Meaning Of Network | Computer Network

A computer network is a group of more computers connected to each electronically. This means that the computers can "talk" to each other and that every computer in the network can send information to the others. Usually, this means that the speed of the connection is fast - faster than a normal connection to the Internet. Some basic types of computer networks include:

• A local area network (often called a LAN) connects two or more computers, and may be called a corporate network in an office or business setting.
• An "internetwork", sometimes called a Wide Area Network (because of the wide distance between networks) connects two or more smaller networks together. The largest internetwork is called the Internet .

Computers can be part of several different networks. Networks can also be parts of bigger networks. The local area network in a small business is usually connected to the corporate network of the larger company. Any connected machine at any level of the organization may be able to access the Internet , for example to demonstrate computers in the store, display its catalogue through a web server , or convert received orders into shipping instructions.

Microsoft Windows , Linux and most other operating systems use TCP/IP for networking. Apple Macintosh computers used Appletalk in the past, but it uses TCP/IP now.

To set up a network an appropriate media is required. This can be wired or wireless. Twisted-pair, co-axial or fiber-optic are examples of cable and infra-red, blue-tooth, radio-wave, micro-wave etc. are wireless media used for networking. When you are working with a mere LAN, computers, media and peripherals are sufficient. But when you are working with a wider range you have use some additional devices like bridge, gateway or router to connect different small or large networks. And obviously a protocol must be maintained.

To set up a network you have to select an appropriate topology to arrange the hardware devices using the media. Topologies generally used are bus-topology, ring-topology, star-topology, tree-topology, object-oriented topology etc. Among these star-topology and tree-topology are most popular nowadays.

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Meaning Of Network

Understanding Network

Network is a set of computers connected by cable to each computer so that other computers can be mutual communication, exchange of information sharing files, printers, etc..Network is divided into 2

1. Standalone
2. Network

Type - Type of Coverage Based Networks

1. Local Area Networking (LAN)The network that is bounded by a relatively small area, generally bounded by the area like an office environment in a building, or a school, and usually not far from about 1 km square.

2. Metropolitan Area Networking (MAN)That is a wider network of LAN, MAN typically covers an area larger areas such as provincial, inter-building. Why MAN is said to be more extensive than a LAN?, Well, because the MAN network is connected from multiple LAN networks connected through a switch again.

3. Wide Area Networking (WAN)A network that is usually already in scope by means of satellite or submarine cable as an example of a whole network BANK BNI in Indonesia or in other States. Using the WAN infrastructure, a bank that is in Bandung can contact the branch office in Hong Kong, in just a few minutes. WANs are usually rather complicated and very complex, using many means for connecting between the LAN and WAN to the Global Communications such as the Internet.

• Physical topology refers to the physical design of a network including the devices, location and cable installation.
• Logical topology refers to how data is actually transferred in a network as opposed to its physical design. In general physical topology relates to a core network whereas logical topology relates to basic network.

Network Topology

Any particular network topology is determined only by the graphical mapping of the configuration of physical and / or logical connections the between nodes. The study of network topology uses graph theory. Distances the between nodes, physical interconnections, transmission rates, and / or signal types may differ in two networks and yet Their topologies may be identical.

• A - Point-to-point  ( Permanent (Dedicated) - Switched )         
• B - Bus                   (Linear Bus - Distributed Bus)                     
• C - Star                  (Extended Star - Distributed Star)              
• D - Ring                                                                                            
• E - Mesh                (Fully Connected - Partially Connected)    
• F - Tree                                                                                             
• G - Hybrid                                                                                        
• H - Daisy chain                                                                              

Type - the type of network topology 

A- Point-to-point Topology

The simplest topology is a permanent link between two endpoints. Switched point-to-point topologies are the basic model of conventional telephony. The value of a permanent point-to-point network is unimpeded communications between the two endpoints. The value of an on-demand point-to-point connection is proportional to the number of potential pairs of subscribers, and has been expressed as Metcalfe's Law.

    Permanent (dedicated)

 Easiest to understand, of the variations of point-to-point topology, is a point-to-point communications channel that appears, to the user, to be permanently associated with the two endpoints. A children's tin can telephone is one example of a physical dedicated channel.

Within many switched telecommunications systems, it is possible to establish a permanent circuit. One example might be a telephone in the lobby of a public building, which is programmed to ring only the number of a telephone dispatcher. "Nailing down" a switched connection saves the cost of running a physical circuit between the two points. The resources in such a connection can be released when no longer needed, for example, a television circuit from a parade route back to the studio.

    Switched:

 Using circuit-switching or packet-switching technologies, a point-to-point circuit can be set up dynamically, and dropped when no longer needed. This is the basic mode of conventional telephony.

B- Bus Topology 

Bus topology is the topology that thinking about one cable that connects to the server computer so who wants to get into a bus topology must connect the cable to the BNC cable BNCnya server. Because this topology using a BNC cable.

