Glossary

Table Of Contents

Glossary

A
AAL5	ATM adaptation layer 5. One of four AALs recommended by the ITU-T.
ABR	available bit rate. A class of service defined for ATM connections by the ATM Forum. Devices using ABR are guaranteed no more than a certain rate of throughput. This rate dynamically changes and the current value is relayed to the sending device by resource management (RM) cells.
ACR	allowed cell rate. In ABR connections, the current rate in cells per second at which a source is allowed to send.
AIS	alarm indication signal. In a T1 transmission, an all-ones signal is transmitted in lieu of the normal signal. This signal maintains transmission continuity, and indicates to the receiving terminal that a transmission fault is located either at, or upstream from, the transmitting terminal.
alarm indication signal	See AIS.
allowed cell rate	See ACR.
APS	automatic protection system. SONET switching mechanism that routes traffic from working lines to protect them in case of a line card failure or fiber cut.
ASN1	abstract syntax notation one. OSI language for describing data types independent of particular computer structures and representation techniques. Described by ISO International Standard 8824.
AutoRoute	Feature that automatically routes connections once the endpoints are specified. AutoRoute is standard with the BPX and IGX switches.
available bit rate	See ABR.

B
B3ZS	bipolar with three zero suppression. Protocol for T3 lines that converts a channel word with three consecutive zeros into a code which at the far end is converted back to three zeros.
backward explicit congestion notification	See BECN.
Bc	committed burst. Maximum amount of data (in bits) that a Frame Relay internetwork is committed to accept and transmit at the committed information rate (CIR).
Be	excess burst. Number of bits that a Frame Relay internetwork attempts to transmit after Bc is accommodated. Be data is delivered with a lower probability than Bc data because Be data can be marked as DE by the network.
BECN	backward explicit congestion notification. Bit set by a Frame Relay network in frames traveling in the opposite direction of frames encountering a congested path. DTE receiving frames with the BECN bit set can request that higher-level protocols take flow control action as appropriate.
BIP	bit interleaved parity. In ATM, a method used to monitor errors on a link. A check bit or word is sent in the link overhead for the previous block or frame. Bit errors in the payload can then be detected and reported as maintenance information.

C
C-bit parity code violation	See CCV.
CAC	connection admission control. Set of actions taken by each ATM switch during connection setup to determine whether the requested QoS of the connection violates the QoS guarantees for established connections. CAC is also used when routing a connection request through an ATM network.
CBR	constant bit rate. ATM connection type for constant bit rate traffic such as voice or synchronized data requiring a low variation in delay. See also VBR and ABR.
CBS	committed burst size. The maximum amount of data (in bits) that a Frame Relay internetwork is committed to accept and transmit at the committed information rate.
CCV	C-bit parity code violation. Error checking process for DS3 lines. The C-bits in the M-subframes carry parity bit error notification.
CDV	cell delay variation. Component of cell transfer delay that is induced by buffering and cell scheduling. CDV is a QoS delay parameter associated with CBR and VBR service. See also CBR and VBR.
cell delay variation	See CDV.
cell loss priority	See CLP.
CIR	committed information rate. Guaranteed traffic rate. This rate is guaranteed as long as the rate of input is less that the CIR.
CLP	cell loss priority. Field in the ATM cell header that determines the probability of a cell being dropped if the network becomes congested. Cells with CLP equal to 0 are insured traffic that is unlikely to be dropped. Cells with CLP equal to 1 are best-effort traffic that might be dropped in congested conditions in order to free up resources to handle insured traffic.
committed burst size	See CBS.
committed information rate	See CIR.
connection admission control	See CAC.
constant bit rate	See CBR.
CPE	customer premises equipment. Terminating equipment that is connected to the telephone company network and includes terminals, telephones, and modems.
CRC	cyclic redundancy check. Method of error checking that detects errors in a block of data. Unlike parity checks, the CRC can detect multiple data errors within the block, and thus derive an error rate.
cyclic redundancy check	See CRC.

D
DE	discard eligible. ATM cells that have their CLP bit set to 1. If the network is congested, tagged traffic can be dropped to ensure delivery of higher-priority traffic.
discard eligible	See DE.
DLCI	data-link connection identifier. Field in a Frame Relay data packet that identifies the destination for the data.

E
EA	extended address. Each octet in the Frame Relay frame header ends with an EA bit. The EA bit is 1 in the last octet of the header and 0 in all other octets.
EFCI	explicit forward congestion indication. In ATM, one of the congestion feedback modes allowed by ABR service. A network element in an impending congestion state or in a congested state sets the EFCI. The destination end-system implements a protocol that lowers the cell rate of the connection based on the value of the EFCI.
EFCN	See EFCI.
egress	Traffic that travels away from the bus to the CPE.
end of frame	See EOF.
EOF	end of frame. Last cell that encapsulates the frame. Some data transport space is wasted in the last cell.
errored second	A one-second interval during which one or more errors are detected. Errored seconds are performance meter parameters that are measured on a per-channel basis.
extended address	See EA.
explicit forward congestion indicator	See EFCI.
explicit forward congestion notification	See EFCI.
extended Local Management Interface	See XLMI.
extended permanent virtual circuit	See XPVC.

