, and a binary "0" by absence of pulses.
- BISDN - Broadband Integrated Services
Digital Network. The next generation of ISDN, which is intended to carry
digital data, voice, and video. ATM provides the switching fabric and SONET
or SDHthe physical transport.
- Bit - The smallest unit of information
in a binary system. Represents either a one or zero ("1" or "0").
- Bit Interleaving/Multiplexing - A
process used in time division multiplexing where individual bits from different
lower speed channel sources are combined (one bit from one channel at a
time) into one continuous higher speed bit stream.
- Bps (Bits Per Second) - A measure
of data transmission rate in serial transmission.
- Bridge - A device interconnecting
local area networks at the OSI Data Link Layer, filtering and forwarding
frames according to media access control (MAC) addresses.
- Broadband - Wideband technology
capable of supporting voice, video and data, possibly using multiple channels.
- Buffer - A storage device. Commonly
used to compensate for differences in data rates or event timing when transmitting
from one device to another. Also used to remove jitter.
- Bus - A transmission path or channel.
A bus is typically an electrical connection with one or more conductors,
where all attached devices receive all transmissions at the same time.
- Byte - A group of bits (normally
8 bits in length).
Network Glossary
- CAS (Channel Associated Signaling) - Voice
signaling based on bits taken from voice timeslots, used by many PABXs.
- CBR (Constant Bit Rate) - One of
the five ATM classes of service. CBR supports the transmission of a continuous
bit-stream of information, such as voice and video traffic, which require
a constant amount of bandwidth allocated to a connection for the duration
of the transmission.
- CC (Continuity Cell) - A cell used
periodically to check whether a connection is idle or has failed. Continuity
checking is one of the OAM function types for fault management.
- CCR (Current Cell Rate) - The currently
acceptable transmission rate for an end-system as defined by RM cells within
ABR. The field in the RM cell indicates the current complying cell rate
(i.e., ACR) a user can transmit over a virtual connection (VC).
- Carrier - A continuous signal at
a fixed frequency that is capable of being modulated with a second (information
carrying) signal.
- CD (Carrier Detect) - A modem interface
signal indicating to an attached terminal that the local modem is receiving
a signal from the remote modem.
- CDP (Conditional Di-Phase) - a
digital encoding technique which is a variant of Manchester encoding, and
is not sensitive to polarity of wires (wires in a pair can be crossed).
- CDV (Cell Delay Variation) - A
QoS parameter that measures the difference between the transfer delay of
a single cell (CTD) and the expected transfer delay. This parameter is
important for time-sensitive virtual circuits such as CBR and VBR-RT.
- CDVT (Cell Delay Variation Tolerance) - Used
in CBR traffic, it specifies the acceptable tolerance of the CDV (jitter).
- Central Office (CO) - A telephone
company office which connects to all local loops in a given area and where
circuit switching of customer lines occurs.
- CER (Cell Error Rate) - A QoS parameter
that measures the number of transmitted cells that are erroneous over a
specific period of time (i.e., those that contain errors when they arrive
at the destination).
- CES (Circuit Emulation Service) - An
ATM service in which constant bit rate (CBR) virtual circuits use AAL1
to emulate an end-to-end physical circuit by providing a TDM-like virtual
circuit between local access circuits.
- Channel - A path for electrical
transmission between two or more points. Also called a link, line, circuit
or facility.
- Channel Bank - Equipment that connects
multiple voice channels to high speed links by performing voice digitization
and Time Division Multiplexing. Voice is converted to a 64 kbps signal
(24 channels into 1.544 Mbps in countries offering T1 services, such as
the U.S.A.; 30 channels into 2.048 Mbps in countries offering E1 or CEPT
services, such as in Europe).
- Characteristic Impedance - The
termination impedance of an electrically uniform transmission line.
- CIR (Committed Information Rate) - A
term used in Frame Relay which defines the information rate the network
is committed to provide the user.
