ARP Address Resolution Protocol Internet protocol used to map an IP address to a MAC address.. bootstrap The protocol used by a network node to determine the IP address of its Ethernet i
Trang 1Appendix B
Glossary of Key Terms
wave-length for a long-haul fiber-optic cable for a maximum wave-length of 10,000 (32808.4 ft.)
1000BASE-SX 1000-Mbps baseband Gigabit Ethernet specification using a short laser wavelength on multimode fiber-optic cable for a maximum length of 550m (1804.5 ft.)
1000BASE-T 1000-Mbps baseband Gigabit Ethernet specification using four pairs of Category 5 UTP cable for a maximum length of 100m (328 ft.)
multimode fiber-optic cable per link To guarantee proper signal timing, a 100BASE-FX link cannot exceed 400m (1312 ft.) in length It is based on the IEEE 802.3 standard
100BASE-TX 100-Mbps baseband Fast Ethernet specification using two pairs of either UTP or STP wiring The first pair of wires is used to receive data; the second is used to transmit To guarantee proper signal timing, a 100BASE-TX segment cannot exceed 100m (328 ft.) in length It is based on the IEEE 802.3 standard
10BASE2 10-Mbps baseband Ethernet specification using 50-ohm thin coaxial cable
10BASE2, which is part of the IEEE 802.3 specification, has a distance limit of 185m (606 ft.) per segment
baseband coaxial cable 10BASE5, which is part of the IEEE 802.3 baseband physical layer specification, has a distance limit of 500m (1640 ft.) per segment
10BASE-T 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 100m (328 ft.) per segment
Trang 210-Gb Ethernet Built on the Ethernet technology used in most of today’s LANs, 10-Gb Ethernet is described as a technology that offers a more efficient and less expensive approach to moving data on backbone connections between networks, while also providing a consistent technology end to end Ethernet now can step up to offering data speeds at 10 Gbps
quinary symbols (4D) received from the 8B1Q4 data encoding are transmitted using five voltage levels (PAM5) Four symbols are transmitted in parallel each symbol period
converting GMII data (8B-8 bits) to four quinary symbols (Q4) that are transmitted during one clock (1Q4)
acknowledgment Notification sent from one network device to another to acknowl-edge that some event (for example, receipt of a message) occurred Sometimes abbrevi-ated ACK
ACL (access control list) A means of controlling or limiting network traffic that com-pares different criteria to a defined rule set
active hub Must be plugged into an electrical outlet because it needs power to amplify the incoming signal before passing it out to the other ports
adjacent neighbor Two directly connected routers that participate in the exchange of
routing information are said to be adjacent.
administrative distance A rating that shows trustworthiness of a routing information source This value is shown as a numeric value between 0 and 255 The higher the value is, the lower the trustworthiness rating is
algorithm A well-defined rule or process for arriving at a solution to a problem In networking, algorithms are commonly used to determine the best route for traffic from
a particular source to a particular destination
alien crosstalk When crosstalk is caused by a signal from outside the cable
alignment error A message that does not end on an octet boundary
AM (amplitude modulation) Modulates the height of the carrier wave
used code for representing alphanumeric data in a computer Uses binary digits (bits)
to represent the symbols typed on the keyboard
amplitude The amplitude of an electrical signal represents its height, but it is measured
in volts instead of meters
Trang 3analog bandwidth Typically refers to the frequency range of an analog electronic
system Analog bandwidth can be used to describe the range of frequencies transmitted
by a radio station or an electronic amplifier
angle of incidence Angle of incidence is the angle at which the ray hits the glass surface
angle of reflection The angle between the reflected ray and the normal
ANSI American National Standards Institute
application layer Layer 7 of the OSI reference model This layer provides services
to application processes (such as e-mail, file transfer, and terminal emulation) that are
outside the OSI reference model The application layer identifies and establishes the
availability of intended communication partners (and the resources required to
con-nect with them), synchronizes cooperating applications, and establishes agreement on
procedures for error recovery and control of data integrity
application Interprets the data and displays the information in a comprehensible
format as the last part of an Internet connection Applications work with protocols
to send and receive data across the Internet
ARP (Address Resolution Protocol) Internet protocol used to map an IP address to a
MAC address
ASCII (American Standard Code for Information Interchange) An 8-bit code (7 bits
plus parity) for character representation
attenuation The decrease in signal amplitude over the length of a link
AUI (attachment unit interface) The 15-pin physical connector interface between a
computer’s NIC and Ethernet cable
autonomous system A network or set of networks that are under the administrative
control of a single entity, such as the cisco.com domain
backbone A backbone is the part of a network that acts as the primary path for traffic
that is most often sourced from, and destined for, other networks
backoff The retransmission delay enforced when a collision occurs
