glossary

Symbols

1+1 APS

See APS.

A

AAA

Authentication, authorization, and accounting.

Access list

List kept by a router to control access to or from the router for a number of services. For example, access lists can be used to prevent packets with a certain IP address from leaving a particular interface on the router.

Alarm

A status condition that shows that a module or port is experiencing an abnormal operating condition. See also Critical alarm, Major alarm, and Minor alarm.

APS

Automatic protection switching. A SONET switching mechanism that achieves network resiliency by automatically switching from a primary circuit to a secondary circuit. This switching process occurs if the primary circuit fails or if the error rate on the primary line exceeds a set threshold. The Cisco 10000 ESR supports 1+1 APS, which provides permanent electrical bridging to the service and protection equipment, placed at both ends of the circuit.

Authentication

In security, the verification of the identity of a person or process.

Automatic protection switching

See APS.

B

Bellcore

Bell Communications Research. An organization that performs research and development on behalf of the Regional Bell Operating Companies (RBOCs).

BER

Bit error rate. The ratio of received bits that contain errors to all received bits.

BGP

Border Gateway Protocol. An interdomain routing protocol that replaces EGP. BGP exchanges connection information with other BGP systems. It is defined by RFC 1163.

Bit error rate

See BER.

Border Gateway Protocol

See BGP.

C

CAR

Committed Access Rate. A QoS feature that classifies packets based on such things as access lists, a MAC address, and IP precedence. It measures traffic rates and can be configured to take actions such as dropping packets or changing the ToS value.

C-bit parity

A modification of the M23 framing method for DS3 which frees the C bits for additional uses. See also M23.

CB-WRED

Class-based weighted random early detection. Class-based WRED applies WRED to packets in different traffic classes. See also WRED.

Channel

Communication path. Multiple channels can be multiplexed over a single cable in certain environments.

Channel service unit

See CSU.

Cisco IOS

Cisco system software that provides common functionality, scalability, and security for Cisco products. Cisco IOS allows centralized, integrated, and automated installation and management of internetworks, while ensuring support for a wide variety of protocols, media, services, and platforms.

Clear channel DS3

A framed DS3 signal that is not multiplexed from 28 DS1 signals. Sometimes referred to as unchannelized DS3.

CLI

Command line interface. Interface that allows the user to interact with the operating system by entering commands and optional arguments at the command prompt.

Command Line Interface

See CLI.

Committed access rate

See CAR.

CRC

Cyclic redundancy check. Error-checking technique in which the frame recipient calculates a remainder by dividing frame contents by a prime binary divisor and then compares the calculated remainder to a value stored in the frame by the sending node.

Critical alarm

An alarm condition that might affect most or all subscribers that connect to the reporting node. To obtain more information about a problem, use the
show facility-alarm status command. See also Major alarm and Minor alarm.

CSU

Channel service unit. Digital interface device that connects end-user equipment to the local digital telephone loop. Often referred to, together with DSU, as CSU/DSU. See also DSU.

Cyclic redundancy check

See CRC.

D

Data service unit

See DSU.

Differentiated service code point

See DSCP.

DS0

Digital signal level 0. Framing specification used in transmitting digital signals over a single channel at 64 kbps on a T1 facility. Compare with DS1 and DS3.

DS1

Digital signal level 1. Framing specification used in transmitting digital signals at 1.544 Mbps on a T1 facility (in the United States) or at 2.108 Mbps on an E1 facility (in Europe). Compare with DS0 and DS3.

DS3

Digital signal level 3. Framing specification used for transmitting digital signals at 44.736 Mbps on a T3 facility. Compare with DS0 and DS1.

DSCP

Differentiated service code point. Specifies a precedence value for handling packets belonging to the specified class.

DSU

Data service unit. Device used in digital transmission that adapts the physical interface on a DTE device to a transmission facility such as T1 or E1. The DSU is also responsible for such functions as signal timing. Often used with CSU, as in CSU/DSU. See also CSU.

E

Edge Services Router

See ESR.

ESF

Extended superframe. Framing type used on T1 circuits that consists of 24 frames of 192 bits each, with the 193rd bit providing timing and other functions. ESF is an enhanced version of SF. See also SF.

