Network Topologies and Access Methods Explained
Network Topologies and Access Methods
The topology of a network is the pattern of interconnection between nodes and a server. There is the logical topology (the way the flow of data is regulated), and the physical topology, which is simply the way a network is laid out through its wiring.
Types of Network Topologies
There are three main types of topologies: bus, star, and ring. Bus and star topologies are often used in Ethernet networks, which are the most popular. Ring topologies are used for Token Ring, which are less popular but still functional.
FDDI (Fiber Distributed Data Interface) networks, which run through optical fiber cables (instead of copper), use a complex star topology. The main differences between Ethernet, Token Ring, and FDDI topologies lie in the way they enable communication between computers.
Bus Topology
In a bus topology, all computers are connected to a central cable, called the bus or backbone. Linear bus networks are easier to install and relatively inexpensive. The advantage of a 10Base2 network with bus topology is its simplicity.
Once the computers are physically connected to the wire, the next step is to install the network software on each computer. The negative side of a bus network is that it has many points of failure. If a link between any of the computers is broken, the network stops working.
Star Topology
More complex networks are built with star topology. These networks have a connection box called a hub at the center. All PCs are connected to the hub, which handles communications between computers.
In a star topology, the communication network terminals are connected to a central core. If a computer does not work, it does not affect the others, unless the server is down.
Networks built with star topologies have a couple of advantages over bus topologies. The first and most important is reliability. In a bus topology network, disconnecting a computer is sufficient for the whole network to collapse. In a star topology, however, computers can be connected even though the network is in operation, without causing flaws.
Ring Topology
In a ring topology (used in Token Ring networks and FDDI), the wiring and physical layout are similar to those of a star topology. However, instead of a hub, a ring network has a device called a MAU (Multistation Access Unit).
The MAU performs the same task as the hub, but instead of working with Ethernet networks, it works with Token Ring networks and manages communications between computers in a slightly different way.
All computers or nodes are connected to each other, forming a chain or circle.
Star-Bus Topology
This topology combines the two types of networks mentioned above. A signal multiplexer takes the place of the central computer of the star configuration, with specific workstations connected to it, and others connected by bus with multiplexers.
This type of network offers advantages in buildings that have working groups separated by large distances.
As seen, there are different types of networks to connect computers, workstations, servers, and other computing and network elements. Depending on the type of business or company, we find one system or another.
Network Access Methods
The access method is the set of rules that define how a computer puts data into the network and takes data from the cable. Once the data are moving in the network, access methods help to regulate the flow of network traffic.
Controlling Traffic on the Cable
A network is somewhat like a train route, along which several trains travel. In addition to the road, there are often train stations. When a train is on track, other trains must comply with a procedure that governs how and when to enter the traffic flow. Without this procedure, the entry of a train could collide with one already on the road.
However, there are important differences between a set of railroad tracks and a computer network. In a network, it appears that all traffic moves simultaneously, without interruption. However, this appearance is an illusion. In fact, the computers take turns accessing the network for short periods of time. The major difference is the increased speed in moving the network traffic.
Several computers can share access to the cable. However, if two computers try to put data on the cable at the same time, packets of data from one computer could collide with data packets from the other computer, and both sets of data packets can be damaged.
If a user is sending data to another user through the network, or accessing data on a server, there must be a way for the cable to access the data without interfering with each other. The destination computer must have a guarantee that the data is not destroyed in a collision during transmission.
Access methods must be consistent in how they manipulate the data. If computers use different access methods, the network could have problems because some methods may dominate the cable.
Access methods prevent computers from simultaneously accessing the cable. By ensuring that only one computer puts data into the network cable, access methods ensure that sending and receiving data from the network is done in an orderly manner.
Main Access Methods
The three main methods designed to prevent simultaneous use of the network medium include:
- Carrier Sense Multiple Access (CSMA)
- With Collision Detection (CSMA/CD)
- With Collision Avoidance (CSMA/CA)
- Token-Passing methods that allow a unique opportunity to send data.
- Demand Priority methods.