Symbols
GLOSSARY
1+1 APS
10BASE-T
100BASE-T
1000BASE-LX/LH
1000BASE-SX
1000BASE-T
See APS.
10-Mbps baseband Ethernet specification using two pairs of twisted-pair cabling (Category 3, 4, or 5):
one pair for transmitting data and the other for receiving data. 10BASE-T, which is part of the IEEE
802.3 specification, has a distance limit of approximately 328 feet (100 meters) per segment. See also
IEEE 802.3 and Ethernet.
100-Mbps baseband Fast Ethernet specification using UTP wiring. Like the 10BASE-T technology on
which it is based, 100BASE-T sends link pulses over the network segment when no traffic is present.
However, these link pulses contain more information than those used in 10BASE-T. The 100BASE-T
specification is based on the IEEE 802.3 standard. See also 10BASE-T, Fast Ethernet, and
IEEE 802.3.
1000-Mbps gigabit Ethernet specification using two strands of multimode or single mode fiber-optic
cable per link. To guarantee proper signal recovery, a 1000BASE-LX/LH link cannot exceed 1804 feet
(550 meters) in length over multimode fiber or 32,810 feet (10 km) in length over single mode fiber.
Based on the IEEE 802.3 standard with reach over single mode fiber extended from 5 km to 10 km. See
also 1000BASE-SX, 1000BASE-ZX, Gigabit Ethernet, and
IEEE 802.3.
1000-Mbps gigabit Ethernet specification using two strands of multimode fiber-optic cable per link. To
guarantee proper signal recovery, a 1000BASE-SX link cannot exceed 1804 feet (550 meters) in length.
The 1000BASE-SX specification is based on the IEEE 802.3 standard. See also 1000BASE-LX/LH,
1000BASE-ZX, Gigabit Ethernet, and IEEE 802.3.
1000BASE-T (GLC-T) SFP module connects a Cisco Gigabit Interface Converter (GBIC) port to
Category 5 wiring via a standard RJ-45 interface. The maximum Category 5 wiring distance is 100 m.
The module provides with an option of connecting to a backhaul network interface.
1000BASE-X
1000BASE-ZX
802.x
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1000-Mbps gigabit Ethernet specification that refers to the 1000BASE-CX, 1000BASE-SX, and
1000BASE-LX standards for gigabit Ethernet over fiber-optic cabling. The 1000BASE-X specification
is based on the IEEE 802.3 standard. See also 1000BASE-SX, 1000BASE-LX/LH, 1000BASE-ZX,
Gigabit Ethernet, and
IEEE 802.3.
1000-Mbps gigabit Ethernet specification using two strands of single mode fiber-optic cable per link.
To guarantee proper signal recovery, a 1000BASE-ZX link cannot be longer than 62.1 mi (100 km).
This is a Cisco specification. See also 1000BASE-SX, 1000BASE-LX/LH, Gigabit Ethernet, and IEEE
802.3.
A set of IEEE standards for the definition of LAN protocols.
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GL-1
A
Glossary
AAL
Access list
Add drop
Multiplexer
ADM
Alarm
Application-specific
integrated circuit
APS
ATM adaptation layer. Service-dependent sublayer of the data link layer. The AAL accepts data from
different applications and presents it to the ATM layer in the form of 48-byte ATM payload segments.
AALs consist of two sublayers:the convergence sublayer and the segmentation and reassembly
sublayer. Four types of AAL recommended by the ITU-T are AAL1, AAL2, AAL3/4, and AAL5; the
Cisco uBR10012 uses AAL5.
List kept by routers 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.
See ADM.
Add Drop Multiplexer. A multiplexer that allows a signal to be added into or dropped out of a SONET
span. See also SONET.
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.
See ASIC.
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.
ASIC
Asynchronous
Transfer Mode
ATM
Authentication
Automatic
protection
switching
Alarm
Application-specific integrated circuit. A chip that is built for a specific application.
See AT M.