ESR

Edge Services Router. A router that aggregates traffic from thousands of low- and medium-bandwidth subscriber connections and routes it on a few high-bandwidth connections to the Internet core.

Ethernet

Baseband LAN specification. Ethernet networks use CSMA/CD and run over a variety of cable types at 10 Mbps, 100 Mbps, or 1000 Mbps. Ethernet is similar to the IEEE 802.3 series of standards. See also Fast Ethernet, Gigabit Ethernet.

Extended Superframe Format

See ESF.

F

Facility data link

See FDL.

Fast Ethernet

Any of a number of 100 Mbps Ethernet specifications. Fast Ethernet offers a speed increase 10 times that of the 10BaseT Ethernet specification, while preserving qualities such as frame format, MAC mechanisms, and MTU. Existing 10BaseT applications and network management tools can be used on Fast Ethernet networks. The Fast Ethernet specification is based on an extension to the IEEE 802.3 specification. Compare with Ethernet and Gigabit Ethernet.

FDL

Facility data link. Embedded communications channel in ESF DS1 framing. Used to convey both bit-oriented and message-oriented signals.

Flash memory

Nonvolatile storage that can be electrically erased and reprogrammed so that software images can be stored, booted, and rewritten as necessary. Flash memory was developed by Intel and is licensed to other semiconductor companies.

Frame Relay

Industry-standard, switched data link layer protocol that handles multiple virtual circuits using HDLC encapsulation between connected devices. Frame Relay is more efficient than X.25, the protocol for which it is generally considered a replacement.

G

Gigabit Ethernet

Gigabit Ethernet. Ethernet running at a transmission speed of 1 billion bits per second.

H

HDLC

High Level Data Link Control. Bit-oriented synchronous data link layer protocol developed by ISO. Derived from SDLC, HDLC specifies a data encapsulation method on synchronous serial links using frame characters and checksums.

High Level Data Link Control

See HDLC.

I

IOS

Internet Operating System. See Cisco IOS.

IP

Internet Protocol. Network layer protocol in the TCP/IP stack offering a connectionless internetwork service. IP provides features for addressing, type-of-service specification, fragmentation and reassembly, and security. Defined in RFC 791.

K

Keepalive message

Message sent by one network device to inform another network device that the virtual circuit between the two is still active.

L

LAIS

Line Alarm Indication Signal. A SONET port status indicator that activates when an LAIS defect occurs and does not clear throughout the alarm integration period, which is typically 2.5 seconds. An LAIS defect occurs when bits 6, 7, and 8 of the K2 byte are 111 for three consecutive frames. This occurrence begins the alarm integration period. If this period elapses without the detection of three consecutive frames in which K2 bits 6, 7, and 8 show any pattern other than 111, the LAIS indicator activates. The LAIS indicator clears when an LAIS defect does not occur for a time interval equal to the alarm deactivation period (typically 10 seconds).

Line card

Any I/O card that can be inserted in a modular chassis.

LOF

Loss of Frame. A 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, which is typically 2.5 seconds. An LOF defect occurs when an out-of-frame (OOF) condition occurs and does not clear for more than 3 microseconds (ms). This occurrence begins the alarm integration period. (OOF occurs when four consecutive frames do not contain a valid frame word. OOF clears when two valid consecutive frames are detected.) The LOF indicator clears when an LOF defect is not detected for a time interval that is equal to the alarm deactivation period (typically 10 seconds).

Loopback test

A test in which signals are sent and then directed back toward their source from some point along the communications path. Loopback tests are often used to check network interface usability.

LOS

Loss of signal. A SONET port status indicator that activates when an LOS defect occurs and does not clear throughout the alarm integration period, which is typically 2.5 seconds. An LOS defect occurs when the OC-3 port receives all zeros for 20 microseconds (+.3 ms). This occurrence begins the alarm integration period. If this period elapses without the detection of two consecutive frames in which there are no 20-ms periods of signal loss, the LOS indicator activates. The LOS indicator clears when an LOS defect is not detected for an interval equal to the alarm deactivation period (typically 10 seconds).