 In local area networks where the bus topology is used, each node is connected to a single cable. Each computer or server is connected to the single bus cable. A signal from the source Travels in Both directions to all machines connected on the bus cable until it finds the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data matches the machine address, the data is accepted. Since the bus topology consists of only one wire, it is rather inexpensive to implement compared to other topologies Pls. However, the low cost of implementing the technology is offset by the high cost of managing the network. Additionally, since only one cable is utilized, it can be the single point of failure. If the network cable is terminated on Both ends and without termination Pls and Pls stop the data transfer cable breaks, the entire network Will be down.

    Linear bus

The type of network topology in the which all of the nodes of the network are connected to a common transmission medium of the which has exactly two endpoints (this is the 'bus', the which is also commonly Referred to as the backbone, or trunk) - all data That is the between-transmitted nodes in the network is transmitted over this common transmission medium and is Able to be received by all nodes in the network simultaneously.
Note: The two endpoints of the common transmission medium are normally terminated with a device Called a terminator That Exhibits the characteristic impedance of the transmission medium and the which dissipates or absorbs the energy That Remains in the signal to Prevent the signal from being reflected or propagated back onto the transmission medium in the Opposite direction, the which would cause interference with and degradation of the signals on the transmission medium.

    Distributed bus

The type of network topology in the which all of the nodes of the network are connected to a common transmission medium of the which has more than two endpoints That are created by adding branches to the main section of the transmission medium - the physical distributed bus topology functions in exactly the same fashion as the physical linear bus topology (ie, all nodes share a common transmission medium).
        Notes:

1. All of the endpoints of the common transmission medium are normally terminated using a 50 ohm resistor.
2. The linear bus topology is Sometimes Considered to be a special case of the distributed bus topology - ie, a distributed bus with no branching segments.
3. The physical distributed bus topology is incorrectly Sometimes Referred to as a physical tree topology - however, although the physical distributed bus topology resembles the physical tree topology, it differs from the physical tree topology in That there is no central node to the which any other nodes are connected, since this hierarchical functionality is replaced by the common bus.

C- Star Topology

 Star topology is a topology that uses the switch as the connecting cable between jaringa. Thus, this topology is more frequently used than the topology that because the cost is cheaper and faster trasperdata. Since switching the speed governing data.

 In local area networks with a star topology, each network host is connected to a central hub with a point-to-point connection. The network does not necessarily have to resemble a star to be classified as a star network, but all of the nodes on the network must be connected to one central device. All traffic that traverses the network passes through the central hub. The hub acts as a signal repeater. The star topology is considered the easiest topology to design and implement. An advantage of the star topology is the simplicity of adding additional nodes. The primary disadvantage of the star topology is that the hub represents a single point of failure.

    Notes

•  A point-to-point link (described above) is sometimes categorized as a special instance of the physical star topology – therefore, the simplest type of network that is based upon the physical star topology would consist of one node with a single point-to-point link to a second node, the choice of which node is the 'hub' and which node is the 'spoke' being arbitrary.
• After the special case of the point-to-point link, as in note (1) above, the next simplest type of network that is based upon the physical star topology would consist of one central node – the 'hub' – with two separate point-to-point links to two peripheral nodes – the 'spokes'.
• Although most networks that are based upon the physical star topology are commonly implemented using a special device such as a hub or switch as the central node (i.e., the 'hub' of the star), it is also possible to implement a network that is based upon the physical star topology using a computer or even a simple common connection point as the 'hub' or central node.
• Star networks may also be described as either broadcast multi-access or nonbroadcast multi-access (NBMA), depending on whether the technology of the network either automatically propagates a signal at the hub to all spokes, or only addresses individual spokes with each communication.

Extended star

• A type of network topology in which a network that is based upon the physical star topology has one or more repeaters between the central node (the 'hub' of the star) and the peripheral or 'spoke' nodes, the repeaters being used to extend the maximum transmission distance of the point-to-point links between the central node and the peripheral nodes beyond that which is supported by the transmitter power of the central node or beyond that which is supported by the standard upon which the physical layer of the physical star network is based. 

• If the repeaters in a network that is based upon the physical extended star topology are replaced with hubs or switches, then a hybrid network topology is created that is referred to as a physical hierarchical star topology, although some texts make no distinction between the two topologies.

    Distributed Star

• A type of network topology that is composed of individual networks that are based upon the physical star topology connected together in a linear fashion – i.e., 'daisy-chained' – with no central or top level connection point (e.g., two or more 'stacked' hubs, along with their associated star connected nodes or 'spokes').

D- Ring Topology 

Ring topology is topologically connected to the two landcard. So the data delivery form clockwise and counter-clockwise. So that data transmission is often not up to the destination computer because it must pass through another computer first.

A network topology that is set up in a circular fashion in which data travels around the ring in one direction and each device on the right acts as a repeater to keep the signal strong as it travels. Each device incorporates a receiver for the incoming signal and a transmitter to send the data on to the next device in the ring. The network is dependent on the ability of the signal to travel around the ring.