Asynchronous Transfer Mode. International standard for cell relay in which multiple service types
(such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. Fixed-length cells allow
cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to take
advantage of high-speed transmission media such as E3, SONET, and T3.
In security, the verification of the identity of a person or process.
See APS.
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.
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B
Glossary
Backplane
Bellcore
BER
BGP
Bit error rate
Border Gateway
Protocol
Broadcast
C
CCITT
The circuit board at the back of the chassis that all components plug into. It provides the physical
connection between an interface processor or line card, and the data and power distribution buses inside
a chassis.
Bell Communications Research. Former name of the organization that performs research and
development on behalf of the Regional Bell Operating Companies (RBOCs). Bellcore is now called
Telcordia.
Bit error rate. The ratio of received bits that contain errors.
Border Gateway Protocol. An interdomain routing protocol that replaces EGP. BGP exchanges
connection information with other BGP systems. It is defined by RFC 1163.
See BER.
See BGP.
Data packet that is sent to all nodes on a network. Broadcasts are identified by a broadcast address.
Compare with Multicast and Unicast.
Consultative Committee for International Telegraph and Telephone. International organization
responsible for the development of communications standards. Now called the ITU-T. (See ITU-T.)
CEF
Central Office
Channel
Cisco Express
Forwarding
Cisco IOS
Clear channel DS3
CLI
Cisco Express Forwarding. An advanced Layer 3 IP switching technology designed for
high-performance, highly resilient Layer 3 IP backbone switching. CEF optimizes network
performance and scalability for networks with large and dynamic traffic patterns, such as the Internet,
on networks characterized by intensive Web-based applications or interactive sessions.
See CO.
Communication path. Multiple channels can be multiplexed over a single cable in certain
environments.
See CEF.
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.
A framed DS3 signal which is not multiplexed from 28 DS1 signals. Sometimes referred to as
unchannelized DS3.
Command line interface. Interface that allows the user to interact with the operating system by entering
commands and optional arguments at the command prompt.
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GL-3
Glossary
CO
Command Line
Interface
Console
Critical alarm
D
Data terminal
equipment
DCE
DRAM
Central office. The local telephone company office to which all local loops in a given area connect and
in which circuit switching of subscriber lines occurs.
See CLI.
Data terminal equipment (DTE) through which commands are entered into a host.
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.
See DTE.
Data circuit-terminating equipment (ITU-T expansion). Devices and connections of a communications
network that comprise the network end of the user-to-network interface. The DCE provides a physical
connection to the network, forwards traffic, and provides a clocking signal used to synchronize data
transmission between DCE and DTE devices. Modems and interface cards are examples of DCE.
Compare with DTE.
Dynamic random access memory. RAM that stores information in capacitors that must be periodically
refreshed. Delays can occur because DRAMs are inaccessible to the processor when refreshing their
contents. However, DRAMs are less complex and have greater capacity than SRAMs. See also SRAM.
DS0
DS1
DS3
DSU
DTE
Dynamic random
access memory
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.
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.
Digital signal level 3. Framing specification used for transmitting digital signals at 44.736 Mbps on a
T3 facility. Compare with DS0 and DS1.
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.
Data terminal equipment. Device at the user end of a user-network interface that serves as a data source,
destination, or both. DTE connects to a data network through a DCE device (for example, a modem)
and typically uses clocking signals generated by the DCE. DTE includes devices such as computers,
protocol translators, and multiplexers.
See DRAM.
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E
Glossary
E1
Edge Services
Router
Electromagnetic
interference
Electrostatic
discharge
EMI
EMP
ESD
ESR
Ethernet
Wide-area digital transmission scheme used predominantly in Europe that carries data at a rate of 2.048
Mbps. E1 lines can be leased for private use from common carriers. Compare with T1; see also DS1.
See ESR.
See EMI.
See ESD.
Electromagnetic interference. Interference by electromagnetic signals that can cause reduced data
integrity and increased error rates on transmission channels.