F
far end bit error	See FEBE.
far end receive failure	See FERF.
FastPacket	See FP.
FCS	frame check sequence. Extra characters added to a frame for error control purposes. Used in Frame Relay and other data link layer protocols.
FEBE	far end bit error. Error condition on a DS3 line resulting from parity-bit errors received by the network equipment. The FEBE alarm notification is sent by a device that is receiving parity bits in error.
FECN	forward explicit congestion notification. Bit set by a Frame Relay network to inform the DTE receiving the frame that the path experiences congestion from the source to destination. DTE receiving frames with the FECN bit set can request that higher-level protocols take flow-control action as appropriate.
FERF	far end receive failure. OAM message sent by an ATM network device in response to an AIS message. Similar to a yellow alarm, but at the cell level, rather than the physical level. See also AIS.
fixed round trip time	See FRTT.
forward explicit congestion notification	See FECN.
FP	FastPacket. Cisco WAN cell relay technology that uses fixed-size 24-byte length cells to carry narrowband traffic on the IPX and IGX switch platforms.
frame check sequence	See FCS.
FRTT	fixed round trip time. Estimate of the amount of time for an resource management (RM) cell to be transmitted from the source, to the destination, and back.

G
generic flow control	See GFC.
GFC	generic flow control. A four bit field in the ATM UNI cell header that provides local standardized flow control. In most cases flow control is not implemented, and the GFC is all 0 bits.

H
header error control	See HEC.
HEC	header error control. Algorithm for checking and correcting an error in an ATM cell. Using the fifth octet in the ATM cell header, ATM equipment checks for an error and corrects the contents of the header. The check character is calculated using a CRC algorithm allowing a single bit error in the header to be corrected or multiple errors to be detected.

I
ICP	IMA control protocol. Cells that determine the differential delay between the links in the IMA group. ICP cells are sent on each link once per IMA frame.
ILMI	interim local management interface. Specification developed by the ATM Forum for incorporating network management capabilities into the ATM UNI.
IMA	inverse multiplexing over ATM. MGX card module that supports T3 or E3 inverse multiplexing on up to 8 T1 or E1 lines.
IMA control protocol	See ICP.
ingress	Traffic that travels toward the bus from the CPE.

L
LCN	logical channel number. A 12-bit field in an X.25 PLP header that identifies an X.25 virtual circuit. Allows DCE to determine how to route a packet through the X.25 network.
LCV	line code violation. Occurrence of a bipolar violation event.
line code violation	See LCV.
LMI	Local Management Interface. Protocol and procedures for control of IPX Frame Relay connections. Used for configuration, flow control, and maintenance of these connections.
LOC	loss of cell delineation. In ATM, the terminating equipment receives seven consecutive header error control headers.
Local Management Interface	See LMI.
LOF	loss of frame. SONET port status indicator that activates when an LOF defect occurs and does not clear for an interval of time equal to the alarm integration period, typically 2.5 seconds.
logical channel number	See LCN.
LOP	loss of pointer. Failure state in the SONET signal where a receiving network cannot identify or lock on the pointer value of the header one and two bytes to show the location of synchronous payload envelope (SPE).
LOS	loss of signal. Loss of signal occurs when consecutive zeros are detected on an incoming signal.
loss of cell delineation	See LOC.
loss of frame	See LOF.
loss of pointer	See LOP.
loss of signal	See LOS.

N
network interworking	See NIW.
NIW	network interworking. Connects two Frame Relay devices over an ATM network. This method uses a tunneling protocol to cut through the ATM network. The header, payload, and trailer of the frame remain together when passing through the network.
NNI	network-to-network interface. Protocol on a Frame Relay port that serves as a bidirectional interface between a local Cisco WAN switching network and a separate network.

O
OAM cell	operation, administration, and maintenance cell. ATM Forum specification for cells used to monitor virtual circuits. OAM cells provide a virtual circuit-level loopback in which a router responds to the cells, demonstrating that the circuit is up, and the router is operational.
OOF	out of frame. Framing bits that cannot be identified.
out of frame	See OOF.

P
parity code violation	See PCV.
PCR	peak cell rate. Maximum cell rate at which the source can transmit.
PCV	parity code violation. General term used for an illegal parity bit. The parity bits validate the data and detect transmission problems in the cell.
PDU	protocol data unit. Unit containing both data and control information that is passed through the layers of the OSI model.
peak cell rate	See PCR.
permanent virtual circuit	See PVC.
PLCP	physical layer convergence protocol. Protocol defined for use with Switched Megabit Data Service. Used on DS3 ATM trunks in the BPX switch.
PNNI	Private Network-to-Network Interface. A routing protocol used between ATM switches in an ATM network. This protocol allows switches to exchange information about network topology.
protocol data unit	See PDU.
PVC	permanent virtual circuit. Virtual circuit that is permanently established. PVCs save bandwidth associated with circuit establishment and tear down in situations where certain virtual circuits must exist all the time. In ATM terminology, called a permanent virtual connection.

