Protocol standard used for the transport of time-dependent Constant Bit Rate (CBR) traffic (e.g. audio and video) and the emulation of TDM-based circuits (i.e. DS1, E1). Timing information is required to be exchanged between the source and the destination. AAL1 supports QoS Class A.
AAL2 - AAL type 2
|
Protocol standard for supporting time-dependent slow or Variable Bit Rate (VBR-RT) connection-oriented traffic (e.g. packetized and compressed audio and video). Timing information is required to be exchanged between the source and the destination. AAL2 supports QoS Class B.
AAL 3/4 - AAL type 3 and 4
|
Protocol standard for supporting both connectionless and connection-oriented Variable Bit Rate (VBR-NRT) traffic. AAL3 supports QoS class C while AAL4 supports QoS class D. They are currently combined into one type. AAL3/4 also performs resequencing and cell identification operations. AAL3/4 services are suitable for supporting interworking with Frame Relay, SMDS and X.25.
AAL5 - AAL type 5
|
Protocol standard for supporting connection-oriented Variable Bit Rate (VBR-NRT) data traffic and signaling messages. AAL5 supports QoS Class X. AAL5 services are suitable for supporting interworking with most data networking protocols, such as Frame Relay, SMDS, Ethernet and IP.
2-Wire Analog Circuit
|
A telephone line or trunk that has just one current loop (one pair), most commonly FXS, FXO or E&M.
4-Wire Analog Circuit
|
A telephone circuit having two pairs, TX and RX. Provides higher quality signal than two-wire circuit, most commonly E&M.
4-Wire Circuit
|
A communications path consisting of two pairs of conductors (wires), one pair for transmitting and one pair for receiving.
AAL (ATM Adaptation Layer)
|
A collection of standardized protocols that adapt user traffic to the cell format. The AAL is subdivided into the Convergence Sublayer (CS) and the Segmentation and Reassembly (SAR) sublayer. There are several types of AALs (AAL1, AAL2, AAL3/4 and AAL5) to support the various AAL service classes.
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.
A-bis
|
This is a GSM term for an interface linking between the BTS (base transceiver station) and the BSC (base station controller). Other GSM interfaces are the A between the BSC and the MSC (mobile switching controller), and the E between the MSC and the PSTN.
ABR (Available Bit Rate)
|
One of five ATM Forum-defined service categories. In this service type, the network makes the best effort to pass the maximum number of cells but does not guarantee cell delivery. Supports variable bit rate data traffic with flow control, a minimum guaranteed data transmission rate and specified performance parameters. In exchange for regulating user traffic flow, the network offers minimal cell loss of accepted traffic. Traffic parameters are PCR and MCR. QoS parameters are CLR and CER.
Address
|
A coded representation of the origin or destination of data.
An ITU standard technique for encoding analog voice signals into a digital form at 32 kbps (half the standard PCM rate).
Agent
|
In SNMP, this refers to the managed system.
AIM (ATM Inverse Multiplexing)
|
See IMA.
AIS (Alarm Indication Signal)
|
One of the OAM function types used for fault management (see also CC, RDI).
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.
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 Transmission.
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 is used for transmission of integrated services, broadband switching and multiplexing with high-performance and cost-effectiveness under certain QoS guarantees.
ATM-ARP (ATM Address Resolution Protocol)
|
An address resolution protocol for mapping ATM and IP addresses (each host is assigned a unique IP address). It can be used for discovering LAN hosts attached to an ATM network or in classical IP over ATM.
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.
Backhaul
|
Transporting traffic between distributed sites (typically access points) and more centralized points of presence. See Cellular Backhaul.
Balanced
|
A transmission line in which voltages on the two conductors are equal in magnitude, but opposite in polarity, with respect to ground.
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 time.
Baseband
|
Refers to transmission of a digital or analog signal at its original frequency, as an unmodulated signal.
Baud
|
Unit of signaling speed equivalent to the number of discrete conditions or events per second. If each signal event represents only one bit condition, baud rate equals bps (bits per second).
BERT (Bit Error Rate Test/Tester)
|
A device used to test the bit error rate of a communications circuit (i.e. the ratio of received erroneous bits to received bits, usually a number referenced to a power of 10).
Best effort
|
A QoS class in which no specific traffic parameters and no absolute guarantee are provided. Best effort includes UBR and ABR.
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.
Bit
|
The smallest unit of information in a binary system. Represents either a one or zero (“1” or “0”).
Bit Interleaving /Multiplexing
|
A process used in time division multiplexing where individual bits from different lower speed channel sources are combined (one bit from one channel at a time) into one continuous higher speed bit stream.
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 rate in serial transmission.
Bridge
|
A device interconnecting local area networks at the OSI Data Link Layer, filtering and forwarding frames according to media access control (MAC) addresses.
Bridging
|
Interconnecting local area networks at the OSI Data Link Layer, filtering and forwarding frames according to media access control (MAC) addresses.
Wideband technology capable of supporting voice, video and data, possibly using multiple channels.
BSC (Base Station Controller)
|
Provides the intelligence behind the BTSs. Typically a BSC has 10s or even 100s of BTSs under its control. The BSC handles allocation of radio channels, receives measurements from the mobile phones, and controls handovers from BTS to BTS (except in the case of an inter-BSC handover in which case control is in part the responsibility of the anchor MSC). A key function of the BSC is to act as a concentrator where many different low capacity connections to BTSs (with relatively low utilization) become reduced to a smaller number of connections towards the mobile switching center (MSC) with a high level of utilization.
BTS (Base Transceiver Station)
|
The equipment which facilitates the wireless communication between a user’s handset and the network. BTS can also be referred to as RBS (radio base station), Node B (in 3G networks) or simply BS (base station). Typically a BTS will have several transceivers (TRXs), which allow it to serve several different frequencies and different sectors of the cell. The BTS includes equipment for encrypting and decrypting communications with the base station controller (BSC).
Buffer
|
A storage device. Commonly used to compensate for differences in data rates or event timing when transmitting from one device to another. Also used to remove jitter.
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 time.
Byte
|
A group of bits (normally 8 bits in length).
Carrier
|
A continuous signal at a fixed frequency that is capable of being modulated with a second (information carrying) signal.
