Glossary of Networking Terms   ADSL: The variation called ADSL (Asymmetric Digital Subscriber Line) is the form of DSL that will become most familiar to home and small business users. ADSL is called "asymmetric" because most of its two-way or duplex bandwidth is devoted to the downstream direction, sending data to the user. Only a small portion of bandwidth is available for upstream or user-interaction messages. However, most Internet and especially graphics- or multi-media intensive Web data need lots of downstream bandwidth, but user requests and responses are small and require little upstream bandwidth.   ATM (Asynchronous Transfer Mode): a dedicated-connection switching technology that organizes digital data into 53-byte cell units and transmits them over a physical medium using digital signal technology. Individually, a cell is processed asynchronously relative to other related cells and is queued before being multiplexed over the transmission path. Because ATM is designed to be easily implemented by hardware (rather than software), faster processing and switch speeds are possible. ATM runs as a layer on top of SONET.   Bandwidth: Bandwidth (the width of a band of electromagnetic frequencies) is used to mean (1) how fast data flows on a given transmission path, and (2), somewhat more technically, the width of the range of frequencies that an electronic signal occupies on a given transmission medium. Any digital or analog signal has a bandwidth.   Bridge: In telecommunication networks, a bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or token ring).   CAT 5: ANSI/EIA (American National Standards Institute/Electronic Industries Association) Standard 568 is one of several standards that specify "categories" of twisted pair cabling systems (wires, junctions, and connectors) in terms of the data rates that they can sustain. The specifications describe the cable material as well as the types of connectors and junction blocks to be used in order to conform to a category. The two most popular specifications are CAT 5 and CAT 6. While the two cables may look identical, CAT 5 is tested to a lower set of specifications and can cause transmission errors if pushed to faster speeds.    Category   Maximum Data Rate   CAT 5   100 Mbps   CAT 6  1000 Mbps or 1 Gb   Central Office: In telephone communication in the United States, a central office (CO) is an office in a locality to which subscriber home and business lines are connected on what is called a local loop. The central office has switching equipment that can switch calls locally or to long-distance carrier phone offices.   Coaxial Cable: Coaxial cable is the kind of copper cable used by cable TV companies between the community antenna and user homes and businesses. Coaxial cable is sometimes used by telephone companies from their central office to the telephone poles near users. It is also widely installed for use in business and corporation Ethernet and other types of local area network.   Co-location: the provision of space for a customer's telecommunications equipment on the service provider's premises. Pure play co-location operators specialize in supplying the basics of premises, power and connectivity to the highest standards. They leverage economies of scale to provide absolute reliability at a commodity price. Value-added co-location operators supplement the basic co-location offering with optional services such as accelerated content distribution, utility storage and security.   Dedicated Access: see Dedicated Line   Dedicated Line: A dedicated line is a telecommunications path between two points that is available 24 hours a day for use by a designated user (individual or company). It is not shared in common among multiple users as dial-up lines are. Also called a nonswitched line.   Dedicated Hosting: see Dedicated Server   Dedicated Server: In the Web hosting business, a dedicated server refers to the rental and exclusive use of a computer that includes a Web server, related software, and connection to the Internet, housed in the Web hosting company's premises. A dedicated server is usually needed for a Web site (or set of related company sites) that may develop a considerable amount of traffic. The server can usually be configured and operated remotely from the client company. The use of a dedicated server saves the client router, Internet connection, security system, and network administration costs.   Dial-up: a telephone connection in a system of many lines shared by many users. A dial-up connection is established and maintained for a limited time duration. The alternative is a dedicated connection, which is continuously in place. Also called a switched line.   DSL (Digital Subscriber Line): a technology for bringing high-bandwidth information to homes and small businesses over ordinary copper telephone lines. A DSL line can carry both data and voice signals and the data part of the line is continuously connected.   Ethernet: the most widely installed LAN technology. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Fast Ethernet or 100BASE-T provides transmission speeds up to 100 megabits per second and is typically used for LAN backbone systems, supporting workstations with 10BASE-T cards. Gigabit Ethernet provides an even higher level of backbone support at 1000 megabits per second (1 gigabit or 1 billion bits per second).   