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Networking Solution Glossary
- 2/4-Wire Analog
- 2-wire circuit: A telephone line or trunk that has just one current loop
(one pair- most commonly FXS, FXO or E&M). 4-wire circuit: A circuit having
two pairs, TX and RX. Provides higher quality signal than two-wire circuit,
most commonly E&M. RAD voice interfaces can usually be ordered in any
of these formats.
- 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 to support the various AAL service classes: AAL1, AAL2, AAL3/4 and
- ABCD Bit Manipulation
- The signaling bits are used by telephone switches and PBXs for call
answer and disconnect supervision. Flexibility in manipulating these bits
simplifies installation and configuration when matching the voice system with
the existing switches.
- 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.
- AC/DC - Support
for AC (usually 90-240 VAC) and DC (usually -48 VDC).
- Address - A coded
representation of the origin or destination of data.
- Agent - In SNMP,
this refers to the managed system.
- AIM (ATM Inverse Multiplexing)
- See IMA.
- Alternate Routing
- In switching, alternate routing is the choice of the next-best path
when the best path is blocked.
- AMI (Alternate Mark
Inversion) - A bipolar coding scheme in which successive 1s (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.
- Async - See Asynchronous
- 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 Forum - A
worldwide organization that promotes and sets standards for ATM networks and
- Attenuation -
Signal power loss through equipment, lines or other transmission devices.
Measured in decibels.
- Automatic Rate Fallback
- Ensures that the logical channel remains open even if individual links
fail, by automatically dropping to the next lower rate. When failed links
are recovered, the original rate is restored.
- AWG - The American
Wire Gauge system, which specifies wire width.
- Balanced Line -
A circuit in which neither side of the line is grounded. This minimizes crosstalk
or noise pickup between pairs in the same cable.
- 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
- 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
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 SDH the physical transport.
- Bit - The smallest
unit of information in a binary system. Represents either a one or zero ("1"
- 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.
- BOD (Bandwidth on
Demand) - A concept in digital communications that enables users to request
additional network bandwidth as the application warrants, allowing them to
pay for only the bandwidth they use.
- Bps (Bits Per Second)
- A measure of data transmission rates 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.
- Bridging - 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
- Buffering - 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
- Byte - A group
of bits (normally 8 bits in length).
- CAS (Channel Associated
Signaling) - Voice signaling based on bits taken from voice time slots,
used by many PBXs.
- 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 requires a constant amount of bandwidth allocated to a connection for
the duration of the transmission.
- CC (Continuity check)
- 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
- CCS 7 (Common Channel
Signaling Version 7) - Also known as Signaling System 7 (SS7), a network
standard that transmits call-handling information for telecom calls over a
separate channel than that taken by the calls.
- CCS Compression (Common
Channel Signaling Co) - Signaling information is transported out-of-band.
CCS compression takes advantage of the idle flags between HDLC formatted messages
to reduce signaling bandwidth required.
- CCS Transparency -
Passes the out-of-band signaling channel transparently with no compression
or store-and-forward delay characteristics.
- 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).
- CDR (Call Detail Recording)
- A device and method used to record statistics about telephone calls such
as the number dialed, cost of the call extension from which the call was made,
duration of the call, and trunk or trunk group used to place the call.
- 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).
- Cell - In asynchronous
transfer mode (ATM), a 53-byte fixed-length data packet.
- Central Office Line
- The link connecting a station to a central office.
- Central Office Trunk
- The link connecting a central office to a PBX or another switch.
- Centrex - A type
of direct inward dialing (DID) offered by local telcos.
- CES (Circuit Emulation
Service) - ATM Forum-defined service that provides a virtual circuit connection,
which emulates the characteristics of a real, constant-bit-rate, dedicated-bandwidth
circuit. Traffic over ATM networks that complies with the other ATM Forum
interoperability agreements. Specifically, this specification supports emulation
of existing TDM circuits over ATM networks.
- 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).
- Channelized T1/E1
- T1 or E1 service that is divided into individual 64 kbps channels (or
channels that are multiples of 64 kbps such as a 256 kbps channel made from
four 64 kbps channels), as opposed to unchannelized service, which uses the
entire bandwidth of the T1 (1.544 Mbps) or E1 (2.048 Mbps). Channelized T1
or E1 lines can consist of switched lines with in-band signaling or leased
- 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,
- Clock - A term
for the source(s) of timing signals used in synchronous transmission.
- CLR (Cell Loss Ratio)
- 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).
- CO (Central Office)
- Telephone company switching office. This is where you would find the
local telco switch that connects to your telephone.
- CODEC (Coder/Decoder)
- An audio codec converts analog audio signals to digital signals for
transmission over digital circuits, and then converts the digital signals
back to analog signals for reproduction.
- Committed Rate Measurement
- 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 which reduce the number of bits required to represent
information in data transmission or storage, thereby conserving bandwidth
- Configuration Planner
- RADview configuration planner makes it possible to configure products
in advance, without having to connect to a physical product.
- 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.
- 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 - An
undesirable condition that happens when a communication from one line can
be heard on another independent line. This is usually caused by inductive
or capacitive coupling, or by an electrical short circuit between lines.
- 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/DSU (Channel Service
Units/Data Service Units) - CSUs and DSUs are usually grouped together.
They convert carrier line signals to digital signals.
- 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
- 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.
- D4-frame - A T1
line uses the D4 format, also known as the superframe (SF) format, to frame
data at the physical layer. The D4 format consists of 12 consecutive frames,
each separated by framing bits.