Electromagnetic pulse. Caused by lightning and other high-energy phenomena. Capable of coupling
enough energy into unshielded conductors to destroy electronic devices.
Electrostatic discharge. Discharge of stored static electricity that can damage electronic equipment and
impair electrical circuitry, resulting in complete or intermittent failures.
Edge Services Router. A router that aggregates and routes traffic from thousands of low- and
medium-bandwidth subscriber connections Into a few high-bandwidth connections to the Internet core.
Baseband LAN specification. Ethernet networks use CSMA/CD and run over a variety of cable types
at 10 Mbps, 100 Mbps, and 1000 Mbps. Ethernet is similar to the IEEE 802.3 series of standards. See
also Fast Ethernet, Gigabit Ethernet, IEEE 802.3.
F
Fast Ethernet
Fiber-optic cable
Field-replaceable
unit
Flash memory
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Any of a number of 100-Mbps Ethernet specifications. Fast Ethernet offers a speed increase 10 times
that of the 10BASE-T Ethernet specification, while preserving qualities such as frame format, MAC
mechanisms, and MTU. Existing 10BASE-T 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. See also 100BASE-T and IEEE 802.3.
Physical medium capable of conducting modulated light transmission. Compared with other
transmission media, fiber-optic cable is more expensive, but it is not susceptible to electromagnetic
interference and is capable of higher data rates. Sometimes called optical fiber.
See FRU.
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.
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GL-5
Glossary
Frame Relay
FRU
G
GBIC
Gigabit Ethernet
Gigabit Interface
Converter
H
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.
Field replaceable unit. A component that can be removed from a network device and replaced in the
field. Line cards, power modules, and fan modules are typically FRUs.
Gigabit Ethernet converter. An interface module used by gigabit Ethernet and Fibre Channel to convert
the serial electrical signals to the transmission medium’s physical layer signalling, which is typically
optical. GBIC modules can be hot-swapped and contain ID and system information that a switch or
router can use to determine the network device's capabilities. Different GBICs handle different types
of fiber cable. See 1000BASE-LX/LH, 1000BASE-SX, and 1000BASE-ZX.
Gigabit Ethernet. Ethernet running at a transmission speed of 1 billion bits per second.
See GBIC.
HHGE
Hot swapping
I
IEEE
IEEE 802.3
Institute of Electrical
and Electronics
Engineers
Intermediate reach
Internet service
provider
half-height gigabit Ethernet
Feature that permits the addition, replacement, or removal of cards without interrupting the system
power, entering console commands, or causing other software or interfaces to shut down. Sometimes
called online insertion and removal (OIR).
Institute of Electrical and Electronics Engineers. Professional organization whose activities include the
development of communications and network standards. IEEE LAN standards are the currently
predominant LAN standards.
IEEE LAN protocol that specifies an implementation of the physical layer and the MAC sublayer of
the data link layer. IEEE 802.3 uses CSMA/CD access at a variety of speeds over a variety of physical
media. Extensions to the IEEE 802.3 standard specify implementations for Fast Ethernet and gigabit
Ethernet.
See IEEE.
See IR.
See ISP.
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Glossary
IOS
IP
IP multicast
IR
ISP
ITU-T
L
LAN
Internet Operating System. See Cisco IOS.
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.
Routing technique that allows IP traffic to be propagated from one source to a number of destinations
or from many sources to many destinations. Rather than sending one packet to each destination, one
packet is sent to a multicast group identified by a single IP destination group address.
Intermediate reach. SONET/SDH specification for transmit power and receive sensitivity that achieves
a 9.3-mile (15-km) reach.
Internet Service Provider. A company that provides Internet access to other companies and individuals.
International Telecommunication Union Telecommunication Standardization Sector. International
body that develops worldwide standards for telecommunications technologies. The ITU-T carries out
the functions of the former CCITT.