M

M13

Generic term for equipment that multiplexes DS1s into DS3s. Sometimes used to describe a specific DS3 multiplex format. Some standards use this term to describe a synchronous multiplexing format also know as SYNTRAN. In many cases, however, M13 does not refer to the SYNTRAN format; it refers instead to the format also known as M23.

M23

A method of multiplexing four DS1 signals into a DS2 signal, then multiplexing seven DS2 signals into a DS3 signal.

MAC

Media Access Control. The lower of the two sublayers of the data link layer defined by the IEEE. The MAC sublayer handles access to shared media.

MAC address

Standardized data link layer address that is required for each port or device that connects to a LAN. Other devices in the network use these addresses to locate specific ports in the network, and to create and update routing tables and data structures. MAC addresses are 6 bytes long and are controlled by the IEEE. Also known as a hardware address, MAC-layer address, or physical address.

Maintenance data link

See MDL.

Major alarm

One of a group of alarm conditions that are considered the second most severe of all reportable alarms. Major alarms affect several subscribers who connect to the reporting node. You can use the show facility-alarm status IOS command to obtain more information about the problem. See also Critical alarm and Minor alarm.

Maximum transmission unit

See MTU.

MDL

Maintenance data link. Embedded communications channel in C-bit parity DS3 framing. Used to convey message-oriented signals.

Minor alarm

One of a group of alarm conditions that are considered the third most severe of all reportable alarms. Minor alarms affect a single or small number of subscribers who connect to the reporting node. You can use the show facility-alarm status IOS command to obtain more information about the problem. See also Critical alarm and Major alarm.

MLP

Multilink Point-to-Point Protocol. A method of splitting, recombining, and sequencing datagrams across multiple logical data links.

MTU

Maximum transmission unit. Maximum packet size, in bytes, that a particular interface can handle.

Multilink Point-to-Point

See MLP.

N

NEBS

Network Equipment Building Systems. The Bellcore requirement for equipment deployed in a central office environment. Covers spatial and thermal requirements as well as requirements for hardware, crafts person interface, fire resistance, handling and transportation, earthquake and vibration, airborne contaminants, grounding, acoustical noise, illumination, EMC, and ESD.

Network Equipment Building Systems

See NEBS.

Nonvolatile RAM

See NVRAM.

NVRAM

Nonvolatile RAM. RAM that retains its contents when a unit is powered off.

P

Packet

Logical grouping of information that includes a header containing control information and (usually) user data. Packets are most often used to refer to network layer units of data. The terms datagram, frame, message, and segment are also used to describe logical information groupings at various layers of the OSI reference model and in various technology circles.

Packet over SONET

See POS.

PCMCIA Flash disk card

A portable (credit-card size), nonvolatile storage device. PCMCIA Flash disk cards use Flash technology to store data. PCMCIA stands for Personal Computer Memory Card International Association, which sets the standard for this technology. Also called PC card.

Performance Routing Engine

See PRE.

Point-to-Point Protocol

See PPP.

POS

Packet Over SONET. A high-speed means of transmitting data over a SONET fiber-optic transmission system through a direct fiber connection to a data switch or router. POS is a point-to-point dedicated leased-line approach intended purely for high-speed data applications. POS allows a user organization to pass data in its native format, without the addition of any significant level of overhead in the form of signaling and control information.

PPP

Point-to-Point Protocol. Provides router-to-router and host-to-network connections over synchronous and asynchronous circuits.

PRE

Performance routing engine. The central routing unit for the Cisco 10000 ESR. The PRE performs all Layer 2 and Layer 3 packet manipulation related to routing and forwarding through the Cisco 10000 ESR. Dual PREs can be configured in a single chassis for redundancy.

Q

QoS

Quality of service. A measure of performance for a transmission system that reflects its transmission quality and service availability.

QoS Policy Propagation on BGP

See QPPB.

QPPB

QoS Policy Propagation on BGP. A feature involving the classification of packets by IP precedence based on BGP community lists, BGP autonomous system paths, and access lists. After a packet is classified, other quality of service features such as committed access rate (CAR) and weighted random early detection (WRED) can specify and enforce policies to fit a business model.