- Circuit Emulation - In ATM, a connection
over a virtual circuit-based network providing service to the end users
that is indistinguishable from a real point-to point, fixed-bandwidth circuit.
- CLLM (Consolidated Link Layer Management)
- A Frame Relay network control mechanism that uses out-of-band
signaling to pass status information about the physical and logical connection
over the user-to-network interface.
- Clock - A term for the source(s)
of timing signals used in synchronous transmission.
- Committed Rate Measurement Interval - See
Tc.
- Composite Link - The line or circuit
carrying multiplexed data which connects a pair of multiplexers or concentrators.
Also called aggregate or main link.
- Compression - Any of several techniques
that reduce the number of bits required to represent information in data
transmission or storage, thereby conserving bandwidth and/or memory.
- Concentrator - Device that serves
as a wiring hub in star-topology network. Sometimes refers to a device
containing multiple modules of network equipment.
- Congestion - A state in which the
network is overloaded and starts to discard user data (frames, cells or
packets).
- Congestion control - In ATM networks,
congestion control schemes may be based on fields within the ATM cell header
(CLP, EFCI within the PTI) or may be based on a more sophisticated mechanism
between the ATM end-system and ATM switches. The ATM Forum has developed
a mechanism based on rate control for ABR-type traffic. In Frame Relay
networks, congestion is handled by the FECN, BECN and DE bits.
- Constant Bit Rate - See CBR
- Contention - A condition arising
when two or more data stations attempt to transmit at the same time using
the same link or channel.
- Control Characters - In communications,
any extra transmitted characters used to control or facilitate data transmission
(for example, characters associated with polling, framing, synchronization,
error checking, or message delimiting).
- Control Signals - Signals passing
between one part of a communications system and another (such as RTS, DTR,
or DCD), as part of a mechanism for controlling the system.
- CRC (Cyclic Redundancy Check) - A
data transmission error-detection scheme. A polynomial algorithm is performed
on the data, and the resultant checksum is appended at the end of the frame.The
receiving equipment performs a similar algorithm.
- Crosstalk - Unwanted transfer of
energy from one circuit to another. Crosstalk typically occurs between
adjacent circuits.
- CRS (Cell Relay Service) - A bearer
service offered by an ATM network to the end users that delivers ATM cells
directly over the network.
- CSMA/CD - Carrier sense multiple
access/collision detection. In this protocol, stations listen to the bus
and only transmit when the bus is free. If a collision occurs, the packet
is retransmitted after a random time-out. CSMA/CD is used in Ethernet.
- CSU (Channel Service Unit) - Equipment
installed on customer premises at the interface to phone company lines
to terminate a DDS or T1 circuit. CSUs provide network protection and diagnostic
capabilities.
- CTD (Cell Transfer Delay) - A QoS
parameter that measures the average time for a cell to be transferred from
its source to its destination over a virtual connection (VC). It is the
sum of any coding, decoding, segmentation, reassembly, propagation, processing
and queuing delays.
- CTS (Clear To Send) - A modem interface
control signal from the data communications equipment (DCE) indicating
to the data terminal equipment (DTE) that it may begin data transmission.
- Current Loop - Method of data transmission.
A mark (binary "1") is represented by current on the line, and
a space (binary "0") is represented by the absence of current.
Network Glossary
- DACS (Digital Access and Cross Connect System)-
A time-slot switch which allows T1 or E1 lines to be remapped electronically
at the DS-0 (64 kbps) level. Also called DCS or DXS.
- Data - Information represented,
in digital form, including voice, text, facsimile and video.
- Data Link Layer - Layer 2 of the
OSI model. The entity which establishes, maintains, and releases data-link
connections between elements in a network. Layer 2 is concerned with the
transmission of units of information, or frames, and associated error-checking.
- dB (Decibel) - Unit for measuring
relative strength (ratio) of two signals.