- DACS (Digital Access
and Cross Connect System) - A digital switching device for routing and
switching DS0s within T1 and E1 lines.
- Data - Information
represented in digital form, including voice, text, facsimile and video.
- Data Interface Variety
- More than one serial or LAN interface option is available for this product.
Please refer to data sheet for product selection. Interfaces available from
RAD include: V.35, RS-530, V.36/RS-449, X.21, V.24/RS-232, G.703, HSSI, Ethernet,
Fast Ethernet, Token Ring, and FDDI.
- 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.
- Data Relay - Transferring
low speed data in the forms of V.22 and V.22 bis through compressed voice
systems. With the emergence of the Internet, modem traffic acrosinternational
voice circuits is becoming increasingly rare.
- dB (Decibel) -
A unit used to measure relative increase or decrease in power, voltage or
current, using a logarithmic scale.
- DB Agenda/Flip -
User programmable configuration can be set to switch between configuration
databases in case of any network event. This feature enables alternate routing
in case of failure, as well as for adjustment to different time schedules,
work hours, weekends, holidays, etc.
- dBm - A logarithmic
scale for measurement of power. On the dBm scale, one milliwatt is 0 dBm.
- DCD - Data and
- DCE (Data Communications
Equipment) - or data circuit-terminating equipment. Devices and connections
of a network that make up the network end of the interface between the network
and the user. A modem is an example of a DCE.
- DDS (Digital Data
Service) - A trademark of AT&T, identifying a private line service
for digital data communications in the data rate range between 2,400 and 56,000
bps. Commonly used in countries other than the U.S.A. at 64 or 128 kbps or
- 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
- Decibel (dB) -
A unit used to measure relative increase or decrease in power, voltage or
current, using a logarithmic scale.
- Diagnostics -
The detection and isolation of a malfunction or mistake in a communications
device, network or system.
- DID (Direct Inward
Dialing) - A technique that allows an outside party to call an extension
in a PBX directly, by dialing an ordinary telco telephone number.
- Differential Delay
- Products like the RAD IMX-2T1/E1 compensate for any differential delay
(up to 64 ms) between the T1 lines, to properly reconstruct the original stream.
The differential delay is caused by the T1 lines traversing shorter and longer
- Digital - The
binary ("1/0") output of a computer or terminal. In data communications,
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
- DLC (Digital Loop
Carrier) - DLC is equipment that concentrates analog local loop lines,
digitizing and multiplexing calls for transmission to the central office.
- DLCI (Data Link Connection
Indicator) - In a Frame Relay network, DLCIs uniquely identify each virtual
circuit number corresponding to a particular destination. The DLCI is part
of the Frame Relay header and is usually ten bits long. In most circumstances,
DLCIs have strictly local significance at each Frame Relay interface.
- DLCI Multiplexing
- Encapsulates several voice and data channels over a single DLCI, in
order to minimize the monthly service charges over public Frame Relay networks.
- Drop-and-Insert -
A process of adding data (insert) to a T1 data stream, or terminating data
(drop) from a T1 data stream to other devices connected to the drop-and-insert
- Dry Contact Alarms
- Contact pins on a connector are closed or opened to indicate alarms.
External alarm monitoring equipment uses the change in current flow across
these pins to set off an alarm.
- DS0 (Digital Subscriber
Level Zero) - A 64 kbps unit of transmission bandwidth. A worldwide standard
speed for digitizing one voice conversation, and more recently, for data transmission.
Twenty-four DS0s (24x64 kbps) equal one DS1.
- DS-1 (Digital Signal
Level 1) - Framing specification used in transmitting digital signals
at 1.544 Mbps on a T1 facility or 2.048 Mbps on an E1 facility.
- DS2 Channel - For
a T1 line, a 6.312 Mbps channel that consists of four DS1 channels; for an
E1 line, an 8.45 Mbps channel that consists of four DS1 channels.
- DS3 Channel -
A 44.736 Mbps line consisting of seven DS2 channels. A DS3 line is also called
a T3 line.
- DSL (Digital Subscriber
Line) - A modem technology for transmitting information at high speeds
on existing copper phone lines to homes and businesses. DSL operates over
existing copper telephone lines and requires runs of usually less than 20,000
feet to a central telephone office. Types of DSL include asymmetric DSL (ADSL),
symmetric DSL (SDSL), and high bit rate DSL (HDSL).
- DTE (Data Terminal
Equipment) - As defined in the RS-232 specification, equipment to which
DCE (Data Communications Equipment) is connected, such as personal computers
or data terminals. DTE refers to application equipment, such as a videoconference
terminal or LAN bridge or router, while DCE refers to equipment such as network
- DTMF (Dual-Tone Multifrequency)
- DTMF is a technology enabling a touch-tone telephone to create 16 tones
- 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.
- E1 Line - A 2.048
Mbps line that supports thirty-two 64 kbps channels, each of which can transmit
and receive data or digitized voice. The line uses framing and signaling to
achieve synchronous and reliable transmission. The most common configurations
for E1 lines are E1 PRI, and unchannelized E1.
- E1 PRI Line -
An ISDN line that consists of thirty-two 64 kbps channels. This type of line
uses 30 B channels for user data, one x 64 kbps D channel for ISDN D-channel
signaling, and one framing channel. The B channels can be all switched, nailed
up, or a combination of switched and nailed up. This type of PRI line is a
standard in Europe and Asia called CEPT G.703.
- E3 - The European
standard for high speed digital transmission, operating at 34 Mbps.
- E&M - A form
of DC signaling in which the battery voltage is used to indicate the status
of the line.
