Advanced Glossary Of Internet Terms
ADC: Analog to Digital Converter
ADM: Add/Drop Multiplexer
AMI: Alternate Mark Inversion
ANSI: American National Standards Institute
API: Application Programming Interface
APNIC: Asia-Pacific Network Information Center
ARIN: American Registry for Internet Numbers
ARP: Address Resolution Protocol
ARPA: Advanced Research Projects Agency
ARQ: Automatic Repeat Request
ASN: Autonomous System Number
ATM: Asynchronous Transfer Mode
B3Z3: Bipolar 3-Zero Substitution
B8ZS: Binary 8-Zero Substitution
BRI: Basic Rate Interface
BER: Bit Error Rate
BOC: Bell Operating Company
BOOTP: Bootstrap Protocol
bps: bits per second
CatX: Category X cabling
CD: Carrier Detect
CHAP: Challenge Handshake Authentication Protocol
CHDLC: Cisco High-level Data Link Control
CIDR: Classless Internet Domain Routing
CIX: Commercial Internet eXchange association
CLEC: Competitive Local Exchange Carrier
CO: Central Office
CPE: Customer Provided Equipment/Customer Premise Equipment
cps: Cells per second
CRC: Cyclical Redundancy Check
CSMA/CD: Carrier Sense Multiple Access with Collision Detection
CSU/DSU: Channel Service Unit/Data Service Unit
CTE: Connected Telecommunication Equipment
CTS: Clear To Send
DB-X: Data Bus Connector-X
DCD: Data Carrier Detect
DCE: Data Carrier Equipment
DHCP: Dynamic Host Configuration Protocol
DLC: Digital Loop Carrier
DNS: Domain Name System
DS-0: Digital Signal, Level 0
DS-1 (T-1): Digital Signal, Level 1
DS-3 (T-3): Digital Signal, Level 3
DSP: Digital Signal Processing
DTE: Data Terminal Equipment
DTR: Data Terminal Ready
EGP: Exterior Gateway Protocol
EIA: Electronic Industries Association
EIGRP: Enhanced Interior Gateway Routing Protocol
EMI: ElectoMagnetic Interference
ESD: ElectroStatic Discharge
ESF: Extended Super Frame
FCC: Federal Communications Commission
FCS: Frame Check Sequence
FDDI: Fiber Distribution Data Interface
FQDN: Fully Qualified Domain Name
FDM: Frequency Division Multiplexing
FTP: File Transfer Protocol
Gbps: Giga-bits per second
GPIO: General Purpose Input Output
HDLC: High-level Data Link Control
HSP: Host Signal Processing
HTML: Hypertext Markup Language
HTTP: Hypertext Transfer Protocol
HTTPS: Hypertext Transfer Protocol Secure
IANA: Internet Assigned Numbers Authority
ICANN: Internet Corporation for Assigned Names and Numbers
ICMP: Internet Control Message Protocol
IEC: International Electrotechnical Commission
IEEE: Institute of Electric and Electronic Engineers
IESG: Internet Engineering Steering Group
IETF: Internet Engineering Task Force
IGMP: Internet Group Message Protocol
IGRP: Interior Gateway Routing Protocol
ILEC: Incumbent Local Exchange Carrier
IP: Internet Protocol
ISDN: Integrated Services Digital Network
ISO: Internet Standards Organization
ISOC: Internet Society
ISP: Internet Service Provider
ITU: International Telecommunications Union
IXC: IntereXchange Carrier
Kbps: Kilo-bits per second
L-X: Layer X in OSI Reference Model
LAN: Local Area Network
LATA: Local Access and Transport Area
LEC: Local Exchange Carrier
MAC: Media Access Control
Mbps: Mega-bits per second
MIB: Management Information Base
MTU: Maximum Transmission Unit
NAP: Network Access Point
NAT: Network Address Translation
NIC: Network Interface Card
NSF: National Science Foundation
NTP: Network Time Protocol
NNTP: Network News Transfer Protocol
NOC: Network Operations Center
OC-X: Optical Carrier, Level X
OSI: Open Systems Interconnection
OSIRM: OSI Reference Model
PAP: Point-to-point Authentication Protocol
PAT: Port Address Translation
POP: Point of Presence
POP: Post Office Protocol
POTS: Plain Old Telephone Service
PPP: Point to Point Protocol
pps: Packets per second
PRI: Primary Rate Interface
PSTN: Public Switched Telephone Network
PUC/PUCO: Public Utilities Commission
RARP: Reverse Address Resolution Protocol
RAS: Remote Access Server
RBOC: Regional Bell Operating Company
RFC: Request For Comment
RIPE NCC: Reseaux IP Europeens Network Coordination Center
RJ-X: Registered Jack-X
RS-X: Recommended Standard-X
RTS: Ready To Send
SF: Super Frame
SMTP: Simple Mail Transport Protocol
SNMP: Simple Network Management Protocol
SONET: Synchronous Optical Network
STA: Spanning Tree Algorithm
STP: Shielded Twisted Pair
STS-X: Synchronous Transport Signal, Level X
TCP: Transmission Control Protocol
TCP/IP: Transmission Control Protocol/Internet Protocol
TDM: Time Division Multiplexing
TFTP: Trivial File Transfer Protocol
TP: Twisted Pair
UDP: User Datagram Protocol
UTP: Unshielded Twisted Pair
VLAN: Virtual Local Area Network
VLSM: Variable Length Subnet Mask
VPN: Virtual Private Network
W3C: World Wide Web Consortium
WAN: Wide Area Network
WDM: Wavelength Division Multiplexing
Standards and Regulations Making Organizations
- American National Standard Institute (ANSI): Standards-setting, private,
non-profit organization which develops and promulgates standards for voluntary
use in the United States. ANSI was founded in 1918 and is supported by member
groups from private and public sector organizations. The primary goal of ANSI
is to improve the competitiveness of American business by facilitating the
development and promotion of standards. ANSI does not develop standards
itself, but facilities the development process by building consensus among
qualified groups. The principles of ANSI's standards process are consensus,
due process and openness. Internationally, ANSI promotes the use of American
standards and advocates American policy and technical positions. ANSI is the
sole American representative to the two major non-treaty international
standards organizations, the ISO and the IEC.
- American Registry for Internet Numbers (ARIN): Organization primarily
responsible for managing the allocation of IP Address space in North America,
South America, sub-Saharan Africa and the Caribbean. Specifically, ARIN is
charged with maintaining impartiality in the allocation and conservation of
Internet Protocol version 4 (IPv4) address space. Among ARIN's tasks in this
regard are IP Number registration including ISP CIDR, IP Network Number,
Autonomous System Number (ASN), Inverse Mapping (IN-ADDR), and Reassign (SWIP)
- Advanced Research Projects Agency (ARPA): Research and development arm of
the U.S. Department of Defense. ARPA was responsible for the development of
the Advanced Research Projects Agency Network (ARPANET), an experimental
network designed to connect computers in different geographic locations to
allow researchers to share information and other resources. In the mid 1970s,
ARPA became the Defense Advanced Research Projects Agency (DARPA). DARPA
continued to operate ARPANET, which eventually transformed into a
packet-switched network using TCP/IP protocols and subsequently laid the
groundwork for the development of the network now known as the Internet.
- Asia-Pacific Network Information Center (APNIC): APNIC is a collaborative
effort consisting of national Network Information Centers (NICs) and Internet
Service Providers within the Asian-Pacific region. The APNIC acts as a
regional Internet registry (the role ARIN plays in North America), providing
the allocation of IP address space to the Asian-Pacific region.
- Electronic Industries Association (EIA): Organization of manufacturers of
electronic equipment. The EIA is consortium of industry specific
sub-organizations. These organizations groups are the Consumer Electronics
Manufacturers Association (CEMA); the Electronic Components, Assemblies,
Equipment and Supplies Association (ECA); the Telecommunications Industry
Association (TIA); the Electronics Information Group (EIG); the Government
Electronics and Information Technology Association (GETA); JEDEC Solid State
Technology Association; and the Electronics Industries Foundation (EIF). The
EIA works to set standards for use by its members, raise public awareness of
the activity of its members, and lobby on behalf of its members.
- Federal Communications Commission (FCC): U.S. government regulatory
commission with oversight of radio, television, telephone, wireless and cable
communications. The FCC aims to promote competition, availability and quality
of communications services for the public good.
