computer network internet security phần 10 pot

280280 Digital Certificate An electronic passport that consists of a numerical pattern, value, or key and used for personal identification. Creating a digital certificate involves a user identifying a specific personal trait to a trusted third party, which issues the certificate. Digital Communication Refers to any type of communication in which data are represented in the form of binary digits. Digital Signature A security authorization method in which a user “signs” a document so that the document’s authenticity can be confirmed by checking the signature. A digital signature proves a message was not modified. Digital Subscriber Loop The formal term used to denote the local loop, which is the circuit between a customer’s premise equipment (CPE) and the telco’s equipment. DIN Connector Similar to a DB connector, but is circular instead of rectangular and typically used to connect a keyboard to a computer; “DIN” stands for “Deutsche Industrie Norm,” a German industrial standard. Directed IR A “point-to-point” infrared transmission method that requires an unob- structed line-of-sight connection between transmitter and receiver. It is basically a “point and beam” medium. Discard Eligibility The name of a field in a frame relay frame, which, if set to 1 by an end node, denotes that the frame can be discarded in the presence of congestion Discarded frames will then be retransmitted at a later time when congestion has subsided. Distance-vector Algorithm A routing algorithm that determines the distance between source and destination nodes by calculating the number of router hops a packet traverses en route from the source network to the destination network. An example of a distance- vector algorithm is the Bellman-Ford algorithm. Distributed System Computers that are linked together to provide, in a transparent manner, the required computing resources and information processing needs of an entire organization. Distributed systems bear the greatest resemblance to computer networks. DLCI An acronym for data link connection identifier, which is a term used in frame relay to denote virtual circuit addresses assigned to PVCs or SVCs. Domain Name A logical name assigned to an IP address and used as another type of addressing construct for identifying Internet nodes. The translation between logical name and IP address is called name resolution, which is provided by a domain name service. Domain Name Service (DNS) An Internet translation service that resolves domain names to IP addresses and vice versa. DNS is provided by DNS servers. 281281 DQDB An acronym for distributed queue dual bus, which is a data link layer protocol (IEEE 802.6) that specifies the medium access method for MANs. Used in SMDS. DS-0 A single, digital voice channel rated at 64 kbps. The notation DS-0 stands for digital signal at level 0, which refers to a voice channel multiplexed into a digital signal. DS-1 A digital signal that carries 24 DS-0 channels plus one 8 kbps channel reserved for framing for an aggregate bandwidth of 1.544 Mbps. A T1 circuit carries a DS-1 signal. DS-2 A digital signal that carries 4 DS-1 channels for an aggregate bandwidth of 6.312 Mbps. A T2 circuit carries a DS-2 signal. DS-3 A digital signal that carries 28 DS-1 channels for an aggregate bandwidth of 44.736 Mbps. A T3 circuit carries a DS-3 signal. DS-4 A digital signal that carries 168 DS-1 channels for an aggregate bandwidth of 274.176 Mbps. A T4 circuit carries a DS-4 signal. DSL An acronym for digital subscriber line, which is a technology that enables data, voice, and video to be mixed and carried over standard analog, (copper) telephone lines. This is accomplished by using the unused frequencies that are available on a telephone line. Thus, DSL can deliver data services without interfering with voice transmissions. There are at least nine DSL variants: ADSL, ADSL lite, HDSL, HDSL 2,IDSL, RADSL, SDSL, UDSL, and VDSL. DSLAM An acronym for DSL access multiplexer, which is a device that aggregates DSL signals so they can be transferred directly into a data switch for transmission across the telco’s data network backbone. DSSS An acronym for direct sequence spread spectrum, which is a physical layer technology used in wireless LANs (IEEE 802.11). DSSS operates by spreading a signal over a wide range of the 2.4 GHz band. DSU An acronym for data (or digital) service unit, which is a device used for terminating a Tx circuit. A DSU provides the interface (usually V.35, a type of serial interface) for connecting a remote bridge, router, or switch to a Tx circuit. The DSU also provides flow control between the network and the CSU. Usually combined with a CSU to form a single unit called a CSU/DSU or DSU/CSU. DTE An acronym for data terminal equipment. Computers (PCs, workstations) are data terminal equipment. DTEs are the end points of a link and communicate through their serial ports or expansion buses. See also data communications equipment (DCE). 