In communication networks, a node (Latin nodus, ‘knot’) is a connection point, either a redistribution point or a communication endpoint (some terminal equipment). The definition of a node depends on the network and protocol layer referred to. A physical network node is anactive electronic device that is attached to a network, and is capable of sending, receiving, or forwarding information over a communications channel.A passive distribution point such as a distribution frame is consequently not a node.In network theory or graph theory, the term node refers to a point in a network topology at which lines intersect or branchIn data communication, a physical network node may either be a data circuit-terminating equipment (DCE) such as a modem, hub, bridge or switch; or a data terminal equipment (DTE) such as a digital telephone handset, a printer or a host computer, for example a router, a workstation or a server.If the network in question is a LAN or WAN, every LAN or WAN node (that are at least data link layer devices) must have a MAC address. Examples are computers, packet switches and ADSL modem (with Ethernet interface). Note that a hub constitutes a physical network node, but not a LAN node in this sense, since a hubbed network logically is a bus network. Analogusly, a repeater or PSTN modem (with serial interface) are physical network nodes but not LAN nodes in this sense.If the network in question is the Internet, many physical network nodes are host computers, also known as Internet nodes, identified by an IP address, and all hosts are physical network nodes. However, datalink layer devices such as switches, bridges and WLAN access points do not have an IP host address (except sometimes for administrative purposes), and are not considered as Internet nodes, but as physical network nodes or LAN nodes.If the network in question is a distributed system, the nodes are clients, servers or peers. In a peer-to-peer or overlay network, nodes that actively route data for the other networked devices as well as themselves are called supernodesIn the fixed telephone network, a node may be a public or private telephone exchange, a remote concentrator or a computer providing some intelligent network service. In cellular communication, switching points and databases such as the Base station controller, Home Location Register, Gateway GPRS Support Node (GGSN) and Serving GPRS Support Node (SGSN) are examples of nodes. Cellular network base stations are not considered as nodes in this context.In cable television systems (CATV), this term has assumed a broader context and is generally associated with a fiber optic node. This can be defined as those homes or businesses within a specific geographic area that are served from a common fiber optic receiver. A fiber optic node is generally described in terms of the number of "homes passed" that are served by that specific fiber node.
Client
A client is an application or system that accesses a remote service on another computer system, known as a server, by way of a network.[1] The term was first applied to devices that were not capable of running their own stand-alone programs, but could interact with remote computers via a network. These dumb terminals were clients of the time-sharing mainframe computer.The client-server model is still used today on the Internet, where a user may connect to a service operating on a remote system through the Internet protocol suite. Web browsers are clients that connect to web servers and retrieve web pages for display. Most people use e-mail clients to retrieve their e-mail from their internet service provider's mail storage servers. Online chat uses a variety of clients, which vary depending on the chat protocol being used. Game Clients usually refer to the software that is the game in only multiplayer online games for the computer. Increasingly, existing large client applications are being switched to websites, making the browser a sort of universal client. This avoids the hassle of downloading a large piece of software onto any computer you want to use the application on. An example of this is the rise of webmail.In personal computers and computer workstations, the difference between client and server operating system is often just a matter of marketing - the server version may contain more operating system components, allow more simultaneous logins, and may be more expensive, while the client version may contain more end-user software. There are three types as in thin,fat and hybrid.
Server
In information technology, a server is a computer program that provides services to other computer programs (and their users) in the same or other computers.The computer that a server program runs in is also frequently referred to as a server (though it may be used for other purposes as well).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.Specific to the Web, a Web server is the computer program (housed in a computer) that serves requested HTML pages or files. A Web client is the requesting program associated with the user. The Web browser in your computer is a client that requests HTML files from Web serversAny computer or device serving out applications or services can technically be called a server. In an office or enterprise environment, the network server is easy to identify. A DSL/Cable modem router qualifies as a server because it provides a computer with application services like IP address assignment (via DHCP), NAT, and a firewall that helps protect a computer from external threats. iTunes software implements a music server to stream music between computers. Many home users create shared folders and printers. Another example are the many servers that are used for hosting online games such as Everquest, World of Warcraft, Counter-Strike and Eve Online.
No comments:
Post a Comment