backplane A large circuit board that contains sockets for expansion cards
balanced hybrid routing protocol Routing protocols that utilize elements of distance
vector and link-state routing protocols
in a given period of time
binary A number system characterized by 1s and 0s (1 = on, and 0 = off)
Trang 4bit The smallest unit of data in a computer A bit equals 1 or 0 It is the binary for-mat in which data is processed, stored, and transmitted by computers In a computer, bits are represented by on/off switches or the presence or absence of electrical charges, light pulses, or radio waves
bit bucket The destination of discarded bits (dropped packets), as determined by the router
blueprint An architectural plan or technical drawing that provides details of a con-struction project or an existing structure
Boolean logic In computer operation with binary values, Boolean logic can describe electromagnetically charged memory locations or circuit states that are either charged (1 or true) or not charged (0 or false) The computer can use an AND gate or an OR gate operation to obtain a result that can be used for further processing
bootstrap The protocol used by a network node to determine the IP address of its Ethernet interfaces to affect network booting
border router A router situated at the edges or end of the network boundary, which provides basic security from the outside network or from a less controlled area of the network into a more private area of the network
BPDU (bridge protocol data unit) Spanning Tree Protocol hello packet that is sent out at configurable intervals to exchange information among bridges in the network
bridge A Layer 2 device designed to create two or more LAN segments, each of which is a separate collision domain
broadcast A data packet that is sent to all nodes on a network Broadcasts are identi-fied by a broadcast address
broadcast address Used to broadcast packets to all the devices on a network
broadcast domain A set of all devices that receive broadcast frames originating from any device within the set Broadcast domains are typically bounded by routers (or, in a switched network, by VLANs) because routers do not forward broadcast frames
bullwheel A large-diameter pulley that is used in a mechanical cable-pulling process
bus topology Commonly called a linear bus, this topology connects all the devices with a single cable This cable proceeds from one computer to the next like a bus line going through a city
bus A collection of circuits through which data is transmitted from one part of a computer to another
Trang 5byte A unit of measure that describes the size of a data file, the amount of space on
a disk or another storage medium, or the amount of data being sent over a network
1 byte equals 8 bits of data
cable tree A device that supports a number of small reels of cable This enables the
cable installer to pull multiple runs of cable simultaneously
CDP (Cisco Discovery Protocol) Used to obtain information about neighboring
devices, such as the types of devices connected, the router interfaces they are connected
to, the interfaces used to make the connections, and the model numbers of the devices
cell-switched services Provide a dedicated-connection switching technology that
organizes digital data into cell units and transmits them over a physical medium using
digital signal technology
Committee for Electrotechnical Standardization
central processing unit (CPU) The computer’s “brain,” where most of the calculations
take place
circuit switching A WAN switching method in which a dedicated physical circuit
through a carrier network is established, maintained, and terminated for each
commu-nication session ISDN is an example of a circuit-switched WAN technology
Cisco Internetwork Operating System (IOS) Software Software stored as an image
file in Flash memory on the router that, when loaded into RAM, provides the operating
system that runs the router
Class A address Designed to support extremely large networks A Class A IP address
uses only the first octet to indicate the network address The remaining three octets
enumerate host addresses
Class B address Designed to support the needs of moderate- to large-sized networks
A Class B IP address uses two of the four octets to indicate the network address The
other two octets specify host addresses
Class C address The most commonly used of the original address classes This address
space was intended to support a lot of small networks
Class D address Created to enable multicasting in an IP address
Class E address The IETF reserves these addresses for its own research Therefore,
no Class E addresses have been released for use in the Internet
Trang 6classless interdomain routing (CIDR) A technique supported by BGP and based on route aggregation CIDR allows routers to group routes to cut down on the quantity
of routing information carried by the core routers With CIDR, several IP networks appear to networks outside the group as a single, larger entity
CLI (command-line interface) An interface that enables the user to interact with the operating system by entering commands and optional arguments
coaxial cable A coaxial cable is a cable consisting of a hollow outer cylindrical con-ductor that surrounds a single inner wire concon-ductor
collision In Ethernet, the result of two nodes transmitting simultaneously The frames
from each device impact and are damaged when they meet on the physical media See
also collision domain.
