Computer network - Wikipedia
Everything is in the book. A computer network, or data network, is a digital telecommunications network which allows nodes to share resources. In computer networks, computing devices exchange data with each other Two such devices can be said to be networked together when one device is able to exchange. Classification of Complex Networks Based on Topological Prop- erties. likely to represent systems with functional similarities, whereas network classes with the probability for a link to exist between two randomly picked. Networks are divided into two types, a LAN (Local Area Network) or a up an ISDN or leased line or PPP link (WAN) to an Internet Service.
In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than meters. With fiber optics, repeaters can be tens or even hundreds of kilometers apart. A repeater with multiple ports is known as an Ethernet hub.
Repeaters work on the physical layer of the OSI model. Repeaters require a small amount of time to regenerate the signal. This can cause a propagation delay that affects network performance and may affect proper function. As a result, many network architectures limit the number of repeaters that can be used in a row, e. Hubs and repeaters in LANs have been mostly obsoleted by modern switches. Bridges[ edit ] A network bridge connects and filters traffic between two network segments at the data link layer layer 2 of the OSI model to form a single network.
This breaks the network's collision domain but maintains a unified broadcast domain. Network segmentation breaks down a large, congested network into an aggregation of smaller, more efficient networks.
Bridges come in three basic types: Directly connect LANs Remote bridges: Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers.
Switches[ edit ] A network switch is a device that forwards and filters OSI layer 2 datagrams frames between ports based on the destination MAC address in each frame. It can be thought of as a multi-port bridge. If an unknown destination is targeted, the switch broadcasts to all ports but the source. Switches normally have numerous ports, facilitating a star topology for devices, and cascading additional switches.
Routers[ edit ] A typical home or small office router showing the ADSL telephone line and Ethernet network cable connections A router is an internetworking device that forwards packets between networks by processing the routing information included in the packet or datagram Internet protocol information from layer 3.
The routing information is often processed in conjunction with the routing table or forwarding table.
A router uses its routing table to determine where to forward packets. A destination in a routing table can include a "null" interface, also known as the "black hole" interface because data can go into it, however, no further processing is done for said data, i. Modems[ edit ] Modems MOdulator-DEModulator are used to connect network nodes via wire not originally designed for digital network traffic, or for wireless.
To do this one or more carrier signals are modulated by the digital signal to produce an analog signal that can be tailored to give the required properties for transmission. Modems are commonly used for telephone lines, using a Digital Subscriber Line technology. Firewalls[ edit ] A firewall is a network device for controlling network security and access rules.
Firewalls are typically configured to reject access requests from unrecognized sources while allowing actions from recognized ones. The vital role firewalls play in network security grows in parallel with the constant increase in cyber attacks.
Network structure[ edit ] Network topology is the layout or organizational hierarchy of interconnected nodes of a computer network.
Different network topologies can affect throughput, but reliability is often more critical. With many technologies, such as bus networks, a single failure can cause the network to fail entirely. In general the more interconnections there are, the more robust the network is; but the more expensive it is to install.
Common network topologies Common layouts are: This is still a common topology on the data link layeralthough modern physical layer variants use point-to-point links instead.
- Computer network
- Network topology
This is the typical layout found in a Wireless LANwhere each wireless client connects to the central Wireless access point. A fully connected network: Note that the physical layout of the nodes in a network may not necessarily reflect the network topology. As an example, with FDDIthe network topology is a ring actually two counter-rotating ringsbut the physical topology is often a star, because all neighboring connections can be routed via a central physical location.
Overlay network[ edit ] A sample overlay network An overlay network is a virtual computer network that is built on top of another network. Nodes in the overlay network are connected by virtual or logical links. Each link corresponds to a path, perhaps through many physical links, in the underlying network.
The topology of the overlay network may and often does differ from that of the underlying one. For example, many peer-to-peer networks are overlay networks. They are organized as nodes of a virtual system of links that run on top of the Internet. The most striking example of an overlay network is the Internet itself. The Internet itself was initially built as an overlay on the telephone network. Address resolution and routing are the means that allow mapping of a fully connected IP overlay network to its underlying network.
Another example of an overlay network is a distributed hash tablewhich maps keys to nodes in the network. In most cases, line-of-sight propagation is used, which limits the physical positioning of communicating devices.
Exotic technologies[ edit ] There have been various attempts at transporting data over exotic media: It was implemented in real life in Node networking Network nodes are the points of connection of the transmission medium to transmitters and receivers of the electrical, optical, or radio signals carried in the medium. Nodes may be associated with a computer, but certain types may have only a microcontroller at a node or possibly no programmable device at all. In the simplest of serial arrangements, one RS transmitter can be connected by a pair of wires to one receiver, forming two nodes on one link, or a Point-to-Point topology.
Some protocols permit a single node to only either transmit or receive e. Other protocols have nodes that can both transmit and receive into a single channel e. While the conventional system building blocks of a computer network include network interface controllers NICsrepeatershubsbridgesswitchesroutersmodemsgatewaysand firewallsmost address network concerns beyond the physical network topology and may be represented as single nodes on a particular physical network topology.
Network interfaces[ edit ] An ATM network interface in the form of an accessory card. A lot of network interfaces are built-in. A network interface controller NIC is computer hardware that provides a computer with the ability to access the transmission media, and has the ability to process low-level network information.
For example, the NIC may have a connector for accepting a cable, or an aerial for wireless transmission and reception, and the associated circuitry.
Two Types of Networks: LANs and WANs
In Ethernet networks, each network interface controller has a unique Media Access Control MAC address—usually stored in the controller's permanent memory. The size of an Ethernet MAC address is six octets. The three most significant octets are reserved to identify NIC manufacturers.
These manufacturers, using only their assigned prefixes, uniquely assign the three least-significant octets of every Ethernet interface they produce. Repeaters and hubs[ edit ] A repeater is an electronic device that receives a network signalcleans it of unnecessary noise and regenerates it. The signal may be reformed or retransmitted at a higher power level, to the other side of an obstruction possibly using a different transmission medium, so that the signal can cover longer distances without degradation.
Commercial repeaters have extended RS segments from 15 meters to over a kilometer . In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than meters.
With fiber optics, repeaters can be tens or even hundreds of kilometers apart. Repeaters work within the physical layer of the OSI model, that is, there is no end-to-end change in the physical protocol across the repeater, or repeater pair, even if a different physical layer may be used between the ends of the repeater, or repeater pair.
Two Types of Networks: LANs and WANs – Router Switch Blog
Repeaters require a small amount of time to regenerate the signal. This can cause a propagation delay that affects network performance and may affect proper function. As a result, many network architectures limit the number of repeaters that can be used in a row, e. USB networks use hubs to form tiered-star topologies.
Ethernet hubs and repeaters in LANs have been mostly obsoleted by modern switches. Bridges[ edit ] A network bridge connects and filters traffic between two network segments at the data link layer layer 2 of the OSI model to form a single network.
This breaks the network's collision domain but maintains a unified broadcast domain. Network segmentation breaks down a large, congested network into an aggregation of smaller, more efficient networks. Bridges come in three basic types: