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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.
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
AAL5.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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).
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.
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.
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.
A device interconnecting local area networks at the OSI Data Link Layer, filtering and forwarding frames according to media access control (MAC) addresses.
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.
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.
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.
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).
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.
Signaling information is transported out-of-band. CCS
compression takes advantage of the idle flags between HDLC formatted messages
to reduce signaling bandwidth required.
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.
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.
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.
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).
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 lines.
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.
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).
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.
Any of several techniques
which reduce the number of bits required to represent information in data
transmission or storage, thereby conserving bandwidth and/or memory.
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.
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).
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.
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.
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.
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.
) A modem
interface control signal from the data communications equipment (DCE) indicating
to the data terminal equipment (DTE) that it may begin data transmission.
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.
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.
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.
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.
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.
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.
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.
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 higher.
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).
- 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
paths.
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.
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.
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 equipment.
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.
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.
- 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).
- 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
access equipment.
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.
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.
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.
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.
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 of headers.
- 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.
- 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
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.
- 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 Mbps.
- 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 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.
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 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.
- A
device responsible for framing data with header and trailer information
(control information) before presenting the frame to the Frame Relay switch.
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 intact.
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.
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.
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.
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.
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.
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.
- 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.
Pronounced
"gooey," this software interface is based on pictorial representations
and menus of operations and files. Opposite of command line interface.
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.
- 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.
- 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.
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.
- 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.
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 time.
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.
- 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 their call.
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.
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.
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.
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.
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.
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.
- 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.
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.
- 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.
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.
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 cables.
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 than LED).
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.
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.
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 Mbps.
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.
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.
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.
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.
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.
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
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.
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)
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
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
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.
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
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
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
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
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
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. See Bit
Interleaving/Multiplexer
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
(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
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).
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.
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
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
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
Management framework defined by the ITU. In telecommunications,
OA&M denotes functions such as technical interfaces, diagnostics, service
measurements and status reports
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
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
A
private switching system, usually serving an organization, such as a business
or a government agency, and is usually located on the customer's premises
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
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)
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
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
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
networks (PSTNs).
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 circuits
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 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
- 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 service.
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 by AAL5.
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 and diagnostics
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
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
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
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
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.
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.
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 format
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 the equator.
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.
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.
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.
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.
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).
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.
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.
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
cycles).
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.
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.
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 or PBX.
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.
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.
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.
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.
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.
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 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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
A single circuit between
two points, both of which are switching centers or individual distribution
points. A trunk usually handles many channels simultaneously.
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.
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.
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.
A connection
established between end users, where packets are forwarded along the same
path and bandwidth is not permanently allocated until it is used.
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.
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.
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
"U".
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
cycles.
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.
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.
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 of fiber.
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.
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.
Control characters used for flow control, instructing
a terminal to start transmission (X-ON) or end transmission (X-OFF).
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