- Institute of Electrical and Electronic Engineers (IEEE): World's largest
technical professional society. IEEE is a not-for-profit association with an
origin dating back to 1884. IEEE aims to promote technological innovation. It
is a significant standards-making body responsible for many telecommunications
and computing standards, including many of the standards used in local area
networking. Through its technical publishing, conferences and consensus-based
standards activities, the IEEE produces 30 percent of the world's published
literature in electrical engineering, computers and control technology, holds
annually more than 300 major conferences and has more than 800 active
standards with 700 under development.
- International Standards Organization (ISO): Voluntary organization charted
by the United Nations which defines international standards covering all
fields other than electrical and electronic engineering which is the
responsibility of the IEC. In computing, the ISO is best known for the 7-Layer
OSI Reference Model. The U.S. representative to the ISO is ANSI.
- International Electrotechnical Commission (IEC): International standards
and conformity assessment body for all fields of electrotechnology. The
mission of the IEC is to promote, through its members, international
cooperation on all questions of electrotechnical standardization. The IEC
publishes standards and technical reports on a wide variety of subjects
including telecommunications, networking, electronics and communication
- International Telecommunications Union (ITU): Organization charted by the
United Nations with the aims of defining and adopting telecommunications
standards, regulating the use of radio frequency spectrum, and furthering
telecommunications development around the world.
- Internet Architecture Board (IAB): A technical advisory group of the ISOC.
It is chartered to provide oversight of the architecture of the Internet and
its protocols, and to serve, in the context of the Internet standards process,
as a body to which the decisions of the IESG may be appealed. The IAB is
responsible for approving appointments to the IESG from among the nominees
submitted by the IETF nominations committee. The IAB is also responsible for
editorial management and publication of the Request for Comments (RFC)
- Internet Assigned Numbers Authority (IANA): Organization that oversees the
registration of various Internet Protocol parameters, such as port numbers,
SMNP private enterprise numbers, protocol numbers, multicast addresses, PPP
numbers, and MIME media types.
- Internet Corporation for Assigned Names and Numbers (ICANN):
- Internet Engineering Steering Group (IESG): Group responsible for
day-to-day management of the IETF. The IESG is responsible for technical
management of IETF activities and the Internet standards process. As part of
the ISOC, it administers the process according to the rules and procedures
which have been ratified by the ISOC Trustees. The IESG is directly
responsible for the actions associated with entry into and movement along the
Internet "standards track," including final approval of specifications as
Internet Standards. The IESG is composed of the IETF Area Directors and the
- Internet Engineering Task Force (IETF): International, voluntary body
consisting of network designers, engineers, researchers, vendors, and other
interested individuals who work together to address and resolve technical and
operational problems on the Internet and develop Internet standards and
protocols. The IETF is divided into eight functional areas: applications,
internet, IP:next generation, network management, operational requirements,
routing, security, transport and user services. Each area has one or two area
directors. The area directors, along with the IETF/IESG Chair, form the IESG.
Each area has several working groups. A working group is a group of people who
work under a charter to achieve a certain goal. That goal may be the creation
of an informational document, the creation of a protocol specification, or the
resolution of problems in the Internet. Most working groups have a finite
- Internet Society (ISOC): International organization that was founded in
1992. The ISOC is dedicated to the growth, development and availability of the
Internet worldwide. It concerns itself with social, political and technical
issues related to the Internet. The ISOC is the charter organization for the
IETF and the IAB (the ISOC approves appointments to the IAB).
- InterNIC: Name given to a project which originated under a cooperative
agreement between Network Solutions, Inc and the National Science Foundation.
Under this agreement, the InterNIC provides domain name registration services
for domains ending in .com, .net, .org, and .edu.
- National Science Foundation (NSF): Independent U.S. government agency that
sponsors, funds, and fosters research and development in science and
engineering. In the mid-1980s, the NSF founded NSFNET, a network connecting
academic and research institutions. NSFNET was later connected to the Advanced
Research Projects Agency Network (ARPANET); this network developed in time
into what is now commonly called the Internet. The NSF has, over time,
transitioned itself out of the duties it had performed for the Internet.
- Reseaux IP Europeens Network Coordination Center (RIPE NCC): Collaborative
effort consisting of European organizations to oversee the allocation of IP
address space to the European region. Similar to role played by ARIN in North
- World Wide Web Consortium (W3C): International consortium that aims to
promote the continued development of World Wide Web. Specifically, W3C acts as
a clearinghouse for information about the web, oversees the standards process
for www protocols, provides implementations of protocols as samples for
developers, and develops applications to highlight new web technology.
OSI Reference Model
- Encapsulation: Method of data exchange between adjacent layers of systems
developed along the lines suggested by the OSI Reference Model (such as the
Internet). A protocol operating at a particular layer encloses the data it
wants to send in a data envelope. Besides the message, called the payload, the
data envelope also contains layer-to-layer protocol control information, such
as the size of the message and its destination. Once the data envelope is
made, it is handed down to next layer for processing. This layer, in turn,
encapsulates the envelope it receives as the payload in an envelope it builds,
adds its transmission control data, and passes the envelope to the layer below
it. At the receiving end of the communication, the opposite of encapsulation
occurs. A layer receives its data envelope, processes it, strips off the
transmission control information and hands the payload to the layer above it
- Open Systems Interconnection (OSI): Framework of standards for the
development of elements in a network aimed to increase overall compatible
among the elements. The framework proposed is called the OSI Reference Model.
OSI was developed by the ISO.
- OSI Layer X (Layer-X, L-X): Refers to a layer in the OSI Reference Model.
- OSI Reference Model (OSIRM): General model, developed by the ISO, for
network organization. The Model proposes a high-level framework for the
development of networking and computing elements. Its aim is to increase the
overall compatibility among computing elements by providing a common frame of
reference for hardware and software developers. The Model was developed after
the inception of the Internet. The Model does not precisely correspond to the
Internet, but is the common frame of reference used when discussing the
abstract design of the Internet. The Model has seven layers. Layer 1, the
Physical Layer, physical connectivity; Layer 2, the Data Link Layer, protocols
for communication between physical connections; Layer 3, the Network Layer,
protocols for host to host, network to network communication; Layer 4, the
Transport Layer, reliable, end-to-end communication; Layer 5, the Session
Layer; Layer 6, the Presentation Layer; Layer 7, the Application Layer.
Comparing the Model to the real world implementation of the Internet: Layer 1,
Ethernet cards, Token ring cards, cabling, multiplexers; Layer 2, electrical
signaling, ARP, PPP, HDLC, V.34, B8ZS; Layer 3, IP (and supporting protocols
like ICMP and IGMP); Layer 4, TCP; Layers 5-7, SMTP, POP, HTTP, FTP and the
client/server programs which implement these Internet services.
- Protocol: Rules, guidelines or procedures by which data is exchanged
between two or more communicating elements. The aim of a protocol is to define
as well as possible the parameters of data transfer. In data communications
and computing, a protocol might specify data format, characteristics of
signaling, timing, and error handling.
Glossary of Relevant Telecommunication Terms
- A & B Signaling: In DS-1 signaling, one bit
is removed from the sixth frame in each of the twenty channels. The bit is
used for control signaling. A & B Signaling reduces the effective bandwidth of
a DS-1 from 1.544Mbps to 1.536Mbps.
- Add/Drop Multiplexer (ADM): Multiplexer in
which capacity is expanded by adding cards to slots in the multiplexer
- Alternate Mark Inversion (AMI): Line-coding method
used on T1 and E1 circuits. In MI, szeros are represented by 01 during each
bit cell, and ones are represented by 11 or 00, alternately, during each bit
cell. AMI requires that the sending device maintain ones density. One density
is not maintained independent of the data stream.
- Analog to Digital Converter
(ADC): Converter commonly found at the local switching office where the
subscribers analog line is attached to the telephone switching equipment.
- Analog Signaling: Voice or data signaling in
which the source sound, a voice or modem, is converted into an electrical
signal which changes continuously, not discretely as with digital signaling,
relative to changes in the source. The electrical signal oscillates, with
respect to frequency, amplitude and phase, in a manner which directly
corresponds to changes in the qualities of the source sound: an analog signal
is analogous to the auditory shape of the source sound.
- Asynchronous Communication: Method of data
transmission in which data is transmitted at irregular intervals. Generally
asynchronous transfers will propend a start of transmission flag before the
transmission unit and follow it with an end of transmission flag. Data
communication down without clocking.