- Echo Cancellation
- Echo cancellation improves the quality of voice transmissions. It eliminates
the echo that results from the reflection of the telephony signal back to
the caller, which can occur in a 4-wire to 2-wire hybrid connection between
the VFRAD and the telephones or PBX. The longer it takes the signals to return
to the caller, the more perceptible the echo.
- Echo Signal - Distortion
occurring when a transmitted signal is echoed back (reflected) to the originating
- 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.
- Encapsulation -
Encapsulating data is a technique used by layered protocols in which a low
level protocol accepts a message from a higher level protocol, then places
it in the data portion of the lower-level frame. The logistics of encapsulation
require that packets traveling over a physical network contain a sequence
- Enterprise Network
- An information infrastructure, often combining private and public facilities,
to cover all of the locations operated by a single company or corporate enterprise
with a single communications fabric.
- 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 Super
Frame) - ESF is a framing format that consists of 24 consecutive frames
separated by framing bits. The ISDN specification advises that you use ESF
with ISDN D-channel signaling.
- Ethernet - A local
area network that connects devices like computers, printers and terminals.
Ethernet operates over twisted-pair or coaxial cable at speeds of 10 or 100
- Fanout - The ability
of a digital access cross connect (DAC) to split and switch channels between
incoming and outgoing circuits.
- Fault Tolerance -
A way to provide redundancy in hardware systems to protect against doif
one of the redundant systems or components fails. For RAD products, fault
tolerance is provided by means of redundant I/O modules, common logic and/or
power supplies. See also Redundancy/CL/ML/PS.
- Fax Relay - Fax
Group III support with automatic fallback. The fax signal is demodulated back
to the original 0s and 1s and transmitted as a data stream using less bandwidth
across the voice compression system. The data content is returned to fax format
at the far end.
- 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 - Hair-thin
glass structures, usually cylindrical in shape, for transmitting optical signals.
- Fiber Optics -
A transmission medium consisting of thin glass filaments. Light beams travel
through the fiber optic line, carrying large amounts of data over long distances.
- FR+ with Funnel -
FR+ with enhanced funnel. Proprietary RAD protocol for reducing packet delay
times across public Frame Relay networks by fragmenting, prioritizing and
traffic shaping to prevent congestion at remote bottlenecks. Similar to "leaky
bucket" in ATM.
- Fractional T1 -
Service offering data rates between 64 kbps (DS0 rate) and 1.536 Mbps (DS1
rate), in specified intervals of 64 kbps.
- Fractional T1 Line
- A T1 line that contains both switched and nailed-up channels. T1 PRI
and ISDN BRI lines can also be Fractional T1 lines.
- 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.
- Fragmentation -
RAD's MP-2100H and MAXcess products incorporate fragmentation schemes to improve
performance. Data packets are divided into small fragments, allowing higher
priority voice packets to receive the right-of-way without waiting for the
end of long data transmissions. The remaining data packets in the data stream
are momentarily halted until the voice transmission gets through. The down-side
of fragmentation is that it increases the number of data frames, thereby increasing
the number of flags and headers. This increases overhead and reduces bandwidth
efficiency. RAD's FR+ application provides an enhanced fragmentation mechanism,
which fragments data frames only in cases where voice packets arrive at the
switch during a data transmission. Otherwise, the long data frames are sent
- 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 -
An efficient packet switching technology providing high speed frame or packet
transmission with minimum delay and efficient bandwidth utilization over virtual
circuits. The link layer handles much of the network layer functionality.
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.
- Framing - At the
physical and data link layers of the OSI model, bits are fit into units called
frames. Frames contain source and destination information, flags to designate
the start and end of the frame, plus information about the integrity of the
frame. All other information, such as network protocols and the actual payload
of data, is encapsulated in a packet, which is encapsulated in the frame.
- Full Duplex -
Circuit in telecommunications with channels for both sending and receiving.
- 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 PBX extension, as it appears
to the C.O. (Central Office) for connecting a PBX extension to a multiplexer.
- FXS (Foreign Exchange
Subscriber) - A voice interface, emulating the extension interface of
a PBX (or subscriber interface of a CO) for connecting a regular telephone
set to a multiplexer.
- 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.723.1 - An ITU
standard for voice compression.
- G.802 - ITU standard
for carrying T1 traffic over E1 networks.
- Gatekeeper - A
device that manages an IP network, supporting all gateways, user profiles,
and authentication. A gatekeeper is defined by the H.323 standard.
- Gateway - Gateways
are points of entrance and exit from a communications network. Viewed as a
physical entity, a gateway is that node that translates between two otherwise
incompatible networks or network segments. Gateways perform code and protocol
conversion to facilitate traffic between data highways of differing architecture.
- Glare - A signal
the switch sends when you attempt to place an outgoing call and answer an
incoming call simultaneously.
- Grooming - In
telecommunications, the process of separating and segregating channels by
combing, such that the broadest channel possible can be assembled and sent
across the longest practical link. The aim is to minimize de-multiplexing
traffic and reshuffling it electrically.
- Ground Start - A
signaling method in which the customer premises equipment (CPE) transmits
an off-hook condition by creating a zero-voltage condition.
- GUI (Graphical User
Interface) - Pronounced "gooey," this software interface is
based on pictorial representations and menus of operations and files. Opposite
of command line interface.
- H.323 - A set
of International Telecommunication Union (ITU) standards that define a framework
for the transmission of real-time voice communications by means of IP-based
packet-switched networks. Created in response to customers who needed to use
their existing IP networks to support voice communications, the H.323 standards
define a gateway and a gatekeeper.