Quality of Service

See QoS.

R

RAM

Random-access memory. Volatile memory that can be read and written by a microprocessor.

Random Access Memory

See RAM.

Redundancy

In internetworking, the duplication of devices, services, or connections so that, in the event of a failure, the redundant devices, services, or connections can perform the work of those that failed.

RMON

Remote Monitoring. MIB agent specification described in RFC 1271 that defines functions for the remote monitoring of networked devices. The RMON specification provides numerous monitoring, problem detection, and reporting capabilities.

ROM

Read only memory. Nonvolatile memory that can be read, but not written, by the microprocessor.

S

SDH

Synchronous Digital Hierarchy. European standard that defines a set of rate and format standards that are transmitted using optical signals over fiber. SDH is similar to SONET, with a basic rate of 155.52 Mbps, designated as STM-1. See also SONET and STM-1.

SF

Super frame. Common framing type used on T1 circuits. SF consists of 12 frames of 192 bits each, with the 193rd bit providing error checking and other functions. SF has been superseded by ESF, but is still widely used. Also called D4 framing. See also ESF.

Simple Network Management Protocol

See SNMP.

SNMP

Simple Network Management Protocol. Network management protocol used almost exclusively in TCP/IP networks. SNMP provides a means to monitor and control network devices, and to manage configurations, statistics collection, performance, and security. See also SNMP2.

SNMP2

SNMP Version 2. Version 2 of the network management protocol. SNMP2 supports centralized as well as distributed network management strategies, and includes improvements in the SMI, protocol operations, management architecture, and security. See also SNMP.

SONET

Synchronous Optical Network. High-speed synchronous network specification developed by Bellcore and designed to run on optical fiber. STS-1 is the basic building block of SONET. It was approved as an international standard in 1988. See also SDH and STS-1.

SPE

Synchronous Payload Envelope. The major portion of the SONET frame format used to carry the STS-1 signal; it is divided into an information payload section and a transport overhead system. SPE is used to address three payload structures: direct to STS-1 line rate muliplexing; asynchronous DS3 multiplexing; and synchronous DS3 multiplexing.

STM-1

Synchronous Transport Module level 1. Basic building block signal of SDH, operating at 155.52 Mbps. Faster SDH rates are defined as STS-n, where n is a multiple of 155.52 Mbps. See also SDH.

STS-1

Synchronous Transport Signal level 1. Basic building block signal of SONET, operating at 51.84 Mbps. Faster SONET rates are defined as STS-n, where n is a multiple of 51.84 Mbps. See also SONET.

Subrate DS3

A generic term to describe a process in which the bandwidth of a clear channel DS3 is limited to a lower rate. Many proprietary formats exist.

Super Frame

See SF.

T

T1

Digital WAN carrier facility. T1 transmits DS1-formatted data at 1.544 Mbps through the telephone switching network.

T3

Digital WAN carrier facility. T3 transmits DS3-formatted data at 44.736 Mbps through the telephone switching network.

TAC

A Cisco Technical Assistance Center. There are four TACs worldwide.

TELNET

Standard terminal emulation protocol in the TCP/IP protocol stack. Telnet is used for remote terminal connection, enabling users to log in to remote systems and use resources as if they were connected to a local system. Telnet is defined in RFC 854.

TFTP

Trivial File Transfer Protocol. A simplified version of FTP that allows files to be transferred from one computer to another over a network.

U

Unchannelized DS3

See Clear channel DS3.

V

VT-n

Virtual tributary level n. The SONET format for mapping a lower-rate signal into a SONET payload. For example, VT-1.5 is used to transport a DS1 signal. See also DS1 and SONET.

W

Weighted Random Early Detection

See WRED.

WRED

Weighted random early detection. RED uses an algorithm to randomly discard packets.The result of the drop is that the source detects the dropped traffic and slows its transmission. WRED combines the capabilities of the RED algorithm with IP precedence. This combination provides for preferential traffic handling for higher-priority packets. It can selectively discard lower-priority traffic when the interface starts to get congested and provide differentiated performance characteristics for different classes of service.