- Asynchronous Transfer Mode (ATM): High
bandwidth networking media and protocol capable of supporting many types of
traffic, such as voice, data and video. ATM is used as the low level carrying
protocol in both local and wide-area networking scenarios. The transmission
unit of ATM is a 53 byte packet, called a cell. A 5 byte header and 48 byte
payload comprise the cell. Having a fixed cell size makes management of ATM
traffic flow and allocation of ATM bandwidth to particular services efficient
and simple. The header field in an ATM cell identifies the virtual path
(virtual circuit) over which a packet is to travel, the virtual channel,
payload type, cell loss priority, and header error check.
- Automatic Repeat Request (ARQ):
Communication technique in which the receiving device detects errors and
- Bipolar 3-Zero Substitution (B3ZS): Line
coding methodology used on Ameritech DS-3 circuits.
- Binary 8-Zero Substitution (B8ZS): Line
coding methodology used on Ameritech DS-1 circuits. Line coding method on T1
and E1 circuits in which a special code is substituted whenever 8 consecutive
zeros are sent through the link. Tis code is then interpreted at the remote
end of the connection. This technique guarantees ones density independent of
the data stream. Also called bipolar 8-zero substitution.
- Bandwidth: 1) Maximum amount of data that
can be carried over a communication channel. Bandwidth is generally measured
in some multiples of bits per second. Common examples of bandwidth measures
are 56Kbps, 56 Kilo-bits per second, and 1.544Mbs, 1.544 Mega-bits per second.
In packet-switched networks, bandwidth is often measured in Packets per second
(pps). As packet-switched networks often have variable length packets, this is
often not a very reliable statistic. In ATM networks, bandwidth is sometimes
measures in Cells per second (cps). 2) The original meaning: The difference
between the highest and lowest frequencies available for network signals.
- Baud: Unit of signaling speed equal to the
number of discrete signal elements transmitted per second. Baud is synonymous
with bits per second, if each signal element represents exactly 1 bit.
- B-Channel: 64K channel in an ISDN BRI or PRI
- Bit Error Rate (BER): Ratio of bits received
in error to the total number of bits transmitted.
- Bell Operating Company (BOC): One of the 22
local telephone companies formed after the breakup of AT&T in the 1980s (e.g.,
The Pacific Telephone and Telegraph Company, The Ohio Bell Telephone Company,
South Central Bell Telephone Company). The BOCS were organized into seven
Regional Bell Operating Companies (RBOCs) with each RBOC owning some subset of
- Bonding: In ISDN BRI transmissions, refers
to the joining of the two 64K B-Channels to make one 128K channel.
- Basic Rate Interface (BRI): Form of ISDN
communication; made up of two 64K B-Channels for user data and one 16K
D-Channel for line control data.
- Carrier: Company which provides
communications circuits such as Ameritech.
- Cells per second (cps):
- Central Office (CO): Telephone company
facility where subscribers' lines are joined to switching equipment for
connecting subscribers to local and long distance services.
- Channel Service Unit/Data Service Unit (CSU/DSU):
Equipment which terminates a digital channel; the CSU/DSU is the 'modem' for
ISDN BRI, DS-1 and DS-3 communications.
- Checksum: Method for checking the integrity
of transmitted data. A checksum is an integer value computed from a sequence
of octets taken through a series of arithmetic operations. The value is
recomputed at the receiving end and comported for verification.
- Circuit: Connection (or path) made between
two points which are to communicate. A circuit is established before the
transfer of data and remains open for at least the duration of the session.
Through the circuit all the data of the session is sent. A circuit may be open
permanently between two points (a nailed-up circuit) or may be created for the
duration of the communication session and then taken down.
- Circuit Switched: Data transfer type in
which two points in a communication session have, or create, a circuit
connecting them over which they will communicate. Circuit switching differs
from Packet Switching in that the communication channel is created prior to
actual data transfer and is the sole channel through which data travels. In
Circuit Switching, routing decisions are not made by any intervening device
along the path of the circuit: a route is implicit in the circuit itself. In
Circuit Switching, data is sent and is received serially; circuit switched
data packets typically are not sequenced for re-assembly purposes, although
ATM is a notably exception to this.
- Cisco High-level Data Link Control (CHDLC):
Cisco's version of HDLC.
- Clear Channel: Digital circuit where no
framing or control bits (i.e. for signaling) are required, making the full
bandwidth available for communications.
- Clear To Send (CTS): Pin 5 on the
25-conductor RS-232-C interface or a signal used for hardware flow control
between the computer and a serial device.
- Clocking: In synchronous communication, a
periodic signal supplied to synchronize the transmission and reception of
- Clock Source: In synchronous communication,
the unit which provides clocking. Ameritech does not provide clocking on their
DS-1 or DS-3 circuits; this must be provided by one of the CSU/DSU's at the
ends of the circuit. Typically, the clock source of the CSU/DSU which is to
provide clocking designates it clock source as 'internal'; the other CSU/DSU
on circuit designates it clock source as 'external' or 'line'.
- Coder-Decoder (CODEC): Chip in a modem which
converts analog signals to digital ones to pass one to the modem datadump or
controller and reconverts the digital signal received by the datapump back
into an analog signal.
- Colocation: Situating equipment from one
company within the facilities of another. Companies colocate to save the cost
of developing their own facilities.
- Common Carrier: Licensed, private utility
company that supplies communication services to the public at regulated
- Competitive Local Exchange Carrier (CLEC):
Company which competes for local exchange and long distance service against an
Incumbent Local Exchange Carrier. CLECs were created out of the
Telecommunications Act of 1996.
- Connected Telecommunications Equipment (CTE):
Telephone equipment which is purchased by customer or resides on the
- Cross Connection: The point at which two
systems are linked together. Specifically, a Cross Connection is a connection
in which the pin order at the connecting point is reversed; cross connections
are made by modifying the pin order in the wire, at the patch plug or in the
- Cross Talk: Interfering energy transferred
from one circuit to another.
- Customer Provided Equipment/Customer Premise
Equipment (CPE): Telephone equipment which resides on the customer's premises.
- D-Channel: 16K control channel on ISDN BRI
circuits; the 64K control channel on ISDN PRI circuits.
- Data Bus Connector-X (DB-X): Hardware
connector, usually given with a number which represents the number of wire
conductors in the connector. Two common DB-X connectors are DB-9, the standard
nine pin RS-232-C serial port, and DB-25, the standard 25-pin, RS-232-C serial
- Data Carrier Detect (DCD): Signal sent from
the DCE device (typically, a modem) to the DTE device (typically, a computer)
to indicate that the modem is receiving a carrier signal from the DCE
(typically, a remote modem) at the other end of the telephone circuit.
- Data Communications Equipment (DCE): In the
RS-232 standard developed by the EIA, there are DCE devices (typically,
modems) and DTE devices (typically, PC's). The main difference between a DCE
and DTE in RS-232 is the wiring of pins two and three.
- Data Terminal Equipment (DTE): See
description of Data Communications Equipment.
- Data Terminal Ready (DTR): In the RS-232
standard, a control signal which is sent from the DTE to the DCE which
indicates that the DTE is powered on and ready to communicate. DTR can also be
used for hardware flow control.
- Digital Line Converter (DLC): Equipment that
aggregates lines and performs analog to digital signal conversion.
- Digital Signaling: Signaling method which
encodes a voice or data source into a series of 0s and 1s for transferring.
Unlike analog signaling, which mimics the source by mapping it into an
electrical wave which varies in frequency, amplitude, and phase, digital
signaling is discrete, that is, it represents the sound using only a stream of
0s and 1s.
- Digital Signal, Level 0 (DS-0): 56K or 64K
- Digital Signal, Level 1 (DS-1/T-1): In North
America, a DS-1 is a circuit is made up of 24 DS-0 channels. The total
bandwidth of a DS-1 circuit is 24 x 64K = 1.544Mbps. A DS-1 is commonly
referred to as a T-1.
- Digital Signal, Level 3 (DS-3/T-3): DS-3
circuit is made up of 28 DS-1. The total bandwidth of a DS-3 is 28 x 1.544M =
44.736Mbps. A DS-3 is commonly referred to as a T-3.
- Digital Signal Processing (DSP): A DSP modem
is own that uses its own chipset to handle the modem communications E1:
Wide-area digital transmission scheme used predominantly in Europe that
carries data at a rate of 2.048Mbps. E3: Wide-area digital transmission
scheme, used predominantly in Europe that carries data at a rate of
34.368Mbps. Error Control: Techniques for detecting and correcting errors in
data transmissions. ElectroStatic Discharge (ESD): Discharge of stored static
electricity that can damage electronic equipment and impair electrical
circuitry, resulting in complete or intermittent failures.