282282 DTE-to-DCE Rate The speed at which a computer “talks” to its modem. Typical rates include a 4:1 compression ratio between DTE and DCE speeds. Thus, for a V.34 modem (28,800 bps), the DTE-DCE rate is 115,200 bps. This rate is user configurable. Dual-attachment Station (DAS) An FDDI node that is connected to two full, dual- fiber rings and have the ability to reconfigure the network to form a valid network from components of the two rings in case of a failure. A DAS is also called Class A node. E.164 An ITU-T standard network addressing format that resemble telephone numbers. E.164 addresses are 15 decimal digits long and include a country code, area or city code, and a local number. Country codes are two or three digits long and consist of a zone code followed by a one- or two-digit national identifier. Area or city codes are up to four digits long. If an address contains less than 15 digits, then it is padded with hexadecimal Fs. Australia does not use city codes, and the United States and Canada use the zone code 1 followed by a three-digit area code and a seven digit local number in lieu of county codes. E-1 Describes the multiplexing of 30 separate 64 kbps voice channels, plus one 64 kbps control channel, into a single, wideband digital signal rated at 2.048 Mbps. E-1 is the basic telecommunications service used in Europe. E-2 A multiplexed circuit that combines four E-1 circuits and has an aggregate bandwidth of 8.448 Mbps. E-3 A multiplexed circuit that combines 16 E-1 circuits and has an aggregate bandwidth of 34.368 Mbps. E-4 A multiplexed circuit that combines 64 E-1 circuits and has an aggregate bandwidth of 139.264 Mbps. E-5 A multiplexed circuit that combines 256 E-1 circuits and has an aggregate bandwidth of 565.148 Mbps. E-commerce Short for electronic commerce, which involves using the Internet for credit card purchases of items such as automobiles, airline tickets, computer hardware and software, and books. EGP An acronym for exterior gateway protocol, which refers to any Internet interdomain routing protocol used to exchange routing information with other autonomous systems. Also refers to Exterior Gateway Protocol, which is a specific EGP defined in RFC 904. Another EGP is the Border Gateway Protocol (BGP), defined in RFC 1105 and RFC 1771. Both EGP and BGP are part of the TCP/IP protocol suite. Of the two, however, BGP has evolved into a robust Internet routing protocol and the term “Border Gateway Protocol” is used in favor of the term “Exterior Gateway Protocol.” 283283 EIGRP An acronym for enhanced IGRP, which is routing protocol designed by Cisco that combines the best features of distance-vector and link-state routing protocols. Encapsulation A process in which a packet or frame is enclosed or “wrapped” in a specific protocol header. For example, routers typically perform protocol encapsulation in which packets from one network protocol are wrapped into the header of another network protocol so the packet can be transmitted to a different network. Also called tunneling. Encryption The process of coding a message so that it is incomprehensible to unauthorized users. When retrieved by authorized users, encrypted messages are then reconverted (i.e., decoded) into meaningful text. Encrypted output is called ciphertext. Error Control The process of guaranteeing reliable delivery of data. Error control can be provided through error detection or error correction. Error Correction The process in which a destination node, upon detecting a data transmission error, has sufficient information to correct the error autonomously. Error correction implies error detection. Error Detection The process in which a destination node detects a data transmission error and requests a retransmission from the sending node. Error detection is also called error correction through retransmission. Ethernet A local area network protocol developed jointly by Xerox, Intel, and Digital Equipment Corporation (DEC) at the Xerox Palo Alto Research Center (PARC) in the mid-1970s. The name “Ethernet” was derived from the old electromagnetic theoretical substance called luminiferous ether, which was formerly believed to be the invisible universal element that bound together the entire universe and all its associated parts. Thus, an “ether” net is a network that connects all components attached to the “net.” Excessive Burst (B e ) A term used in frame relay to denote the maximum amount of uncommitted data a provider will attempt to deliver within a specified time period. A provider will guarantee a committed burst of B c bits and will attempt to deliver (but not guarantee) a maximum of B c + B e bits. Exchange Access SMDS (XA-SMDS) A special SMDS service through which LECs offered SMDS to IECs for delivery across LATAs. Extranet A popular networking term that describes an interconnection from an internal intranet to a customer or noncompany network that is not the Internet connection. 4B/5B A data encoding method, which stands for four bits in five baud, or four-bit to five-bit, used in FDDI networks. 