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Classification by Network Topology

Classification 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.
Bus network
Image showing bus network layout
bus network 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.
Bus networks are the simplest way to connect multiple clients, but often 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.
Advantages and Disadvantages of a Bus Network
Advantages
• Easy to implement and extend
• Requires less cable length than a star topology
• Well suited for temporary or small networks not requiring high speeds(quick setup)
• Initially less expensive than other topologies
• Cheap
Disadvantages
• Difficult to administer/troubleshoot.
• Limited cable length and number of stations.
• If there is a problem with the cable, the entire network goes down.
• Maintenance costs may be higher in the long run.
• Performance degrades as additional computers are added or on heavy traffic.
• Low security (all computers on the bus can see all data transmissions).
• One virus in the network will affect all of them (but not as badly as a star or ring network).
• Proper termination is required.(loop must be in closed path).
• If one node fails, the whole network will shut down.
• If many computers are attached, the amount of data flowing causes the network to slow down.
Star network
Star network layout
Star 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 router to transmit messages.
If the central node is passive, the originating node must be able to tolerate the reception of an echo of its own transmission, delayed by the two-way transmission time (i.e. to and from the central node) plus any delay generated in the central node.
An active star network has an active central node that usually has the means to prevent echo-related problems.
The star topology reduces the chance of network failure by connecting all of the systems to a central node.
When applied to a bus-based network, 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.
Strictly speaking only networks that use switches have a true star topology.
If the network uses a hub, the network topology has the physical appearance of a star, but is actually a bus.
Advantages
• Good performance.
• Easy to set up and to expand.
• Any non-centralised failure will have very little effect on the network, whereas on a ring network it would all fail with one fault.
• Easy to detect faults
• Data Packets are sent quickly as they do not have to travel through any unnecessary nodes.
Disadvantages
• Expensive to install
• Extra hardware required
• If the host computer fails the entire system is affected.
Ring network
Ring network layout
ring network is a topology of computer networks where each node is connected to two other nodes, so as to create a ring.
Ring networks tend to be inefficient when compared to Star networks because data must travel through more number of points before reaching its destination.
For example, if a given ring network has eight computers on it, to get from computer one to computer four, data must travel from computer one, through computers two and three, and to its destination at computer four.
It could also go from computer one through eight, seven, six, and five until reaching four, but this method is slower because it travels through more computers.
Ring networks also carry the disadvantage that if one of the nodes in the network breaks down then the entire network will break down with it as it requires a full circle in order to function.
The token ring network is a ring topology only at the logical level, it runs on a physical Star network, using central devices called MSAUs or MAUs.
Advantages
• Data is quickly transferred without a ‘bottle neck’. (very fast, all data traffic is in the same direction)
• The transmission of data is relatively simple as packets travel in one direction only.
• Adding additional nodes has very little impact on bandwidth
• It prevents network collisions because of the media access method or architecture required.
Disadvantages
• Data packets must pass through every computer between the sender and recipient therefore this makes it slower.
• If any of the nodes fail then the ring is broken and data cannot be transmitted successfully.
• It is difficult to troubleshoot the ring.
• Because all stations are wired together, to add a station you must shut down the network temporarily.
• In order for all computers to communicate with each other, all computers must be turned on.
• Total dependence upon the one cable.
Mesh networking
Image showing mesh network layout
Mesh networking is a way to route data, voice and instructions between nodes.
It allows for continuous connections and reconfiguration around broken or blocked paths by “hopping” from node to node until the destination is reached.
mesh network whose nodes are all connected to each other is a fully connected network.
Mobile ad-hoc networking (MANET), featured in many consumer devices, is a subsection of mesh networking.
Mesh networks are self-healing: the network can still operate even when a node breaks down or a connection goes bad. As a result, a very reliable network is formed.
This concept is applicable to wireless networks, wired networks, and software interaction.
mesh network is a networking technique which allows inexpensive peer network nodes to supply back haul services to other nodes in the same network.
. It effectively extends a network by sharing access to higher cost network infrastructure.
Mesh networks differ from other networks in that the component parts can all connect to each other via multiple hops, and they generally are not mobile.
Tree and hypertree networks
A hypertree is an acyclic hypergraph.
Tree and hypertree networks are important special cases of star network topologies.
Tree Network consists of star-configured nodes connected to switches/concentrators, each connected to a linear bus backbone.
Each hub/concentrator 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.