- Extended Super Frame (ESF): Framing mode
used by Ameritech on DS-0, DS-1 and DS-3 circuits. Circuits using ESF have
DS-0 channels that utilize the entire 64K DS-0 frame. Such a circuit is
characterized as Clear Channel.
- Fiber Optics: Communication technology in
which light is used to transport information from one point to another.
- Flow Control: Technique for ensuring that a
transmitting entity, such as a modem, does not overwhelm a receiving entity
with data. When the buffers on the receiving device are full, a message is
sent to the sending device to suspend the transmission until the data in the
buffers has been processed.
- Fractional DS-1 (Fractional T-1): DS-1
circuit in which a fraction of the 24 DS-0 channels are utilized.
- Frame Check Sequence (FCS): Refers to the
extra characters added to a frame for error control purposes. Used in HDLC,
Frame Relay and other data link layer protocols.
- Frame Relay: With regard to delivery of DS-1
or DS-3 service and contrasted to a Point-to-point implementation of these two
circuit types, frame relay bundles a customer's circuit into a set. This set
is then carried over a frame relay cloud and delivered to the opposing end of
the circuit. Frame Relay is used mainly to link sites that are a good distance
apart and in which the mileage charge of a Point-to-point link would be
prohibitive. Industry-standard, switched dat link layer protocol that handles
multiple virtual circuits using HDLC encapsulation between connected devices.
Frame Relay is more efficient that X.25, the protocol for which it is
generally considered a replacement.
- Frequency: Number of cycles, measured in
hertz, of an alternating current signal per unit of time.
- Frequency Division Multiplexing (FDM):
Signaling technique in which transmission bandwidth is divided by frequency
into bands for carrying separate data or voice traffic.
- Handshake: Sequence of messages exchanged
between two or more network devices to ensure transmission synchronization.
Headend: End point of a broadened network. Al stations transmit toward the
headend; the headend then transmits toward the destination stations.
- High-level Data Link Control (HDLC):
Protocol standard for point-to-point and multi-point connections; it or PPP is
the protocol most commonly used to link the routers at the endpoints of a DS-1
or DS-3 circuit. 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.
- Host Signal Processing (HSP): Software-based
modems. Modems which use the host PC's CPU to do most of the processing work.
- Incumbent Local Exchange Carrier (ILEC):
Carrier created from the break up of AT&T in the 1980s or having existed
separately from AT&T altogether. GTE (Verizon), Cincinnati Bell, and Ameritech
are examples of ILEC's.
- Integrated Services Digital Network (ISDN):
Form of digital data delivery. Ameritech supports two types of ISDN service:
Basic Rate Interface (BRI) and Primary Rate Interface (PRI).
- IntereXchange Carrier (IXC): Long-haul long
distance carrier. Also known as IEC, InterExchange Carrier. Some IXC's are
AT&T, MCI and Sprint.
- Isochronous Communication: Data
communication in which there is no delay (or very minimal delay) between the
send and receive sides of the channel. Isochronous Communication is needed for
services like voice and video conferencing where a delay is intolerable.
- Jabber: Error condition in which a network
device continually transmits random, meaningless data onto the network. In
IEEE 802.3, a data packet whose length exceeds that prescribed in the
standard. Jitter: Analog communication line distortion caused by the variation
of a signal from its reference time positions. Jitter can cause data loss,
particularly at high speeds. Load Coil:
- Local Access and Transport Area (LATA):
Telephone service region. The court decision which broke up AT&T in the early
1980s defined nearly 200 distinct telephone service regions. Region boundaries
were drawn, for the most part, in consideration of geographical distances.
These regions, the LATAs, were generally provided with service by one BOC
(and, hence, one RBOC). The main purpose of the LATA concept was to delineate
what service would fall to the LEC (e.g., Ameritech, Nynex) and what to the
IXCs (e.g., AT&T, MCI): intraLATA traffic belonged to the LECs; interLATA, to
- Local Exchange Carrier (LEC): A local phone
company. Ameritech is a LEC to Lancaster. GTE (Verizon) is a LEC to those
areas around Lancaster not serviced by Ameritech.
- Local Loop: Link from premise to central
office. In a DS-1 or DS-3 circuit, there are two local loops: one from each
end back to the CO. At the CO the loops are joined to complete the circuit.
- Loopback: Diagnostic test in which a signal
is transmitted across a medium by a sending device which, after sending, waits
for the return of the signal. Loopbacks are used to verify the integrity of a
- Modulator/De-Modulator (Modem): Equipment
which converts digital signals to analog and vice-versa for communication over
the analog PSTN.
- Multiplexer (MUX): Electronic equipment
which allows two or more signals to pass over or share one communications
- Ones Density: scheme that allows a CSU/DSU
to recover the data clock reliably. The CSU/DSI derives the data clock from
the data that passes through it. In order to recover the clock, the CSU/DSU
hardware must receive at least one 1 bit value for every 8 bits of data that
pass through it. Also called pulse density.
- Optical Carrier-X (OC-X): Scale used to
measure the carrying capacity or bandwidth of a SONET network. The base rate,
OC-1, is 51.84Mbps. A SONET of OC-X has a rate, or bandwidth capacity, of X x
OC-1. Accordingly, an OC-3 SONET has the bandwidth capacity of 3x51.84M=
155.52Mbps; an OC-12 SONET, the bandwidth capacity of 12x51.84M= 622.08Mbps.
OC-X scaling corresponds directly to electrical STS-X scaling.
- Packets per second (pps):
- Plain Old Telephone Service (POTS): Regular
analog phone service. Also refers to the components that go into regular phone
service: the telephone, the lines and the phone network.
- Point of Presence (POP): Place within a
telecommunications service region where telecommunication providers locate
their equipment to interface with the LEC of that region.
- Point-to-point: With regard to delivery of
DS-1 or DS-3 service and contrasted to a Frame Relay implementation of these
circuit types, Point-to-point circuits are directly connected to one another
and not bundled with other circuits at either end of the circuit or along any
section of the route taken by the circuit.
- Point-to-point Protocol (PPP): Protocol
standard for point-to-point and multi-point connections; it or HDLC is the
protocol most commonly used to link the routers at the endpoints of a DS-1 or
DS-3 circuit. PPP is the most common protocol used to link Internet dial-up
users with their provider.
- Primary Rate Interface (PRI): Form of ISDN
delivery. A PRI is delivered on top of a DS-1 circuit and is made up of twenty
three 64K B-Channels for user data and one 64K D-Channel for line control
- Public Switched Telephone Network (PSTN):
Local telephone company.
- Public Utilities Commission (PUC/PUCO):
State commission charged with overseeing public utility companies such as the
telephone and electric companies.
- Regional Bell Operating Company (RBOC): One
of the seven companies created out of the divesture of AT&T in the 1980's.
Each of the RBOCs were given some number of the 22 BOCs to oversee. The
original seven were Ameritech, Bell Atlantic, BellSouth, Nynex, Pacific
Telesis, Southwestern Bell and US West.
- Recommended Standard-232 (RS-232/RS-232-C):
Set of standards which specify the electrical, wiring and connector pin
assignments for interfacing modems (DCE devices) with terminals and computers
(DTE devices). Typically an RS-232-C connector has either 25 or 9 pins. Most
PC's are built with support for both pin types.
- Registered Jack-X (RJ-X): Telephone and
networking plugs that have been registered with the FCC. Some common RJ jacks
are: RJ-11, 2-pair (4 wire), used to connect a phone or modem to wall jack;
RJ-22, 2-pair (4 wire), used to connect a telephone handset to the telephone
unit, the plugs are slightly more narrow than RJ-11 ones; RJ-45, 4-pair (8
wire), used in the cabling for many computer networking types such as Ethernet
and Token Ring; RJ-48C, 4-pair (8 possible wire, only 4 used), used to deliver
DS-1 service from the teleco customer premise demark into customer T-1
terminating equipment (i.e. from the smart jack to the CSU/DSU), two wires
used for sending and two for receiving.
- Ready To Send (RTS): Hardware flow control
signal. Used in an RS-232-C connector to place a modem in originate mode for
- Self-healing: Ability for a local or wide
area network to re-route traffic around a failed link or failed piece of
equipment to maintain uninterrupted service.
- SONET Ring: Network having a ring topology
and using SONET protocols.