- Half Duplex -
A circuit or device capable of transmitting in two directions, but not at
the same time.
- HDLC (High-Level Data
Link Control) - A synchronous, bit-oriented link layer protocol for data
transmission. Frame Relay is an example of an HDLC-based packet protocol.
- 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.
- HSSI (High-Speed Serial
Interface) - A serial interface that operates at speeds up to 52 Mbps
at distances up to 50 feet. It is similar to, but faster than, RS-232 and
V.35 serial interfaces.
- Hunt Group - A
group of channels that share the same phone number. When a call comes in using
the phone number assigned to the hunt group, the switch hunts for an available
channel in the group.
- Hybrid Circuit - A
transformer arrangement that permits the transmitted and received signals
to be separated and then put back together. Used to connect a 2-wire line
to a 4-wire line.
- Idle Disconnects -
The breaking or release of a circuit connecting two telephones or data devices
that occurs when no data is transmitted on a link in a specified amount of
- 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 pasATM 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
- The transmission of signaling information over the same path as data
and/or voice information. Another term for in-band signaling is robbed-bit
signaling. Robbed-bit refers to the 8 kbps of each channel used for signaling.
T1 access lines containing one or more switched channels, and switched-56
lines use in-band signaling.
- Interactive Voice
Response - A specialized computer that accepts input from either a telephone
keypad or the caller's voice, and on the basis of that input, uses synthesized
voice or pre-recorded messages to offer callers choices on how to complete
- 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.
- Inverse Multiplexing
- A method in which the inverse multiplexer slices the data stream into
equal portions and transmits each portion over an available circuit. The receiving
end adjusts for network-induced delay and reassembles the data packets into
their proper order. Therefore, an inverse multiplexer allows lower speed channels
across a network to be combined into a single, higher speed data stream.
- IP (Internet Protocol)
- A networking protocol for providing a connectionless service to the higher
transport protocol. It is responsible for discovering and maintaining topology
information and for routing packets across homogeneous networks. Combined
with TCP, it is commonly known as the TCP/IP platform.
- IP Address - An
address that uniquely identifies each host on a network or Internet.
- 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.
- IP Telephony -
The transmission of voice over an Internet Protocol (IP) network. Also called
Voice over IP (VoIP), IP telephony allows users to make phone calls over the
Internet, intranets, or private LANs and WANs that use the TCP/IP protocol.
- IPX (Internetwork
Packet Exchange) - Netware network layer (layer 3) protocol for transferring
data from servers to workstations.
- ISDN (Integrated Services
Digital Network) - A carrier-provided service that allows a variety of
switched digital data and voice transmissions to be accommodated simultaneously.
ISDN is available as BRI, PRI and B-ISDN.
- ISDN Backup -
Alternate routing of traffic over ISDN, PRI, and BRI for backup purposes when
the main link fails.
- ISDN BRI Line -
An ISDN basic rate interface (BRI) line that uses two B channels for user
data, and one 16 kbps D channel for ISDN D-channel signaling. Both B channels
can be switched or nailed up, or one channel can be switched and the other
nailed up. A line of this type can connect to standard voice service, switched
56 kbps data service or switched 64 kbps data service.
- ISDN D-Channel Signaling
- A type of signaling in which a D channel handles WAN synchronization
and signaling and the B channels carry the user data. Another term for ISDN
D-channel signaling is out-of-band signaling. T1 PRI, E1 PRI, and ISDN BRI
lines use ISDN D-channel signaling.
- ISDN Multirate -
A network-based ISDN service which allows users network access equipment to
dial network channels of bandwidth in increments of 64 kbps, up to 1536 kbps.
Access to ISDN multirate service is obtained over ISDN PRI lines.
- ISO (International
Standards Organization) - An international organization involved in writing
- ITU (International
Telecommunication Union) - A European-based, international advisory committee
recommending worldwide standards for transmission.
- Jitter Buffer - Variation
in the arrival times between packets, also called jitter, causes unnatural-sounding
voice instead of a smooth voice stream. If a packet does not arrive in time
to fit into the voice stream, the previous packet is replayed. This can seriously
detract from voice quality. To avoid the effect of jitter, VoFR and VoIP devices
such as RAD's MP-2100H detain each packet in a jitter buffer, giving subsequent
packets time to arrive and still fit into a natural voice flow. Since the
jitter buffer adds to the overall delay of voice transmissions, the optimal
jitter buffer should fit the network's differential delay. Better access devices,
like those from RAD, employ adaptive jitter buffering which continuously monitors
the network delay and adjusts the queuing period accordingly.
- KTS (Key Telephone
System) - Customer premises equipment (CPE) used to route calls both within
an organization and to the outside telephone network. A key system is a scaled-down
version of a PBX, usually with less functionality, and is geared toward smaller
organizations. A key system can be either analog or digital. Some digital
key systems can terminate digital as well as analog connections. Moreover,
key systems work in conjunction with channel banks to distribute channels
from the T1/E1 circuit for voice, video, fax and data.
- LAN (Local Area Network)
- A network that interconnects devices over a geographically small area,
typically in one building or part of a building. The most popular LAN type
is Ethernet, a 10 Mbps standard that works with 10BaseT, 10Base2, or 10Base5
- Laser - A device
that transmits an extremely narrow and coherent beam of electromagnetic energy
in the visible light spectrum. Used as a light source for optical-fiber transmission
(generally more expensive, shorter lived, single mode only, for greater distances
- Latency - The
time between initiating a request for data and the beginning of the actual
data transfer. Network latency is the delay introduced when a packet is momentarily
stored, analyzed and then forwarded.