Carrier Ethernet is a ubiquitous service based on standardized equipment and protocols providing seamless connectivity between high speed Ethernet-based LANs and WANs. Carrier Ethernet is characterized by industry-defined attributes for service level agreements, provisioning, system-wide management, and carrier-class OAM. Originally implemented in the core network, Carrier Ethernet is now being extended to the edge and access segment.
Carrier Ethernet deployment is picking up pace as Ethernet becomes a widely-accepted, carrier-grade service suite, however, it depends on service providers’ ability to cost-effectively overcome two key challenges: The diversity of existing access and transport networks, and the need to meet user expectations for SLA accountability.
CAS (Channel Associated Signaling)
|
Voice signaling based on bits taken from voice timeslots, used by many PBXs.
CAT-3 (Category 3 UTP)
|
Unshielded Twisted Pair standard, commonly used with ATM for cell transmission at low speeds up to 25 or 51 Mbps at very short distances (few hundred meters).
CAT-5 (Category 5 UTP)
|
Unshielded Twisted Pair standard, commonly used with ATM interfaces for higher-speed cell transmission (more than 50 Mbps).
CBR (Constant Bit Rate)
|
One of the five ATM classes of service. CBR supports the transmission of a continuous bit-stream of information, such as voice and video traffic, which require a constant amount of bandwidth allocated to a connection for the duration of the transmission.
CC (Continuity Cell)
|
A cell used periodically to check whether a connection is idle or has failed. Continuity checking is one of the OAM function types for fault management.
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 that 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
|
The 53-byte basic information unit within an ATM network. The user traffic is segmented into cells at the source and reassembled at the destination. An ATM cell consists of a 5-byte ATM header and a 48-byte ATM payload, which contains the user data.
Central Office (CO)
|
Telephone company switching office. This is where you would find the local telco switch that connects to your telephone.
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.
CER (Cell Error Rate)
|
A QoS parameter that measures the number of transmitted cells that are erroneous over a specific period of time (i.e., those that contain errors when they arrive at the destination).
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 services, such as in Europe).
Channelized ATM STM-1
|
An STM-1 ATM circuit, which can handle VC-12 traffic individually or in bundles via the SDH network
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 lines.
Characteristic Impedance
|
The termination impedance of an electrically uniform transmission line.
CI (Congestion Indicator)
|
A field in the RM-cell that indicates congestion in the network which can ultimately lead to the source reducing its allow cell rate (ACR).
CIF (Cell Information Field)
|
The payload (48 bytes) of the ATM cell.
CIR (Committed Information Rate)
|
A term used in Frame Relay, which defines the information rate that the network is committed to provide to the user, under any network conditions.
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. Services based on circuit emulation (Circuit Emulation Services or CES) offer traditional TDM trunking (at n x 64 kbps, fractional T1/E1, T1/E1 or T3/E3) over a range of transport protocols, including ATM, Internet Protocol (IP), MPLS and Ethernet.
Circuit Emulation Service
|
New technology for offering circuit emulation services over packet-switched networks. The service offers traditional TDM trunking (at n x 64 kbps, fractional E1/T1, E1/T1 or E3/T3) over a range of transport protocols, including Internet Protocol (IP), MPLS and Ethernet.
Clock
|
A term for the source(s) of timing signals used in synchronous transmission.
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.
Composite Link
|
The line or circuit carrying multiplexed data which connects a pair of multiplexers or concentrators. Also called aggregate or main link.
Compression
|
Any of several techniques that reduce the number of bits required to represent information in data transmission or storage, thereby conserving bandwidth and/or memory.
Concentrator
|
Device that serves as a wiring hub in star-topology network. Sometimes refers to a device containing multiple modules of network equipment.
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
|
A resource and traffic management mechanism to avoid and/or prevent excessive situations (buffer overflow, insufficient bandwidth) that can cause the network to collapse. In ATM networks, congestion control schemes may be based on fields within the ATM cell header (CLP, EFCI within the PTI) or may be based on a more sophisticated mechanism between the ATM end-system and ATM switches. The ATM Forum has developed a mechanism based on rate control for ABR-type traffic. In Frame Relay networks, congestion is handled by the FECN, BECN and DE bits.
Constant Bit Rate
|
See CBR.
Contention
|
A condition arising when two or more data stations attempt to transmit at the same time using the same link or channel.
Control Characters
|
In communications, any extra transmitted characters used to control or facilitate data transmission (for example, characters associated with polling, framing, synchronization, error checking, or message delimiting).
Control Signals
|
Signals passing between one part of a communications system and another (such as RTS, DTR, or DCD), as part of a mechanism for controlling the system.
CORBA
|
The acronym for Common Object Request Broker Architecture, OMG's open, vendor-independent architecture and infrastructure that computer applications use to work together over networks. One of its most important uses is in servers that must handle large number of clients, at high hit rates, with high reliability, such as network management systems.
CPE (Customer Premises Equipment)
|
Generally refers to communications equipment located at the customers' premises for use with communication service providers' services. In some cases, these are customer-owned or leased; in other cases, these are the property of the service provider.
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.
A network device used by telecom carriers and large enterprises to switch and multiplex low-speed voice and data signals onto high-speed lines and vice versa. It is typically used to aggregate several E1/T1 lines into a higher-speed electrical or optical line as well as to distribute signals to various destinations.
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 adjacent 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 timeout. CSMA/CD is used in Ethernet.
CSU (Channel Service Unit)
|
Equipment installed on customer premises at the interface to phone company lines to terminate a DDS or T1 circuit. CSUs provide network protection and diagnostic capabilities.
CSU/DSU (Channel Service Units/Data Service Units)
|
CSUs and DSUs are usually grouped together. They convert carrier line signals to digital signals.
CTS (Clear To Send)
|
A modem interface control signal from the data communications equipment (DCE) indicating to the data terminal equipment (DTE) that it may begin data transmission.
Current Loop
|
Method of data transmission. A mark (binary “1”) is represented by current on the line, and a space (binary “0”) is represented by the absence of current.
D4-Frame
|
A T1 line uses the D4 format, also known as the Super Frame (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 time-slot switch which allows T1 or E1 lines to be remapped electronically at the DS-0 (64 kbps) level. Also called DCS or DXS.
Data
|
Information represented, in digital form, including voice, text, facsimile and video.