- dBm - A measure of power in communications:
the decibel in reference to one milliwatt (0 dBm = 1 milliwatt and -30
dBm = .001 milliwatt)
- DCD (Data and Carrier Detect) - see
CD.
- DCE (Data Communications Equipment) - The
equipment providing functions which establish, maintain and terminate a
data transmission connection (such as a modem).
- DDS (Digital Data Service) - A
trademark of AT&T, identifying a private line service for digital data
communications in the data rate range between 2400 and 56,000 bps. Commonly
used in countries other than the U.S.A. at 64 or 128 kbps or higher.
- DE (Discard Eligibility) - A bit
indicating that a frame may be discarded in case of congestion on a Frame
Relay network, in order to help maintain the committed information rate
(CIR).
- Diagnostics - Procedures and systems
which detect and isolate a malfunction or mistake in a communications device,
network, or system.
- Digital - The binary ("I/0")
output of a computer or terminal. In data communication, an alternating,
non-continuous (pulsating) signal.
- Digital Loopback - A technique
for testing the digital processing of a communications device. The loopback
is toward the line side of a modem, but tests most of the circuitry in
the modem under test.
- Distortion - The unwanted change
in a signal's waveform occurring between two points in a transmission system.
- DLCI (Data Link Connection Identifier) - A
unique number assigned to a PVC endpoint in a Frame Relay network.
- DOV (Data Over Voice) - A technology
for transmitting data and voice simultaneously over twisted-pair copper
wiring.
- DS-3 - Digital Signal level 3.
Term used to refer to the 45 Mbps digital signal carried on a T3 facility.
- DSU (Digital Service Unit) - A
user device interfacing to a digital circuit (such as DDS or T1 when combined
with a CSU). The DSU converts the user's data stream to bipolar format
for transmission.
- DTE (Data Terminal Equipment) - A
device transmitting data to, and/or receiving data from, a DCE (for example,
a terminal or printer).
- DTR (Data Terminal Ready) - A modem
interface control signal sent from the DTE to the modem, usually telling
the modem that the DTE is ready to transmit data.
- DXI - Data Exchange Interface.
Protocols used between routers and DSUs for SMDS and ATM.
Network Glossary
- E & M Signaling - Voice transmission
system that uses separate paths for signaling and voice. The "M"
lead (mouth) transmits signals to the remote end of the circuit while the
"E" lead (ear) receives incoming signals.
- E1 - The 2.048 Mbps digital carrier
system common in Europe.
- E3 - The European standard for
high-speed digital transmission, operating at 34 Mbps
- Echo Cancellation - A technique
used in high speed modems and voice ciruits to isolate and filter out unwanted
signal energy caused by echoes from the main transmitted signal.
- Echo-Signal - Distortion occurring
when a transmitted signal is echoed back (reflected) to the originating
station.
- EIA (Electronic Industries Association) -
A standards organization in the U.S. specializing in the electrical
and functional characteristics of interface equipment.
- EMI (Electromagnetic Interference) - Radiation
leakage outside a transmission medium resulting mainly from the use of
high frequency wave energy and signal modulation. EMI can be reduced by
appropriate shielding.
- Equalizer - A device that compensates
for distortion due to signal attenuation and propagation time with respect
to frequency. It reduces the effects of amplitude, frequency and/or phase
distortion.
- ESF (Extended Superframe Format) - A
T1 framing format that uses the framing bit to provide maintenance and
diagnostic functions.
- Ethernet - A local area network
standardized as IEEE 802.3. Ethernet uses 10 Mbps transmission and the
CSMA/CD access method.
- Excess Burst Size - See Be
Network Glossary
- FCC (Federal Communications Commission) -
The regulatory agency established in the United States for all
interstate radio and electronic communications.
- FDDI (Fiber Distributed Data Interface) -
An ANSI standard for fiber optic links with data rates up to
100 Mbps.
- FECN (Forward Explicit Congestion Notification)
- A bit set by a Frame Relay network to notify an interface
(DTE) that congestion avoidance procedures should be initiated by the receiving
device.