284284 5-4-3 Repeater Rule A general rule of thumb to follow when configuring an Ethernet/ 802.3 LAN to ensure that it follows IEEE specifications. The 5-4-3 rule requires: no more than 5 segments of up to 500 m each; no more than 4 repeaters; and no more than 3 segments can have end nodes connected to them. This rule is also known as the 4-repeater rule, or the 5-4-3-2-1 rule. In the latter, the “2” implies that two of the five segments are used as interrepeater links, and the “1” implies that a configuration using the maximum parameters permitted results into one collision domain. Fast Ethernet 100 Mbps Ethernet (IEEE 802.3u). Three different media specifications are defined: 100BASE-TX, 100BASE-T4, and 100BASE-FX. FDDI Fiber Distributed Data Interface. FDDI networks are described by ANSI standard X3T9.5 and created in 1986 for interconnecting computer systems and network devices typically via a fiber ring topology at 100 Mbps. FECN An acronym for forward explicit congestion notification, which is a one-bit field in a frame relay frame that is set to 1 by a frame relay switch to denote that a frame transmitted toward the receiving node experienced congestion. FDDI-II A now defunct second generation FDDI technology that was intended to handle traditional FDDI network traffic as well as synchronous, circuit-switched PCM data for voice or ISDN systems. FHSS An acronym for frequency hopping spread spectrum, which is a physical layer technology used in wireless LANs (IEEE 802.11). FHSS operates by transmitting short bursts of data on different frequencies. One burst is transmitted on one frequency, a second burst is transmitted on a second and different frequency, and so forth. Fiber-optic Cable A type of cable that carries data signals in the form of modulated light beams. The cable’s conductor can be either glass or plastic. Fiber- optic cable is immune to electromagnetic interference (EMI) and other types of externally induced noise, including lightning, it is unaffected by most physical factors such as vibration, its size is smaller and its weight lighter than copper, it has much lower attenuation per unit of length than copper, and it can support very high bandwidth. Two general types are available: single-mode fiber and multimode fiber. Fibre Channel A family of ANSI standards that defines a specific communications interface for high-speed data transfers between different hardware systems. Applications include the medical profession, where large images (e.g., 100 MB+ X- rays) are transferred from a scanner to a computer to a screen, and the electronic publishing industry, where large files are transferred from an designer/creator’s machine to a publisher’s computer. It has also become the “backbone” of high- speed data storage systems. Firewall A device or product that allows systems or network manager to restrict access to components on a network. Five generally accepted types of firewalls are 285285 used on Internet connections are frame-filtering, packet-filtering, circuit gateways, stateful and application gateways, and proxy servers. FIX An acronym for federal Internet exchange, which is an Internet interconnect site similar to a NAP. Flow Control A process that controls the rate at which data messages are exchanged between two nodes. Flow control provides a mechanism to ensure that a sending node does not overwhelm a receiving node during data transmission. Fractional T1 T1 service that is sold in 64 kbps increments. FRAD An acronym for frame relay access device, which is a term used to denote any frame relay end node. Fragmenting A process in which a packet is broken into smaller units to accommodate the maximum transmission unit a physical network is capable of supporting. Fragmented packets are sent to the destination separately and then reassembled at the destination node before it is passed to the higher levels. In IP, reassembly of a datagram occurs at the destination node and not at any of the intermediary nodes the packet traverses. Frame A specially formatted sequence of bits that incorporates both data and control information. Frame-filtering Firewall A firewall device or product that filters (permits or denies access) at the data link layer by examining frames for both layout and content. Framing A data link layer process that partitions a bit stream into discrete units or blocks of data called frames. Frame Relay A public WAN packet-switching protocol that provides LAN-to-LAN connectivity. Its name implies what it does, namely, relays frames across a network between two sites. Frame relay was originally part of the ISDN standard. Frequency Division Multiplexing (FDM) A multiplexing technique that partitions the available transmission frequency range into narrower bands (subfrequencies), each of which is a separate channel. FDM-based transmissions are parallel in nature. Full-duplex Transmission A data transmission method that involves the simultaneous sending and receiving of data in both directions. GAN An acronym for global area network, which refers to a collection of WANs that span the globe. Gateway A software application that converts between different application protocols. The host on which this software resides is called a gateway machine. Historically, this term also refers to a router in the IP community. 