Data Link Layer
|
Layer 2 of the OSI model. The entity, which establishes, maintains, and releases data-link connections between elements in a network. Layer 2 is concerned with the transmission of units of information, or frames, and associated error checking.
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 across international 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 measure of power in communications: the decibel in reference to one milliwatt (0 dBm = 1 milliwatt and -30 dBm = .001 milliwatt).
DCC (Data Country Code)
|
Part of an ATM address, DCC contains the code for the country in which the ATM address is registered.
Digital Circuit Multiplication Equipment (DCME) performs voice compression over TDM and IP networks to reduce bandwidth requirements for microwave, wireline and costly satellite links while preserving voice quality.
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.
DE (Discard Eligibility)
|
A bit indicating that a frame may be discarded in case of congestion on a Frame Relay network, in order to help maintain the committed information rate (CIR).
Decibel
|
See dB.
DI (Direction Indicator)
|
A 1-bit field in the RM-cell to indicate whether it is an RM-cell traveling from the source to the destination or returning to the destination.
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
|
Differential delay is caused when traffic is split over different lines that may traverse shorter and longer paths. Products like the RAD IMX-2T1/E1 inverse multiplexer compensate for any differential delay (up to 64 msec) between the T1 lines, to properly reconstruct the original stream.
DiffServ or DS (Differentiated Services)
|
QoS method to differentiate and control IP traffic so that the traffic’s relative priority can be determined on a per-hop basis.
Digital
|
The binary (“1” or “0”) output of a computer or terminal. In data communication, an alternating, non-continuous (pulsating) signal.
Digital cross-connects (DACs) (see Cross Connect) come large and small, handling only a few ports up to a couple of thousand. Narrowband, wideband and broadband cross-connects support channels down to DS0, DS1 and DS3 respectively.
Digital Loopback
|
A technique for testing the digital processing of a communications device. The loopback is toward the line side of a modem, but tests most of the circuitry in the modem under test.
Distortion
|
The unwanted change in a signal’s waveform occurring between two points in a transmission system.
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)
|
Uniquely identifies each virtual circuit number corresponding to a particular destination in a Frame Relay network, DLCIs u. 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.
DOV (Data Over Voice)
|
A technology for transmitting data and voice simultaneously over twisted-pair copper wiring.
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 equipment.
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.
DSCP (Differentiated Services Code Point)
|
A field in the header of IP packets for packet classification purposes.
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 (24 x 64 kbps) equal one DS1.
DS1 (Digital Signal Level 1) Channel
|
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), high-bitrate DSL (HDSL) and the latest, symmetric high-bitrate DSL (SHDSL).
DSU (Digital Service Unit)
|
A user device interfacing to a digital circuit (such as DDS or T1 when combined with a CSU). The DSU converts the user’s data stream to bipolar format for transmission.
DTE (Data Terminal Equipment)
|
As defined in the RS-232 specification, equipment to which DCE (Data Communications Equipment) is connected, such as personal computers, data terminals or printers. 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.
DTMF (Dual-Tone Multifrequency)
|
DTMF is a technology enabling a touch-tone telephone to create 16 tones using frequencies.
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.
E&M Signaling
|
Voice transmission system that uses separate paths for signaling and voice. The “M” lead (mouth) transmits signals to the remote end of the circuit while the “E” lead (ear) receives incoming signals.
A 2.048 Mbps line, common in Europe, 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.
Combining (bonding) multiple PPP (Point-to-Point Protocol) links between two systems into one logical data pipe. MLPPP is a standard IETF protocol.
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 G.703.
E3
|
The European standard for high speed digital transmission, operating at 34 Mbps.
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 station.
EFM Ethernet in the First Mile (also known as IEEE 802.3ah)
|
A collection of protocols specified in IEEE 802.3, defining Ethernet in the access networks, i.e. First/Last Mile. EFM also addresses other issues required for mass deployment of Ethernet services, such as operations, administration and maintenance (OAM) and compatibility with existing technologies (e.g. spectral compatibility for copper).
EIA (Electronic Industries Association)
|
A standards organization in the U.S. specializing in the electrical and functional characteristics of interface equipment.
E-LAN (Ethernet Local Area Network)
|
A Fast Ethernet or Gigabit Ethernet service used for multipoint-to-multipoint transparent Ethernet LAN connectivity, allowing any location to speak with any other location in a customer’s Metro Ethernet network (see MEF).
E-Line (Ethernet Line)
|
A service providing a point-to-point Ethernet Virtual Connection (EVC) between two customer user interfaces or two locations in a Metro Ethernet network (see MEF).
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 of headers.
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.
ESI (End System Identifier)
|
The 6-octet field within the ATM NSAP format address, which identifies an end system. Equivalent to the MAC address of the device.
Ethernet
|
Most popular local area network (LAN) technology in use today. All stations on the LAN share the total bandwidth, which is at speeds of 10 Mbps (Ethernet), 100 Mbps (Fast Ethernet), or 1000 Mbps (Gigabit Ethernet).
A key element in Carrier Ethernet transport and services, Ethernet demarcation provides a clear separation between the user and the network, allowing carriers to extend network visibility up to the user premises.
Ethernet signal degradation typically limits Ethernet cable runs to 100 meters (328 feet). To achieve longer distances, an Ethernet extender is required. These devices can be used to drive Ethernet up to 5.5 kilometers over copper and more than 100 kilometers over fiber.
RAD Data Communications has a wide range of Ethernet modems with combined E1/T1 multiplexing capabilities for point-to-point Ethernet extension over any type of infrastructure or media.
Ethernet OAM (Operation, Administration and Maintenance) is a set of functions designed to monitor network operation in order to detect network faults and measure its performance. Carrier-class Ethernet services require automated end-to-end management and monitoring, including OAM capabilities such as connectivity verification, fault detection, performance monitoring, and alarm indication.
Ethernet over PDH (Plesiochronous Digital Hierarchy) is a method for carrying Ethernet traffic over PDH network lines such as E1/T1 or E3/T3. It is one of several technologies available to service providers who wish to offer new carrier-class Ethernet services over existing legacy infrastructure.
