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A

The AAL enables engineers to adapt the Asynchronous Transfer Mode (ATM) layer to particular services. The AAL consists of two sublayers: the Convergence Sublayer (CS) and the Segmentation And Reassembly (SAR) sublayer.

Available Bit Rate. ABR is an Asynchronous Transfer Mode (ATM) service class that handles bursty LAN traffic, as well as data that is tolerant of delays and cell loss. ABR is a best-effort, managed service. Compare with CBR, UBR, VBR-NRT, VBR-RT.

ADSL is a standard that enables devices attached to twisted-pair copper wiring to transmit data at rates from 1.5 Mbps to 9 Mbps downstream, and 16 kbps to 640 Kbps upstream. ADSL devices can transmit data at distances of up to 18,000 feet

A code transmitted downstream in a digital network indicating that an upstream failure has been detected and alarmed if the upstream alarm has not been suppressed.

A line code that employs a ternary signal to convert binary digits, in which successive binary ones are represented by signal elements that are normally of alternative positive and negative polarity but equal in amplitude, and in which binary zeros are represented by signal elements that have zero amplitude

ANSI creates standards for networking and communications. It is the U.S. representative to the International Standards Organization (ISO). See also ISO

A standard 7-bit code that represents letters, numbers, punctuation marks, and special characters in the interchange of data among computing and communications equipment.

A high-speed transmission technology characterized by high bandwidth and low delay. It utilizes a packet switching and multiplexing technique which allocates bandwidth on demand.

An Administrative Unit (AU) is the information structure that provides adaptation between the higher order path layer and the Multiplex Section layer. The AU consists of a higher order Virtual Container information payload and an AU pointer. The AU pointer indicates the offset of the payload frame start relative to the Multiplex Section frame start. An AU-4 consists of a VC-4 plus an AU pointer. An AU-3 consists of a VC-3 plus an AU pointer.

An AUG consists of one or more byte-interleaved AUs. For an STM-1, an AUG can be either a single AU-4 or three byte-interleaved AU-3s

B

Background Block Errors (BBEs) are the number of Errored Blocks that were detected. A block is a set of consecutive bits associated with the path; each bit belongs to only one block. An Errored Block is a block in which one or more bits are in error.

The BER is the number of received bits with errors as a percentage of the total number of bits received. It is commonly expressed as a number to the power of 10.

BIP is an error-detection method that uses odd or even parity to verify the accuracy of a transmission.

C

In CAS, control signals are carried in the same channel as voice and data signal.

CBR is a Quality of Service (QoS) class defined by the Asynchronous Transfer Mode (ATM) forum for ATM networks. CBR is used for connections that depend on precise clocking to ensure undistorted delivery of bits. Compare with ABR, UBR, VBR-NRT, VBR-RT.

Path-level connections between input and output tributaries or specific ports within a single NE. Cross-connections are made in a consistent way even though there are various types of ports and various types of port protection. Cross-Connections are reconfigurable interconnections between tributaries of transmission interfaces.

The CCITT is a disbanded organization whose standards were moved to the UN-sanctioned International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) on March 1,1993.

CD is a signal sent from a modem to a host, indicating that the modem is online.

In an ATM configuration, CDV is a routing metric that measures the average variation in delay between one cell and the next, expressed in fractions of a second. Cell Delay Variation measurements enable the network to determine whether cells are arriving too quickly or too slowly.

A field in ATM cell header. The content of this field determines whether a cell can be preferentially deleted or not in the case of a transmission bottleneck.,

A codec is a device that encodes analog data into a digital signal for transmission over a digital medium.

CPE is equipment connected to the telephone network, and located at the customer’s site. The equipment can be owned or leased.

The CPU is the computer’s main processor.

CRC is an error-detection method that uses a mathematical divisor to check the integrity of the data in a transmitted packet.

CS is a sublayer of ATM Adaptation Layer (AAL). Its primary purpose is to encapsulate the data arriving from the higher layers and to prepare the data for segmentation.

D

The equipment that provides the signal conversion and coding between the data terminating equipment and the line. The DCE may be separate equipment or a part of the data terminating equipment.

The embedded overhead communication channel in the SDH line. This is used for end-to-end communication and maintenance. It carries alarm, control, and status information between network elements in an SDH network

DCS 1800 is a European mobile-telephone service based on European Telecommunications Standards Institute (ETSI) standards

DNS is a TCP/IP service for centralized management of address resolution. Using DNS, you can specify a symbolic name instead of an IP address. A symbolic name consists of a user name and a domain name in the format username@domain_name.