- FEP (Front End Processor) - A communications
device in the IBM/SNA environment responsible for communication between
the mainframe and cluster controllers.
- Fiber Optics - Thin filaments of
glass or plastic carrying a transmitted light beam (generated by an LED
or laser).
- Four-Wire Circuit - A communications
path consisting of two pairs of conductors (wires), one pair for transmitting
and one pair for receiving.
- Fractional T1 - A service provided
by carriers, where a full T1 link is leased to the customer, but the service
charge is calculated based only on the number of timeslots used.
- FRAD (Frame Relay Access Device) A
device responsible for framing data with header and trailer information
(control information) before presenting the frame to the Frame Relay switch.
- Frame - A logical grouping of information
sent as a link-layer unit over a transmission medium. The terms packet,
datagram, segment, and message are also used to describe logical information
groupings.
- Frame Relay - A network interface
providing high speed frame or packet transmission with minimum delay and
efficient line of bandwidth. It has less protocol overhead than X.25.
- Frame Relay Forum - A worldwide
organization that promotes and sets standards for Frame Relay networks
and equipment.
- Frame Relay Frame - A variable-length
unit of data in Frame Relay format that is transmitted as pure data through
a Frame Relay network.
- Full Duplex - A circuit or device
permitting transmission in two directions at the same time.
- FUNI (Frame User Network Interface) - Frame-based
interface to ATM supporting signaling and QoS. To interoperate with a Frame
Relay end system, the ATM switch should support FRF.8, which is the Frame
Relay/ATM Service Internetworking specification. Replaces the ATM-DXI.
- FXO (Foreign Exchange Office) - A
voice interface, emulating a PABX extension, as it appears to the C.O.
(Central Office) for connecting a PABX extension to a multiplexer.
- FXS (Foreign Exchange Subscriber) - A
voice interface, emulating the extension interface of a PABX (or subscriber
interface of a C.O.) for connecting a regular telephone set to a multiplexer.
Network Glossary
- G.703 - An ITU standard for the
physical and electrical characteristics of various digital interfaces,
including those at 64 kbps and 2.048 Mbps.
- G.703.1 - An ITU standard for voice
compression
Network Glossary
- Half Duplex - A circuit or device
capable of transmitting in two directions, but not at the same time.
- HDLC (High-level Data Link Control) - An
international standard communication protocol defined by ISO.
- HDSL (High Bit-Rate Digital Subscriber Line)
- A high-performance twisted pair transmission technology, best
known as an enhanced transport mechanism for T1 or E1 service. It is designed
for the local loop between a customer's premises and an area exchange central
office.
Network Glossary
- IEEE (Institute of Electrical and Electronic
Engineers) - An international professional society issuing its
own standards. The IEEE is a member of ANSI and ISO.
- IEEE 802.3 - The IEEE's specification
for CSMA/CD LANs.
- IEEE 802.5 - The IEEE's specification
for Token Ring LANs
- IMA (Inverse Multiplexing over ATM) - A
method to pass ATM traffic over multiple E1/T1 links while maintaining
the ATM quality of service and optimizing bandwidth usage.
- Impedance - The combined effect
of resistance, inductance and capacitance on a transmitted signal. Impedance
varies at different frequencies.
- In-Band Signaling - Signaling utilizing
frequencies within the information band of a channel.
- Interface - A shared boundary,
defined by common physical interconnection characteristics, signal characteristics,
and meanings of exchanged signals.
- Internet Address - Also known as
an IP address. This is a 32-bit hardware-independent address assigned to
hosts using the TCP/IP protocol suite.
- IP - Internet Protocol. The network
layer protocol of the TCP/IP (Internet) Protocol Suite.