Although SDH networks were originally engineered to transport voice traffic, many carriers are using their ubiquitous SDH infrastructure to deploy Ethernet services. Recent developments in Next Generation SDH have made these networks more cost-effective and "user friendly" for Ethernet traffic.
Although SONET networks were originally engineered to transport voice traffic, many carriers are using their ubiquitous SONET infrastructure to deploy Ethernet services. Recent developments in Next Generation SONET have made these networks more cost-effective and "user friendly" for Ethernet traffic.
One of the key attributes of Carrier Ethernet services, by which the service provider offers business users bandwidth, delivery, and performance guarantees for selected traffic, and allocates the necessary network resources accordingly.
Evolved HSPA, also known as MIMO (multiple-input multiple-output) HSPA, HSPA Evolution and HSPA+, is an upgrade to the 3GPP’s HSPA standard providing theoretical downlink speeds of up to 42 Mbps. HSPA+ is generally regarded as an interim phase between the 3.5G HSPA technology and 4G LTE (long-term evolution).
Fan-Out
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The ability of a digital access cross connect (DAC) to split and switch channels between incoming and outgoing circuits.
Fault Tolerance
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A way to provide redundancy in hardware systems to protect against failure of one of the redundant systems or components. 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
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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)
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The regulatory agency established in the United States for all interstate radio and electronic communications.
FECN (Forward Explicit Congestion Notification)
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A bit set by a Frame Relay network to notify an interface (DTE) that congestion avoidance procedures should be initiated by the receiving device.
A fiber media converter connects standard optical interfaces with electrical interfaces; links single mode fibers with multimode fiber cables; adapts dissimilar data rates; and converts different transmission protocols such as TDM E1/T1 and Ethernet.
Fiber Optics
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A transmission medium consisting of thin glass or plastic filaments. Light beams (generated by an LED or laser) travel through the fiber optic line, carrying large amounts of data over long distances.
Fiber optic multiplexers are devices that combine multiple signals for transport on a common transmission path. RAD’s fiber optic multiplexers enable transmission of E1 or T1 channels, E3 or T3 tributaries and wire-speed Ethernet over a fiber optic link. A fiber optic multiplexer at the other end reverses the process.
Flow Control
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A congestion control mechanism that results in an ATM system implementing flow control.
Fractional T1 Line
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A T1 line that contains both switched and nailed-up channels. T1 PRI and ISDN BRI lines can also be Fractional T1 lines.
Frame
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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
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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.
Framing
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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
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A circuit or device permitting transmission in two directions (sending and receiving) at the same time.
FXO (Foreign Exchange Office)
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A voice interface, emulating a PBX extension, as it appears to the CO (Central Office) for connecting a PBX extension to a multiplexer.
FXS (Foreign Exchange Subscriber)
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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
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An ITU standard for the physical and electrical characteristics of various digital interfaces, including those at 64 kbps and 2.048 Mbps.
G.703.1
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An ITU standard for voice compression.
G.802
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ITU standard for carrying T1 traffic over E1 networks.
Part of ITU-T’s Synchronous Ethernet set of standards, G.8261 specifies the acceptable limits of jitter and wander for packet networks and equipment at the network boundary’s TDM interfaces, as well as the minimum requirements for the synchronization function of network elements.
An ITU-T standard specifying the Synchronization Status Message (SSM) format for Synchronous Etherent.
Gatekeeper
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A device that manages an IP network, supporting all gateways, user profiles, and authentication. A gatekeeper is defined by the H.323 standard.
Gateway
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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.
Gigabit Ethernet, also known as GbE, refers to a transmission rate of 1 Gigabit per second (1,000 Megabit per second) using Ethernet technology. Various Gigabit Etherent standards address GbE transmission over different fiber and copper media. Initially deployed in the LAN, Gigabit Ethernet is now a standard interface for WAN access to Metro Ethernet networks.
Gigabit Ethernet converters typically link copper cabling (UTP) with fiber optics or multimode fiber with single-mode fiber cables, to enable transport of Gigabit Ethernet traffic over diverse media.
GFP (Generic Framing Procedure)
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Defined by ITU-T G.7041, generic framing procedure allows efficient mapping of variable length, higher-layer client signals, such as Ethernet, over a transport network like SDH/SONET. Recently, GFP has been extended to lower speed PDH networks.
Grooming
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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
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A signaling method in which the customer premises equipment (CPE) transmits an off-hook condition by creating a zerovoltage condition.
G.SHDSL, or SHDSL, is a standardized method (ITU-T G.991.2) to transport symmetrical data rates on copper pair access lines. G.SHDSL offers bitrates from 192 kbps to 2.3 Mbps over a 2-wire single pair and up to 9.2 Mbps over four bonded pairs.
A G.SHDSL modem is a customer located transceiver, connecting users to a G.SHDSL service via the local DSLAM.
GSM (Global System for Mobile communications)
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A second generation digital cellular telecommunication system originating in Europe, but now considered the international standard.
GUI (Graphical User Interface)
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Pronounced “gooey,” this software interface is based on pictorial representations and menus of operations and files. Opposite of command line interface.
H.323
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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
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A circuit or device capable of transmitting in two directions, but not at the same time.
HDLC (High-level Data Link Control)
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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)
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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.
High Speed Downlink Packet Access (HSDPA) is an upgrade to W-CDMA technology that provides theoretical downlink speeds of up to 14 Mbps. HSDPA, also known as 3.5G, is an enhancement to UMTS networks.
HSSI (High Speed Serial Interface)
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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
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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
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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
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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.
IEEE (Institute of Electrical and Electronic Engineers)
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An international professional society issuing its own standards. The IEEE is a member of ANSI and ISO.
IEEE C37.94
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A standard providing plug-and-play transparent communications between different manufacturer’s Teleprotection and multiplexer devices using multimode optical fiber. The standard defines clock recovery, jitter tolerances, physical connection method, and the equipment-failure actions for all communications link failures.
IETF (Internet Engineering Task Force)
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Body which was initially responsible for developing the specifications required for the interoperable implementation of IP.
IMA (Inverse Multiplexing over ATM)
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A method to pass ATM traffic over multiple E1/T1 links while keeping the ATM’s quality of service and optimization of bandwidth usage.
Impedance
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The combined effect of resistance, inductance and capacitance on a transmitted signal. Impedance varies at different frequencies.
In-band Signaling
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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.