286286 Gigabit Ethernet 1000 Mbps Ethernet (IEEE 802.3z). Geostationary Earth Orbit (GEO) Satellite A satellite placed into orbit at an altitude of 22,000 miles (36,000 kilometers) above the equator. GEO satellites traverse their orbits at approximately the same rate as the Earth rotates. Thus, the satellite appears stationary with respect to the Earth’s rotation. Also call Geosynchronous Earth Orbit. Only eight GEO satellites are needed to provide global communications coverage. GOSIP An acronym for Government OSI Profile, which mandated all government organizations purchase OSI-compliant networking products beginning in 1992. In 1995, however, GOSIP was modified to include TCP/IP as an acceptable protocol suite for GOSIP compliance. Graded-index Multimode Fiber A type of multimode fiber in which variations in the density of the core medium change its index of refraction such that light is refracted (i.e., bends) toward the center of the fiber. H Channel An ISDN channel used for transmitting user data (not signal or control information) at higher transmission rates than a B channel provides. Four H channels are defined: H0 (six B channels; 384 kbps); H10 (United States-specific; aggregates 23 B channels; 1.472 Mbps); H11(equivalent of North American DS-1; 24 B channels; 1.536 Mbps); and H12 (European-specific; comprises 30 B channels; 1.920 Mbps). Half-duplex Transmission A data transmission method in which may travel in either direction—from sender to receiver or receiver to sender—but only one unit can send at any one time. While one node is in send mode, the other is in receive mode. Harmonic Motion The basic model for vibratory or oscillatory motion. Examples include mechanical oscillators such as mass-spring systems and pendulums; periodic motion found in the earth sciences such as water waves, tides, and climatic cycles; and electromagnetic waves such as alternating electric currents, sound waves, light waves, radio waves, and television waves. HDSL An acronym for high bit-rate digital subscriber line, which is a DSL variant that provides symmetrical service at T1 rates over 2 pairs of UTP, and E1 rates over 3 pairs of UTP. Telephone service not supported. Applications include connecting PBXs, serving as an alternative to T1/E1; suitable for campus networks and ISPs. HDSL 2 A modified HDSL designed and packaged for corporate clients. Hertz A measure of frequency in cycles per second. A frequency rate of one cycle per second is defined as one hertz (abbreviated Hz). Named in honor of Heinrich Rudolf Hertz (1857-1894), a German physicist who in the late 1880s was the first to produce radio waves artificially. HFC An acronym for hybrid fiber cable, which describes a cable TV cable plant that has fiber-optic cable between the head end and neighborhood distribution sites, 287287 but coaxial cable between the neighborhood distribution and residential homes and businesses. Hold-down A strategy used by RIP that requires routers to not update their routing tables with any new information they receive for a prescribed period of time, called the hold-down time. Designed to prevent routing loops. Hold-down is not standardized. Hop A term used to describe the passage of a packet through an intermediate gateway (router) en route to another network. For example, if a packet transverses through two routers in reaching its final destination, then we say the destination is two hops away. Host A networked computer system (see workstation). Also used to describe a computer system that provides service to users (see server). Hub Generically, any device that connects two or more network segments or supports several different media. Examples include repeaters, switches, and concentrators. Hybrid Switching A data transmission method that combines the principles of circuit and packet-switching. This technique first partitions a message into packets (packet- switching) and transmits each packet via a dedicated circuit (circuit- switching). As soon as a packet is ready for transmission, a circuit meeting appropriate bandwidth requirements is established between the sending and receiving nodes. When the packet reaches its destination, the circuit is broken down so that it can be used again. IBM Cable System (ICS) A copper wire classification system established by IBM that specifies nine cable “types” (1 through 9). Of the nine “types” defined, specifications are available for only seven; types 4 and 7 are not defined. ICMP An acronym for Internet control message protocol, which uses an IP datagram to carry messages about the communications environment of the Internet. IDSL An acronym for ISDN-like digital subscriber line, which is a DSL variant that provides symmetrical service at a maximum of 144 kbps each way. Uses ISDN hardware. IEC See IXC. IEEE An acronym