DSL is a technology that provides high bandwidth over conventional copper wiring.

The equipment that originates data for transmission and accepts transmitted data.

E

A 2.048-Mbps line that supports 32 64-kbps channels, each of which can transmit and receive data or digitized voice. The line uses framing and signaling to achieve synchronous and reliable transmission. The most common configurations for E1 lines are E1 PRI and unchannelized E1.

An amplifier that performs by having a light signal pass through a section of erbium- doped fiber and using the laser pump diode to amplify the signal.

A measure of equipment tolerance to external electromagnetic fields.

A performance monitoring parameter. ES "type A" is a second with exactly one error; ES "type B" is a second with more than one and less than the number of errors in a severely errored second for the given signal. ES by itself means the sum of the type A and type B ESs.

Static electrical energy potentially harmful to circuit packs and humans.

ETSI is a European organization established in 1988 to provide telecommunications standards

F

An indication returned to the transmitting node that an errored block has been detected at the receiving node. A block is a specified grouping of bits.

Forward Error Correction (FEC) increases the effective Optical Signal to Noise Ratio (OSNR) by producing an effective bit error rate that is considerably less than the actual bit error rate

An indication returned to a transmitting Network Element that the receiving Network Element has detected an incoming section failure. Also known as RDI (Remote Detect Indication).

G

GFC denotes the field in the ATM cell that controls the flow of traffic across the User-to-Network Interface (UNI) and into the network.

This term has been changed to Coordinated Universal Time(UTC).

GSM is the most commonly used digital wireless telephone technology. It performs analog-to-digital (A-D) conversion, compressing data and transmitting it on a channel with two other data streams, each in its own time slot..

H

Line code for 2 Mb/s transmission systems

HDLC is a synchronous, bit-oriented Data Link layer protocol for data transmission. Frame Relay is an example of an HDLC-based packet protocol. HDLC offers half- or full-duplex communications over circuit- or packet-switched networks, allows point-to-point and multipoint configurations, and provides transmission over both wires and wireless media.

HDSL is a technology that enables modems on either side of copper twisted-pair wires to transmit data at T1 or E1 speeds. HDSL provides 1.544 Mbps of bandwidth each way at distances of up to 12,000 feet. T1 data rates require two lines. E1 data rates require three lines.

In an Asynchronous Transfer Mode (ATM) cell, this field is provided in order to control and, to some extent, correct errors in the header data that may occur. The HEC is used to synchronize the receiver to the start of the cell. A CRC procedure is used for error detection (cyclic redundancy check). The CRC is based on division of the header field by the generator polynomial x⁸ + x² + x + 1.

Function that adapts a lower order Virtual Container to a higher order Virtual Container by processing the Tributary Unit pointer which indicates the phase of the lower order Virtual Container Path Overhead relative to the higher order Virtual Container Path Overhead and assembling/disassembling the complete higher order Virtual Container.

Function that terminates a higher order path by generating and adding the appropriate Virtual Container Path Overhead to the relevant container at the path source and removing the Virtual Container Path Overhead and reading it at the path sink.

HTTP enables Internet users to request, receive, and provide documents on the World Wide Web.

Hz is the measure of a signal’s frequency, calculated in cycles per second.

I

IDSL is a standard that enables devices attached to twisted-pair copper wiring to transmit data at rates of up to 128 Kbps. Compare with ADSL, HDSL, RADSL, SDSL, VDSL.

IP provides connectionless, non-guaranteed transmission of Transport-layer data packets. IP fragments packets, enabling them to take different paths across the WAN, and then reassembles them into the proper order at their destination.

Intermediate System to Intermediate System routing exchange protocol (OSI Network Layer Routing Protocol).

ISDN is a telecommunications architecture capable of sending voice, data, and video in digital form on a digital line. It can support bandwidth of up to 2 Mbps, and uses a single digital line for telephone, fax, computer, and video communications. ISDN supports circuit-switched and Frame Relay connections.

The ISO is an organization devoted to the definition of standards for national and international data communications. The U.S. representative to the ISO is the American National Standards Institute (ANSI). Companies whose products are ISO certified reflect a high quality of consistency and quality.

An ISP is a company that provides access to the Internet. By establishing Points of Presence (POPs) containing remote-access servers and a suite of user software packages, the ISP acts as a commercial onramp to the Internet. Providers typically charge a monthly fee, and supply technical support and advice to customers.

The ITU-T is the committee that replaced the Consultative Committee for International Telegraphy and Telephony (CCITT) on March 1, 1993. The ITU-T is responsible for a wide array of telecommunications and networking standards.