Fiber Optic: refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic wire or fiber. Optical fiber carries much more information than conventional copper wire and is in general not subject to electromagnetic interference and the need to retransmit signals. Most telephone company long-distance lines are now of optical fiber. Transmission on optical fiber wire requires repeater at distance intervals. The glass fiber requires more protection within an outer cable than copper. For these reasons and because the installation of any new wiring is labor-intensive, few communities yet have optical fiber wires or cables from the phone company's branch office to local customers (known as local loop).   FTP (File Transfer Protocol): the simplest way to exchange files between computers on the Internet. Like the Hypertext Transfer Protocol (HTTP), which transfers displayable Web pages and related files, and the Simple Mail Transfer Protocol (SMTP), which transfers e-mail, FTP is an application protocol that uses the Internet's TCP/IP protocols. FTP is commonly used to transfer Web page files from their creator to the computer that acts as their server for everyone on the Internet. It's also commonly used to download programs and other files to your computer from other servers.   Gateway: A gateway is a network point that acts as an entrance to another network. On the Internet, a node or stopping point can be either a gateway node or a host (end-point) node. Both the computers of Internet users and the computers that serve pages to users are host nodes. The computers that control traffic within your company's network or at your local Internet service provider (ISP) are gateway nodes.   Gbps: Gbps stands for Gigabits per second is a measure of bandwidth (the total information flow over a given time) on a network. Depending on the medium and the transmission method, bandwidth is sometimes measured in the Mbps (millions of bits per second or megabits per second) range or the Kbps (thousands of bits or kilobits per second).   Hub: A hub usually includes a switch of some kind. (And a product that is called a "switch" could usually be considered a hub as well.) The distinction seems to be that the hub is the place where data comes together and the switch is what determines how and where data is forwarded from the place where data comes together. Regarded in its switching aspects, a hub can also include a router.   IP (Internet Protocol): the method by which data is sent from one computer to another on the Internet. Each computer (known as a host) on the Internet has at least one IP address that uniquely identifies it from all other computers on the Internet. When you send or receive data the message gets divided into packets. Each of these packets contains both the sender's Internet address and the receiver's address. Any packet is sent first to a gateway computer that understands a small part of the Internet. The gateway computer reads the destination address and forwards the packet to an adjacent gateway that in turn reads the destination address and so forth across the Internet until one gateway recognizes the packet as belonging to a computer within its immediate neighborhood or domain. That gateway then forwards the packet directly to the computer whose address is specified.   ISDN: Integrated Services Digital Network (ISDN) is a set of CCITT/ITU standards for digital transmission over ordinary telephone copper wire as well as over other media. Home and business users who install an ISDN adapter (in place of a modem) can see highly-graphic Web pages arriving very quickly (up to 128 Kbps). ISDN requires adapters at both ends of the transmission so your access provider also needs an ISDN adapter.   Kbps: Kbps stands for thousands of bits or kilobits per second is a measure of bandwidth (the total information flow over a given time) on a network. Depending on the medium and the transmission method, bandwidth is sometimes measured in the Mbps (millions of bits per second or megabits per second) range or the Gbps (billions of bits or gigabits per second) range.   LAN (Local Area Network): a group of computers and associated devices that share a common communications line and typically share the resources of a single processor or server within a small geographic area (for example, within an office building). Usually, the server has applications and data storage that are shared in common by multiple computer users. A local area network may serve as few as two or three users or many as thousands of users.   Mbps: Mbps stands for millions of bits per second or megabits per second and is a measure of bandwidth (the total information flow over a given time) on a telecommunications medium. Depending on the medium and the transmission method, bandwidth is sometimes measured in the Kbps (thousands of bits or kilobits per second) range or the Gbps (billions of bits or gigabits per second) range.   Modem: used to convert the digital information in your computer to analog signals for your phone line and to convert analog phone signals to digital information for your computer.   Point-of-presence (POP): an access point to the Internet. A POP necessarily has a unique Internet Protocol (IP) address. Your Internet service provider (ISP) or online service provider has a point-of-presence on the Internet and probably more than one. The number of POPs that an ISP or OSP has is sometimes used as a measure of its size or growth rate.   RADSL: RADSL (Rate-Adaptive DSL) is an ADSL technology in which software is able to determine the rate at which signals can be transmitted on a given customer phone line and adjust the delivery rate accordingly.   