Everything about Computer Network totally explained
A
computer network is an interconnected group of
computers. Networks may be classified by the network layer at which they operate according to basic reference models considered as standards in the industry, such as the four-layer
Internet Protocol Suite model. While the seven-layer
Open Systems Interconnection (OSI) reference model is better known in academia, the majority of networks use the Internet Protocol Suite (IP).
By scale
Computer networks may be classified according to the scale:
Personal area network (PAN),
Local Area Network (LAN),
Campus Area Network (CAN),
Metropolitan area network (MAN), or
Wide area network (WAN).
As
Ethernet increasingly is the standard interface for networks, these distinctions are more important to the network administrator than the user. Network administrators may have to tune the network, to correct delay issues and achieve the desired performance level.
By connection method
Computer networks can also be classified according to the hardware technology that's used to connect the individual devices in the network such as
Optical fibre,
Ethernet,
Wireless LAN,
HomePNA, or
Power line communication.
Ethernets use physical wiring to connect devices. Often, they employ the use of hubs, switches, bridges, and routers.
Wireless LAN technology is built to connect devices without wiring. These devices use a radio frequency to connect.
By functional relationship (Network Architectures)
Computer networks may be classified according to the functional relationships which exist between the elements of the network, for example,
Active Networking,
Client-server and
Peer-to-peer (workgroup) architectures.
By network topology
Computer networks may be classified according to the
network topology upon which the network is based, such as
Bus network,
Star network,
Ring network,
Mesh network,
Star-bus network,
Tree or Hierarchical topology network, etc.
Network Topology signifies the way in which intelligent devices in the network see their logical relations to one another. The use of the term "logical" here's significant. That is, network topology is independent of the "physical" layout of the network. Even if networked computers are physically placed in a linear arrangement, if they're connected via a hub, the network has a Star topology, rather than a Bus Topology. In this regard the visual and operational characteristics of a network are distinct; the logical network topology isn't necessarily the same as the physical layout.
By protocol
Computer networks may be classified according to the
communications protocol that's being used on the network. See the articles on
List of network protocol stacks and
List of network protocols for more information. For a development of the foundations of protocol design see Srikant 2004 and Meyn 2007
Types of networks:
Below is a list of the most common types of computer networks in order of scale.
Personal Area Network (PAN)
A personal area network (PAN) is a computer network used for communication among computer devices close to one person. Some examples of devices that may be used in a PAN are printers, fax machines, telephones, PDAs or scanners. The reach of a PAN is typically within about 20-30 feet (approximately 6-9 metres).
Personal area networks may be wired with computer buses such as
USB and
FireWire. A wireless personal area network (WPAN) can also be made possible with network technologies such as
IrDA and
Bluetooth.
Local Area Network (LAN)
A network covering a small geographic area, like a home, office, or building. Current LANs are most likely to be based on Ethernet technology. For example, a library will have a wired or wireless LAN for users to interconnect local devices (for example, printers and servers) and to connect to the internet. All of the PCs in the library are connected by
category 5 (Cat5) cable, running the IEEE 802.3 protocol through a system of interconnection devices and eventually connect to the internet. The cables to the servers are on Cat 5e enhanced cable, which will support IEEE 802.3 at 1 Gbit/s.
The staff computers (bright green in the figure) can get to the color printer, checkout records, and the academic network
and the Internet. All user computers can get to the Internet and the card catalog. Each workgroup can get to its local printer. Note that the printers are not accessible from outside their workgroup.
All interconnected devices must understand the network layer (layer 3), because they're handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the central router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand
IP. It would be more correct to call them access routers, where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers.
The defining characteristics of LANs, in contrast to WANs (wide area networks), include their higher data transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines. Current Ethernet or other
IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate.
IEEE has projects investigating the standardization of 100 Gbit/s, and possibly 40 Gbit/s.
Campus Area Network (CAN)
A network that connects two or more LANs but that's limited to a specific and contiguous geographical area such as a college campus, industrial complex, or a military base. A CAN may be considered a type of MAN (metropolitan area network), but is generally limited to an area that's smaller than a typical MAN. This term is most often used to discuss the implementation of networks for a contiguous area. This shouldn't be confused with a
Controller Area Network
Metropolitan Area Network (MAN)
A Metropolitan Area Network is a network that connects two or more Local Area Networks or Campus Area Networks together but doesn't extend beyond the boundaries of the immediate town, city, or metropolitan area. Multiple routers, switches & hubs are connected to create a MAN.
Wide Area Network (WAN)
A WAN is a data communications network that covers a relatively broad geographic area (for example one city to another and one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the
OSI reference model: the
physical layer, the
data link layer, and the
network layer.
Global Area Network (GAN)
Global area networks (GAN) specifications are in development by several groups, and there's no common definition. In general, however, a GAN is a model for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is "handing off" the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial
Wireless local area networks (WLAN).
Internetwork
Two or more networks or network segments connected using devices that operate at layer 3 (the 'network' layer) of the OSI Basic Reference Model, such as a router. Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.
