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In the assignment, I have to answer 2 question that given by my lecturer. I also have to understand what is data communication & networking talking about. Data communication & networking is a set of nodes, consisting of computers, terminals, or some type of communication control units in various locations, connected by links consisting of communication channels providing a data path between the nodes. My question 1 is a group of business employees would like to set up a small networking office. Explain the meaning of topology. Discuss and draw the different types of network topology that are available. So I have to find out the types of topologies and explain all the usage and benefit. I got to understand all of the network topologies. My question 2 is the purpose of data link control is to provide functions like flow control, error detection and error control. Explain each function in detail. So in question 2 I got to understand the data link control and the functions. I also have to explain it in details. I will try my best to answer the question as well as I can. I will use the notes giving by my lecturer and some researches from internet to complete my assignment.
2.0 Question 1
Nowadays is full of networking in the world and our daily life. We can't live without it, it is a useful and help in our life. Especially in our business and working, we need it to measure the work and all the data for our business. So far, we need the network badly, it is important for us. Besides that, inside the networking has an element call network topology. It controlling the network, and also can say that is a computer network. Network topology describes the arrangement of systems on a computerÂ network. It defines how the computers, or nodes, within the network are arranged and connected to each other. Now have many types of topologies inside the networking. All of them have their differences, advantage and disadvantages. As I know, here are some types of topologies. For examples: bus topology, start topology, star topology, ring topology, tree topology and mesh topology.
Figure 1: Bus Topology
This diagram illustrates the bus network topology. A bus topology such as 10Base-2 or 10Base-5 Ethernet uses a single communication backbone for all devices.
In theÂ bus networkÂ topology, everyÂ workstationÂ is connected to a main cable called theÂ bus. Therefore, in effect, each workstation is directly connected to every other workstation in the network. Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.
Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet cabling options many years ago for bus topologies. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.
The advantages of bus topology are easy to handle and implement. It is best suited for small networks. The disadvantages of bus topology are the cable length is limited. This limits the number of stations that can be connected. This network topology can perform well only for a limited number of nodes.
Figure 2: Ring Topology
This diagram illustrates the ring network topology. A ring topology such as FDDI or SONET sends messages clockwise or counter clockwise through the shared link.
In theÂ ring networkÂ topology, the workstations are connected in a closed loop configuration. Adjacent pairs of workstations are directly connected. Other pairs of workstations are indirectly connected, the data passing through one or more intermediate nodes. In a ring network, every device has exactly two neighbours for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counter clockwise"). A failure in any cable or device breaks the loop and can take down the entire network.
To implement a ring network, one typically uses FDDI,Â SONET, orÂ Token RingÂ technology. Ring topologies are found in some office buildings or school campuses.
The advantages of ring topology are the data being transmitted between two nodes passes through all the intermediate nodes. A central server is not required for the management of this topology. The disadvantages of ring topology are the failure of a single node of the network can cause the entire network to fail and the movement or changes made to network nodes affects the performance of the entire network.
Figure 3: Star Topology
This diagram illustrates the star network topology. A star topology typically uses a network hub or switch and is common in home networks.
In theÂ star networkÂ topology, there is a central computer or server to which all the workstations are directly connected. Every workstation is indirectly connected to every other through the central computer. Many home networks use the star topology. A star network features a central connection point called a "hub" that may be aÂ hub,Â switchÂ or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.
Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)
The advantages of star topology are due to its centralized nature, the topology offers simplicity of operation. It also achieves an isolation of each device in the network. The disadvantages of star topology are the network operation depends on the functioning of the central hub. Hence, the failure of the central hub leads to the failure of the entire network.
Figure 4: Tree Topology
This diagram illustrates the tree network topology. A tree topology integrates the star and bus topologies in a hybrid approach to improve network scalability.
TheÂ tree networkÂ topology uses two or more star networks connected together. The central computers of the star networks are connected to a main bus. Thus, a tree network is a bus network of star networks. Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.
The advantages of tree topology are Central hub (repeater) increases the distance a signal can travel between devices. The disadvantages of tress topology are the cabling is required in a tree than in other topologies (except mesh) and the entire network collapse if central Hub fails.
Figure 5: Mesh topology
This diagram illustrates the mesh network topology. A mesh topology provides redundant communication paths between some or all devices (partial or full mesh).
TheÂ mesh networkÂ topology employs either of two schemes, called full mesh and partial mesh. In the full mesh topology, each workstation is connected directly to each of the others. In the partial mesh topology, some workstations are connected to all the others, and some are connected only to those other nodes with which they exchange the most data. Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) SomeÂ WANs, most notably the Internet, employ mesh routing.
A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.
The advantages of mesh topology are the arrangement of the network nodes is such that it is possible to transmit data from one node to many other nodes at the same time. The disadvantages of mesh topology are the arrangement wherein every network node is connected to every other node of the network; many of the connections serve no major purpose. This leads to the redundancy of many of the network connections.
Logical (or signal) topology refers to the nature of the paths the signals follow from node to node. In many instances, the logical topology is the same as the physical topology. But this is not always the case. For example, some networks are physically laid out in a star configuration, but they operate logically as bus or ring networks. Topologies remain an important part of network design theory. You can probably build a home or small business computer network without understanding the difference between a bus design and a star design, but becoming familiar with the standard topologies gives you a better understanding of important networking concepts like hubs, broadcasts, and routes.