- I-PNNI (Integrated Private Network-Network
Interface) - Protocol used to exchange reachability information
between routers that augment or replace protocols such as OSPF and IPX
and is compatible with PNNI. This enables the integration of existing router-based
connectionless networks with ATM networks.
- ISDN (Integrated Services Digital Network)
- A carrier provided service that allows a variety of switched
digital data and voice transmission to be accommodated simultaneously.
- ISO (International Standards Organization)
- An international organization involved in writing communications
standards.
- ITU (International Telecommunication Union)
- A European-based, international advisory committee recommending
worldwide standards for transmission.
Network Glossary
- Jitter - The deviation of a transmission
signal in time or phase. It can introduce errors and loss of synchronization
in high speed synchronous communications.
Network Glossary
No Topics
Network Glossary
- LAN (Local Area Network) - A high
volume data transmission facility connecting a number of communicating
devices (computers, terminals and printers) within a single room, building,
campus or other limited geographical area.
- Leased Line - A line reserved for
the exclusive use of a customer, without inter-exchange switching arrangements.
- LMI (Local Management Interface) - Frame
Relay network management mechanism that uses DLCIs 0 and 1023 to pass management
messages over the user-to-network interface (UNI).
- Line Driver - A signal converter
which conditions a digital signal to ensure reliable transmission over
an extended distance.
- Loading - The addition of inductance
to a line in order to minimize amplitude distortion. Used commonly on public
telephone lines to improve voice quality, it can make the lines impassable
to high speed data, and baseband modems.
- Loopback - A type of diagnostic
test in which the transmitted signal is returned to the sending device
after passing through all or part of a communications link or network.
Network Glossary
- MAC - Media Access Control. A protocol
that defines the way workstations gain access to transmission media, most
widely used in reference to LANs. For IEEE LANs, the MAC layer is the lower
sublayer of the data link layer protocol.
- Mark - In telecommunications, this
means the presence of a signal. A mark is equivalent to a binary 1. A mark
is the opposite of a space ( 0 ).
- Master Clock - The source of timing
signals (or the signals themselves) that all network stations use for synchronization.
- MBS (Maximum Burst Size) - A traffic
parameter that specifies the maximum number of ATM cells in a burst that
can be transmitted at the peak rate (PCR).
- MCR (Maximum Cell Rate) - An ABR
traffic parameter (in cells per second) that gives the slowest rate at
which the network controls the flow of the source on an ABR virtual connection
(VC).
- MIB - Management Information Base.
A collection of objects that can be accessed via a network management protocol
such as SNMP. The objects represent values that can be read or changed.
- Modem (Modulator-Demodulator) - A
device used to convert serial digital data from a transmitting DTE to a
signal suitable for transmission over extended distances. It also reconverts
the transmitted signal to serial digital data for acceptance by a receiving
DTE.
- Modem Eliminator - A device used
to connect a local terminal and a computer port. The modem eliminator replaces
the pair of modems ordinarily required.
- Modulation - The alteration of
a carrier wave in relation to the value or samples of the data being transferred.
- MPMLQ (Multipulse Maximum Likelihood Quantization)
- A speech compression technology which is the ITU compression
standard G.723.1. It is very effective at low bit rates, maintaining a
minimal level of distortion.
- MPOA (Multi-Protocol Over ATM) - IETF-defined
specifications and procedures that enable Network Layer protocols to operate
directly on top of ATM and provide end-to-end internetworking between hosts
in an ATM and non-ATM environment.
- Multidrop - A communications configuration
in which multiple devices share a common transmission facility (or multipoint
line), although generally only one may transmit at a time. Usually used
with some kind of polling mechanism to address each connected terminal
with a unique address code.
- Multiplexer (Mux) - A device allowing
two or more signals to pass over and share a common transmission path simultaneously.
- Multipoint Line - see
Multidrop.
Network Glossary
- NDIS - A standard interface specification
for PC network adapter cards developed by Microsoft to separate the communications
protocol from the PC networking hardware. The driver is able to run multiple
protocol stacks concurrently.