A
AAA	Authentication, authorization, and accounting.
Access list	List kept by a router to control access to or from the router for a number of services. For example, access lists can be used to prevent packets with a certain IP address from leaving a particular interface on the router.
Alarm	A status condition that shows that a module or port is experiencing an abnormal operating condition. See also Critical alarm, Major alarm, and Minor alarm.
APS	Automatic protection switching. A SONET switching mechanism that achieves network resiliency by automatically switching from a primary circuit to a secondary circuit. This switching process occurs if the primary circuit fails or if the error rate on the primary line exceeds a set threshold. The Cisco 10000 ESR supports 1+1 APS, which provides permanent electrical bridging to the service and protection equipment, placed at both ends of the circuit.
Authentication	In security, the verification of the identity of a person or process.
Automatic protection switching	See APS.

B
Bellcore	Bell Communications Research. An organization that performs research and development on behalf of the Regional Bell Operating Companies (RBOCs).
BER	Bit error rate. The ratio of received bits that contain errors to all received bits.
BGP	Border Gateway Protocol. An interdomain routing protocol that replaces EGP. BGP exchanges connection information with other BGP systems. It is defined by RFC 1163.
Bit error rate	See BER.
Border Gateway Protocol	See BGP.

C
CAR	Committed Access Rate. A QoS feature that classifies packets based on such things as access lists, a MAC address, and IP precedence. It measures traffic rates and can be configured to take actions such as dropping packets or changing the ToS value.
C-bit parity	A modification of the M23 framing method for DS3 which frees the C bits for additional uses. See also M23.
CB-WRED	Class-based weighted random early detection. Class-based WRED applies WRED to packets in different traffic classes. See also WRED.
Channel	Communication path. Multiple channels can be multiplexed over a single cable in certain environments.
Channel service unit	See CSU.
Cisco IOS	Cisco system software that provides common functionality, scalability, and security for Cisco products. Cisco IOS allows centralized, integrated, and automated installation and management of internetworks, while ensuring support for a wide variety of protocols, media, services, and platforms.
Clear channel DS3	A framed DS3 signal that is not multiplexed from 28 DS1 signals. Sometimes referred to as unchannelized DS3.
CLI	Command line interface. Interface that allows the user to interact with the operating system by entering commands and optional arguments at the command prompt.
Command Line Interface	See CLI.
Committed access rate	See CAR.
CRC	Cyclic redundancy check. Error-checking technique in which the frame recipient calculates a remainder by dividing frame contents by a prime binary divisor and then compares the calculated remainder to a value stored in the frame by the sending node.
Critical alarm	An alarm condition that might affect most or all subscribers that connect to the reporting node. To obtain more information about a problem, use the show facility-alarm status command. See also Major alarm and Minor alarm.
CSU	Channel service unit. Digital interface device that connects end-user equipment to the local digital telephone loop. Often referred to, together with DSU, as CSU/DSU. See also DSU.
Cyclic redundancy check	See CRC.

D
Data service unit	See DSU.
Differentiated service code point	See DSCP.
DS0	Digital signal level 0. Framing specification used in transmitting digital signals over a single channel at 64 kbps on a T1 facility. Compare with DS1 and DS3.
DS1	Digital signal level 1. Framing specification used in transmitting digital signals at 1.544 Mbps on a T1 facility (in the United States) or at 2.108 Mbps on an E1 facility (in Europe). Compare with DS0 and DS3.
DS3	Digital signal level 3. Framing specification used for transmitting digital signals at 44.736 Mbps on a T3 facility. Compare with DS0 and DS1.
DSCP	Differentiated service code point. Specifies a precedence value for handling packets belonging to the specified class.
DSU	Data service unit. Device used in digital transmission that adapts the physical interface on a DTE device to a transmission facility such as T1 or E1. The DSU is also responsible for such functions as signal timing. Often used with CSU, as in CSU/DSU. See also CSU.