Local-area network. High-speed, low-error data network covering a relatively small geographic area
(up to a few thousand meters). LANs connect workstations, peripherals, terminals, and other devices
in a single building or some other geographically limited area. LAN standards specify cabling and
signaling at the physical and data link layers of the OSI model. Ethernet, FDDI, and Token Ring are
widely used LAN technologies. Compare with MAN and WA N .
Line card
LMI
Local-area network
Loopback test
LOS
Any I/O card that can be inserted in a modular chassis.
Local Management Interface. A set of enhancements to the basic Frame Relay specification. LMI
includes support for a keepalive mechanism, which verifies that data is flowing; a multicast
mechanism, which provides the network server with its local DLCI and the multicast DLCI; global
addressing, which gives DLCIs global rather than local significance in Frame Relay networks; and a
status mechanism, which provides an on-going status report on the DLCIs known to the switch. Known
as LMT in ANSI terminology.
See LAN.
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 test network interface usability.
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).
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GL-7
M
Glossary
M13
M23
MAC
MAC address
Major alarm
MAN
Management
Information Base
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 M13 does not refer to the SYNTRAN format, but instead
refers to the format also known as M23.
A method of multiplexing four DS1 signals into a DS2 signal, then multiplexing seven DS2 signals into
a DS3 signal.
Media Access Control. Lower of the two sublayers of the data link layer defined by the IEEE. The MAC
sublayer handles access to shared media.
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.
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
facility-alarm status
IOS command to obtain more information about the problem. See also Critical
show
alarm and Minor alarm.
Metropolitan-area network. A network that spans a metropolitan area. Generally, a MAN spans a larger
geographic area than a LAN, but a smaller geographic area than a WAN. Compare with LAN and WA N .
See MIB.
Media Access
Control
Metropolitan-area
network
MIB
Minor alarm
MLP
MMF
MPLS
See MAC.
See MAN.
Management Information Base. Database of network management information that is used and
maintained by a network management protocol such as SNMP or CMIP. The value of a MIB object can
be changed or retrieved using SNMP or CMIP commands, usually through a GUI-based network
management system. MIB objects are organized in a tree structure that includes public (standard) and
private (proprietary) branches.
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.
Multilink Point-to-Point Protocol. A method of splitting, recombining, and sequencing datagrams
across multiple logical data links.
Multimode fiber. Optical fiber supporting propagation of multiple frequencies of light. See also
Single-mode fiber.
Multiprotocol Label Switching. An emerging industry standard upon which tag switching is based.
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Glossary
Multicast
Multilink
Point-to-Point
Multimode fiber
Multiplexing
Multiprotocol Label
Switching
N
NEBS
Network Equipment
Building Systems
Single packets copied by the network and sent to a specific subset of network addresses. These
addresses are specified in the Destination Address field. Compare with Broadcast and Unicast.
See MLP.
See MMF.
An activity in which multiple logical signals are transmitted simultaneously across a single physical
channel.
See MPLS.
Network Equipment Building Systems. The Telcordia (formerly Bellcore) requirements for equipment
deployed in a central office environment. Covers spatial, hardware, crafts person interface, thermal, fire
resistance, handling and transportation, earthquake and vibration, airborne contaminants, grounding,
acoustical noise, illumination, EMC, and ESD requirements.
See NEBS.
Network
termination unit
Nonvolatile RAM
NTU
NVRAM
O
OC
ODL
OIR
Online insertion and
removal
See NTU.
See NVRAM.
Network terminating unit. The network equipment that connects directly to the data terminal
equipment.
Nonvolatile RAM. RAM that retains its contents when a unit is powered off.
Optical carrier. A series of physical protocols (OC-1, OC-2, OC-3, and so forth), defined for SONET
optical signal transmissions. OC signal levels put STS frames onto fiber-optic lines at a variety of
speeds. The base rate is 51.84 Mbps (OC-1); each signal level thereafter operates at a speed divisible
by that number (thus, OC-3 runs at 155.52 Mbps).