- Network - (1) An interconnected
group of nodes.
(2) A series of points, nodes, or stations connected by communications
channels; the collection of equipment through which connections are made
between data stations.
- Network Management System - Systems
equipment used in monitoring, controlling, and managing a data communications
network.
- NNI (Network Node Interface or Network-to-Network
Interface) - ITU-T standard interface between nodes within the
same network. The ATM forum distinguishes between two standards, one for
private networks called PNNI and one for public networks known as public
NNI.
- Node - A point of interconnection
to a network.
- NRZ (Non-Return to Zero) - A binary
encoding scheme representing ones and zeroes by opposite and alternating
high and low voltages, in which there is no return to a zero (reference)
voltage between encoded bits.
- NRZI (Non-Return to Zero Inverted) - A
binary encoding scheme which inverts the signal 1 and leaves the signal
unchanged or a 0. Also called transition coding.
Network Glossary
- OAM - Operation Administration
and Maintenance Management framework defined by the ITU. OAM cells are
special-purpose ATM cells exchanged between two ATM entities for network
fault and performance management, analysis and fault isolation.
- ODI - Open Data Link Interface,
a standard interface specification developed by Novell to enable PC adapter
cards to run multiple protocol stacks.
- OSI (Open Systems Interconnection) Model -
A seven-layer model of network communications developed by the
International Standard Organization (ISO).
Network Glossary
- Packet - An ordered group of data
and control signals transmitted through a network, as a subset of a larger
message.
- Packet Switching - A data transmission
technique, which divides user information into discrete data envelopes
called packets, and sends the information packet by packet.
- Parity Bit - An additional non-information
bit added to a group of bits to ensure that the total number of l bits
in the character is even or odd.
- Payload - The 48-byte segment of
the ATM cell containing user data. Any adaptation of user data via the
AAL will take place within the payload.
- PBX (Private Branch Exchange) - A
private telephone exchange.
- PCM (Pulse Code Modulation) - A
procedure for adapting an analog signal (such as voice) into a 64 kbps
digital bit stream for transmission.
- PCR (Peak Cell Rate) - An ATM traffic
parameter (in cells per second) 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 (the time between two
cells) over a given virtual connection (VC).
- PHY (Physical layer) - The bottom
layer of the ATM protocol reference model, it is subdivided into two sublayers:
Transmission Convergence (TC) and Physical Medium (PM). It provides ATM
cell transmission over the physical interfaces that interconnect the ATM
devices.
- Physical Layer - Layer 1 of the
OSI model. The layer concerned with electrical, mechanical, and handshaking
procedures over the interface connecting a device to the transmission medium.
- PNNI (Private Network-Network Interface) -
The interswitch interface within a private ATM domain. The PNNI
trunking protocol providing for hierarchical ATM-layer routing and QoS
support.
- Policing - A method for verifying
that the incoming VC complies with the user's service contract.
- Polling - see Multidrop.
- Port - The physical interface to
a computer, multiplexer, for connection of terminals and modems.
- Protocol - A formal set of conventions
governing the formatting and relative timing of message exchange between
two communicating systems.
- PSTN (Public Switched Telephone Network) -
The telecommunications network commonly accessed by ordinary
telephones, key systems, PBX trunks and data equipment.
- PVC (Permanent Virtual Connection) - A
permanent, virtual connection established by the network management between
an origin and a destination.
- PVP (Permanent Virtual Path) - A
set of permanent virtual channels (PVCs) that exist between two cross points.
Network Glossary
- Quality of Service (QoS) - Backup
In ATM, for the set of parameters and their value which determine the performance
of a given virtual circuit.
Network Glossary
- Redundancy/Redundant Card or Power - Backup
components used to ensure uninterrupted operation of a system in case of
a failure.
