2A computer network, often simply referred to as a network, is a collection of computers and devices interconnected by communications channels that facilitate communications among users and allows users to share resources.
3LAN - Local Area Network A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings. In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization.
4A metropolitan area network (MAN) is a large computer network that usually spans a city or a large campus. A MAN usually interconnects a number of local area networks (LANs) using a high-capacity backbone technology, such as fiber-optical links, and provides up-link services to wide area networks (or WAN) and the Internet.
5WAN - Wide Area NetworkAs the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth. A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address.
6LOCAL AREA NETWORKWIDE AREA NETWORK1.Diameter of not more than a few kilometers.1.Span entire countries.2.A total data rate of at least several mbps.2.Data rate less than 1 mbps.3.Complete ownership by a single organization.3.Owned by multiple organization.4.Very low error rates.4.Comparitively higher error rates.
7Network topology is the layout pattern of interconnections of the various elements (links, nodes, etc.) of a computer network. Network topologies may be physical or logical. Physical topology means 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.
8Many topologies have been developed, but the major ones are: the Star topologythe Bus topologythe Ring or circularthe Treethe Graphthe Mesh
9STAR TOPOLOGYStar networks are one of the most common computer network topologies. In its simplest form, a star network consists of one central switch, hub or computer, which acts as a conduit to transmit messages. Thus, the hub and leaf nodes, and the transmission lines between them, form a graph with the topology of a star.
11The star topology reduces the chance of network failure by connecting all of the systems to a central node. This central hub rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, sometimes including the originating node. All peripheral nodes may thus communicate with all others by transmitting to, and receiving from, the central node only. The failure of a transmission line linking any peripheral node to the central node will result in the isolation of that peripheral node from all others, but the rest of the systems will be unaffected.
12ADVANTAGES OF STAR TOPOLOGY Better performance: star topology prevents the passing of data packets through an excessive number of nodes. At most, 3 devices and 2 links are involved in any communication between any two devices. Although this topology places a huge overhead on the central hub, with adequate capacity, the hub can handle very high utilization by one device without affecting others.Simplicity: This topology is easy to understand, establish, and navigate. Its simplicity obviates the need for complex routing or message passing protocols. Also, as noted earlier, the isolation and centralization it allows simplify fault detection, as each link or device can be probed individually.
13Isolation of devices: Each device is inherently isolated by the link that connects it to the hub. This makes the isolation of individual devices straightforward and amounts to disconnecting each device from the others. This isolation also prevents any non-centralized failure from affecting the network.Easy to install and wire.Easy to detect faults and to remove parts.No disruptions to the network when connecting or removing devices
14Benefits from centralization: As the central hub is the bottleneck, increasing its capacity, or connecting additional devices to it, increases the size of the network very easily. Centralization also allows the inspection of traffic through the network. This facilitates analysis of the traffic and detection of suspicious behavior.
15DISADVANTGES OF STAR TOPOLOGY High dependence of the system on the functioning of the central hubFailure of the central hub renders the network inoperableThe performance and scalability of the network depends on the capabilities of the hubWiring up of the system can be very complex and expensive
16Network size is limited by the number of connections that can be made to the hub Other nodes may see a performance drop if traffic to another node occupies a significant portion of the central node's processing capability or throughput.
17Bus topologyA bus network topology is a network architecture in which a set of clients are connected via a shared communications line, called a bus. There are several common instances of the bus architecture, including one in the motherboard of most computers, and those in some versions of Ethernet networks.
19Bus networks are the simplest way to connect multiple clients, but may have problems when two clients want to transmit at the same time on the same bus. Thus systems which use bus network architectures normally have some scheme of collision handling or collision avoidance for communication on the bus, quite often using Carrier Sense Multiple Access or the presence of a bus master which controls access to the shared bus resource.A true bus network is passive – the computers on the bus simply listen for a signal; they are not responsible for moving the signal along.
20However, many active architectures can also be described as a "bus", as they provide the same logical functions as a passive bus; for example, switched Ethernet can still be regarded as a logical network, if not a physical one. Indeed, the hardware may be abstracted away completely in the case of a software bus.However, almost all current wireless networks can be viewed as examples of passive bus networks, with radio propagation serving as the shared passive medium.
21Bus network topology uses a broadcast channel which means that all attached stations can hear every transmission and all stations have equal priority in using the network to transmit data.The Ethernet bus topology works like a big telephone party line — before any device can send a packet, devices on the bus must first determine that no other device is sending a packet on the cable.
22Advantages of linear topology Easy to implement and extend.Easy to install.Well-suited for temporary or small networks not requiring high speeds (quick setup), resulting in faster networks.Cheaper than other topologies (But in Recent years has became less Important due Devices like a Switch)Cost effective; only a single cable is used.Easy identification of cable faults.Reduced weight due to fewer wires.
23Disadvantages of linear topology Limited cable length and number of stations.If there is a problem with the cable, the entire network breaks down.Maintenance costs may be higher in the long run.Performance degrades as additional computers are added or on heavy traffic (shared bandwidth).Proper termination is required (loop must be in closed path).
24Significant Capacitive Load (each bus transaction must be able to stretch to most distant link). It works best with limited number of nodes.Commonly has a slower data transfer rate than other topologies.Only one packet can remain on the bus during one clock pulse.
25The ring or circular topology --In ring topology each node is connected to two and only two neighboring nodes.--Data is accepted from one of the neighboring nodes and is transmitted onward to another.--after passing through each node, it returns to the sending node, which removes it.
26advantages DISADVANTAGES SHORT CABLE LENGTHNO WIRING CLOSET SPACE REQUIREDSUITABLE FOR OPTICAL FIBERSDISADVANTAGESNODE FAILURE CAUSES NETWORK FAILUREDIFFICULT TO DIAGNOSE FAULTSNETWORK RECONFIGURATION IS DIFFICULT
27THE TREE TOPOLOGY Also known as a hierarchical network the shape of the network is that of an inverted tree with the central root branching and sub branching to the extremities of the networkIt is best suited for applications which have a hierarchical flow of data and control.It is a modification of a network topology ,bus topology ,it is a hybrid topology.
28Graph topologyIn this nodes are connected together in an arbitrary fashion.A link may or may not connected two or more nodes.If the path is established in two-node via one or more links , it is called a connected graph
29Mesh topologyThe 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 linkIts best for long distance networking.Communication is possible between any two nodes on the network either directly or by passing through.
30Fully connectedWhen in a network each host is connected to other directly then the network is called to be fully connected.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