Integrated access devices (IAD) deliver voice and data services from user equipment to metro or wide area networks, over a shared xDSL access line.
Interactive Voice Response
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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.
Interface
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A shared boundary, defined by common physical interconnection characteristics, signal characteristics, and meanings of exchanged signals.
Interface converters are devices that convert physical media, data rates and transmission protocols, allowing service interworking between different communication interfaces
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)
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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
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Also known as an Internet address. An IP address (Internet Protocol address) is a unique reference number used by devices attached to a network when sending information through a Local LAN, Wide area WAN or the Internet networks.
A central office (CO) device for delivering digital subscriber line services that link DSL connections to a single high-speed broadband (IP) line.
IP Telephony
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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.
IP-based radio access networks (RANs) utilize packet switched technology to transport the data-intensive traffic of mobile broadband, 3.5G, HSPA and LTE.
IPX (Internetwork Packet Exchange)
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Netware network layer (layer 3) protocol for transferring data from servers to workstations.
ISDN (Integrated Services Digital Network)
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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
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Alternate routing of traffic over ISDN, PRI, and BRI for backup purposes when the main link fails.
ISDN D-Channel Signaling
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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 BRI (Basic Rate Interface) Line
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An ISDN line that uses two B-channels for user data, and one 16 kbps D-channel for 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 PRI (Primary Rate Interface) Line
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An ISDN interface providing 23 B-channels, each operating at 64 kbps, and a single D-channel also operating at 64 kbps to customer’s premises.
ISO (International Standards Organization)
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An international organization involved in writing communications standards.
ITU (International Telecommunication Union)
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A European-based, international advisory committee recommending worldwide standards for transmission.
J1
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Digital interconnection protocol similar to T1 and E1 used in Japan.
Jitter
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The deviation of a transmission signal in time or phase. It can introduce errors and loss of synchronization in high speed synchronous communications.
Jitter Buffer
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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. Since the jitter buffer adds to the overall delay of voice transmissions, the optimal jitter buffer should fit the network's differential delay. Adaptive jitter buffering continuously monitors the network delay and adjusts the queuing period accordingly.
KTS (Key Telephone System)
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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)
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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.
LAP-B (Link Access Procedure-Balanced)
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A data link layer protocol, defined by ITU-T, used in X.25. It is very similar to HDLC.
LAP-D (Link Access Procedure for the D-channel)
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A data link layer protocol, defined by ITU-T, for use in ISDN. The LAP-D protocol is based on HDLC.
Laser
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A device that transmits an extremely narrow and coherent beam of electromagnetic energy in the visible light spectrum. Used as a light source for fiber-optical transmission (generally more expensive, shorter lived, single mode only, for greater distances than LED).
Last Mile
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(Sometimes referred to as Local Loop). The final leg of delivering communications connectivity to a resident or customer. Typically seen as an expensive challenge because “fanning out” wires and cables is a considerably expensive and physically difficult task.
Latency
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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.
LCAS (Link Capacity Adjustment Scheme)
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A method to dynamically increase or decrease the bandwidth of virtual concatenated containers in SDH. The LCAS protocol is specified in ITU-T G.7042. It allows on-demand increase or decrease of the bandwidth of the virtual concatenated group in a hitless manner. This brings bandwidth-on-demand capability for data clients like Ethernet when mapped into SDH containers.
Leased Line
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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.
LED (Light Emitting Diode)
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A semiconductor light source that emits light in the optical frequency band or the infrared frequency band. LEDs are a major light source for fiber-optical transmission used with multimode fiber in applications that require a low cost light source.
Line Driver
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A signal converter which conditions a digital signal to ensure reliable transmission over an extended distance.
Load Balancing
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A technique that distributes network traffic along parallel paths in order to maximize the available network bandwidth while providing redundancy.
Loading
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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
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(Sometimes referred to as Last Mile). 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.
Loop Start
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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.
Loopback
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A type of diagnostic test in which the transmitted signal is returned to the sending device after passing through all or part of a communications link or network.
An M13 multiplexer, or M13 mux, integrates 28 T1 tributary channels into a single T3 line using bit-level multiplexing and M13 framing format.
MAC (Media Access Control)
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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.
MAC-in-MAC
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An IEEE 802.1ah standard for layering the Ethernet network into customer and provider domains with complete isolation among their MAC addresses. It enables service providers to separate customer traffic from management traffic and also save on VLAN IDs.
MAN (Metropolitan Area Network)
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A network that provides regional connectivity within a metropolitan area (such as a city).
Manager
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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
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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
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The source of timing signals (or the signals themselves) that all network stations use for synchronization.
MEF (Metro Ethernet Forum)
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A non-profit organization chartered with the mission of accelerating the adoption of optical Ethernet as the technology of choice in future metro networks worldwide. Ethernet was chosen for its relative simplicity and popularity with end-users, as well as for lowering costs of Ethernet equipment.
Metering
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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)
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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)
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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.
MLPPP (Multilink PPP)
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Connects multiple links between two systems as needed to provide extra bandwidth. Remotely accessing resources through MLPPP allows for an increase in overall throughput by combining the bandwidth of two or more physical communication links, such as analog modems, ISDN and other analog/digital links.
Modem (Modulator-Demodulator)
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A device used to convert serial digital data from a transmitting DTE to a signal suitable for transmission over extended distances. It also reconverts the transmitted signal to serial digital data for acceptance by a receiving DTE.
Modem Eliminator
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A device used to connect a local terminal and a computer port. The modem eliminator replaces the pair of modems ordinarily required.
Modular
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Modular interfaces enable field changeable conversion.
Modulation
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The alteration of a carrier wave in relation to the value or samples of the data being transferred.
MPLS (Multiprotocol Label Switching)
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A standards-approved technology that allows core network routers to operate at higher speeds without needing to examine each packet in detail, allows more complex services to be developed, enabling discrimination on a QoS basis. MPLS speeds up network traffic flow by bringing Layer 2 information to Layer 3 (IP) and facilitating network management. It forwards traffic using a label that instructs the routers and the switches in the network where to forward the packets based on pre-established IP routing information. MPLS is called multiprotocol because it works with the IP, ATM, and Frame Relay network protocols.