In modern practice, the interconnected networks use the Internet Protocol. There are at least three variants of internetwork, depending on who administers and who participates in them:
- Intranet
- Extranet
- Internet
Intranets and extranets may or may not have connections to the Internet. If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization. The Internet isn't considered to be a part of the intranet or extranet, although it may serve as a portal for access to portions of an extranet.
Intranet
An
intranet is a set of interconnected networks, using the
Internet Protocol and uses IP-based tools such as web browsers and ftp tools, that's under the control of a single administrative entity. That administrative entity closes the intranet to the rest of the world, and allows only specific users. Most commonly, an intranet is the internal network of a company or other enterprise. A large intranet will typically have its own web server to provide users with browseable information.
Extranet
An
extranet is a network or internetwork that's limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (for example a company's customers may be given access to some part of its intranet creating in this way an extranet, while at the same time the customers may not be considered 'trusted' from a security standpoint). Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although, by definition, an extranet can't consist of a single LAN; it must have at least one connection with an external network.
Internet
A specific internetwork, consisting of a worldwide interconnection of governmental, academic, public, and private networks based upon the
Advanced Research Projects Agency Network (ARPANET) developed by
ARPA of the
U.S. Department of Defense – also home to the
World Wide Web (WWW) and referred to as the 'Internet' with a capital 'I' to distinguish it from other generic internetworks.
Participants in the Internet, or their service providers, use
IP Addresses obtained from address registries that control assignments. Service providers and large enterprises also exchange information on the reachability of their address ranges through the
Border Gateway Protocol (BGP).
Basic Hardware Components
All networks are made up of basic hardware building blocks to interconnect network
nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly
Category 5 cable). Less common are microwave links (as in
IEEE 802.11) or optical cable ("
optical fiber").
Network Interface Cards
A
network card,
network adapter or
NIC (network interface card) is a piece of
computer hardware designed to allow computers to communicate over a
computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of
MAC addresses. It allows users to connect to each other either by using cables or wirelessly.
Repeaters
A
repeater is an
electronic device that receives a
signal and
retransmits it at a higher level or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair ethernet configurations, repeaters are required for cable runs longer than 100 meters.
Hubs
A hub contains multiple ports. When a packet arrives at one port, it's copied to all the ports of the hub. When the packets are copied, the destination address in the frame doesn't change to a broadcast address. It does this in a rudimentary way, it simply copies the data to all of the Nodes connected to the hub.
Bridges
A
network bridge connects multiple
network segments at the
data link layer (layer 2) of the
OSI model. Bridges don't promiscuously copy traffic to all ports, as hubs do, but learns which
MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it'll send traffic for that address only to that port. Bridges do send broadcasts to all ports except the one on which the broadcast was received.
Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.
Bridges come in three basic types:
Local bridges: Directly connect local area networks (LANs)
Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced by routers.
Wireless bridges: Can be used to join LANs or connect remote stations to LANs.
Switches
A switch is a device that performs switching. Specifically, it forwards and filters OSI layer 2 datagrams (chunk of data communication) between ports (connected cables) based on the Mac-Addresses in the packets. This is distinct from a hub in that it only forwards the datagrams to the ports involved in the communications rather than all ports connected. Strictly speaking, a switch isn't capable of routing traffic based on IP address (layer 3) which is necessary for communicating between network segments or within a large or complex LAN. Some switches are capable of routing based on IP addresses but are still called switches as a marketing term. A switch normally has numerous ports with the intention that most or all of the network be connected directly to a switch, or another switch that's in turn connected to a switch.
"Switches" is a marketing term that encompasses routers and bridges, as well as devices that may distribute traffic on load or by application content (for example, a Web URL identifier). Switches may operate at one or more OSI layers, including physical, data link, network, or transport (for example, end-to-end). A device that operates simultaneously at more than one of these layers is called a multilayer switch.
Overemphasizing the ill-defined term "switch" often leads to confusion when first trying to understand networking. Many experienced network designers and operators recommend starting with the logic of devices dealing with only one protocol level, not all of which are covered by OSI. Multilayer device selection is an advanced topic that may lead to selecting particular implementations, but multilayer switching is simply not a real-world design concept.
Routers
Routers are networking devices that forward data packets between networks using headers and forwarding tables to determine the best path to forward the packets. Routers work at the network layer of the TCP/IP model or layer 3 of the OSI model. Routers also provide interconnectivity between like and unlike media (RFC 1812). This is accomplished by examining the Header of a data packet, and making a decision on the next hop to which it should be sent (RFC 1812) They use preconfigured static routes, status of their hardware interfaces, and routing protocols to select the best route between any two subnets. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network. Some DSL and cable modems, for home (and even office) use, have been integrated with routers to allow multiple home/office computers to access the Internet through the same connection. Many of these new devices also consist of wireless access points (waps) or wireless routers to allow for IEEE 802b/g wireless enabled devices to connect to the network without the need for a cabled connection.
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