Optical data link.
Online insertion and removal. Feature that permits the addition, replacement, or removal of cards
without interrupting the system power, entering console commands, or causing other software or
interfaces to shut down. Same as hot-swapping.
See OIR.
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GL-9
Glossary
Optical carrier
Optical fiber
P
Packet
Packet Over SONET
Packet switching
Parallel Express
Forwarding
PCMCIA Flash disk
card
PEM
See OC.
See Fiber-optic cable.
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.
See POS.
Networking method in which nodes share bandwidth with each other by sending packets.
See PXF Network Processors.
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.
Power entry module. A hardware module that distributes power to the chassis.
Performance
Routing Engine
Point of Presence
Point-to-Point
Protocol
POP
POS
POST
Power Entry Module
Power-on self test
PPP
See PRE.
See POP.
See PPP.
Point of presence. A physical location where an interexchange carrier installed equipment to
interconnect with a local exchange carrier.
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.
Power-on self test. A set of hardware diagnostics that runs on a hardware device when that device is
powered on.
See PEM.
See POST.
Point-to-Point Protocol. Provides router-to-router and host-to-network connections over synchronous
and asynchronous circuits.
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Glossary
PRE
PXF Network
Processors
Q
QoS
QPPB
Quality of Service
R
Performance routing engine. The central routing unit for the Cisco uBR10012 universal broadband
router. The PRE performs all Layer 2 and Layer 3 packet manipulation related to routing and
forwarding through the Cisco uBR10012 routers. Use dual PREs in a single chassis for redundancy. See
also PXF Network Processors.
Parallel eXpress Forwarding network processors. A pair of programmable ASICs that perform parallel
processing to support high performance Layer 3 forwarding.
Quality of service. A measure of performance for a transmission system that reflects its transmission
quality and service availability.
QoS Policy Propagation by BGP. A feature that classifies 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.
See QoS.
RAM
Random Access
Memory
Read only memory
Redundancy
Remote monitoring
Request for
comments
RFC
RMON
ROM
Random-access memory. Volatile memory that can be read and written by a microprocessor.
See RAM.
See ROM.
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.
See RMON.
See RFC.
Request for comments. A document series used as the primary means for communicating information
about the Internet. Some RFCs are designated by the IAB as Internet standards. Most RFCs document
protocol specifications such as Telnet and FTP, but some are humorous or historical. RFCs are available
online from numerous sources.
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.
Read only memory. Nonvolatile memory that can be read, but not written, by the microprocessor.
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GL-11
S
Glossary
SAR
SFP
Short reach
Simple Network
Management
Protocol
Single-mode fiber
SMF
SNMP
SNMP2
Segmentation and reassembly. One of the two sublayers of the AAL common part convergence
sublayer, responsible for dividing (at the source) and reassembling (at the destination) the protocol data
units (PDUs) passed from the convergence sublayer. The SAR sublayer takes the PDUs processed by
the convergence sublayer and, after dividing them into 48-byte pieces of payload data, passes them to
the ATM layer for further processing. See also AAL.
small formfactor pluggable (module) as in GBIC
See SR.
See SNMP.
See SMF.
Single-mode fiber. Fiber-optic cabling with a narrow core that allows light to enter only at a single
angle. Such cabling has higher bandwidth than multimode fiber, but requires a light source with a
narrow spectral width (for example, a laser). Also called monomode fiber. See also Multimode fiber.
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.
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
SR
SRAM
Subrate DS3
Synchronous
Optical Network
T
T1
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.
Short reach. SONET/SDH specification for transmit power and receive sensitivity that achieves a
1.2-mile (2 km) reach.
A type of RAM that retains its contents for as long as power is supplied. SRAM does not require
constant refreshing, like DRAM. Compare with DRAM.
A generic term to describe a process in which the bandwidth of a clear channel DS3 is limited to a lower
rate. Several proprietary formats exist.
See SONET.