- Leaky Bucket -
A flow control algorithm, where cells are monitored to check whether they
comply with the established connection parameters. Non-conforming cells are
either tagged or dropped from the network. The analogy is taken from a bucket
with a hole in its bottom that allows the fluid to flow out at a certain rate.
- Leased Line -
A permanent telephone connection between two points that is rented for exclusive
use from a telecommunications common carrier. In contrast to a normal dial-up
connection, a leased line is always active. Typically, the highest speed data
connections require a leased line connection. For example, a T1 channel is
a type of leased line that provides a maximum transmission speed of 1.544
- LED (Light Emitting
Diode) - A semiconductor light source that emits light in the optical
frequency band or the infrared frequency band. LEDs are a major light source
for optical fiber transmission used with multimode optical fiber in applications
that require a low cost light source.
- Line Driver -
A signal converter which conditions a digital signal to ensure reliable transmission
over an extended distance.
- Load Balancing -
A technique that distributes network traffic along parallel paths in order
to maximize the available network bandwidth while providing redundancy.
- 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.
- Local Loop - The
physical wires that run from the subscriber's telephone set, PBX, or key telephone
system to the telephone company's central office. Increasingly, the Local
Loop now goes from the main distribution frame at the customer premises to
the telephone company. The subscriber is responsible for connecting his wires
from the box at the customer's premises to his phone, PBX, or key system.
- Loopback - A type
of diagnostic test in which the transmitted signal is rto the sending device
after passing through all or part of a communications link or network.
- Loop Start - The
most commonly used method of signaling an off-hook condition between an analog
phone set and a switch, where picking up the receiver closes a wire loop,
allowing DC current to flow, which is detected by a PBX or local exchange
and interpreted as a request for service.
- LMI (Local Management
Interface) - An ITU-T defined interface to provide an ATM or Frame Relay
end system user with network management information.
- 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
- MAN (Metropolitan
Area Network) - A network that provides regional connectivity within a
metropolitan area (such as a city). MANs are wider than LANs, but more local
- Manager - An application
that receives Simple Network Management Protocol (SNMP) information from an
agent. An agent and manager share a database of information, called the Management
Information Base (MIB). An agent can use a message called a traps-PDU to send
unsolicited information to the manager. A manager that uses the RADview MIB
can query the RAD device, set parameters, sound alarms when certain conditions
appear and perform other administrative tasks.
- 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 (Minimum 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)
- Metering - This
feature is intended for support of payphones, and therefore includes dedicated
circuits for the detection of polarity and of 16 kHz or 12 kHz metering pulses
- MF Signaling (Multifrequency
Signaling) - A signaling method using frequencies to carry address or
system status information. MF is used internally by telcos and other common
carriers. Similar to DTMF
- MIB (Management Information
Base) - A directory listing the logical names of all information resources
residing in a network and pertinent to the network's management. A key element
of SNMP management systems.
- 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
- Modem Eliminator -
A device used to connect a local terminal and a computer port. The modem eliminator
replaces the pair of modems ordinarily required
- Modular - Modular
interfaces enable field changeable conversion
- Modulation - The
alteration of a carrier wave in relation to the value or samples of the data
- 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
- Multimode Fiber -
A fiber with a large core diameter. 50-200 microns compared with the wavelength
of light. It therefore propagates more than one mode. With multimode fiber,
light traverses multiple paths, some longer than others. This leads to dispersion
which reduces optical range at high bit rates
- Multiplexer -
At one end of a communications link, a device that combines several lower
speed transmission channels into a single high speed channel. A multiplexer
at the other end reverses the process. Sometimes called a mux
- Narrowband - In
communications technology, digital communication at the rate of 64,000 bits
per second or lower.
- NDIS (Network Driver
Interface Specification) - 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
- 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 Layer -
A layer in the OSI reference model. The network layer provides address resolution
and routing protocols. Address resolution enables the network layer to determine
a unique network address for a node. Routing protocols allow data to flow
between networks and reach their proper destination. Examples of network layer
protocols are Address Resolution Protocol (ARP), Datagram Delivery Protocol
(DDP), Internet Control Message Protocol (ICMP), Interior Gateway Protocol
(IGP), Internet Protocol (IP), Internetwork Packet Exchange (IPX) and Packet
Layer Protocol (PLP).
- NFAS (Non-Facility
Associated Signaling) - A special case of ISDN signaling in which two
or more T1 PRI lines use the same D channel. A backup D channel can be added.
When all 24 channels of the T1 PRI line carry user data or voice, the D channel
must be on another line.
- NMS (Network Management
System) - The system that controls network configuration, fault and performance
management, and diagnostic analysis
- 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 1s and 0s 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.
- NT1 (Network Terminator
Type 1) - An ISDN BRI line terminating device at the subscriber's location
that provides line maintenance access, timing and echo cancellation. NT1s
may be built into other pieces of equipment or stand alone
- OAM (Operation Administration
and Maintenance) - Management framework defined by the ITU. In telecommunications,
OA&M denotes functions such as technical interfaces, diagnostics, service
measurements and status reports
- OAM Cells - Special-purpose
ATM cells exchanged between two ATM entities for network fault and performance
management, analysis and fault isolation
- OC (Optical Carrier)
- A hierarchy of optical signals used to classify speeds or capacities
of fiber lines, especially as related to the SONET standard. The basic speed
is OC-1 (52 Mbps). An OC-3 fiber line has a capacity of 155 Mbps
- ODI (Open Data Link
Interface) - A standard interface specification developed by Novell to
enable PC adapter cards to run multiple protocol stacks
- Off-Hook - A state
that results when you lift a telephone receiver, producing a busy signal
- On-Hook - No loop
current flows and the switch recognizes that the telephone is available for
- OSI (Open Systems
Interconnection Model) - A seven-layer model of network communications
developed by the International Standard Organization (ISO).