J

K

L

A LAN is a network in which two or more computers, located within a limited distance of one another, are connected in order to share files and resources. A PC-based LAN consists of a dedicated server running a network operating system and attached to several workstations. A host-based LAN consists of one or more hosts and terminals. Examples of LAN architectures are Ethernet, ARCnet, Fiber Distributed Data Interface (FDDI), and Token Ring.

An attenuating (signal-reducing) element used to keep optical output signal strength within desired limits.

An LED is a semiconductor light source that emits light in the optical frequency band or the infrared frequency band. A major light source for optical fiber transmission, LEDs are used with multimode optical fiber in applications that require a low-cost light source.

A failure to synchronize an incoming signal.

A failure to extract good data from a signal payload.

A failure to indication that a signal has "no transitions" (No incoming Signal) or the level is below a dB level

Function that adapts a PDH signal to a synchronous network by mapping the signal into or de-mapping the signal out of a synchronous container.

Function that provides for flexible assignment of lower order VCs in a higher order VC.

Function that terminates a lower order path by generating and adding the appropriate VC POH to the relevant container at the path source and removing the VC POH and reading it at the path sink.

M

Frame where electrical digital signals are terminated.

A MIB is a Simple Network Management Protocol (SNMP) database of information available to network-management programs. An agent creates a MIB. A network manager queries the MIB for information, and might create a MIB of its own. The MIB on the agent contains machine-specific information. The manager’s MIB has more general information.

Part of the Section Overhead. MSOH is accessible only at line terminals and multiplexers.

Provides capability for switching a signal from a working to a protection section.

A ring in which protection switching is accomplished by switching working traffic into protection time slots in the line going in the opposite direction around the ring.

Function that provides timing reference to the relevant component parts of the multiplex equipment and represents the SDH Network Element clock.

N

A node in a telecommunication network that supports network transport services and is directly manageable by a management system.

NNI is a standard that defines the interface between two Frame Relay switches located in a private or public network. NNI operation enables the TAOS unit to act as a Frame Relay switch communicating with another Frame Relay switch.

Network Service Access Point Address (used in the OSI network layer 3). An automatically assigned number that uniquely identifies a Network Element for the purposes of routing DCC messages.

O

The optical signal that results from an optical conversion of an STS signal; that is, OC-1 from STS-1 and OC-n from STS-n.

The optical channel carrier represents a tributary slot within the OTM-n

Optical Channel Carriers occupying fixed, defined positions in an OTM payload are termed an Optical Carrier Group.

The OCh is the information structure used to support the OCh trail

Frame to terminate optical fibers

The ODU is an information structure consisting of the information payload (OPU) and ODU related overhead

Multiplexed several signals on one fiber.

The OOS is the information structure used for transport of OTM non-associated overhead over the optical supervisory channel

The OPU is the information structure used to adapt client information for transport over an optical channel. It comprises client information together with any overhead needed to perform rate adaptation between the client signal rate and the OPU payload rate and other OPU overhead supporting the client signal transport

The physical carrier outside of the amplifier band that provides transport of the Optical Transport Module (OTM) Overhead Signal

Open Systems Interconnection Reference Model. The OSI Reference Model describes the layers of a network, the functions of each layer, and the way to connect communications devices on a LAN or WAN. Each layer provides services for the layer above it, and uses the services of the layer below it.

All the equipment/cables outside a exchange.

Measurement-equipment to measure the distance and attenuation of a fiber.

The OTH is a hierarchical set of digital transport structures, standardized for the transport of suitably adapted payloads over optical transmission networks

The OTM is the information structure that is transported across an Optical Network Node interface (ONNI).

Unit that translate an optical signal to a specific wavelength.

P

Private Branch Exchange. A PBX is an internal telephone network, such as one used in a large office, in which one incoming number directs calls to various extensions and from one office to another. The PBX routes calls both within an organization and to and from the outside telephone network. A PBX can be either analog or digital. Some digital PBX units can terminate digital as well as analog connections. PBX units work in conjunction with channel banks to distribute channels from the T1/E1 circuit for voice, video, fax, and data. In some cases, digital PBX units contain multiplexing components that distribute channels without a channel bank. See also PRI-to-T1 conversion.

PCMCIA is a standard that supports the devices on a credit-card-sized board.

A PDU is a packet created at any one of the OSI layers.

Measures the quality of service and identifies any degrading or marginally operating systems (before an alarm would be generated).