collision domain In Ethernet, the network area within which frames that have collided are propagated Repeaters and hubs propagate collisions; LAN switches, bridges, and routers do not
command-line interface (CLI) An interface that enables the user to interact with the operating system by entering commands and optional arguments
connectionless Data transfer without the existence of a virtual circuit
connection-oriented Data transfer that requires the establishment of a virtual circuit
convergence The speed and capability of a group of internetworking devices running
a specific routing protocol to agree on the topology of an internetwork after a change
in that topology
count to infinity A problem that can occur in routing algorithms that are slow to converge in which routers continuously increment the hop count to particular networks Typically, some arbitrary hop-count limit is imposed to prevent this problem
crossover cable A cable that crosses the critical pair to properly align, transmit, and receive signals on the device with line connections
crosstalk The transmission of signals from one wire pair to nearby pairs Adjacent wire pairs in the cable act like antennas generating a weaker but similar electrical signal onto the nearby wire pairs This crosstalk causes interference with data that might be present on the adjacent wires
Trang 7CSMA/CD (carrier sense multiple access collision detect) A media-access mechanism
wherein devices ready to transmit data first check the channel for a carrier If no carrier
is sensed for a specific period of time, a device can transmit If two devices transmit at
once, a collision occurs and is detected by all colliding devices This collision subsequently
delays retransmissions from those devices for some random length of time CSMA/CD
access is used by Ethernet and IEEE 802.3
cut-through switching A packet-switching approach that streams data through a switch
so that the leading edge of a packet exits the switch at the output port before the packet
finishes entering the input port A device using cut-through packet switching reads,
processes, and forwards packets as soon as the destination address is looked up and
the outgoing port is determined See also store-and-forward switching.
data center A globally coordinated network of devices designed to accelerate the
delivery of information over the Internet infrastructure
data link layer Layer 2 of the OSI reference model Provides transit of data across a
physical link The data link layer is concerned with physical addressing, network
topol-ogy, line discipline, error notification, ordered delivery of frames, and flow control
datagram A logical grouping of information sent as a network layer unit over a
transmission medium without prior establishment of a virtual circuit IP datagrams are
the primary information units in the Internet The terms cell, frame, message, packet,
and segment also describe logical information groupings at various layers of the OSI
reference model and in various technology circles
daughter card Similar to an expansion board, but it accesses the motherboard
com-ponents (memory and CPU) directly instead of sending data through the slower expansion
bus
DCE (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
debugging To find and remove errors (bugs) from a program or design
decibel An important way of describing networking signals as a unit that measures
the loss or gain of the power of a wave Decibels are usually negative numbers
repre-senting a loss in power as the wave travels, but can also be positive values reprerepre-senting
a gain in power if the signal is amplified
de-encapsulation Unwrapping data in a particular protocol header
Trang 8delay skew The propagation delays of different wire pairs in a single cable can differ slightly because of differences in the number of twists and electrical properties of each wire pair Delay skew is the delay difference between pairs
demarc The point at which the service provider’s cable interfaces with the building distribution cabling
demarcation point Usually the point at which the access provider’s facilities stop and the customer-owned structured cabling begins
another in a given amount of time
dispersion Dispersion is the broadening of light signals along the length of the fiber
distance vector routing protocol A class of routing algorithms that iterate on the number of hops in a route to find a shortest-path spanning tree Distance vector routing algorithms call for each router to send its entire routing table in each update, but only
to its neighbors Distance vector routing algorithms can be prone to routing loops but are computationally simpler than link-state routing algorithms Also called a Bellman-Ford routing algorithm
distance-vector routing A class of routing algorithms that iterate on the number of hops in a route to find a shortest-path spanning tree Distance-vector routing algorithms call for each router to send its entire routing table in each update, but only to its neigh-bors Distance-vector routing algorithms can be prone to routing loops but are compu-tationally simpler than link-state routing algorithms Also called the Bellman-Ford routing algorithm