Router: On the Internet, a router is a device or, in some cases, software in a computer, that determines the next network point to which a packet should be forwarded toward its destination. The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to. A router is located at any gateway (where one network meets another), including each Internet point-of-presence. A router is often included as part of a network switch.   SDSL (Symmetric Digital Subscriber Line): DSL in which the data rate is the same for both upstream and downstream transmission.   Server: 1) a computer program that provides services to other computer programs in the same or other computers; 2) the computer on which a server program runs; 3) in the client/server programming model, a server is a program that awaits and fulfills requests from client programs in the same or other computers. A given application in a computer may function as a client with requests for services from other programs and also as a server of requests from other programs; 4) see also Web Server.   Shared Hosting: hosting in which the service provider serves pages for multiple Web sites, each having its own Internet domain name, from a single Web server. Although shared hosting is a less expensive way for businesses to create a Web presence, it is usually not sufficient for Web sites with high traffic. These sites need a dedicated Web server, either provided by a Web hosting service or maintained in-house.   SONET (Synchronous Optical Network): the US standard for synchronous data transmission on optical media. SONET ensures standards so that digital networks can interconnect internationally and that existing conventional transmission systems can take advantage of optical media through tributary attachments. SONET provides standards for a number of line rates up to the maximum line rate of 9.953 Gbps. Actual line rates approaching 20 gigabits per second are possible. SONET is considered to be the foundation for the physical layer of the broadband ISDN.   Switch: In telecommunications, a switch is a network device that selects a path or circuit for sending a unit of data to its next destination. A switch may also include the function of the router, a device or program that can determine the route and specifically what adjacent network point the data should be sent to. In general, a switch is a simpler and faster mechanism than a router, which requires knowledge about the network and how to determine the route.   T-1: the most commonly used digital line in the United States, Canada, and Japan. In these countries, it carries 24 pulse code modulation (PCM) signals using time-division multiplexing (TDM) at an overall rate of 1.544 million bits per second (Mbps). T1 lines use copper wire and span distances within and between major metropolitan areas.   Token Ring: A token ring network is a local area network (LAN) in which all computers are connected in a ring or star topology and a binary digit- or token-passing scheme is used in order to prevent the collision of data between two computers that want to send messages at the same time. The token ring protocol is the second most widely used protocol on local area networks after Ethernet.   Twisted Pair Cable: Twisted-pair cable consists of copper wires surrounded by an insulator. Two wires are twisted together (the twisting prevents interference problems) to form a pair, and the pair forms a circuit that can transmit data. A cable is a bundle of one or more twisted pairs surrounded by an insulator. Unshielded twisted-pair (UTP) is the most commonly used type of twisted-pair cable. Shielded twisted-pair (STP) provides protection against cross-talk. Twisted-pair cable is now commonly used in Ethernet, Fast Ethernet, token ring, and other network topologies. See also CAT 5.   Virtual Hosting: the provision of Web server hosting service so that a company doesn't have to purchase and maintain its own Web server and connections to the Internet. Typically, virtual hosting provides a customer with: domain name registration assistance, multiple domain names that map to the registered domain name, an allocation of file storage and directory setup for the Web site files (HTML and graphic image files), and e-mail addresses. The customer needs only to have a File Transfer Protocol (FTP) program for exchanging files with the virtual host.   VPN: A virtual private network (VPN) is a private data network that makes use of the public telecommunication infrastructure, maintaining privacy through the use of a tunneling protocol and security procedures. The idea of the VPN is to give the company the same capabilities at much lower cost by using the shared public infrastructure rather than a private one.   WAN (Wide Area Network): a geographically dispersed telecommunications network. The term distinguishes a broader telecommunication structure from a local area network (LAN). A wide area network may be privately owned or rented, but the term usually connotes the inclusion of public (shared user) networks. An intermediate form of network in terms of geography is a metropolitan area network (MAN).   Web Server: the computer program that serves requested HTML pages or files. A Web client is the requesting program associated with the user. The Web browser is a client that requests HTML files from Web servers.   Workstation: a computer intended for individual use but faster and more capable than a personal computer. It's intended for business or professional use (rather than home or recreational use).