- Repeater - A device which automatically
amplifies, restores, or reshapes signals to compensate for distortion and/or
attenuation prior to retransmission.
- RFC 1483 - Specifies the encapsulation
of multiprotocol data for transmission over an ATM network. RFC 1483 make
use of AAL5 in the support of PVCs and SVCs. The two methods defined in
this RFC are VC muxing and LLC/SNAP encapsulation.
- RFC 1490 - Specifies the encapsulation
of multiprotocol data for transmission over Frame Relay. Frame Relay over
ATM uses this encapsulation in combination with AAL5.
- RMON - The Remote Monitoring MIB,
which allows a network monitoring device to be configured and read from
remote locations.
- Routing - The process of selecting
the most efficient circuit path for a message.
- RSVP (Resource reSerVation Protocol) - A
protocol developed for supporting different QoS classes for IP applications.
- RTS (Request To Send) - A modem
control signal sent from the DTE to the modem, which tells the modem that
the DTE has data to send.
- RTT (Round Trip Time) - The round
trip time it takes for a packet to travel between a source and a network
device. In ATM, RTT is usually measured in numbers of cells.
Network Glossary
- SAR (Segmentation And Reassembly) - Segments
the information frames into cells at the source and reassembles these cells
back into information frames at the destination. These activities occur
at the lower part of the AAL. Each AAL type has its own SAR format.
- 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 Data Hierarchy.
The European standard for using optical media as the physical transport
for high speed long-haul networks.
- SDLC - Synchronous Data Link Control.
An IBM protocol for use in SNA environment. SDLC is a bit oriented protocol,
similar to HDLC.
- Serial Transmission - A common
mode of transmission, where the character bits are sent sequentially one
at a time instead of in parallel.
- Sharing Device - A device that
enables sharing of a single resource (modem, mux or computer port) among
several devices (terminals, controllers or modems).
- Shielding - The protective enclosure
surrounding a transmission medium, designed to minimize electromagnetic
interference (EMI/RFI).
- Short Haul Modem - A modem designed
for use in transmitting over relatively short distances across unloaded
metallic circuits. Also called a line driver or limited distance modem
(LDM).
- SMDS - Switched Multimegabit Data
Service. A specification for a connectionless packet - switched data service.
- SNA - Systems Network Architecture.
IBM's layered communications protocol architecture.
- SNMP - Simple Network Management
Protocol now widely used. The network management protocol of the TCP/IP
protocol suite.
- SONET - Synchronous Optical Network.
A standard for using optical media as the physical transport for high-speed
long-haul networks. SONET basic speeds start at 51.84 Mbps and go up to
2.5 Gbps.
- Space - In telecommunications,
the absence of a signal. Equivalent to a binary 0.
- Statistical Multiplexer (STM or STDM) - A
device connecting multiple channels to a single link by dynamically allocating
timeslots to the channels based on their transmission activity.
- STP (Shielded Twisted Pairs) - General
term for cabling systems that are designed specifically for data transmission,
and where the cables are shielded.
- Sub-rate Multiplexing - In the
U.S. this refers generally to time division multiplexing at data rates
less than 64 kbps.
- SVC (Switched Virtual Circuit) - A
logical connection between two points that is established dynamically and
exists during transmission only. In ATM networks, the SVC connection is
established via signaling. End systems transmit their UNI 3.1 or 4.0 signaling
request via the Q.2931 signaling protocol.
- Synchronous Transmission - Transmission
in which data bits are sent at a fixed rate, with the transmitter and receiver
synchronized.
Network Glossary
- Tc (Committed Rate Measurement Interval) -
The time interval during which the user can send only Bc-committed
amount of data and Be excess amount of data. Tc is used to measure only
incoming traffic. The duration of the Tc is usually proportional to the
burstiness of the traffic and is usually computed as Tc = Bc/CIR.
- T1 - An AT&T term for digital
carrier facility used to transmit a DS1-formatted digital signal at 1.544
Mbps. A T1 frame has 24 timeslots or channels.