DNS (Domain Name System) The system used in the Internet for translating names
of network nodes into addresses
DoS (denial-of-service) Type of attack on a network that is designed to bring the net-work to its knees by flooding it with useless traffic
dotted-decimal format In this notation, each IP address is written as four parts sepa-rated by periods, or dots
dotted-decimal notation A syntactic representation for a 32-bit integer that consists
of four 8-bit numbers written in base 10 with periods (dots) separating them Used to represent IP addresses on the Internet, as in 192.67.67.20
DSSS (direct-sequence spread spectrum) A technology in which transmissions are more reliable because each bit (1 or 0) is represented by a string of 1s and 0s, called
a chipping sequence
Trang 9DTE (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
gen-erated by the DCE DTE includes such devices as computers, protocol translators, and
multiplexers
dynamic routing Routing that adjusts automatically to network topology or traffic
changes Also called adaptive routing Requires that a routing protocol be run between
routers
EIA (Electronic Industries Association) EIA is a group that specifies electrical
trans-mission standards The EIA and TIA have developed numerous well-know communication
standards
ELFEXT (equal-level far-end crosstalk) A test that measures FEXT
EMI (electromagnetic interference) EMI is an electromagnetic field that has the
potential to disrupt the operation of electronic components, devices, and systems in its
vicinity
encapsulation Wrapping of data in a particular protocol header For example,
upper-layer data is wrapped in a specific Ethernet header before network transit Also, when
bridging dissimilar networks, the entire frame from one network simply can be placed
behind the header used by the data link layer protocol of the other network
encoding Process by which bits are represented by voltages
equipment room Space for equipment Also can be used as a telecommunications
room
Ethernet A baseband LAN specification invented by Xerox Corporation and
devel-oped jointly by Xerox, Intel, and Digital Equipment Corporation Ethernet networks
use CSMA/CD and run over a variety of cable types at 10, 100, and 1000 Mbps
Ethernet is similar to the IEEE 802.3 series of standards
expansion slot An opening in a computer, usually on the motherboard, where an
expansion card can be inserted to add new capabilities to the computer
extended ACL Compares source IP address, destination IP address, TCP/UDP port
number, and other criteria to the rules defining an extended ACL
extended-star topology A network in which a star network is expanded to include
an additional networking device that is connected to the main networking device
exterior gateway protocol (EGP) A routing protocol designed for use between
networks that are controlled by two different organizations
Trang 10Exterior Gateway Protocol (EGP) An Internet protocol used to exchange routing information between autonomous systems Border Gateway Protocol (BGP) is the most common EGP
exterior router In firewall architecture, the router that is connected to the Internet
is referred to as the exterior router It forces all incoming traffic to pass through the application gateway
exterior routes Routes to networks outside the autonomous system that are consid-ered when identifying a gateway of last resort
extranet Intranet-based applications and services that employ extended, secure access
to external users or enterprises
Fast Ethernet 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 such qualities as frame format, MAC mechanisms, and MTU Such similar-ities allow the use of existing 10BASE-T applications and network-management tools
on Fast Ethernet networks Fast Ethernet is based on an extension to the IEEE 802.3 specification
FDDI (Fiber Distributed Data Interface) A LAN standard, defined by American National Standards Institute (ANSI) 3T9.5, specifying a 100-Mbps token-passing net-work using fiber-optic cable, with transmission distances of up to 2 km FDDI uses a dual-ring architecture to provide redundancy
FEXT (far-end crosstalk) Crosstalk that occurs when signals on one twisted pair are coupled to another pair as they arrive at the far end of a multipair cable system
FHSS (frequency-hopping spread spectrum) A technology in which transmissions hop from one frequency to another in random patterns This feature enables the trans-missions to hop around narrowband interference, resulting in a clearer signal and higher reliability of the transmission
fiber-optic cable A fiber-optic cable is a physical medium capable of conducting modulated light transmission Compared with other transmission media, fiber-optic cable is more expensive but is not susceptible to electromagnetic interference Some-times called optical fiber
File Transfer Protocol An application protocol, part of the TCP/IP protocol suite, used to transfer files between network hosts
firewall One or more network devices, such as routers or access servers, designated
as a buffer between any connected public networks and a private network A firewall router uses access control lists and other methods to ensure the security of the private network