Q
queue	Ordered list of elements waiting to be processed.

R
RAI	remote alarm indicator. Alarm indicating that the remote end of the facility is not receiving a signal. In order for a device to declare a remote alarm, it must be receiving the alarm signal from the remote equipment.
RDI	remote defect identification. In ATM, loss of signal or cell synchronization is detected at the physical layer. RDI cells are used to report a VPC/VCC failure. RDI cells are sent upstream by a VPC/VCC endpoint to notify the source VPC/VCC endpoint of the downstream failure.
remote alarm indicator	See RAI.
remote defect identification	See RDI.
remote failure indication	See RFI.
resource management cell	See RM.
RFI	remote failure indication. A SONET port status indicator that activates when an line remote failure indication (LRFI) defect occurs and does not clear throughout the alarm integration period, which is typically 2.5 seconds. An LRFI defect occurs when bits 6, 7, and 8 of the byte are 110 for three consecutive frames. This occurrence begins the alarm integration period. If this period elapses without the detection of three consecutive frames in which bits 6, 7, and 8 show any pattern other than 110, the LRFI indicator activates. The LRFI indicator clears when a line alarm indication signal defect does not occur for a time interval equal to the alarm deactivation period (typically10 seconds).
RM	resource management cell. In ATM, this cell travels to the destination and back to test for congestion.

S
SAR	segmentation and reassembly. Sublayer in ATM that segments the streams into cells, and passes them to the ATM layer. Conversely, this sublayer reassembles the cells from the ATM layer back into streams.
SCR	sustainable cell rate. Rate above which incoming cells are either tagged or discarded.
SEFS	severely errored framing seconds. Performance meter parameter that counts out-of-frame seconds.
segmentation and reassembly	See SAR.
service interworking	See SIW.
SES	severely errored seconds. Seconds during which the bit error ratio is greater than a specified limit and transmission performance is significantly degraded. A performance monitoring parameter is measured on a per-channel basis.
severely errored framing seconds	See SEFS.
severely errored seconds	See SES.
simple resource coordination protocol	See SRCP.
SIW	service interworking. Connects Frame Relay networks over an ATM backbone.
SRCP	simple resource coordination protocol. Mechanism for communicating between a VISM card and the call agent.
sustainable cell rate	See SCR.
SVC	switched virtual circuit. Virtual circuit that is dynamically established on demand and is torn down when transmission is complete. SVCs are used when data transmission is sporadic. SVC is called a switched virtual connection in ATM terminology.
switched virtual circuit	See SVC.

T
TBE	transient buffer exposure. Number of cells that a source can transmit before receiving feedback from the network via a returned RM cell.
timestamp	Field in certain Fast Packet formats that indicates the amount of time the packet has spent waiting in queues during the transmission between its source and destination nodes. Used to control the delay experienced by the packet.
transient buffer exposure	See TBE.
trap	Message that indicates a significant event has occurred, for example a power supply has failed, a major alarm has occurred, and so forth.

U
UAS	unavailable seconds. At least 10 contiguous severely errored seconds.
unavailable seconds	See UAS.
UNI	user-to-network interface. Used for ATM connection to CPE. See also NNI.
UPC	usage parameter control. General procedure for controlling the rate of user data applied to an ATM network.
usage parameter control	See UPC.

V
variable bit rate	See VBR.
VBR	variable bit rate. Connection type for variable bit rate traffic, for example bursty data. See also CBR and ABR.
VC	virtual circuit. Circuit that acts as an individual transmission path, but is shared with other circuits over a single transmission path. See also PVC.
VCI	virtual channel identifier. A 16-bit field in the header of an ATM cell. The VCI and VPI are used to identify the next destination of a cell as it passes through a series of ATM switches. The function of the VCI is similar to that of the DLCI in Frame Relay. See also VPI.
VD	virtual destination. See VSVD.
virtual channel identifier	See VCI.
virtual path	See VP.
virtual path identifier	See VPI.
virtual switch interface	See VSI.
VP	virtual path. Logical grouping of virtual circuits that connect two sites.
VPI	virtual path identifier. Eight bit field in the header of an ATM cell. The VPI and VCI are used to identify the next destination of a cell as it passes through a series of ATM switches. The function of the VPI is similar to that of the DLCI in Frame Relay. See also VCI.
VS	virtual source. See VSVD.
VSI	virtual switch interface. Interface allows controllers to set-up and tear down virtual circuit converters through the BPX independent of the control protocol (PNNI, MPLS, SS7) and location of the controller. The VSI allows multiple controllers to control the BPX, and the controllers are optimized for the service to be delivered. The VSI manages the resource allocation so the controllers are independent and each service receives the QoS required.
VSVD	virtual source/virtual destination. ATM Forum standard-based closed-loop congestion prevention for ABR traffic.

X
XLMI	extended Local Management Interface. Interface that allows AutoRoute (AR) networks and Private Network-to-Network Interface (PNNI) networks to communicate.
XPVC	extended permanent virtual circuit. An end-to-end connection that spans across multiple networks supporting AR and PNNI protocols