 Welcome to Network Topologies. In this learning activity, you'll explore different ways to connect computers in local area networks, or LANs. We link computers together into groups in order to exchange data. These groups may be in an office area, a building, or among several remote business sites. The process of connecting computers or other types of equipment together is called networking, and the other types of equipment are called nodes. The topology is the configuration used to connect the nodes and create the network. You can connect nodes such as workstations or switching devices through any of several physical arrangements. Selecting the best network topology is based on characteristics including its reliability, its flexibility, the cost of adding another node, the potential for future growth, the connection of data flow. There are four common network topologies, mesh, bus, star, and ring. Mesh topology. A mesh network physically connects each node via a link to every other node in the network. The physical connection is made using a coaxial cable, a twisted pair cable, or a fiber optic cable. The primary advantage of this topology is its reliability. Since all of the nodes are connected, there is always another link available for use if one of them fails. Because alternate links are always available, this network is the most fault tolerant topology available. The disadvantage of mesh topology networks is the high cost of creating all the connections. Connecting five computers requires ten links. Adding a sixth computer requires fifteen links. Adding one hundred computers would require a staggering 4,950 links. In a mesh network, we use this formula to determine how many links are required for the number of nodes we're using. For example, if we're using the mesh network to join sixteen nodes in a small office, the formula would look like this. We would need one hundred twenty links to connect every node in this office. Mesh topologies are used for backbone networks, by the greatest amount of redundancy. The largest mesh topologies are the public telephone network and the internet. Bus topology. A bus network attaches each node to a common set of conductors, called a bus, which transfers the data. No two nodes on the network have the same address because each address is unique. When data is sent, it must include the destination node's address. If the address is different, select the data packet. All network computers have a network interface card, or NIC. This card determines if the data from the transmitting computer is intended for another computer on the same network, or if it's intended for a computer on a distant network. If the data is staying in the same network, it's placed on the bus line and the connecting nodes accept or reject it based on its address. If the NIC determines the packet is intended for a computer network, it's transferred out using a router. The advantages and disadvantages of bus topology. The advantage of a bus topology is that it's easy to add nodes by plugging them into the bus lines. The disadvantage is that an open or short may damage a large portion of the network, rendering it inoperable. Additionally, more users and more nodes slow down network operations. Star topology. A star topology resembles the hub of a wheel with spokes extending outward. The hub is the switching device and the nodes are the spokes. Before sending any data, each transmitting computer must identify the hub's address. Data is sent to the hub which identifies the physical address of the data frame's destination node and then transmits the data on. A star topology offers several advantages, including low cost. It's one of the least expensive topologies in terms of cost per node. It's also easy to add new nodes to the hub, which is appealing if you're expecting your network to grow. Ring topology. In a ring topology, one continuous loop connects all of the nodes. Data passes from one node to the next, usually flowing in one direction. This network uses two different techniques to transmit data. The transmitting node sends the data over the conductors. When the data reaches the desired destination, the receiving node makes a copy of it instead of removing it. The message continues moving around the loop until it returns to where it started, which is the acknowledgement that the message was received. Advantages and disadvantages of ring networks. Ring networks are easy to expand. When adding another node, the ring is broken and then reconnected with a new node. This network suffers from a few disadvantages. The slowest node limits the network's overall performance. The network can only operate as fast as its slowest node. Here, computer 3 considerably slows the transmission because it isn't operating as fast as the other computers. If one of the nodes fails, or if the conducting lines between them open, the whole system fails. You can avoid this by using a spare ring to reroute data around a break. Finally, every time you add a node, you must break the conductor ring. This shuts down the entire network until you add the new node and restore the loop. Today, you've examined four different network topologies. You explored the mesh, bus, star, and ring networks, including their advantages and disadvantages. The network topology you will choose depends on your requirements for flexibility, reliability, and cost. You've completed Network Topologies.