- Out-of-Band Connection
- A remote link, or a link outside connected networks, established over
a modem. It is useful when network communications are not available.
- Out-of-Band Signaling
- The transmission of signaling information over a different path from
data and/or voice information. CCS7 uses out-of-band signaling.
- Outpulse - Sequence
of addressing information, automatically generated and dialed. The RAD VoIP
and VoFR gateways (MP-2100H and MAXcess) use voice switching to reach the
terminating gateway and then DTMF outpulsing to complete the final leg of
a voice call
- Packet - An ordered
group of data and control signals trthrough a network, as a subset of a larger
- 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 1 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 switching system, usually serving an organization,
such as a business or a government agency, and is usually located on the customer's
- PCM (Pulse Code Modulation)
- Technique for digitizing speech that samples sound waves 8,000 times a second
and converts each sample into an 8-bit binary number resulting in a 64,000
bit-per-second signal, the size of a traditional voice channel
- 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
ATM) - 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
- 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
- Port - The physical
interface to a computer or multiplexer, for connection of terminals and modems
- POTS (Plain Old Telephone
Service) - The analog dial tone-type telephone networks and services in
place worldwide with transmission rates up to 52 kbps. In contrast, telephone
services based on digital communications lines, such as ISDN, have higher
speeds and bandwidths. POTS networks are also called public switched telephone
- PPP (Point-to-Point
Protocol) - Provides a standard means of encapsulating data packets sent
over a single-channel WAN link. It is the standard WAN encapsulation protocol
for the interoperability of bridges and routers over synchronous or asynchronous
- PRI (Primary Rate
Interface) - An ISDN subscriber line, consisting of twenty-three 64 kbps
B channels in North America (thirty 64 kbps channels elsewhere) and one 64
kbps D channel, used for signaling purposes.
- Prioritization -
Prioritization schemes "tag" different applications according to
their sensitivity to delay, assigning higher priority to voice and other time-sensitive
data such as SNA. RAD's MP-2100H and MAXcess product lines support seven user-defined
priority levels. The prioritization and fragmentation mechanisms ensure high
quality voice, low delay and minimal bandwidth overhead
- 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
Circuit) - A virtual connection established by the network management
between an origin and a destination that can be left up permanently
- PVP (Permanent Virtual
Path) - A set of permanent virtual channels (PVCs) that exists between
two cross points
- QoS - Quality
Of Service - A group of service classes defined by the ATM forum in terms
of different QoS parameters:
- Class 0 refers to the
best effort service (UBR).
- Class 1 specifies the
parameters for circuit emulation, and the transport of CBR uncompressed video
and for VPNs. AAL1 supports this kind of delay sensitive connection oriented
- Class 2 specifies the
parameters for the transport of VBR (low speed or compressed packetized) audio
and video. AAL2 supports this delay sensitive, connection oriented class.
- Class 3 specifies the
parameters for connection oriented data transfer. AAL3/4 and mostly AAL5 supports
this delay tolerant class which is intended to provide interoperability with
SMDS and IP.
- Class 4 specifies the
parameters for connectionless data transfer. AAL3/4 or AAL5 can be used to
support this delay tolerant class which is also intended to provide interoperability
with SMDS and IP.
- Class X refers to the
connection oriented transport service where the traffic type (CBR or VBR)
and timing requirements (delay sensitive or non-sensitive) are defined by
the user. It is known as an unrestricted service class and which is supported
- RADview - The
RADview Graphical User Interface (GUI) is an SNMP-based management system
enabling complete monitoring and control of LAN and WAN networks from a central
management station. The system provides direct on-line supervision, configuration
- Provides duplicate common logic (CL), main link (ML) and/or power supply
(PS) to immediately take over the function of the equipment in case of failure
- Register - A storage
device capable of receiving and holding a number of digits
- Repeater - A device
which automatically amplifies, restores or reshapes signals to compensate
for distortion and/or attenuation prior to retransmission
- Reverse Polarity -
Signaling call answer and disconnect status is often a problem on analog voice
circuits (FXO). When circuits supporting reverse polarity are available, the
signaling problem can be solved by sensing reverse polarity and toggling the
status of the signaling bits appropriately
- 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 multiplexing and LLC/SNAP encapsulation
- RFC 1490 - Specifies
the encapsulation of multiprotocol data for transmission over Frame Relay
- RIP2 - Routing
Information Protocol used to discover agents and the routes that IP packets
must traverse. This is done automatically using periodic broadcasts. RIP2
also supports IP subnets
- RJ-45 Connector (Registered
Jack-45) - A telephone connector that accomodates up to eight wires. RJ-45
plugs and sockets are used in Ethernet and Token Ring devices.
- RJ-48C - An eight-position
keyed plug most commonly used for connecting T1 circuits. The RJ-48C is an
eight-position plug with four wires (two for transmit, two for receive). When
the phone company delivers T1 to your offices, it usually terminates its T1
circuit on a RJ-48C.