- Super Frame (SF): Framing mode used on DS-0,
DS-1 and DS-3 circuits. This is not the framing mode typically used by
Ameritech. Circuits using SF have DS-0 channels that utilize 56K of the 64K
DS-0 frame for communication and 8K for control and signal information.
Circuits using SF as framing mode are not Clear Channel.
- Switch: In telecommunications, equipment
which concentrates subscribers' lines and creates the circuits necessary for
local and long distance services.
- Synchronous Communication: Transmission
method in which the communicating units synchronize the sending and arrival of
data by agreeing to some clock and timing mechanism. In synchronous
communications, data is spaced by time, not by transmission start and stop
- Synchronous Optical Network (SONET): Suite
of protocols used for optical data communications. SONET supports bandwidth
capacity from 51.84Mbps to 13.21Gbps.
- Synchronous Transport Signal, Level X
(STS-X): Electric signaling rate (the bandwidth) for a SONET transmission
medium. The STS-1 rate is 51.84Mbps; STS-3 rate is 3x51.84M= 155.52Mbps. The
corresponding optical signaling rate is OC-X.
- T1: See Digital Signal, Level 1 (DS-1)
- T3: See Digital Signal, Level 3 (DS-3)
- Time Division Multiplexing (TDM): Technique
for sending multiple signals simultaneously over one communications medium by
interleaving a piece of each signal one after the other.
- Throughput: Amount of error free data
transmission over a communication medium. Bandwidth minus errors.
- V.34: An international standard for speeds
up to 33.6kpbs.
- Wavelength Division Multiplexing (WDM):
Technique of increasing the capacity of an optical fiber by multiplexing
different signals simultaneously. The multiplexing is done by placing the
different signals on different wavelengths.
Glossary of Relevant Local Area Networking Terms (Layers 1 and 2 of OSI
- Address Resolution Protocol (ARP): Protocol
in the TCP/IP protocol suite which maps IP Addresses to their MAC Addresses.
The protocol is used primarily in Ethernet networks. When a host wants to send
data to an IP Address on its own IP Network and does not have the MAC Address
of the recipient already in its ARP cache, it sends a Broadcast Packet asking
other stations on the network if they have that IP Address. The station which
does have the IP Address responds to the sender of the ARP request giving its
own MAC address.
- Baseband: Form of signal modulation in which
signals are pulsed directly onto the transmission medium without Frequency
Division. Local Area Networks will use one of two signal modulation types:
Broadband or Baseband. In Baseband, the entire bandwidth of the LAN cable is
used to transmit a single digital signal; in Broadband, multiple signals are
carried on the cable by using different wave frequencies. Multiple signals may
be carried on Baseband by using a technique called Time Division Multiplexing.
Baseband LAN's generally work using one high speed channel to which all
network devices are attached. Ethernet 10Base-2 (Thin Net) is an common
example of Baseband in a LAN.
- Big-Endian: Method of storing or
transmitting data in which the most significant bit or byte is presented
- Bridge: Data communications device which
connects two or more networks segments and forwards packets between them.
Bridges may also work with similar or dissimilar media and signaling systems.
Bridging works at Layer 2 of the OSI Reference Model. Bridges are also called
Data Link relays or Layer 2 relays.
- Bridging: Connecting two or more networks
segments together and forwarding packets between them.
- Broadband: Transmission facility which may
carry multiple signals simultaneously. Each signal that is carried uses a
different wave frequency on the cable. Coaxial cable delivery of television
service is a familiar example of Broadband.
- Broadcast Domain: The set of all devices
that will receive broadcast frames originating from any device with the set.
Broadcast domains are typically bounded by routers because routers do not
forward broadcast frames.
- Broadcast Packet: Data packet sent to all
devices on a network. Ethernet uses a MAC Address FF-FF-FF-FF-FF-FF as the
destination address. This address is also referred to as the broadcast
address. ARP is a protocol that uses Broadcast Packets when it queries the
network for the MAC Address of an IP Address.
- Cable Plant: Physical makeup of a network:
NIC's, cables, connectors, hubs. In an Ethernet network, the Cable Plant is
also called the Ether.
- Carrier Detect (CD): Signal that indicates
whether an interface is active. Also, a signal generated by a modem indicating
that a call has been connected.
- Carrier Sense Multiple Access with Collision
Detection (CSMA/CD): Layer 2 algorithm used in LAN protocols, most notably,
Ethernet, to handle packet collision. A collision may occur in a network where
multiple, simultaneous access to the Cable Plant is possible. Network devices
wishing to transmit check whether the cable plant is busy (Carrier Sense). If
there are signals on the cable plant, it is said to be busy; if there are no
signals on the cable plant, it is said to be quiet. If the cable plant is
quiet, the device may then send one packet. If another device transmits during
this time, a collision is said to have occurred. Devices detect a collision by
looking for regulates in the signal on the cable plant or in the malformation
of the frame having been delivered (Collision Detection). All devices whether
quiet or sending must continually check the cable plant for collisions. When a
collision occurs, all sending devices invoke a collision back off algorithm to
avoid a subsequent collision.
- Category X Cabling (CatX): Specifications of
quality of electrical cabling used in computer networks. Each category defines
physical characteristics of cabling (e.g., shielding, cable thickness,
materials in outer jacket) and cable connecting devices (e.g., RJ45 mail and
female jacks, RJ45 extenders) that should be met by manufactures in order that
the cabling support a given network transmission speed. Cat3 (10Mbps), Cat5
(100Mbps) and Cat5 Enhanced are common Category X ratings.
- Collision: Overlapping transmission of two
or more data frames across a communication channel incapable of carrying them
simultaneous. Collisions result in the loss of integrity in the frames.
- Collision Domain: That part of the cable
plant in which the possibility for a Collision of packets exists. Also known
as a Collision Zone.
- Concentrator: Device which provides access
to network for multiple network nodes. Also known as a hub.
- Congestion: Condition where available
network capacity is exceeded by network demand. Results in a slowdown in
- Connectionless Networking: Networking in
which data sent between two points does not necessarily follow a well-defined
path. Packets are delivered on a best-effort basis, with generally no
acknowledgment of delivery given by recipient to sender. Connectionless
protocols will generally perform some integrity check on individual packets,
but no expectation is given to recipient that packets will arrive in order.
Proper ordering of data packets is left to higher-level protocols or is
implemented in the connectionless protocol itself through some form of packet
sequencing. In the OSI Reference Model, some examples of Layer 2
Connectionless protocols are Ethernet, Token-Ring, and FDDI; at Layer 3, IP is
an example of a Connectionless protocol.
- Connection-Oriented Networking: Networking
in which data sent between two points takes a well-defined path. The path may
exist permanently or may be created for the duration of a single data transfer
session. One important characteristic of Connection-Oriented Networking is an
expectation that data will arrive at the destination in the order in which it
was sent. Some Layer 2 examples of Connection-Oriented Networking are the PSTN
- Crossover Connection: The point which
bridges two network segments in 10Base-T and 100Base-T Ethernet networks.
Crossovers generally occur between two hubs through special wiring in the
cable which connects them, a crossover cable, or special wiring in one of the
ports being connected, a crossover port.
- Cyclical Redundancy Check (CRC): Method of
error checking in packet transmission to determine whether the packet sent was
the packet received. The sender computes a value based upon the packet and
places it within the packet. When the packet is received, the recipient, using
the same algorithm as the sender, computes a value itself and compares it to
the value that was placed in the packet. If the values are the same this
indicates, with a very high probability, that the transmission was successful;
different values are absolute indicators of transfer fault and results in
packet rejection. CRC checking is implemented in Ethernet NIC's to validate
- Datagram: Transmission unit of a networking
protocol in which a message is broken into pieces, those pieces sequenced and
then sent to the source in no particular order and over no well-defined path.
Properly speaking, networking protocols that are Connectionless and that
sequence their data units (e.g., IP) use a datagram as their data unit, not a
- Destination Address: Address of a network
device that is receiving data. DMA.
- Duplex: Characterizes a device which is
capable of both transmitting and receiving. Moreover, a device which can
transmit and receive simultaneously is called full-duplex; a device unable to
transmit and receive simultaneously, half-duplex.
- Electromagnetic Interference (EMI):
Interference by electromagnetic signals that can cause reduced data integrity
and increased error rates on transmission channels.
- Ether (The Ether): Passive transmission
media in an Ethernet network. Physically, the Ether is made up of NIC's,
cables, connectors and hubs.