E
Edge Services Router	See ESR.
ESF	Extended superframe. Framing type used on T1 circuits that consists of 24 frames of 192 bits each, with the 193rd bit providing timing and other functions. ESF is an enhanced version of SF. See also SF.
ESR	Edge Services Router. A router that aggregates traffic from thousands of low- and medium-bandwidth subscriber connections and routes it on a few high-bandwidth connections to the Internet core.
Ethernet	Baseband LAN specification. Ethernet networks use CSMA/CD and run over a variety of cable types at 10 Mbps, 100 Mbps, or 1000 Mbps. Ethernet is similar to the IEEE 802.3 series of standards. See also Fast Ethernet, Gigabit Ethernet.
Extended Superframe Format	See ESF.

F
Facility data link	See FDL.
Fast Ethernet	Any of a number of 100 Mbps Ethernet specifications. Fast Ethernet offers a speed increase 10 times that of the 10BaseT Ethernet specification, while preserving qualities such as frame format, MAC mechanisms, and MTU. Existing 10BaseT applications and network management tools can be used on Fast Ethernet networks. The Fast Ethernet specification is based on an extension to the IEEE 802.3 specification. Compare with Ethernet and Gigabit Ethernet.
FDL	Facility data link. Embedded communications channel in ESF DS1 framing. Used to convey both bit-oriented and message-oriented signals.
Flash memory	Nonvolatile storage that can be electrically erased and reprogrammed so that software images can be stored, booted, and rewritten as necessary. Flash memory was developed by Intel and is licensed to other semiconductor companies.
Frame Relay	Industry-standard, switched data link layer protocol that handles multiple virtual circuits using HDLC encapsulation between connected devices. Frame Relay is more efficient than X.25, the protocol for which it is generally considered a replacement.

G
Gigabit Ethernet	Gigabit Ethernet. Ethernet running at a transmission speed of 1 billion bits per second.

H
HDLC	High Level Data Link Control. Bit-oriented synchronous data link layer protocol developed by ISO. Derived from SDLC, HDLC specifies a data encapsulation method on synchronous serial links using frame characters and checksums.
High Level Data Link Control	See HDLC.

I
IOS	Internet Operating System. See Cisco IOS.
IP	Internet Protocol. Network layer protocol in the TCP/IP stack offering a connectionless internetwork service. IP provides features for addressing, type-of-service specification, fragmentation and reassembly, and security. Defined in RFC 791.

K
Keepalive message	Message sent by one network device to inform another network device that the virtual circuit between the two is still active.

L
LAIS	Line Alarm Indication Signal. A SONET port status indicator that activates when an LAIS defect occurs and does not clear throughout the alarm integration period, which is typically 2.5 seconds. An LAIS defect occurs when bits 6, 7, and 8 of the K2 byte are 111 for three consecutive frames. This occurrence begins the alarm integration period. If this period elapses without the detection of three consecutive frames in which K2 bits 6, 7, and 8 show any pattern other than 111, the LAIS indicator activates. The LAIS indicator clears when an LAIS defect does not occur for a time interval equal to the alarm deactivation period (typically 10 seconds).
Line card	Any I/O card that can be inserted in a modular chassis.
LOF	Loss of Frame. A 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, which is typically 2.5 seconds. An LOF defect occurs when an out-of-frame (OOF) condition occurs and does not clear for more than 3 microseconds (ms). This occurrence begins the alarm integration period. (OOF occurs when four consecutive frames do not contain a valid frame word. OOF clears when two valid consecutive frames are detected.) The LOF indicator clears when an LOF defect is not detected for a time interval that is equal to the alarm deactivation period (typically 10 seconds).
Loopback test	A test in which signals are sent and then directed back toward their source from some point along the communications path. Loopback tests are often used to check network interface usability.
LOS	Loss of signal. A SONET port status indicator that activates when an LOS defect occurs and does not clear throughout the alarm integration period, which is typically 2.5 seconds. An LOS defect occurs when the OC-3 port receives all zeros for 20 microseconds (+.3 ms). This occurrence begins the alarm integration period. If this period elapses without the detection of two consecutive frames in which there are no 20-ms periods of signal loss, the LOS indicator activates. The LOS indicator clears when an LOS defect is not detected for an interval equal to the alarm deactivation period (typically 10 seconds).

