Lecture 5: Network Topologies PDF

Lecture 5 Network Topologies  Topology Topology refers to the physical layout of its computers, cables, and other resources, and also to how those components communicate with each other. Topology has a significant effect on the network’s performance and growth, and eq...

Lecture 5 Network Topologies  Topology Topology refers to the physical layout of its computers, cables, and other resources, and also to how those components communicate with each other. Topology has a significant effect on the network’s performance and growth, and equipment decisions. Physical topology Vs. Logical Topology Physical: the arrangement of cabling that interconnects network devices (bus, ring, star) Logical : the path that data travels between computers on network (bus, ring, switching)  What are the differences of physical topology and logical topology A network can be wired using one physical topology but pass data from machine to machine by using a different logical topology. Example: The logical topologies (bus, ring, switching) are usually implemented as a physical star.  Bus Topology The network is configured in the shape of an open ended line with all nodes connected to the bus individually  Physical Bus topology Bus Topology is the simplest of network topologies. In this type of topology, all the nodes (computers as well as servers) are connected to the single cable (called bus), by the help of interface connectors. This central cable is the backbone of the network and is known as Bus.  Physical Bus topology Advantages of Bus Topology Easy to connect a computer or peripheral to a linear bus. Disadvantages of Bus Topology Entire network shuts down if there is a break in the main cable. Property inherent on a physical bus Signal bounce  Physical Bus topology Signal bounce A signal traveling across a network continuously, bouncing back and forth and preventing other computers from sending data. To prevent this, a terminator is used. Terminator is attached to each end of a cable to prevent signals from bouncing. The terminator absorbs all signals that reach it, clearing the network for new communications.  Logical Bus topology Although physical bus is obsolete, logical bus topology is still in use. When a computer has data to send it addresses that data, breaks it into manageable chunks, and send it across the network as electronic signals All computers on a logical bus receive them Only the destination computer accepts the data All users must share the available amount of transmission time, therefore network performance is reduced  Logical Bus topology The more computers that are ready to send data at the same time, the longer some computers must wait to send data; which slows the overall network performance.  Ring Topology Ring topology refers to a specific kind of network setup in which devices are connected in a ring and pass information to or from each other  Physical Ring topology A physical ring network is when each computer connects directly to the next computer in line, ending at the starting computer. Because the circle has no end, signals travel in one direction around the ring; this eliminates the need for termination. Every computer in a ring is responsible for retransmitting the data, making it an active topology. A typical ring network can fail if one computer in the ring fails, but a dual-ring network can still operate is such a failure occurs.  Physical Ring topology Ring network topology is usually used to connect LANs with a technology called Fiber Distributed Data Interface (FDDI). This devices used to connect buildings form a ring, but computers in each LAN are connected with a physical star topology.  Logical Ring topology The data in a logical ring topology travels from one device to the next until it reaches its destination. token passing; when small packet called a token passes around the ring to each computer in turn. If a computer has information to send, it modifies the token, adds address information and the data, then sends it around the ring. The information travels around the ring until it reaches its destination or returns to the sender. When the intended destination receives the information, it returns a message to the sender to acknowledge its safe arrival.  Star Topology A star topology is a topology for a Local Area Network (LAN) in which all nodes are individually connected to a central connection point, like a hub or a switch.  Physical Star topology A star topology describes computers connected by cable segments to a central device. Advantages: Centralization of resources, easy for administration and trouble shooting. Robust: network still works even any computer or cable segment fails.  Physical Star topology Disadvantages: Single point for failure. Requires more cable installation.  Logical Star topology 1- Logical Bus on Physical Star (Star bus) When the arrangement cables forms a physical star, but data traveling to the computers follows a logical bus, the result is referred to as a “star bus.” A hub or switch is the central device in this topology. All computers hear the signal and check the destination address, but only the computer to which the data is addresses processes the data further.  Logical Star topology 2- Logical Ring on Physical Star (Star ring) A “star ring” topology also uses a star’s physical cable arrangement, but data travel within the central device is in a ring configuration. The central device in this topology is called a concentrator, or multistation access unit (MAU).  Logical Star topology 3- Switching on physical star A switch takes a signal coming from a device connected and builds a circuit on the fly to forward the signal to the intended destination computer. This process is called switching because at one moment the circuit between two computers does not exist and the next moment it does, like tuning on a switch. Superior to other logical topologies because, unlike bus and ring, multiple computers can communicate simultaneously without affecting each other Dominant method used in almost every LAN design Variations of physical Topologies Combination Star Bus Topology (Tree) Mesh Tree Topology In computer networks, a tree topology is also known as a star bus topology. It incorporates elements of both a bus topology and a star topology. Below is an example network diagram of a tree topology, in which the central nodes of two star networks are connected to one another. if the main cable between each of the two star topology networks were to fail, those networks would be unable to communicate with each other. However, computers on the same star topology would still be able to communicate. Mesh Topology A fully connected network, or mesh topology is a network topology in which there is a direct link between all pairs of nodes. In a fully connected network with n nodes, there are n(n-1)/2 direct links. Wireless Topologies Wireless networking has a logical and physical topology Ad hoc topology: two computers can communicate directly with one another; sometimes called a peer-to peer topology IBSS (Independent Basic Service Set): a group of nodes communicating in ad-hoc mode Infrastructure mode: Use a central device, called an access point (AP), to control communications Star physical topology because all the signals travel through one central device Logical bus topology BSS (Basic Service Set): a group of nodes communicating in infrastructure mode.