E- Mesh Topology

The value of fully meshed networks is proportional to the exponent of the number of subscribers, assuming that communicating groups of any two endpoints, up to and including all the endpoints, is approximated by Reed's Law.

The value of fully meshed networks is proportional to the exponent of the number of subscribers, assuming that communicating groups of any two endpoints, up to and including all the endpoints, is approximated by Reed's Law.

    Fully connected

Fully connected mesh topology
The number of connections in a full mesh = n(n - 1) / 2.

Note: The physical fully connected mesh topology is generally too costly and complex for practical networks, although the topology is used when there are only a small number of nodes to be interconnected (see Combinatorial explosion).

    Partially connected

Partially connected mesh topology

The type of network topology in which some of the nodes of the network are connected to more than one other node in the network with a point-to-point link – this makes it possible to take advantage of some of the redundancy that is provided by a physical fully connected mesh topology without the expense and complexity required for a connection between every node in the network. 

Note: In most practical networks that are based upon the partially connected mesh topology, all of the data that is transmitted between nodes in the network takes the shortest path between nodes, except in the case of a failure or break in one of the links, in which case the data takes an alternative path to the destination. This requires that the nodes of the network possess some type of logical 'routing' algorithm to determine the correct path to use at any particular time.

F-Tree Topology

The type of network topology in which a central 'root' node (the top level of the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level) with a point-to-point link between each of the second level nodes and the top level central 'root' node, while each of the second level nodes that are connected to the top level central 'root' node will also have one or more other nodes that are one level lower in the hierarchy (i.e., the third level) connected to it, also with a point-to-point link, the top level central 'root' node being the only node that has no other node above it in the hierarchy (The hierarchy of the tree is symmetrical.) Each node in the network having a specific fixed number, of nodes connected to it at the next lower level in the hierarchy, the number, being referred to as the 'branching factor' of the hierarchical tree.This tree has individual peripheral nodes.

1.  A network that is based upon the physical hierarchical topology must have at least three levels in the hierarchy of the tree, since a network with a central 'root' node and only one hierarchical level below it would exhibit the physical topology of a star.
2. A network that is based upon the physical hierarchical topology and with a branching factor of 1 would be classified as a physical linear topology.
3.  The branching factor, f, is independent of the total number of nodes in the network and, therefore, if the nodes in the network require ports for connection to other nodes the total number of ports per node may be kept low even though the total number of nodes is large – this makes the effect of the cost of adding ports to each node totally dependent upon the branching factor and may therefore be kept as low as required without any effect upon the total number of nodes that are possible.
4. The total number of point-to-point links in a network that is based upon the physical hierarchical topology will be one less than the total number of nodes in the network.
5.  If the nodes in a network that is based upon the physical hierarchical topology are required to perform any processing upon the data that is transmitted between nodes in the network, the nodes that are at higher levels in the hierarchy will be required to perform more processing operations on behalf of other nodes than the nodes that are lower in the hierarchy. Such a type of network topology is very useful and highly recommended. 

definition : Tree topology is a combination of Bus and Star topology.

G- Hybrid Topology

Hybrid networks use a combination of any two or more topologies in such a way that the resulting network does not exhibit one of the standard topologies (e.g., bus, star, ring, etc.). For example, a tree network connected to a tree network is still a tree network topology. A hybrid topology is always produced when two different basic network topologies are connected. Two common examples for Hybrid network are: star ring network and star bus network

1. A Star ring network consists of two or more star topologies connected using a multistation access unit (MAU) as a centralized hub.
2. A Star Bus network consists of two or more star topologies connected using a bus trunk (the bus trunk serves as the network's backbone).

While grid and torus networks have found popularity in high-performance computing applications, some systems have used genetic algorithms to design custom networks that have the fewest possible hops in between different nodes. Some of the resulting layouts are nearly incomprehensible, although they function quite well.

A Snowflake topology is really a "Star of Stars" network, so it exhibits characteristics of a hybrid network topology but is not composed of two different basic network topologies being connected together. Definition : Hybrid topology is a combination of Bus ,Star and ring topology.

H- Daisy chain Topology

 Except for star-based networks, the easiest way to add more computers into a network is by daisy-chaining, or connecting each computer in series to the next. If a message is intended for a computer partway down the line, each system bounces it along in sequence until it reaches the destination. A daisy-chained network can take two basic forms: linear and ring.

• A linear topology puts a two-way link between one computer and the next. However, this was expensive in the early days of computing, since each computer (except for the ones at each end) required two receivers and two transmitters.

• By connecting the computers at each end, a ring topology can be formed. An advantage of the ring is that the number of transmitters and receivers can be cut in half, since a message will eventually loop all of the way around. When a node sends a message, the message is processed by each computer in the ring. If a computer is not the destination node, it will pass the message to the next node, until the message arrives at its destination. If the message is not accepted by any node on the network, it will travel around the entire ring and return to the sender. This potentially results in a doubling of travel time for data.

Source Brandon Harris Wikipedia
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