- Ethernet: Family of Connectionless LAN
communications media and protocols which operate at Layers 1 and 2 of the OSI
Reference Model. The communication channel in Ethernet is a passive
transmission medium shared by all attached devices. Packet address recognition
in each station is used to take packets from the channel. Access to the
channel by stations wishing to transmit is coordinated in a distributed
fashion by the stations themselves, using a statistical arbitration scheme,
CSMA/CD. IEEE 802.3 is the standard Ethernet specification. Ethernet networks
typically operate at speeds of 10Mbps or 100Mbps in half-duplex or full-duplex
modes. Some common Ethernet implementations are: 10Base-2 (aka. Thin Net),
10Mbps half-duplex, signal pulsed Baseband over coaxial cable, bus topology,
T-connector to bus; 10Base-T, 10Mbps half-duplex, signal pulsed Baseband over
Cat 3 or better Twisted Pair wiring, star topology connecting into an Ethernet
Hub, RJ-45 connector to hub; 100Base-TX (aka. Fast Ethernet) 100Mbps half- or
full-duplex, signal pulsed Baseband over Cat 5 or better UTP wiring or Type 1
STP wiring, star topology connecting into an Ethernet Hub, RJ-45 connector to
hub; 100Base-FX, 100Mbps half- or full duplex modes, optical signaling over
62.5/125-micron fiber cable, star topology connecting into a fiber Ethernet
hub. Ethernet is the most popular LAN media/protocol.
- Ethernet Hub: A device which concentrates
the network connection in an Ethernet network having a star topology. There
are two basic types of Ethernet Hubs: passive and active. A passive hub
forwards any packet it receives to all its ports. Passive hubs are often
called simply Ethernet concentrators. An active hub forwards a packet only to
the port (or ports) through which the packet's destination can be reached. An
active hub improves network performance by reducing packeting Collision
Domains to those of the sending and receiving ports (i.e. packets are
switched). Moreover, many active hubs are built with buffers for caching which
can detain a packet if sending would result in collision, furthering network
performance. Active Ethernet Hubs are commonly called Ethernet Switches or
Layer 2 Ethernet Switches. Besides concentrating network connections, Ethernet
Hubs often are used as Bridges from one Ethernet media to another (for
example, 10Base-2 to 10Base-T) or from one network segment to another.
- Fiber Distribution Data Interface (FDDI):
100Mbps fiber optic LAN technology. FDDI uses dual-ring topology with data
transferring managed by token ring passing.
- Fragmentation: Process of breaking a packet
into smaller units when transmitting over a network medium that cannot support
a packet of the original size. See also reassembly.
- Frame: Group of data bits sent serially with
a flag at the beginning and at the end of the transmission unit to indicate
the start and the end of frame. Data packets in Layer 2 transmissions are
often called frames.
- Latency: Delay in the time it takes for a
packet to reach its destination. Factors which affect latency are speed of
physical media, bandwidth of media, bandwidth of media, packet size, route
lookup, traffic load and any protocol conversion. In the context of a router,
switch or bridge device, latency is the length of time it takes for a packet
be transmitted after it has been received.
- Layer-2 Switch (L-2 Switch): Ethernet hub in
which data is sent only to the port (or ports) where it is destined. Also
called an active Ethernet hub.
- Local Area Network (LAN): Network that
covers a relatively short distance. Generally a LAN is implemented using one
type of physical media and will use common set of protocols throughout it.
Typical media used for LANS are Ethernet and Token Ring.
- MAC Address: Address of an Network Interface
Card (NIC) or other network interface device. Often called a physical address,
hardware address or PROM address; with an Ethernet card, also called the
Ethernet address. All MAC addresses for are 48 bits long and are expressed
hexadecimally. Typically, MAC Addresses are stored on PROM by the
manufacturer, although some NIC MAC Addresses are programmable. The first
three bytes in MAC Address on non-programmable NICs will indicate the
manufacturer. All MAC Address on the same network must have different MAC
Addresses. An example of an Ethernet MAC Address is 08-00-20-d3-7f-05.
- Maximum Transmission Unit (MTU): Maximum
packet size, i butes, that a particular interface can handle.
- Media Access Control (MAC): Specifications
on LAN frame format and logic for accessing the physical medium of a network.
In the OSI Reference Model, MAC specifications would be placed at the bottom
half of Layer 2.
- Multicast Packet: Packet which is sent to
some number of network devices. At Layer 2 of the OSI Reference Model, a
Multicast Packet is identified by having a particular bit set in its
destination MAC address. When set, the remainder of the MAC Address is used to
indicate the type of multicast service. The combination of multicast bit and
remainder bits in the destination MAC Address is called a Multicast Address. A
Multicast Address may be reserved by some standard multicasting service or may
be used by some local multicasting service. Spanning Tree is an example of a
multicasting service that has a Multicast Address reserved for it. When a
bridge needs to send Spanning Tree information to other bridges, it will set
the destination address of the packet to the Multicast Address reserved by
Spanning Tree. Other bridges participating in Spanning Tree accept the packet
for processing, while all other network devices ignore the packet.
- Network: Entity composed of things and
connections among those things. The term network is over-used in computing.
Often it is confusing to understand its meaning when it is not used in context
or when not properly qualified. It might mean, for example, a homogeneous
segment in which the same physical media and low-level protocols are used,
such as an Ethernet Network, a Token Ring Network, an ATM Network. It might be
used to describe the geographical area covered, such as a Local Area Network,
a Wide Area Network or a Metropolitan Area Network. It might be refer the area
over which high-level protocols are carried, such as an IP Network, an
Appletalk Network, an SNA Network.
- Network Interface Card (NIC): Card which
attaches a host or other device into a network. NICs are responsible for
electronic or optical signaling with the LAN. Ethernet, Token Ring, and FDDI
cards are types of NIC's.
- Packet: Generic term for a bundle of data,
usually in binary form, organized in a specific way for transmission. The
specific native protocol of the data network may term the packet as a packet,
block, frame or cell. A packet consists of the data to be transmitted and
certain transmission control information. The three principal parts of a
packet include: the header, control information such as synchronizing bits,
address of destination or target device, address of originating device, length
of packet; text or payload, the data to be transmitted; the trailer, end of
packet, error detection and correction bits.
- Packet Switched: Data transfer type that
bundles transfer data into semi-independent data units, packets, which
traverse between two points over no single pre-defined route. Packet Switching
differs from Circuit Switching most essentially in that no end-to-end route is
established prior to transfer. In Packet Switched networks data packets are
neither sent nor received serially; intervening devices along a path
connecting end-points may make decisions as to what route to send along a
packet; different packets may take different routes from source to
destination. Often sequence information is stored in packets (in which case
the packet is called a Datagram) so that they may be properly put into order
at the destination.
- Payload: Data carried in a packet: the
packet minus addressing information, checksum, type field and other transfer
control information. The payload is the data which represents the reason for
sending a data packet.
- Peer-to-Peer Network: Network in which there
is not a single device having control of network activity: each host may send
and receive equally. 10Base-2 Ethernet is an example of Layer 2 Peer-to-Peer
networking. Peer-to-peer networks do not scale well to larger networks because
of issues with performance and security.
- Physical Network: The physical components of
a network: hosts, devices, cabling, connectors.
- Promiscuous Mode: When an Ethernet
controller is set to receive all packets. An Ethernet controller is the
component in an Ethernet NIC that monitors the cable plant for electrical
signaling. Generally, an Ethernet controller accepts a packet under one the
following conditions: 1) the destination MAC Address is the MAC Address of the
controller; 2) the destination address is the broadcast address; 3) the
destination address is a multicast address; 4) the NIC is set to accept all
packets, promiscuous mode. Promiscuous mode is typically used for network
analysis. The Unix command tcpdump places a NIC in promiscuous mode.
- Repeater: Device added to a run of cable to
boost the electrical signal between the endpoints. Repeaters are used to
extend the cable range.
- Shielded Twisted Pair (STP): A pair of
insulated wires which are twisted together in a spiral manner. In addition,
the pair is wrapped with metallic foil or braid, designed to insulate the pair
from electromagnetic interference.
- Source Address: Address of a network device
that is sending data. SMAC.
- Spanning Tree Algorithm (STA): An algorithm
run by Bridges and used to prevent logic loops in a bridged network which may
contain loops in its physical design. When multiple paths exist, STA lets a
Bridge use only the most efficient one. If that path fails, STA automatically
re-configures the network to make another path become active. Bridges using
Spanning Tree communicate with one another through Multicasting Spanning Tree
- Thick Ethernet Cable (Thick Net): 0.4 inch
diameter, 50-ohm coaxial cable.
