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Advanced Glossary Of Internet Terms
doc title: Introductory Internet Glossary
orig date: 05-10-98
last update: 10-17-01

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Common Acronyms

ACK: Acknowledgment
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
CODEC: Coder-Decoder
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
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
Modem: MOdulator/DEModulator
MTU: Maximum Transmission Unit
MUX: Multiplexer
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) requests.

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 protocols.

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) documents.

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 IETF Chair.

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 lifetime.

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 America.

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 for processing.

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 chassis.

     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 requests retransmissions.

      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 circuit.

      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 the 22.

      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 data.

      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 prices.

      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 customer's premises.

      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 switch.

      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 port.

      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 data channel.

      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 the IXCs.

      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 communication channel.

      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 channel.

      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 dialup 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 data.

      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 sending.

      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 flags.

      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 Ref Model)

      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 first.

      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 network.

      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 and ATM.

      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 frame transmission.

      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 packet.

      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 information.

      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 packet.

      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, other networks.

      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 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. 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. 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 and In Classful IP Networking, the addresses belong to separate IP Networks: and, respectively. In Classless IP Networking, the two may belong to the same IP Network by using a Netmask that is 23 bits long: or 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 Server.

      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 and belong to the Domain

      Domain Name: The name of a particular machine that includes both the machines Hostname and its Domain. For example, and 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 prescription.

      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 private network.

      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 failures.

      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, and are both FQDNs: both names indicate a hostname and a domain, and is an officially registered Domain.

      Gateway: Machine that connects two networks together. Network device that interconnects dissimilar types of network elements.

      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 fails.

      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, heterogeneous networks.

      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 multicast router.

      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 (Email), 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. and 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 Secure (HTTPS):

      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 networks.

      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 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.

      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, un-encrypted.

      Port Address Translation (PAT):

      Post Office Protocol (POP): Protocol for sending email from an email 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 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 breaks this network into two Subnets: with netmask and with netmask 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 Protocol (TCP/IP):

      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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