Multidrop
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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
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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 (Mux)
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A device allowing two or more signals to pass over and share a common transmission path simultaneously.
Multipoint Line
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See Multidrop.
Multiservice Access Platform (MAP)
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A scalable, integrated system that can provide a wide range of voice, video and data services in a single chassis. A MAP can be located at the customer premises, in the Local Loop/Last Mile or at the carrier’s point of presence (POP).
Narrowband
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In communications technology, digital communication at the rate of 64,000 bits per second or lower.
Network
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(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
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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).
NIC (Network Interface Card)
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The hardware communication interface (circuit board) required for the DTE (workstation, PC) to access the network.
NMS (Network Management System)
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The system that controls the network configuration, fault and performance management, and diagnostic analysis.
NNI (Network Node Interface or Network-to-Network Interface)
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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
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A point of interconnection to a network.
NRZ (Non-Return to Zero)
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A binary encoding scheme representing ones and zeroes by opposite and alternating high and low voltages, in which there is no return to a zero (reference) voltage between encoded bits.
NRZI (Non-Return to Zero Inverted)
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A binary encoding scheme which inverts the signal 1 and leaves the signal unchanged or a 0. Also called transition coding.
OAM (Operation Administration and Maintenance)
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A set of network management functions that provide for network fault and performance management, analysis and fault isolation. OAM functions exist in carrierclass TDM and ATM networks, but are now also being implemented in MPLS and Ethernet networks. These capabilities will provide the basic tools for carriers to monitor, diagnose, and troubleshoot first-mile Ethernet access links.
OC (Optical Carrier)
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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.
Off-Hook
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A state that results when you lift a telephone receiver, producing a busy signal.
Omnibus
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Instant multi-party voice communications between distant operators in a non-service-intrusive fashion.
On-Hook
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A state that results when the telephone receiver is in place. No loop current flows and the switch recognizes that the telephone is available for incoming calls.
OSI (Open Systems Interconnection) Model
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A seven-layer model of network communications developed by the International Organization for Standardization (ISO).
OSPF (Open Shortest Path First)
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A protocol which is a hierarchical IGP for routing in IP, using a link-state in the individual areas that make up the hierarchy.
Out-of-Band Connection
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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
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The transmission of signaling information over a different path from data and/or voice information. CCS7 uses out-ofband signaling.
Packet
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An ordered group of data and control signals transmitted through a network, as a subset of a larger message.
Packet Switching
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A data transmission technique, which divides user information into discrete data envelopes called packets, and sends the information packet by packet.
Parity Bit
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An additional non-information bit added to a group of bits to ensure that the total number of l bits in the character is even or odd.
Payload
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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)
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A private telephone switching system, usually serving an organization, such as a business or a government agency, and is usually located on the customer’s premises.
PCM (Pulse Code Modulation)
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A procedure for adapting an analog signal (such as voice) into a 64 kbps digital bit stream for transmission.
PHY (Physical layer)
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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
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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.
Policing
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A method for verifying that the incoming VC complies with the user’s service contract.
Polling
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See Multidrop.
PON (Passive Optical Network)
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A high bandwidth, point-to-multipoint optical fiber network based on ATM, Ethernet or TDM. In this type of optical network, wavelengths of light are divided into timeslots so that each wavelength can be shared by a number of users. With PONs, a single fiber from the carrier’s exchange can service 16, 32 or more buildings through the use of both passive devices to split the optical signal, and PON protocols to control the sending and transmission of signals across the shared access facility.
PoP (Point of Presence)
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An access point to the rest of the network.
Port
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The physical interface to a computer, multiplexer, for connection of terminals and modems.
POTS (Plain Old Telephone Service)
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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).
PPP (Point-to-Point Protocol)
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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.
PRI (Primary Rate Interface)
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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
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Also called CoS (class of service), classifies traffic into categories such as high, medium, and low. The lower the priority, the more “drop eligible” is a packet. E-mail and Web traffic are often placed in the lowest categories. When the network gets busy, prioritization ensures critical or high-rated traffic is passed first, and packets from the lowest categories may be dropped.
Protocol
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A formal set of conventions governing the formatting and relative timing of message exchange between two communicating systems.
Pseudowire
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Point-to-point connections set up between pairs of Provider Edge routers. Their primary function is to emulate (typically layer 2) native services like ATM, Frame Relay, Ethernet, low-rate TDM, or SONET/SDH over an underlying common packet switched network (MPLS, IP, or L2TPv3) network core. To achieve this, each of these technologies is encapsulated into a common MPLS format. Pseudowires are defined by the IETF PWE3 (Pseudowire Edge to Edge Emulation) WG.
PSTN (Public Switched Telephone Network)
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The telecommunications network commonly accessed by ordinary telephones, key systems, PBX trunks and data equipment.
PVC (Permanent Virtual Circuit)
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A virtual connection established by the network management between an origin and a destination that can be left up permanently.
PVP (Permanent Virtual Path)
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A set of permanent virtual channels (PVCs) that exist between two cross points.
Q-in-Q
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See MAC-in-MAC.
QoS (Quality of Service)
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Refers to the capability of a network to provide better service to selected network traffic over various technologies, including Frame Relay, Asynchronous Transfer Mode (ATM), Ethernet and 802.1 networks.
QSIG
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An ISDN-based signaling protocol for signaling between private branch exchanges (PBXs) in a private integrated services network.
RADIUS (Remote Authentication Dial-In User Service)
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An authentication, authorization and accounting protocol for applications such as network access or IP mobility. Many network services require the presentation of security credentials (such as a username and password or security certificate) in order to connect to the network. Before access to the network is granted, this information is passed to a network access server (NAS) device over the link-layer protocol, then to a RADIUS server over the RADIUS protocol. The RADIUS server checks that the information is correct using authentication schemes like PAP, CHAP or EAP.
RADview
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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.
Redundancy /Redundant Card or Power
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Backup components used to ensure uninterrupted operation of a system in case of a failure.
Register
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A storage device capable of receiving and holding a number of digits.
Repeater
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A device which automatically amplifies, restores or reshapes signals to compensate for distortion and/or attenuation prior to retransmission.
Reverse Polarity
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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 1490
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Specifies the encapsulation of multiprotocol data for transmission over Frame Relay. Frame Relay over ATM uses this encapsulation in combination with AAL5.
