| add/drop |
the process where a part of the information carried in a transmission system is demodulated (dropped) at an intermediate point and different information is entered (added) for subsequent transmission; |
| add/drop multiplexer (ADM) |
the process where a part of the information carried in a transmission system is demodulated (dropped) at an intermediate point and different information is entered (added) for subsequent transmission; |
| alarm indicating signal (AIS) |
a code sent downstream indicating an upstream failure has occurred; SONET defines the following four categories of AIS: line AIS, STS path AIS, VT path AIS, DS–n AIS |
| alternate mark inversion (AMI) |
the line-coding format in transmission systems where successive ones (marks) are alternatively inverted (sent with polarity opposite that of the preceding mark) |
| American National Standards Institute (ANSI) |
a membership organization that develops U.S. industry standards and coordinates U.S. participation in the International Standards Organization (ISO) |
| asynchronous |
a network where transmission system payloads are not synchronized, and each network terminal runs on its own clock |
| asynchronous transfer mode (ATM) |
a multiplexing or switching technique in which information is organized into fixed-length cells with each cell consisting of an identification header field and an information field; the transfer mode |
| attenuation |
reduction of signal magnitude or signal loss, usually expressed in decibels |
| bandwidth |
information-carrying capacity of a communication channel; analog bandwidth is the range of signal frequencies that can be transmitted by a communication channel or network |
| bidirectional |
operating in both directions; bidirectional APS allows protection switching to be initiated by either end of the line |
| bit 7 |
one binary digit; a pulse of data |
| bit error vs. block error |
error rate statistics play a key role in measuring the performance of a network; as errors increase, user payload (especially data) must be retransmitted; the end effect is creation of more (nonrevenu |
| bit interleaved parity (BIP) |
a parity check that groups all the bits in a block into units (such as byte), then performs a parity check for each bit position in a group |
| bit interleaved parity–8 (BIP–8) |
a method of error checking in SONET that allows a full set of performance statistics to be generated; for example, a BIP–8 creates eight-bit (one-byte) groups, then does a parity check for each o |
| bit stuffing |
in asynchronous systems, a technique used to synchronize asynchronous signals to a common rate before multiplexing |
| bit synchronous |
a way of mapping payload into VTs that synchronizes all inputs into the VTs, but does not capture any framing information or allow access to subrate channels carried in each input; for example, bit sy |
| bits per second (BPS) |
the number of bits passing a point every second; the transmission rate for digital information |
| broadband |
services requiring 50–600 Mbps transport capacity |
| broadband integrated services digital network (BISDN) |
a single ISDN that can handle voice, data, and eventually video services |
| byte interleaved |
bytes from each STS–1 are placed in sequence in a multiplexed or concatenated STS–N signal; for example, for an STS–3, the sequence of bytes from contributing STS–1s is 1, 2, 3, 1, |
| byte synchronous |
a way of mapping payload into VTs that synchronizes all inputs into the VTs, captures framing information, and allows access to subrate channels carried in each input; for example, byte synchronous ma |
| CCITT |
the technical organs of the United Nations specialized agency for telecommunications, now the International Telecommunications Union–Telecommunications; they function through international commit |
| channel |
the smallest subdivision of a circuit that provides a type of communication service; usually a path with only one direction |
| circuit |
a communications path or network; usually a pair of channels providing bidirectional communication |
| circuit switching |
basic switching process whereby a circuit between two users is opened on demand and maintained for their exclusive use for the duration of the transmission |
| coding violation (CV) |
a transmission error detected by the difference between the transmitted and the locally calculated bit-interleaved parity |
| concatenate |
the linking together of various data structures—for example, two bandwidths joined to form a single bandwidth |
| concatenated STS–Nc |
A signal in which the STS envelope capacities from the N STS–1s have been combined to carry an STS–Nc SPE; it is used to transport signals that do not fit into an STS–1 (52 Mbps) payloa |
| concatenated VT |
a VT x Nc that is composed of N x VTs combined; its payload is transported as a single entity rather than separate signals |
| cyclic redundancy check (CRC) |
a technique for using overhead bits to detect transmission errors |
| data communications channels |
OAM&P channels in SONET that enable communications between intelligent controllers and individual network nodes as well as internode communications |
| defect |
a limited interruption in the ability of an item to perform a required function |
| demultiplexing |
a process applied to a multiplex signal for recovering signals combined within it and for restoring the distinct individual channels of the signals |
| digital cross-connect system (DCS) |
an electronic cross-connect that has access to lower-rate channels in higher-rate multiplexed signals and can electronically rearrange (cross-connect) those channels |
| digital signal |
an electrical or optical signal that varies in discrete steps; electrical signals are coded as voltages; optical signals are coded as pulses of light |
| DSX–1 |