Digital WAN carrier facility. T1 transmits DS1-formatted data at 1.544 Mbps through the telephone
switching network.
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Glossary
T3
TAC
TACACS
TACACS+
TCC+
TDM
Telcordia
TELNET
Digital WAN carrier facility. T3 transmits DS3-formatted data at 44.736 Mbps through the telephone
switching network.
A Cisco Technical Assistance Center. There are four TACs worldwide.
Terminal Access Controller Access Control System. Authentication protocol, developed by the DDN
community, that provides remote access authentication and related services, such as event logging.
User passwords are administered in a central database rather than in individual routers, providing an
easily scalable network security solution.
Terminal Access Controller Access Control System Plus. Proprietary Cisco enhancement to Terminal
Access Controller Access Control System (TACACS). Provides additional support for authentication,
authorization, and accounting.
See Timing, Communication, and Control Plus (TCC+) card.
Time-division multiplexing. A technique in which information from multiple channels can be allocated
bandwidth on a single wire based on preassigned time slots. Bandwidth is allocated to each channel
regardless of whether the station has data to transmit.
Organization that performs research and development on behalf of the Regional Bell Operating
Companies (RBOCs). Formerly called Bellcore.
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.
Terminal Access
Controller Access
Control System Plus
TFTP
Time-division
multiplexing
Timing,
Communication,
and Control Plus
Traffic management
Traffic shaping
See TAC ACS +.
Trivial File Transfer Protocol. Simplified version of FTP that allows files to be transferred from one
computer to another over a network.
See TDM.
The Timing, Communication, and Control Plus (TCC+) card in the Cisco uBR10012 chassis monitors
the cable interface line cards and power supply usage, controls the LCD display on the front panel, and
provides inputs for an external reference clock that is synced to a Stratum 1 source.
A technique for avoiding congestion and shaping and policing traffic. It allows links to operate at high
levels of utilization by scaling back lower-priority, delay-tolerant traffic at the edge of the network
when congestion begins to occur.
Use of queues to limit surges that can congest a network. Data is buffered and then sent into the network
in regulated amounts to ensure that the traffic will fit within the promised traffic envelope for the
particular connection. Traffic shaping is used in ATM, Frame Relay, and other types of networks. Also
known as metering, shaping, or smoothing.
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U
Glossary
UBR
Unchannelized DS3
Unicast
Universal
Broadband Router
Utility Card
V
Virtual Private
Network
VLAN
VoIP
See Universal Broadband Router.
See Clear channel DS3.
A message sent to a single network destination. Compare with Broadcast and Multicast.
A Cisco Cable Modem Termination System (CMTS) and carrier-class router that provides broadband
high-speed data, broadband entertainment, and IP telephony solutions over a coaxial cable network.
Another name used in the software screens for the Timing, Communication, and Control Plus (TCC+)
card.
See VPN.
Virtual LAN. A group of devices on one or more LANs that are configured (using management
software) so that they can communicate as if they were attached to the same wire, when in fact they are
located on a number of different LAN segments. Because VLANs are based on logical instead of
physical connections, they are extremely flexible.
Voice over IP. Voice over IP enables a router to carry voice traffic (for example, telephone calls and
faxes) over an IP network.
VPN
VT-n
W
WAN
Weighted Fair
Queuing
Weighted Random
Early Detection
WFQ
Virtual private network. A secure, end-to-end private network constructed over a third-party or public
network such as the Internet.
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.
Wide-area network. A data communications network that serves users across a broad geographic area
and often uses transmission devices provided by a common carrier (such as a telephone company or
service provider).
See WFQ.
See WRED.
Weighted Fair Queuing. Congestion management algorithm that identifies conversations (in the form
of traffic streams), separates packets that belong to each conversation, and ensures that capacity is
shared fairly between these individual conversations. WFQ is an automatic way of stabilizing network
behavior during congestion and results in better performance and fewer retransmissions.
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Glossary
Wide-area network
WRED
See WA N.
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.
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