- RMON - The Remote
Monitoring MIB, which allows a network monitoring device to be configured
and read from remote locations
- Router - An interconnection
device that connects individual LANs. Unlike bridges, which logically connect
at OSI layer 2, routers provide logical paths at OSI layer 3. Like bridges,
remote sites can be connected using routers over dedicated or switched lines
to create WANs.
- 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.
- SAR (Segmentation
and Reassembly) - Segments thinformation frames into cells at the source
and reassembles them back into information frames at the destination. These
activities occur at the lower part of the AAL. Each AAL type has its own SAR
- Satellite Link -
A microwave link that uses a satellite to receive and retransmit signals.
Uses a geosynchronous orbit to keep a satellite above a fixed position on
- Scalable - Able
to be changed in size or configuration to suit changing conditions. For example,
a scalable network can be expanded from a few nodes to thousands of nodes.
- 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
- 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.
- SF - Also known
as D4, T1 lines use this format to frame data at the physical layer. The SF
format consists of 12 consecutive frames, each separated by framing bits.
- Sharing Device -
A device that enables sharing of a single resource (modem, mux or computer
port) among several devices (terminals, controllers or modems).
- Shielded Twisted Pair
Cable (STP) - Consists of two wires twisted two or more times per inch
in order to help cancel out noise. The entire cable has a protective covering
which should be connected to a single ground.
- 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
- Silence Suppression
- In a telephone conversation, only about 50% of the full duplex connection
is used at any given time. This is generally because only one person talks
while the other person listens. In addition, voice packets are not sent during
interword pauses and natural pauses in the conversation, reducing the required
bandwidth by another 10%. Silence suppression frees this 60% of bandwidth
on the full duplex link for other voice or data transmissions.
- Single Mode -
Describing an optical waveguide or fiber that is designed to propogate light
of only a single wavelength (typically 5-10 microns in diameter).
- SLIP (Serial Link
Internet Protocol) - An Internet protocol for host dial- up connection.
SLIP frames are encapsulated IP datagrams in which SLIP adds just a few bytes
of control data.
- SMDS (Switched Multimegabit
Data Service) - A specification for a connectionless packet-switched data
- SNA (Systems Network
Architecture) - IBM's layered communications protocol architecture.
- SNMP (Simple Network
Management Protocol) - The Internet standard protocol for managing nodes
on an IP network.
- 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.
- SS7 (Signaling System
7 - ) A signaling method separate from the voice or data channel that
lets intelligent network elements exchange information among themselves.
- Statistical Multiplexer
- 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 where the cables are shielded.
- Sub-rate Multiplexing
- In the U.S. this refers generally to time division multiplexing at data
rates lower than 64 kbps.
- Super Tandem -
A - feature that eliminates the need for compression/decompression on each
cascaded link (for example, an embedded pattern can switch the system to super
tandem mode to remove the cumulative distortion of consecutive compression/decompression
- 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.
- T1 - A digital
transmission link with a capacity of 1.544 Mbps used in North America. Typically
channelized into 24 DS0s, each capable of carrying a single voice conversation
or data stream. Uses two pairs of twisted pair wires.
- T3 - A digital
transmission link with a capacity of 45 Mbps, or 28 T1 lines.
- Tandem Encoding -
Maintains a minimal level of distortion when the voice signal undergoes two
or more consecutive compression/decompression cycles (e.g., in applications
where voice calls carried over digital links are switched via a central switch
- Tandem Switching -
Routing a call through a switch to another switch.
- 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.
- TCP/IP (Transmission
Control Protocol/Internet Protocol) - A protocol platform, known also
as the Internet protocol suite, that combines both TCP and IP. Widely used
applications, such as Telnet, FTP and SMTP, interface to TCP/IP.
- TDM (Time Division
Multiplexer) - A device that 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.
- TDMoATM - Transparently
carrying TDM bit streams over packet technology as found in the ACE product
line for TDM over ATM (circuit emulation).
- TDMoFR - Transparently
carrying TDM bit streams over packet technology as found in the MAXcess product
line for TDM over Frame Relay. Analogous to circuit emulation over Frame Relay.
- TDMoIP - Transparently
carrying TDM bit streams over packet technology as found in the IPmux for
TDM over IP. Analogous to circuit emulation over IP.
- Telnet - The virtual
terminal protocol in the Internet suite of protocols. It lets users on one
host access another host and work as terminal users of that remote host. Instead
of dialing into the computer, you connect to it over the Internet using Telnet.
When you issue a Telnet session, you connect to the Telnet host and log in.
The connection enables you to work with the remote machine as though you were
a terminal connected to it.
- Terminal Adapter -
A device that allows analog voice and data devices to work through an ISDN
connection. The terminal adapter is a protocol converter that adapts equipment
not designed for ISDN, such as phones, faxes, and modems.
- TFTP (Trivial File
Transfer Protocol) - A simplified version of the File Transfer Protocol
that transfers files but does not provide password protection or user directory
- TFTP/CFG - TFTP
of configuration: TFTP download and upload of configuration files (using an
application such as Pumpkin or Netmanage). This feature is useful in creating
an exact image of a product's configuration. Even though the configuration
file cannot be read or understood using standard tools such as RADview or
text editors, it can be copied to diskette for backup purposes. Restore is
performed in a similar manner. This feature is particularly useful when diagnosing
serious problems. The customer downloads the exact image of the configuration
and emails it to RAD Tech Support or Engineering where it is used to simulate
the customer's exact configuration and diagnose the problem.
- TFTP/SW (Trivial File
Transfer Protocol) - is a simple file transfer protocol based on UDP transport.