may refer to either a cross-connect for DS–1 rate signals or the signals cross-connected at an DSX–1 |
| DSX–3 |
may refer to either a cross-connect for DS–3 rate signals or the signals cross-connected at an DSX–1 |
| envelope capacity |
the number of bytes the payload envelope of a single frame can carry; the SONET STS payload envelope is the 783 bytes of the STS–1 frame available to carry a signal; each VT has an envelope capac |
| European Conference of Postal and Telecommunications Administrations (CEPT) |
the CEPT format defines the 2.048–Mbps European E1 signal made up of 32 voice-frequency channels |
| Exchange Carrier Standards Association (ECSA) |
an organization that specifies telecommunications standards for ANSI |
| failure |
a termination of the ability of an item to perform a required function; a failure is caused by the persistence of a defect |
| far end block error (FEBE) |
a message sent back upstream that receiving network element is detecting errors, usually a coding violation |
| far end receive failure (FERF) |
a signal to indicate to the transmit site that a failure has occurred at the receive site |
| fixed stuff |
a bit or byte whose function is reserved; fixed-stuff locations, sometimes called reserved locations, do not carry overhead or payload |
| floating mode |
a VT mode that allows the VT synchronous payload envelope to begin anywhere in the VT; pointers identify the starting location of the VT SPE; VT SPEs in different superframes may begin at different lo |
| framing |
method of distinguishing digital channels that have been multiplexed together |
| frequency |
the number of cycles of periodic activity that occur in a discrete amount of time |
| grooming |
consolidating or segregating traffic for efficiency |
| interleave |
the ability of SONET to mix together and transport different types of input signals in an efficient manner, thus allowing higher transmission rates |
| isochronous |
all devices in the network derive their timing signal directly or indirectly from the same primary reference clock |
| jitter |
short waveform variations caused by vibration, voltage fluctuations, control system instability, etc. |
| line |
one or more SONET sections, including network elements at each end, capable of accessing, generating, and processing line overhead |
| line alarm indication signal (AIS–L) |
AIS–L is generated by section terminating equipment (STE) upon the detection of a loss of signal or loss of frame defect, on an equipment failure; AIS–L maintains operation of the downstream |
| line overhead (LOH) |
18 bytes of overhead accessed, generated, and processed by line terminating equipment; this overhead supports functions such as locating the SPE in the frame, multiplexing or concatenating signals, pe |
| line remote defect indication (RDI–L) |
a signal returned to the transmitting line terminating equipment (LTE) upon detecting a loss of signal, loss of frame, or AIS–L defect; RDI–L was previously known as line FERF |
| line terminating equipment (LTE) |
network elements such as add/drop multiplexers or digital cross-connect systems that can access, generate, and process line overhead |
| locked mode |
a VT mode that fixes the starting location of the VT SPE; locked mode has less pointer processing than floating mode |
| map/demap |
a term for multiplexing, implying more visibility inside the resultant multiplexed bit stream than available with conventional asynchronous techniques |
| mapping |
the process of associating each bit transmitted by a service into the SONET payload structure that carries the service; for example, mapping a DS–1 service into a SONET VT1.5 associates each bit |
| mesochronous |
a network whereby all nodes are timed to a single clock source; thus, all timing is exactly the same (truly synchronous) |
| multiplex/demultiplex (MUX/DEMUX) |
multiplexing allows the transmission of two or more signals over a single channel; demultiplexing is the process of separating previously combined signals and restoring the distinct individual channel |
| multiplexer |
a device for combining several channels to be carried by one line or fiber |
| narrowband |
services requiring up to 1.5–Mbps transport capacity |
| operations system (OS) |
sophisticated applications software that overlooks the entire network |
| operations, administration, maintenance, and provisioning (OA&M or OAM&P) |
provides the facilities and personnel required to manage a network |
| orderwire |
a channel used by installers to expedite the provisioning of lines |
| OSI seven-layer model |
a standard architecture for data communications; layers define hardware and software required for multivendor information-processing equipment to be mutually compatible; the seven layers from lowest t |
| overhead |
extra bits in a digital stream used to carry information besides traffic signals; orderwire, for example, would be considered overhead information |
| packet switching |
an efficient method for breaking down and handling high-volume traffic in a network; a transmission technique that segments and routes information into discrete units; packet switching allows for effi |
| parity check |
an error-checking scheme that examines the number of transmitted bits in a block that hold the value one; for even parity, an overhead parity bit is set to either one or zero to make the total number |
| path |
a logical connection between a point where an STS or VT is multiplexed to the point where it is demultiplexed |
| path overhead (POH) |
overhead accessed, generated, and processed by path-terminating equipment; POH includes 9 bytes of STS POH and, when the frame is VT–structured, 5 bytes of VT POH |
| path terminating equipment (PTE) |
network elements, such as fiber-optic terminating systems, which can access, generate, and process POH |
| payload |