Overhead assigned to and transported with the payload until the payload is demultiplexed. It is used for functions that are necessary to transport the payload.

PPP 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 routers. PPP also allows direct dial-up access from a personal computer to a corporate LAN or Internet Service Provider (ISP). Using PPP ensures basic compatibility with non-Lucent devices. Both the dialing side and the answering side of the link must support PPP.

The main timing clock reference in SDH equipment.

Public Switched Telephone Network. A PTSN is a public circuit-switched network for telephone users. Typically, real-time voice information is sent over the PSTN. Circuit-switched technology provides every call with dedicated bandwidth, usually 64Kbps. End-to-end calls are established on the basis of a sequence of dialed digits, and the PSTN dedicates a physical path between callers. Because the telephone equipment establishes the call path at the beginning of the call, the path can change between calls, but never while a call is active.

A PTI is Field in a ATM cell header. This field indicates the type of data in the information field. A distinction is made between network and user information.

A PVC is a path maintained by two stations. The path can include a number of hops. The circuit is through the packet-switched network, but stays up all the time, regardless of whether or not data is on the line. Because the circuit is always up, there is no circuit setup time.

Q

R

RAM is computer memory that holds data temporarily.

An indication returned to a transmitting terminal that the receiving terminal has detected an incoming section failure. [Previously called far-end-receive failure (FERF).]

Function that generates the Regenerator Section Overhead (RSOH) in the transmit direction and terminates the RSOH in the receive direction.

S

SAR is a sublayer of the ATM Adaptation Layer (AAL). The SAR sublayer is responsible for fragmenting the packets passed from the Convergence Sublayer (CS) in cells.

A hierarchical set of digital transport structures, standardized for the transport of suitable adapted payloads over transmission networks.

This performance monitoring parameter is a second in which a signal failure occurs, or more than a preset amount of coding violations (dependent on the type of signal) occur.

Capacity added to either an AU-4 or assembly of AU-3s to create an STM-1. Contains always STM-1 framing and optionally maintenance and operational functions. SOH can be subdivided in MSOH (multiplex section overhead) and RSOH (regenerator section overhead).

Snchronization Supply Unit — Transit

The basic building block of SDH. A building block information structure that supports SDH section layer connections, where N represents a multiple of 155.52 Mb/s. Normally N=0,1, 4, 16, 64 or 256.

The basic logical building block signal of SONET with a rate of 51.840 Mb/s for an STS-1 signal and a rate of n times 51.840 Mb/s for an STS-n signal.

An SVC is a path over a packet-switched network. It appears to be a dedicated circuit, but the connection stays up only as long as needed.

T

TCP/IP is a family of protocols that defines the format of data packets sent across a network, and is the communications standard for data transmission between different platforms.

A technique for transmitting a number of separate data, voice, and/or video signals simultaneously over one communications medium by interleaving a portion of each signal one after another.

An information structure which provides adaptation between the lower order path layer and the higher path layer. Consists of a VC-n plus a tributary unit pointer TU PTR.

U

In performance monitoring, the count of seconds in which a signal is declared failed or in which 10 consecutively severely errored seconds (SES) occurred, until the time when 10 consecutive non-SES occur.

UBR is an Asynchronous Transfer Mode (ATM) service class that handles bursty LAN traffic, as well as data that is tolerant of delays and cell loss. UBR is a best-effort service that does not specify bit-rate or traffic values, and offers no Quality of Service (QoS) guarantees.

Allows connected computer equipment to gracefully shutdown, therefore preventing damage in case of a power fail and to absorb dips in the supplied power.

Formerly known as Greenwich Mean Time (GMT), UTC is the time at the Greenwich observatory, used as a reference point for calculating standard time values.

V

Container with path overhead.

A VCI is a field in the Asynchronous Transfer Mode (ATM) cell header. The VCI identifies a virtual channel between two endpoints. An ATM switch uses the Virtual Path Identifier (VPI) and VCI values when routing packets.

In ATM, a VP is a group of Virtual Channels (VCs) carried between two points. It provides a way to bundle traffic headed in the same direction

Virtual Path Identifier. A VPI is a field in the Asynchronous Transfer Mode (ATM) cell header. The VPI identifies a Virtual Path (VP) to which the cell belongs.

W

A WAN is an internet of devices, generally consisting of several networks distributed over a wide geographic distance, connected by telephone lines, and using different hardware platforms and protocol encapsulation.

A means of increasing the information-carrying capacity of an optical fiber by simultaneously transmitting signals at different wavelengths.

X

Y

Z