- Thin Ethernet Cable (Thin Net): 0.2 inch,
RG58A/U, 50-ohm coaxial cable. Thin net uses cable having a smaller diameter
than Thick Net. Because of its relative in expense and ease in deployment,
Thin Net is a popular type Ethernet wiring, second only to Twisted Pair. An
Ethernet scheme using Thin Net cable is 10Base-2.
- Token Ring: Layer 1 and 2. A ring consists
of stations and transmission medium. Data travels sequentially from station to
station. Only the station in possession of the token is allowed to transmit
data. Each station repeats the data, checks for errors, and copies the data if
appropriate. Then the data is returned to the sending station, it removes the
data from the ring. Token operates at ring speeds of 4Mbs and 16Mbps.
- Token Ring Passing:
- Topology: The physical layout of a LAN. Some
common LAN topologies are Bus, every machine attached to one other machine.
Ring, Mesh, Partial Mesh. Star.
- Twisted Pair (TP): Two insulated copper
wires twisted around each other to reduce induction (thus interference) from
one wire to the other. The twists, or lays, are varied in length to reduce the
potential for signal interference between pairs. Several sets of twisted pair
wires may be enclosed in a single cable. Common such types are four-pair and
25-pair. Twisted pair cable is the most common type of Local Area Network
transmission media. Ethernet cabling schemes using Twisted Pair cable are
10Base-T and 100Base-T.
- Unicast Packet (Frame): A packet sent to a
single network device. At Layer 2 of the OSI Reference Model, Unicast
transmissions use the MAC Address of the recipient as the destination of the
- Unshielded Twisted Pair (UTP):
- Virtual Local Area Network (VLAN):
Workstations or other such devices connected into an active hub that is
capable of defining LAN membership.
- Wide Area Network (WAN): A network that uses
common carrier provided lines to cover extended geographical distances. A WAN
typically uses leased phone lines such as a DS-1. The link between a LAN and
WAN is made through a device called a bridge or a router.
Glossary of Relevant Internet Terms (Layer 3 of OSI Reference Model)
- Access List: List kept by routers to control
access to or from the router for a number of services (for example, to packets
with a certain IP address from leaving a particular interface on the router).
- Acknowledgment (ACK): Notification sent from one network device to another to
acknowledge that some event (for example, receipt of a message) has occurred.
- Application Programming Interface (API): Specifications of function call
conventions that defines an interface to a service.
- Autonomous System Number (ASN):
- Backbone: The part of a network that acts as
the primary path for traffic that is most often source from, and destined for,
- Backbone Provider:
- Blackhole: Routing term for an area of the
network (or Internet) where packets enter, but do not emerge due to adverse
condition or poor system configuration within a portion of the network.
- Bootstrap Protocol (BOOTP): A protocol
within TCP/IP protocol suite which allows machines to retrieve startup
information, such as their IP Address, from the network.
- Border Gateway (Border): Router that
communicates with routers in other autonomous systems.
- Broadcast Packet:
- Challenge Handshake Authentication Protocol
(CHAP): An authentication method at the beginning of a usage session. CHAP is
similar to PAP, another authentication method, but encrypts the authenticating
data, such as the password.
- Classful IP Network: A network that defines
its Internet Protocol behavior based upon the first three bits of the IP
Address. There are three types of Classful IP networks in practice: Class A
(network range of 0.-127.), Class B (network range of 128.-191.), and Class C
(network range of 192.-223.). Class A networks use the first octet to indicate
the network portion of the IP Address and the last three octets to indicate
the host; consequently, there are 126 possible Class A networks (0. and 127.
are reserved) with each of these networks having 2^24 = 16,777,214 possible
hosts. An example of an Class A network is 22.214.171.124. Class B networks use the
first two octets to indicate the network portion of the IP Address and the
last two octets to indicate the host; consequently, there are 16,384 possible
Class B networks with each network having 2^16 = 65,532 possible hosts.
126.96.36.199 is an example of a Class B network. Class C networks use the first
three octets to indicate the network portion of the IP Address and the last
octet to indicate the host; consequently, there are 2,097,152 possible Class C
networks with each network having 2^8 = 256 possible hosts. 188.8.131.52 is an
example of a Class C network. Although it is common practice to use the
terminology of Classful IP Networking when speaking about IP Networking, the
implementation of Classful IP Networking in networks has been superceded by
Classless IP Networking.
- Classless IP Network: A network that defines
its Internet Protocol behavior strictly based upon bit masks that are applied
against IP Addresses. These masks, called Netmasks, indicate how many bits in
a given IP Address are to be used to indicate the IP Network to which that
address belongs. Classless IP networking does not make the assumptions about
the number of networks and hosts using the first three bits in an IP Address
as seen in Classful IP Networking. For example, in Classful IP Networking, an
IP Address in the Class C range may never belong to an IP Network that has
more than 256 hosts, as the network portion of the IP Address is strictly
bound to the first three octets. In Classless IP Networking an IP Address in
the Class C range may belong to an IP Network that has more than 256 hosts by
reducing the number of bits in the IP Address which indicate the IP Network (a
process called Supernetting). Classless IP Networking has superceded Classful
IP Networking for two reasons: it more efficiently distributes IP Address
space and simplifies routing.
- CIDR Block: In Classless IP Networking, a
contiguous block of IP Addresses which are characterized by a single IP
Network. CIDR Blocks tend to be Supernets made from former Class C address
space; less often, CIDR Blocks are Subnets made from former Class B address
space. By way of illustration, consider the two IP Addresses 184.108.40.206 and
220.127.116.11. In Classful IP Networking, the addresses belong to separate IP
Networks: 18.104.22.168 and 22.214.171.124, respectively. In Classless IP
Networking, the two may belong to the same IP Network by using a Netmask that
is 23 bits long: 126.96.36.199/23 or 188.8.131.52 255.255.254.0 are two
expressions of this network.
- Classless Internet Domain Routing (CIDR): IP
Routing which implements Classless IP Networking.
- Client: A device or piece of software that
request information or uses the resources of another device or piece of
software. The device or piece of software being called upon is called the
- Client/Server Computing: Distributed
computing. Term used to describe distributed computing (processing) network
systems in which transaction responsibilities are divided into two parts:
client (front end) and server (back end). BNopth terms (client and server) can
be applied to software programs or actual computing devices. Default Route:
Routing table entry that is used to direct packets for which a next is not
explicitly listed in the routing table. Distance Vector Routing: Routing
algorithm that iterates 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 simple than link state routing algorithms.
- Dynamic Host Configuration Protocol (DHCP):
Protocol which allows a server to dynamically assign IP Addresses to hosts on
the fly. Like its processor, BOOTP, DHCP supports manual, automatic and
dynamic address assignment, provides client information including subnet mask,
gateway address and DNS addresses, and is routable. DHCP offers the advantage
over BOOTP of automatic configuration. A DHCP server, generally in the form of
a dedicated server, verifies the identity of a host, leases it the IP address
for predetermined period of time, and reclaims the address for reassignment a
the expiration of the period.
- DNS Number: The IP Address of the machine
that will do hostname to IP Address lookups (and the reverse: IP to hostname
lookups) for a client; the IP Address of the DNS server.
- Domain: In Internet Domain Name System, a
domain is the super-set name for a collection of machines that share an exact
suffix in at least the last two parts of their Domain Name. For example, the
two Domain Names core.greenapple.com and cider.greenapple.com belong to the
- Domain Name: The name of a particular
machine that includes both the machines Hostname and its Domain. For example,
core.greenapple.com and cider.greenapple.com are two Domain Names.
- Domain Name System (DNS): A standard for
identifying hosts and networks. When used for identification on the Internet,
called Internet Domain Name System. The standard is constituted of a host
naming convention and a mapping of hostnames to IP Addresses.
- E-commerce: Sites must use a blend of
commerce, community and targeted value. Success lies in providing something
the brick-and-mortar stores can't do, like send consumers information about
the latest book from their favorite author or a reminder to refill a
- Enhanced Interior Gateway Routing Protocol (EIGRP):
Enhanced Interior Gateway Routing Protocol. Advanced version of IGRP develop
by Cisco. Provides superior convergence properties and operating efficiency,
and combines the advantages of link state protocols with those of distance
vector protocols. Exterior Gateway Protocol (EGP): Routing protocol for
exchanging routing information between autonomous systems. EGP is an obsolete
protocol that has been replaced by BGP.