the portion of the SONET signal available to carry service signals such as DS–1 and DS–3; the contents of an STS SPE or VT SPE |
| payload pointer |
indicates the beginning of the synchronous payload envelope (SPE) |
| photon |
the basic unit of light transmission used to define the lowest (physical) layer in the OSI seven-layer model |
| plesiochronous |
a network with nodes timed by separate clock sources with almost the same timing |
| point of presence (POP) |
a point in the network where interexchange carrier facilities like DS–3 or OC–N meet with access facilities managed by telephone companies or other service providers |
| pointer |
a part of the SONET overhead that locates a floating payload structure; STS pointers locate the SPE; VT pointers locate floating mode VTs; all SONET frames use STS pointers; only floating mode VTs use |
| poll |
an individual control message from a central controller to an individual station on a multipoint network inviting that station to send |
| regenerator |
device that restores a degraded digital signal for continued transmission; also called a repeater |
| remote alarm indication (RAI) |
a code sent upstream in a DS–n network as a notification that a failure condition has been declared downstream; RAI signals were previously referred to as yellow signals |
| remote defect indication (RDI) |
a signal returned to the transmitting terminating equipment upon detecting a loss of signal, loss of frame, or AIS defect; RDI was previously known as FERF |
| remote error indication (REI) |
an indication returned to a transmitting node (source) that an errored block has been detected at the receiving node (sink); this indication was formerly known as far end block error (FEBE) |
| remote failure indication (RFI) |
a failure is a defect that persists beyond the maximum time allocated to the transmission system protection mechanisms; when this situation occurs, an RFI is sent to the far end and will initiate a pr |
| section |
the span between two SONET network elements capable of accessing, generating, and processing only SONET section overhead; this is the lowest layer of the SONET protocol stack with overhead |
| section overhead |
nine bytes of overhead accessed, generated, and processed by section terminating equipment; this overhead supports functions such as framing the signal and performance monitoring |
| section terminating equipment (STE) |
equipment that terminates the SONET section layer; STE interprets and modifies or creates the section overhead |
| slip |
an overflow (deletion) or underflow (repetition) of one frame of a signal in a receiving buffer |
| stratum |
level of clock source used to categorize accuracy |
| STS path remote defect indication (RDI–P) |
a signal returned to the transmitting STS path terminating equipment (PTE) upon detection of certain defects on the incoming path |
| STS path terminating equipment (PTE) |
equipment that terminates the SONET STS path layer; STS PTE interprets and modifies or creates the STS POH; an NE that contains STS PTE will also contain LTE and STE |
| STS POH |
nine evenly distributed POH bytes per 125 microseconds starting at the first byte of the STS SPE; STS POH provides for communication between the point of creation of an STS SPE and its point of disass |
| superframe |
any structure made of multiple frames; SONET recognizes superframes at the DS–1 level (D4 and extended superframe) and at the VT (500 µs STS superframes) |
| synchronous |
a network where transmission system payloads are synchronized to a master (network) clock and traced to a reference clock |
| synchronous digital hierarchy (SDH) |
the ITU–T–defined world standard of transmission whose base transmission level is 52 Mbps (STM–0) and is equivalent to SONET's STS–1 or OC–1 transmission rate; SDH standards w |
| synchronous optical network (SONET) |
a standard for optical transport that defines optical carrier levels and their electrically equivalent synchronous transport signals; SONET allows for a multivendor environment and positions the netwo |
| synchronous payload envelope (SPE) |
the major portion of the SONET frame format used to transport payload and STS POH; a SONET structure that carries the payload (service) in a SONET frame or VT; the STS SPE may begin anywhere in the fr |
| synchronous transfer module (STM) |
an element of the SDH transmission hierarchy; STM–1 is SDH's base-level transmission rate equal to 155 Mbps; higher rates of STM–4, STM–16, and STM–48 are also defined |
| synchronous transport signal level 1 (STS–1) |
the basic SONET building block signal transmitted at 51.84–Mbps data rate |
| T1X1 subcommittee |
a committee within ANSI that specifies SONET optical interface rates and formats |
| virtual tributary (VT) |
a signal designed for transport and switching of sub–STS–1 payloads |
| VT group |
a 9-row by 12-column structure (108 bytes) that carries one or more VTs of the same size; seven VT groups can be fitted into one STS–1 payload |
| VT path remote defect indication (RDI–V) |
a signal returned to the transmitting VT PTE upon detection of certain defects on the incoming path |
| VT path remote failure indication (RFI–V) |
a signal, applicable only to a VT1.5 with the byte-synchronous DS–1 mapping, that is returned to the transmitting VT PTE upon declaring certain failures; the RFI–V signal was previously know |
| VT path terminating equipment (VT PTE) |
equipment that terminates the SONET VT path layer; VT PTE interprets and modifies or creates the VT POH; an NE that contains VT PTE will also contain STS PTE, LTE, and STE POH |
| VT POH |
four evenly distributed POH bytes per VT SPE starting at the first byte of the VT SPE; VT POH provides for communication between the point of creation of an VT SPE and its point of disassembly |
| wander |
long-term variations in a waveform |
| wideband |
services requiring 1.5– to 50–Mbps transport capacity |