TFTP is small and simple enough to be embedded in boot ROMs. TFTP applications
such asPumpkin (shareware) can be used to download new software versions to
provide enhanced features and fix bugs. The upgrades can be done across IP
networks in-band or out-of-band without the need to send technicians on-site
and without replacing equipment.
- 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).
- Tie Trunk (Tie Line)
- A dedicated trunk used to connect two locations that routinely need
to contact one another. Stations connected to a switch at one end of the tie
trunk may dial stations connected to a switch at the other end directly, without
using the public network.
- 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.
- 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
- Traffic Contract -
An asynchronous transfer mode (ATM) configuration that guarantees the delivery
of a specified amount of data. While data above the traffic contract can still
be delivered when network resources are available, data that exceeds the traffic
contract can be delayed or lost when conditions are congested.
- Traffic Management
- Set of actions and operations performed by the network to guarantee
the operability of the network exercised in the form of traffic control and
flow control. 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.
- Traffic Policing -
Mechanism whereby any traffic that violates the traffic contract agreed to
at connection setup is detected and discarded. A method to verify that the
incoming VP/VC complies with the user's service contract.
- Traffic Shaping -
A method for smoothing the bursty traffic rate that might arrive on an access
virtual circuit so as to present a more uniform traffic rate on the network
and comply with the traffic contract.
- Trunk - A single
circuit between two points, both of which are switching centers or individual
distribution points. A trunk usually handles many channels simultaneously.
- UBR (Undefined Bit
Rate) - An economical best-effort class of service.
- UDP (User Datagram
Protocol) - A connectionless transport protocol without any guarantee
of packet sequence or delivery. It functions directly on top of IP.
- 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).
- UNI (User Network
Interface) - The interface, defined as a set of protocols and traffic
characteristics, between the CPE and the Frame Relay or ATM network.
- UNI 4.0 - This
UNI specification refers to signaling issues in ABR, VP and QoS negotiations.
- UTP (Unshielded Twisted
Pair Cable) - UTP cable consists of two wires twisted two or more times
per inch in order to help cancel out noise. The entire cable has no covering.
UTP cable is typically used in telephone lines for voice service, 10BaseT
Ethernet networks and particular sections of Token Ring networks.
- V.22bis - An extension
of the V.22 standard, providing a data rate of up to 2400 bps at 600 baud.
- 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 Connection)
- A connection established between end users, where packets are forwarded
along the same path and bandwidth is not permanently allocated until it is
- 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 (ATM).
- Voice Compression
- Newer voice compression algorithms try to model PCM (G.711) more efficiently
using fewer bits to reduce the bandwidth required while preserving the quality
or audibility of the voice transmission. Vendors such as RAD support low bit
rate voice compression algorithms such as ITU G.723.1 and G.729A to permit
the greatest number of simultaneous multiple calls while maintaining high
quality voice. In this way, compressed voice systems (CVSTM) can offer greater
bandwidth savings, reduced network congestion and high quality voice transmissions.
- Voice Digitization
(Voice Encoding) - The conversion of an analog voice signal into digital
symbols for storage or for transmission (examples: ADPCM, CVSD or PCM).
- VoFR (Voice over Frame
Relay) - A term applied to a set of facilities for managing the delivery
of voice information using frame relay. A major advantage of VoFR is that
it avoids the tolls charged by ordinary telephone service.
- Voice Interface Variety
- More than one voice interface option is available for many RAD products.
Please refer to data sheets for product selection. Sample interfaces available
from RAD include: FXS, FXO, E&M, T1, E1, ISDN "S", and ISDN
- Voice Switching -
Routing tables are used to manipulate the DTMF dialed digits, thus creating
a flexible and user-transparent dialing plan of three to 22 digits. Switching
the voice calls within the Frame Relay network eliminates switching via an
external PBX, thus saving costs of additional PBX modules. Voice quality is
also improved since there is no need for multiple compression/ decompression
- VoIP (Voice over IP)
- Set of facilities for managing the delivery of voice information using
the Internet Protocol (IP). Voice information is sent in digital form in discrete
packets over the Internet instead of in analog form over the public switched
telephone network (PSTN). A major advantage of VoIP is that it avoids the
tolls charged by ordinary telephone service.
- VP (Virtual Path)
- 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.
- VPN (Virtual Private
Network) - A restricted network that uses public wires to connect nodes.
A VPN provides a way to encapsulate, or "tunnel," private data cheaply,
reliably, and securely through a public network, usually the Internet.
- WAN (Wide Area Network)
- A network that typically spans nationwide distances and usually utilizes
public telephone networks.
- WDM (Wave Division
Multiplexing) - Optical transmission technique in which two or more wavelengths
(each carrying its own information) are combined for transmission over a single
optical fiber. At the receiving end, the wavelengths are separated and directed
to separate receivers. Increases the capacity of data transmission over fiber
optics. Also used to connect two fiber optic devices over a single strand
- Wink - On a telephone
line, a signal that is comprised of an on-hook/off-hook/on-hook transition.
- Wink Start - A
method of trunk signaling that identifies a busy/ready status to receive digits.
The "wink" is sent by the answering switch to indicate that it is
ready to receive the dialed digits from the calling switch.
- Wireless Modem -
A modem that uses radio transmission technology to transmit data between remote
locations. A wireless modem is often used by mobile clients in locations where
access to a terrestrial connection is not feasible.
- X-ON/X-OFF (Transmitter
On/Transmitter Off) - Control characters used for flow control, instructing
a terminal to start transmission (X-ON) or end transmission (X-OFF).