- TCP/IP - Transmission Control Protocol/Internet
Protocol. Also known as the Internet Protocol Suite. This suite of protocols
is used on the Internet and is widely used for heterogeneous internetworking.
- TDM (Time Division Multiplexer) - A
device which divides the time available on its composite link among its
channels, usually interleaving bits (Bit TDM) or characters (Character
TDM) of data from each terminal.
- Throughput - The amount of information
transferred through the network between two users in a given period, usually
measured in the number of packets per second (pps).
- Timeslot - A portion of a serial
multiplex of timeslot information dedicated to a single channel. In T1
and E1, one timeslot typically represents one 64 kbps channel.
- TM (Traffic Management) - Set of
actions and operations performed by the network to guarantee the operability
of the network. TM is exercised in the form of traffic control and flow
control. The ATM traffic management includes the following: CAC, FRM, NRM,
Priority Control (PC), Traffic Shaping (TS) and UPC , the goal of which
is to maintain the required QoS.
- Token Ring - A local area network
standardized as IEEE 802.5. A supervisory frame, or token, is passed from
station to adjacent station sequentially. Stations wishing to gain access
to the network must wait for the token to arrive before transmitting data.
- Traffic policing - Mechanism whereby
any traffic which violates the traffic contract agreed to at connection
setup is detected and discarded.
- Traffic Shaping - A method of smoothing
bursty traffic in order to present a more uniform traffic rate to the network.
- Trunk - A single circuit between
two points, both of which are switching centers or individual distribution
points. A trunk usually handles many channels simultaneously.
Network Glossary
- Unbalanced Line - A transmission
line in which a single conductor is used to transmit a signal, in reference
to ground (for example, in a coaxial cable).
- Undefined Bit Rate (UBR) - An economical
class of on a moment-to-moment basis, without guaranteeing service levels
- UNI (User Network Interface) - The
interface, defined as a set of protocols and traffic characteristics, between
the CPE and the ATM network.
- UNI 4.0 - This UNI specification
refers to signaling issues in ABR, VP and QoS negotiations.
- UTP (Unshielded Twisted Pair) - General
term for all cabling systems used for transmission of data which are not
shielded.
Network Glossary
- VBR-NRT (Variable Bit Rate Non Real Time)
- One of the two VBR service types for transmitting traffic
where timing information is not critical. Since this service type is delay-tolerant,
it is well suited for bursty traffic such as data communications.
- VBR-RT (Variable Bit Rate Real Time) - One
of the two VBR service types for transmitting traffic that depends on timing
and control information. It is suitable for carrying delay-sensitive traffic
such as packetized video and audio.
- VC (Virtual Channel) - A connection
established between end users, where packets are forwarded along the same
path and bandwidth is not permanently allocated until it is used.
- VCC (Virtual Channel Connection) - An
end to end connection consisting of a concatenation of two or more Virtual
Channels between two end points. VCCs may be bundled into a VPC.
- Voice Compression - The conversion
of an analog voice signal into a digital signal using minimum bandwidth
(16 kbps or less).
- Voice Digitization (Voice Encoding) - The
conversion of an analog voice signal into digital symbols for storage or
for transmission (examples: ADPCM, CVSD, or PCM).
- VP (Virtual Path) - A term to describe
a set of Virtual Channels (VCs) between cross points, grouped together.
- VPC (Virtual Path Connection) - An
end-to-end connection consisting of two or more Virtual Path (VP) links.
Network Glossary
- WWW (World Wide Web) - The internet-based
Global information system based on a combination of information retrieval
and hypertext techniques.
Network Glossary
- X-ON/X-OFF (Transmitter On/Transmitter Off)
- Control characters used for flow control, instructing a terminal
to start transmission (X-ON) and end transmission (X-OFF).
Network Glossary
No Topics
Network Glossary
No Topics