M
M13	Generic term for equipment that multiplexes DS1s into DS3s. Sometimes used to describe a specific DS3 multiplex format. Some standards use this term to describe a synchronous multiplexing format also know as SYNTRAN. In many cases, however, M13 does not refer to the SYNTRAN format; it refers instead to the format also known as M23.
M23	A method of multiplexing four DS1 signals into a DS2 signal, then multiplexing seven DS2 signals into a DS3 signal.
MAC	Media Access Control. The lower of the two sublayers of the data link layer defined by the IEEE. The MAC sublayer handles access to shared media.
MAC address	Standardized data link layer address that is required for each port or device that connects to a LAN. Other devices in the network use these addresses to locate specific ports in the network, and to create and update routing tables and data structures. MAC addresses are 6 bytes long and are controlled by the IEEE. Also known as a hardware address, MAC-layer address, or physical address.
Maintenance data link	See MDL.
Major alarm	One of a group of alarm conditions that are considered the second most severe of all reportable alarms. Major alarms affect several subscribers who connect to the reporting node. You can use the show facility-alarm status IOS command to obtain more information about the problem. See also Critical alarm and Minor alarm.
Maximum transmission unit	See MTU.
MDL	Maintenance data link. Embedded communications channel in C-bit parity DS3 framing. Used to convey message-oriented signals.
Minor alarm	One of a group of alarm conditions that are considered the third most severe of all reportable alarms. Minor alarms affect a single or small number of subscribers who connect to the reporting node. You can use the show facility-alarm status IOS command to obtain more information about the problem. See also Critical alarm and Major alarm.
MLP	Multilink Point-to-Point Protocol. A method of splitting, recombining, and sequencing datagrams across multiple logical data links.
MTU	Maximum transmission unit. Maximum packet size, in bytes, that a particular interface can handle.
Multilink Point-to-Point	See MLP.

N
NEBS	Network Equipment Building Systems. The Bellcore requirement for equipment deployed in a central office environment. Covers spatial and thermal requirements as well as requirements for hardware, crafts person interface, fire resistance, handling and transportation, earthquake and vibration, airborne contaminants, grounding, acoustical noise, illumination, EMC, and ESD.
Network Equipment Building Systems	See NEBS.
Nonvolatile RAM	See NVRAM.
NVRAM	Nonvolatile RAM. RAM that retains its contents when a unit is powered off.

P
Packet	Logical grouping of information that includes a header containing control information and (usually) user data. Packets are most often used to refer to network layer units of data. The terms datagram, frame, message, and segment are also used to describe logical information groupings at various layers of the OSI reference model and in various technology circles.
Packet over SONET	See POS.
PCMCIA Flash disk card	A portable (credit-card size), nonvolatile storage device. PCMCIA Flash disk cards use Flash technology to store data. PCMCIA stands for Personal Computer Memory Card International Association, which sets the standard for this technology. Also called PC card.
Performance Routing Engine	See PRE.
Point-to-Point Protocol	See PPP.
POS	Packet Over SONET. A high-speed means of transmitting data over a SONET fiber-optic transmission system through a direct fiber connection to a data switch or router. POS is a point-to-point dedicated leased-line approach intended purely for high-speed data applications. POS allows a user organization to pass data in its native format, without the addition of any significant level of overhead in the form of signaling and control information.
PPP	Point-to-Point Protocol. Provides router-to-router and host-to-network connections over synchronous and asynchronous circuits.
PRE	Performance routing engine. The central routing unit for the Cisco 10000 ESR. The PRE performs all Layer 2 and Layer 3 packet manipulation related to routing and forwarding through the Cisco 10000 ESR. Dual PREs can be configured in a single chassis for redundancy.

Q
QoS	Quality of service. A measure of performance for a transmission system that reflects its transmission quality and service availability.
QoS Policy Propagation on BGP	See QPPB.
QPPB	QoS Policy Propagation on BGP. A feature involving the classification of packets by IP precedence based on BGP community lists, BGP autonomous system paths, and access lists. After a packet is classified, other quality of service features such as committed access rate (CAR) and weighted random early detection (WRED) can specify and enforce policies to fit a business model.
Quality of Service	See QoS.