for Institute of Electrical and Electronics Engineers, which is a professional society of engineers, scientists, and students. One of its many activities is to act as a coordinating body for computing and communication standards. IEEE 802 The primary IEEE standard for the 802.x series for LANs and MANs. IEEE 802.1 IEEE standard that defines an architectural overview of LANs. 288288 IEEE 802.2 IEEE standard that defines the Logical Link Control, which describes services for the transmission of data between two nodes. IEEE 802.3 IEEE standard that defines the Carrier Sense Multiple Access/Collision Detection (CSMA/CD) access method commonly referred to as Ethernet. Supplements include 802.3c (10 Mbps Ethernet); 802.3u (100 Mbps Ethernet known as Fast Ethernet), and 802.3z and 802.3ab (1000 Mbps Ethernet known as Gigabit Ethernet). IEEE 802.4 IEEE standard that defines the token bus network access method. IEEE 802.5 IEEE standard that defines the logical ring LAN that uses a token- passing access method; known also as Token Ring. IEEE 802.6 IEEE standard that defines metropolitan area networks (MANs). IEEE 802.7 IEEE standard that defines broadband LANs (capable of delivering video, data, and voice traffic). IEEE 802.9 IEEE standard that defines integrated digital and video networking— Integrated Services LANs (ISLANs). IEEE 802.10 IEEE standard that defines standards for interoperable LAN/MAN security services. IEEE 802.11 IEEE standard that defines standards for wireless media access control and physical layer specifications. IEEE 802.12 IEEE standard that defines the “demand priority” access method for 100Mbps LANs; known also as 100 Base-VG or 100VG-AnyLAN. IEEE 802.13 (Defines nothing—IEEE was concerned about the superstitious overtones associated with “13.”) IEEE 802.14 IEEE standard that defines a standard for Cable-TV based broadband communication. IGP An acronym for interior gateway protocol, which is any intradomain Internet protocol used to exchange routing information within an autonomous system. Examples include RIP, RIP-2, OSPF, IGRP, and Enhanced IGRP (EIGRP). IGRP An acronym for interior gateway routing protocol, which was developed by Cisco to address some of the problems associated with routing in large, heterogeneous networks. ILEC An acronym for incumbent local exchange carrier, which is the contemporary name given to the RBOCs relative to the United States Telecommunications Act of 1996. Impedance A measure of the opposition to the flow of electric current in an alternating current circuit. Measured in ohms (abbreviated by the Greek symbol, 289289 omega, ¾), impedance is a function of capacitance, resistance, and inductance. Impedance mismatches, caused by mixing cables of different types with different characteristic impedances, can result in signal distortion. Impulse Noise Electrical noise that consists of intermittent, undesirable signals induced by external sources such as lightning, switching equipment, and heavy electrically operated machinery such as elevator motors and copying machines. Impulse noise increases or decreases a circuit’s signal level, which causes the receiving equipment to misinterpret the signal. Infrared (IR) A line-of-sight transmission method that uses electromagnetic radiation of wavelengths between radio waves and visible light, operating between 100 GHz and 100 THz (Terahertz). IR transmission can occur in one of two ways: directed and diffused. Insulation Material surrounding the conductor of a wire. The insulation serves as a protective “barrier” to the conductor by preventing the signal from “escaping” and preventing electrical interference from “entering.” Intermodulation Noise Electrical noise that occurs when two frequencies interact to produce a phantom signal at a different frequency. Occurs in frequency-division multiplexed channels. Internet When used as a noun and spelled with a lowercase i, “internet” is an abbreviation for internetwork, which refers to a collection of interconnected networks that functions as a single network. When used as a proper noun and spelled with a capital I, “Internet” refers to the world’s largest internetwork, which consists of hundreds of thousands of interconnected networks worldwide and based on a specific set of network standards (TCP/IP). Internet Architecture Board (IAB) An organization that is part of the Internet Society responsible for the overall planning and designing of the Internet. Responsibilities include setting Internet standards, managing the publication of RFC documents, and resolving technical issues. Assigned to the IAB are the Internet Engineering Task Force and the Internet Research Task Force. Formerly known as the Internet Activities Board. Internet Assigned Numbers Authority (IANA) An organization that has authority over all number spaces used in the Internet including IP addresses. IANA control will soon be transferred to the Internet Corporation for Assigned Names and Numbers (ICANN). Internet Corporation for Assigned Names and Numbers (ICANN) A private, non- profit corporation with international representation expressly formed to assume the responsibilities currently being performed by IANA and other government organizations that provide domain name service. Internet Engineering Task Force (IETF) An organization that is part of the Internet Architecture Board and primarily concerned with addressing short- or [...]