- File Transfer Protocol (FTP): Protocol for
sending (uploading) and receiving (downloading) of computer files.
- Fire-wall: A combination of hardware and
software used to limit the exposure of a network to an outside attack. Route
or access server, or several routers or access servers, designate as a bugger
between any connected public networks and a private network. A fire-wall
router users access lists and other methods to ensure the security of the
- Flapping (Route Flapping): Routing problem
where an advertised route between tow nodes alternates (flaps) back and forth
between two paths due to a network problem that causes intermittent interface
- Fully Qualified Domain Name (FQDN): In
Internet Domain Name System, a FQDN is the full, unabbreviated name of a host.
It differs from a Domain Name in that the Domain portion of the Domain Name is
officially registered. The important characteristic of a FQDN is that it can
uniquely identify a host from all the hosts that exist on the Internet. For
example, core.greenapple.com and cider.greenapple.com are both FQDNs: both
names indicate a hostname and a domain, and greenapple.com is an officially
- Gateway: Machine that connects two networks
together. Network device that interconnects dissimilar types of network
- Holddown: State into which a route is placed
so that routers will neither advertise the route nor accept advertisements
about the route for a specific length of time (the holddown period. Holddown
is used to flush bad information about a route from all routers in the
network. A route is typically placed in holddown when a link in that route
- Hypertext Transfer Protocol (HTTP): The
protocol used for communications between web-browsers and web-servers. The
protocol of the world-wide-web.
- Hypertext Transfer Protocol Secure (HTTPS):
Similar to HTTP except that the data communications between web client and
server is encrypted.
- Interior Gateway Routing Protocol (IGRP):
Develop by CISCO to address the problems associated with routing in large,
- Internet: The largest global internetwork,
connecting tens of thousands of networks worldwide and having a "culture" that
focuses on research and standardization bas3ed on real-life use. Many
leading-edge network technologies come from the Internet community. The
Internet evolved in part from ARPANET. At one time, called the DAPRA Internet.
- Internet Control Message Protocol (ICMP): A
part of the TCP/IP protocol suite, ICMP interacts with the IP layer to provide
it feedback about the condition of the communication environment.
- Internet Feed:
- Internet Group Message Protocol (IGMP): Used
by IP hosts to report their multicast group memberships to an adjacent
- Internet Protocol (IP): A connectionless
communication protocol operating at Layer 3 of the OSI Reference Model, IP is
responsible for routing data between hosts, whether those hosts exists on the
same IP Network or on different ones. IP is also responsible for acceptance of
data when an IP packet has reached its final destination.
- Internet Service Provider (ISP): A company
that provides Internet connectivity and services. Green Apple is an ISP.
- Internet Services: Services commonly
performed by machines in a network so that the network can interact with the
Internet. Typical Internet Services are DNS, POP/SMTP (E-Mail), HTTP
(world-wide-web), and FTP.
- Internetworking: General tem used to refer
to the industry that has arisen around the problem of connecting networks
together. The term can refer to products, procedures and technologies.
- IP Address: A four part octet that uniquely
identifies a host. Within a network or across different networks. An IP
address has two logical parts, a network part and a host part, which are
determined by whether the address exist in a Classful or Classless IP Network
and whether any netmask are applied to it. 184.108.40.206 and 220.127.116.11 are
two examples of IP Addresses.
- IP Network: A group of IP Addresses that are
identified as a single logical unit for IP routing purposes. There are two
types of IP Networks: Classful and Classless.
- Hop: In IP, the step from one machine to the
next in the route of an IP datagram. For example, suppose an IP datagram must
pass through two routers from source to reach destination. A simple diagram of
the IP route, might look like source >> router1 >> router2 >> destination. The
hops are the connecting >>, and it would be said here that three hops separate
source from destination.
- Hop Count: Routing metric used to measure
the distance between a source and a destination.
- Hostname: The name of machine without
mention of a Domain portion. For example, core and cider are two Hostnames.
- Hypertext Markup Language (HTML): Simple
hypertext document formatting language that uses tags to indicate how a given
part of a document should be interpreted by a viewing application, such as a
web browser. Hypertext Transfer Protocol (HTTP): Hypertext Transfer Protocol
- Layer-3 Switch (L-3 Switch):
- Loopback Interface:
- Management Information Base (MIB):
- Multihomed: In IP, a host or other device
which exists on two IP networks and so may act as a gateway between those
- Netmask: In IP, a four octet number that is
used as a bit mask to determine which bits in an IP Address are to represent
the IP Network to which that IP Address belongs. In a Classful IP Network, a
Netmask may be used to Subnet that network. In a Classless IP Network, as no
assumptions are made about the network bits, a Netmask must be given with an
IP Address. It is generally regarded as good practice to mask the network bits
strictly from left to right. When such a practice is followed a slash notation
may be used to represent the netmask. For example, the netmask 255.255.128.0
means that the first 17 bits in an IP Address are to be used to determine the
IP Network; as a consecutive set of bits are used, this Netmask may also be
represented in slash notation and would be represented as /17.
- Network Access Point (NAP): A point of
access into the Internet.
- Network Address Translation (NAT):
- Network News Transfer Protocol (NNTP):
Protocol used by Usenet news.
- Network Operations Center (NOC): Group
responsible for day-to-day operations, oversight and eminence of a network.
- Network Time Protocol (NTP): Protocol used
to synchronize computer clocks.
- Next Hop: In IP, the step between one node
and the next in the route of an IP datagram.
- Packetiser: Group of conditions for control serial line data stream to ethernet packets convertion.
- Packet filtering:
- Point-to-point Authentication Protocol
(PAP): Authentication protocol that uses PPP to send account and password
information. Authentication information is sent clear-text, that is,
- Port Address Translation (PAT):
- Post Office Protocol (POP): Protocol for
sending e-mail from an e-mail server to a client application.
- Private IP Address:
- Proxy ARP: When a machine answers ARP
requests with its own MAC address.
- Public IP Address:
- Remote Authentication Server (RAS):
Equipment which enables access to a system through dial-in in lines.
- Request For Comment (RFC): Proposals on
standards, procedures and specifications concerning the Internet. The issuance
of RFS's is overseen by the IETF. RFC are finally adopted as standards or
discarded. The RFC process is overseen by the IETF.
- Reverse Address Resolution Protocol (RARP):
Broadcast MAC address to request an IP address
- Routing Metric:
- Simple Network Management Protocol (SNMP):
An industry-standard management protocol for monitoring and controlling
devices and for the exchange of information or objects.
- Static Routing:
- Subnet: For example, the network
18.104.22.168 in a Classful network has 254 available IP Addresses (.0 is
reserved for the network address; .255 is reserved for the broadcast address).
Applying a Netmask of 255.255.255.128 breaks this network into two Subnets:
22.214.171.124 with netmask 255.255.255.128 and 126.96.36.199 with netmask
255.255.255.128. In a Classless IP Network, a Netmask may be used to Subnet
number of bits which represent the network portion In a Classful IP Network, a
Netmask may be applied to the network address to break an IP Address to
- Teir X Provider:
- Transmission Control Protocol (TCP):
- Transmission Control Protocol/Internet
- Trivial File Transfer Protocol (TFTP):
- User Datagram Protocol (UDP):
- Variable Length Subnet Mask (VLSM):
- Virtual Private Network (VPN):
- Ballew, Scott M., Managing IP Networks with Cisco Routers
O'Reilly & Associates, 1997, ISBN 1-56592-320-0
- Giles, Roosevelt, Cisco CCIE Study Guide
McGraw-Hill, 1998, ISBN 0-97-913728-8
- Graham, Buck, TCP/IP Addressing
AP Professional, 1997, ISBN 0-12-294630-8
- LeValley, Jim, Fairweather, Julie, et al., Cisco IOS Solutions for Network
Protocols, Volume I:IP
Cisco Systems, Inc, 1998, ISBN 1-57870-049-3
- Newton, Harry, Newton's Telecom Dictionary, Thirteenth Edition
Telecom Books and Flatiron Publishing, 1998, ISBN 1-57820-018-0
- Spohn, Darren L., Data Network Design, Second Edition
McGraw-Hill, 1997, ISBN 0-07-060363-4
- Stevens, Richard W., Unix Network Programming, Vol 1, Second Edition
Prentice-Hall Inc, 1998, ISBN 0-13-490012-X
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Green Apple, Inc, 1995-2003.
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