R
RAM	Random-access memory. Volatile memory that can be read and written by a microprocessor.
Random Access Memory	See RAM.
Redundancy	In internetworking, the duplication of devices, services, or connections so that, in the event of a failure, the redundant devices, services, or connections can perform the work of those that failed.
RMON	Remote Monitoring. MIB agent specification described in RFC 1271 that defines functions for the remote monitoring of networked devices. The RMON specification provides numerous monitoring, problem detection, and reporting capabilities.
ROM	Read only memory. Nonvolatile memory that can be read, but not written, by the microprocessor.

S
SDH	Synchronous Digital Hierarchy. European standard that defines a set of rate and format standards that are transmitted using optical signals over fiber. SDH is similar to SONET, with a basic rate of 155.52 Mbps, designated as STM-1. See also SONET and STM-1.
SF	Super frame. Common framing type used on T1 circuits. SF consists of 12 frames of 192 bits each, with the 193rd bit providing error checking and other functions. SF has been superseded by ESF, but is still widely used. Also called D4 framing. See also ESF.
Simple Network Management Protocol	See SNMP.
SNMP	Simple Network Management Protocol. Network management protocol used almost exclusively in TCP/IP networks. SNMP provides a means to monitor and control network devices, and to manage configurations, statistics collection, performance, and security. See also SNMP2.
SNMP2	SNMP Version 2. Version 2 of the network management protocol. SNMP2 supports centralized as well as distributed network management strategies, and includes improvements in the SMI, protocol operations, management architecture, and security. See also SNMP.
SONET	Synchronous Optical Network. High-speed synchronous network specification developed by Bellcore and designed to run on optical fiber. STS-1 is the basic building block of SONET. It was approved as an international standard in 1988. See also SDH and STS-1.
SPE	Synchronous Payload Envelope. The major portion of the SONET frame format used to carry the STS-1 signal; it is divided into an information payload section and a transport overhead system. SPE is used to address three payload structures: direct to STS-1 line rate muliplexing; asynchronous DS3 multiplexing; and synchronous DS3 multiplexing.
STM-1	Synchronous Transport Module level 1. Basic building block signal of SDH, operating at 155.52 Mbps. Faster SDH rates are defined as STS-n, where n is a multiple of 155.52 Mbps. See also SDH.
STS-1	Synchronous Transport Signal level 1. Basic building block signal of SONET, operating at 51.84 Mbps. Faster SONET rates are defined as STS-n, where n is a multiple of 51.84 Mbps. See also SONET.
Subrate DS3	A generic term to describe a process in which the bandwidth of a clear channel DS3 is limited to a lower rate. Many proprietary formats exist.
Super Frame	See SF.

T
T1	Digital WAN carrier facility. T1 transmits DS1-formatted data at 1.544 Mbps through the telephone switching network.
T3	Digital WAN carrier facility. T3 transmits DS3-formatted data at 44.736 Mbps through the telephone switching network.
TAC	A Cisco Technical Assistance Center. There are four TACs worldwide.
TELNET	Standard terminal emulation protocol in the TCP/IP protocol stack. Telnet is used for remote terminal connection, enabling users to log in to remote systems and use resources as if they were connected to a local system. Telnet is defined in RFC 854.
TFTP	Trivial File Transfer Protocol. A simplified version of FTP that allows files to be transferred from one computer to another over a network.

V
VT-n	Virtual tributary level n. The SONET format for mapping a lower-rate signal into a SONET payload. For example, VT-1.5 is used to transport a DS1 signal. See also DS1 and SONET.

W
Weighted Random Early Detection	See WRED.
WRED	Weighted random early detection. RED uses an algorithm to randomly discard packets.The result of the drop is that the source detects the dropped traffic and slows its transmission. WRED combines the capabilities of the RED algorithm with IP precedence. This combination provides for preferential traffic handling for higher-priority packets. It can selectively discard lower-priority traffic when the interface starts to get congested and provide differentiated performance characteristics for different classes of service.

Table of Contents

glossary