RIP2
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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)
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A telephone connector that accommodates up to eight wires. RJ-45 plugs and sockets are used in Ethernet and Token Ring devices.
Router
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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
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The process of selecting the most efficient circuit path for a message.
RSVP (Resource reSerVation Protocol)
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A protocol developed for supporting different QoS classes for IP applications.
RTS (Request To Send)
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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)
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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.
Satellite Link
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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.
Scalable
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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.
SDH (Synchronous Data Hierarchy)
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The European standard for using optical media as the physical transport for high speed long-haul networks.
Serial Transmission
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A common mode of transmission, where the character bits are sent sequentially one at a time instead of in parallel.
SFP
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The Small Form-factor Pluggable (SFP) is a compact optical transceiver used in telecom and datacom applications. It is a popular industry format supported by most fiber optic component vendors. The primary advantages of this approach are hot pluggability, field replacabilty, and mix and match optical reach and type. Using the SFP platform, RAD has engineered a "System on an SFP" for extension of Ethernet and LAN over E1/T1 and E3/T3 connections.
SF (Super Frame)
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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
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A device that enables sharing of a single resource (modem, mux or computer port) among several devices (terminals, controllers or modems).
SHDSL, (ITU-T G.991.2, Single-pair High-speed Digital Subscriber Line), is a standardized method of extending the range of copper telephone lines for broadband services. SHDSL technology is used to transport data symmetrically at rates of 192 kbps to 2.3 Mbps over 2-wire, or 384 kbps to 4.6 Mbps over 4-wire. The latest SHDSL standard is SHDSL.bis. Based on ITU-T G.991 and ETSI TS 101524, SHDSL.bis uses TC-PM 16 or TC-PAM 32 line coding and multi-pair bonding technology to reach transmission rates up to 5.69 Mbps on 1 pair (2-wire) for a rate up to 22.8 Mbps over 8-wire.
Shielded Twisted Pair Cable (STP)
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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
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The protective enclosure surrounding a transmission medium, designed to minimize electromagnetic interference (EMI/RFI).
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).
Silence Suppression
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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
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Describing an optical wave-guide or fiber that is designed to propagate light of only a single wavelength (typically 5-10 microns in diameter).
SIP (Session Initiation Protocol)
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is a real-time signaling protocol for Internet conferencing, telephony, video, events notification and instant messaging. SIP initiates call setup, routing, authentication and other feature messages to endpoints within an IP domain.
SLA (Service Level Agreement)
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A formal negotiated agreement between customers and their service provider, or between service providers. It records the common understanding about services, priorities, responsibilities, guarantees, etc. with the main purpose to agree on the level of service. For example, it may specify the levels of availability, serviceability, performance, operation, or other attributes of the service like billing and even penalties in the case of violation of the SLA.
SLIP (Serial Link Internet Protocol)
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An Internet protocol for host dialup connection. SLIP frames are encapsulated IP datagrams in which SLIP adds just a few bytes of control data.
The Internet standard protocol for managing nodes on an IP network.
SONET (Synchronous Optical Network)
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A North American 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
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In telecommunications, the absence of a signal. Equivalent to a binary 0.
SS7 (Signaling System 7)
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A signaling method separate from the voice or data channel that lets intelligent network elements exchange information among themselves.
SSH (Secure Shell)
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A network protocol that allows data to be exchanged over a secure channel between two computers. Encryption provides confidentiality and integrity of data.
Statistical Multiplexer (STM or STDM)
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A device connecting multiple channels to a single link by dynamically allocating timeslots to the channels based on their transmission activity.
STP (Shielded Twisted Pair)
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Cable consisting of a pair of twisted wires surrounded by a metallic shield.
Subrate Multiplexer
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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.
Subrate Multiplexing
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In the U.S. this refers generally to time division multiplexing at data rates less than 64 kbps.
Super Tandem
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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).
Sync
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See Synchronous Transmission.
Synchronous Transmission
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Transmission in which data bits are sent at a fixed rate, with the transmitter and receiver synchronized.
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.
Combining (bonding) multiple PPP (Point-to-Point Protocol) links between two systems into one logical data pipe. MLPPP is a standard IETF protocol.
T3
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A digital transmission link with a capacity of 45 Mbps, or 28 T1 lines.
Tandem Encoding
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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.
Tandem Switching
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Routing a call through a switch to another switch.
TCP/IP (Transmission Control Protocol/Internet Protocol)
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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)
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A device which divides the time available on its composite link among its channels, usually interleaving bits (Bit TDM) or characters (Character TDM) of data from each terminal.
TDMoIP®
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TDM over IP is a standards-based transport technology that extends voice, video or data circuits across packet-switched networks simply, transparently and economically. Acting as a pseudowire, TDMoIP is unique in that it supports the multiple signaling standards, OAM mechanisms and clock recovery features demanded by TDM networks for carrying voice-grade telephony channels. A simple alternative to VoIP, TDMoIP enables using legacy TDM equipment while facilitating a smooth migration to newer IP, Ethernet and MPLS networks. TDMoIP technology was developed and patented by RAD, and is found in RAD’s IPmux, Vmux and Megaplex products.
Telnet
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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, the user connects to it over the Internet using Telnet. When issuing a Telnet session, it connects to the Telnet host and logs in. The connection enables the user to work with the remote machine as though it were a terminal connected to it.
Terminal Adapter
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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.
TETRA (Terrestrial Trunked Radio)
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A wireless communications standard for Professional Mobile Radio (PMR) and Private Access Mobile Radio (PAMR) applications. It is a digital format, i.e. speech is transmitted as binary data, which makes it far more difficult to monitor or eavesdrop.
TFTP (Trivial File Transfer Protocol)
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A simplified version of the File Transfer Protocol that transfers files but does not provide password protection or user directory capability.
Throughput
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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)
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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
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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.
Various methods and standards developed to ensure that accurate time and frequency is distributed in packet-based networks.
ToS (Type of Service) Field
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In a QoS scheme, an eight-bit field that lets values from 0 to 15 be assigned to request special handling of traffic (for example, minimize delay, maximize throughput). The ToS field is being phased out in favor of DSCP.