... exactly the same time Subnet Mask A special network address used to identify a specific subnetwork Using a unique bit combination, a mask partitions an address into a network ID and a host ID Subnetting Refers to the partitioning of a network address space into separate, autonomous subnetworks Key to subnetting is a network s subnet mask Subnetwork Refers to a network segment Commonly abbreviated as subnet... network access point, which is an Internet traffic exchange point that provides centralized Internet access to Internet service providers A NAP serves as a critical, regional “switching station” where all different network backbone providers meet and exchange traffic on each other’s backbone NSAP An acronym for network service access point, which is an OSI addressing mechanism used by private ATM networks... workstation of some sort NCs are stripped-down systems that use the network to access their applications dynamically Network Diameter nodes The overall length between a network s two most remote 296 Network Ethics Refers to specific standards of moral conduct by network users for the responsible use of network devices and resources Network Interface Card A layer 2 device that performs standard data... known as a LAN adapter, network adapter, network card, and network board When used in Ethernet/802.e networks, a NIC is called an Ethernet card or adapter Network Operating System (NOS) Software that is installed on a system to make it network- capable Examples include IBM’s LAN Server, Banyan’s VINES, and Novell’s NetWare (also known as IntranetWare) A NOS is independent of a computer s native operating... system—it is loaded “on top” of the computer s operating system and provides the computer with networking capability based on a particular protocol If an operating system provides built-in network support (e.g., Microsoft’s Windows NT and Sun’s Solaris), then the OS is called a networkable operating system Network Protocol Suite A set of related and interoperating network protocols For example, the... authoritative organization of the Internet Internet2 A collaborative project of the University Corporation for Advanced Internet Development (UCAID), which comprises over 100 U.S universities, government organizations, and private sector firms Internet2 ’s mission is to develop advanced Internet tech nologies and applications that support the research endeavors of colleges and universities Internet2 members use...medium-term Internet engineering issues Relies on the Internet Engineering Steering Group (IESG) to prioritize and coordinate activities Internet Registry (IR) A formal hierarchical system used for assigning IP addresses From top to bottom, this hierarchy consists of IANA, Regional Internet Registries (RIR), and Local Internet Registries (LIR), and works as follows:... videoconferencing and telephony IsoEthernet runs both conventional 10 Mbps Ethernet and ISDN B channels over the same network The Ethernet channel is used for normal data networking needs; the ISDN B channels are used for time-sensitive applications ISP An acronym for Internet Service Provider, which is an organization that provides its customers with access to the Internet ITU An acronym for International Telecommunications... either end users or ISPs Internet Research Task Force (IRTF) An organization that is part of the Internet Architecture Board and primarily concerned with addressing long-term research projects Relies on the Internet Research Steering Group (IRSG) to prioritize and coordinate activities Internet Society (ISOC) An international organization comprised of volunteers who promote the Internet as a medium for... file transfers, and routing Network Security Refers to the proper safeguarding of everything associated with a network, including data, media, and equipment It involves administrative functions, such as threat assessment, and technical tools and facilities such as cryptographic products, and network access control products such as firewalls It also involves making certain that network resources are used . domain. Fast Ethernet 100 Mbps Ethernet (IEEE 802.3u). Three different media specifications are defined: 100 BASE-TX, 100 BASE-T4, and 100 BASE-FX. FDDI Fiber Distributed Data Interface. FDDI networks are. frequency-division multiplexed channels. Internet When used as a noun and spelled with a lowercase i, internet is an abbreviation for internetwork, which refers to a collection of interconnected networks that functions. single network. When used as a proper noun and spelled with a capital I, Internet refers to the world’s largest internetwork, which consists of hundreds of thousands of interconnected networks