Node

노드의 예가 end host , router 등등으로 알고 있는데, 
네트워크의 계층 어떤 것을 말하고 있는지에 따라서 달라진다는 말이 눈에 확들어오는..
노드의 개념이 추상적이니깐.

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Node (networking)

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For other uses, see Node.

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 an active electronic device that is attached to a network, and is capable of sending, receiving, or forwarding information over a communications channel.^[1] 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 branch^[2].

Computer network nodes

In 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. Analogously, 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 supernodes.

Telecommunication network nodes

In 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.