TM (Traffic Management)
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Set of actions and operations performed by the network to guarantee the operability of the network. TM is exercised in the form of traffic control and flow control. The ATM traffic management includes the following: CAC, FRM, NRM, Priority Control (PC), Traffic Shaping (TS) and UPC, the goal of which is to maintain the required QoS.
Traffic Contract
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An agreement between the user and the network management agent regarding the expected QoS provided by the network and the user’s compliance with the pre-determined traffic parameters (i.e. PCR, MBS, burstiness, average cell rate).
Traffic Management
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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
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Mechanism whereby any traffic which violates the traffic contract agreed to at connection setup, is detected and discarded.
Traffic Shaping
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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.
Transparent LAN Service (TLS)
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A high speed data service which allows for the interconnection of different LANs across an extended campus, metropolitan area or national network. Using VLANs and native LAN interfaces (such as 10/100 Mbps Ethernet), TLS provides a much simpler solution to the customer for connection of dispersed sites, than other forms of WAN, such as ATM or Frame Relay.
Trunk
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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)
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An economical best-effort class of service, without a guaranteed performance level.
UDP (User Datagram Protocol)
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A connectionless transport protocol without any guaranteed of packet sequence or delivery. It functions directly on top of IP.
UMTS (Universal Mobile Telecommunications System) is a 3G mobile technology using W-CDMA (Wideband Code Division Multiple Access) air interface. Developed to support voice and broadband services, such as video telephony and video conferencing, UMTS offers data rates of up to 2 Mbps, compared to the 64 kbps bandwidth supported by 2G networks.
V.22bis
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An extension of the V.22 standard, providing a data rate of up to 2400 bps at 600 baud.
VBR (Variable Bit Rate)
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Traffic containing bursts but centered around an average bandwidth. VBR, divided into real-time (RT-VBR) and non-realtime (NRT-VBR) traffic, requires the same service guarantees (that is delay, cell loss and timing) provided by CBR.
VBR-NRT (Variable Bit Rate Non Real Time)
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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)
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One of the two VBR service types for transmitting traffic that depends on timing and control information. It is suitable for carrying delay-sensitive traffic such as packetized video and audio.
VC (Virtual Channel)
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A connection established between end users, where packets are forwarded along the same path and bandwidth is not permanently allocated until it is used.
VCAT (Virtual Concatenation)
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An inverse multiplexing technique used to split SDH/SONET bandwidth into logical groups, which may be transported or routed independently.
VCC (Virtual Channel Connection)
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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.
VLAN (Virtual LAN)
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A network architecture which allows geographically distributed users to communicate as if they were on a single physical LAN by sharing a single broadcast and multicast domain.
VLAN-Aware
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A device that is doing the Layer 2 bridging according to the VLAN tag in addition to the standard bridging parameters. A VLAN-aware device will not strip or add any VLAN header.
A mechanism specified in IEEE standard 802.1ad (“Provider Bridges”) to extend the IEEE VLAN tagging standard (802.1Q). Also known as double VLAN tagging or Q-in-Q, VLAN stacking allows service providers to assign service VLAN tags (S-VLAN) to Ethernet frames that are already marked with customer VLAN tags (C-VLAN), resulting in hierarchical or “stacked” VLAN tags.
Newer voice compression algorithms try to model 64 kpbs 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 (CVS) can offer greater bandwidth savings, reduced network congestion and high quality voice transmissions.
Voice Digitization (Voice Encoding)
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The conversion of an analog voice signal into digital symbols for storage or for transmission (examples: ADPCM, CVSD, or PCM).
Voice Interface Variety
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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”.
Voice Switching
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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.
VoIP (Voice over IP)
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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)
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Set of virtual channels (VCs) between cross points, grouped together.
VPC (Virtual Path Connection)
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An end-to-end connection consisting of two or more virtual path (VP) links.
VPLS (Virtual Private LAN Service)
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An IETF (Internet Engineering Task Force) proposal for providing Layer 2 VPNs that can support the connection of multiple sites in a single bridged domain over a managed IP/MPLS network. Edge routers, inter-connected by a full mesh of MPLS label switched path (LSP) “tunnels” through which run multiple pseudowires, enable any-to-any connectivity on a per-VPLS basis.
To the customer, all services in a VPLS appear to be on the same Ethernet LAN, regardless of actual geographic location. This removes complexity from enterprise networks, and lets carriers scale the networks.
VPN (Virtual Private Network)
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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)
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A network that typically spans nationwide distances and usually utilizes public telephone networks.
WDM (Wave Division Multiplexing)
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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.
Wink
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On a telephone line, a signal that is comprised of an on-hook/offhook/ on-hook transition.
Wink Start
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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
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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)
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Control characters used for flow control, instructing a terminal to start transmission (X-ON) and end transmission (X-OFF).
xDSL modems use digital subscriber line (DSL) technology to transmit high-bandwidth information over existing copper phone lines to homes and businesses. xDSL modems support various data rates and ranges, depending on the type of DSL technology they incorporate. Common xDSL services include asymmetric DSL (ADSL, ADSL2, ADSL2+), symmetric DSL (SDSL), high-bitrate DSL (HDSL), symmetric high-bitrate DSL (SHDSL, SHDSL.bis) and very high bit-rate DSL (VDSL, VDSL2).
ITU-T standard Y.1731 is an Ethernet OAM (operations, administration and maintenance) standard for testing an Ethernet service and for monitoring its performance.
IEEE standard 1588-2008, previously known as pre-standard 1588v2, is the latest version of Precision Time Protocol (PTP) for frequency and time of day distribution over packet switched networks. It is based on timestamp information exchange in a master-slave hierarchy.
IEEE standard 1588v2, also known as 1588-2008, is the latest version of Precision Time Protocol (PTP) for frequency and time of day distribution over packet switched networks. It is based on timestamp information exchange in a master-slave hierarchy.
IEEE standard 802.1ag, also known as “Connectivity Fault Management (CFM)”, is an Ethernet OAM (operations, administration and maintenance) standard for testing an Ethernet service over any path, whether a single link or end-to-end.
IEEE standard 802.3-2005, also known as 802.3ah clause 57, is an Ethernet OAM (operations, administration and maintenance) standard for testing the status of a single Ethernet link within a network. It is also known as Ethernet Link OAM and EFM (Ethernet in the First Mile) OAM.
