Topologies and Network Hardware

After Simas cleared up one of the five topologies, I will hopefully clear up the other four. I will also discuss the various different types of hardware involved in setting up a network.

I will begin with the hardware required, this may make it easier to understand when I start to describe the topologies.

Node - A physical network node is an active electronic device that is attached to a network, and is capable of sending, receiving, or forwarding information. For example, a computer, a printer, hub, switch.

Ethernet – The ethernet protocol is by far the most widely used. Ethernet uses an access method called CSMA/CD (If you remember this is the phrase Mr.McGivern wanted us to revise and learn), it stands for Carrier Sense Multiple Access / Collision Detection. This is a system where each computer ‘listens’ to the cable before sending anything through the network. If the network is clear, the computer will transmit. If another node is already transmitting on the cable, the computer will wait and try again when the line is clear. Sometimes, two computers attempt to transmit at the same time. When this happens a collision occurs. Each computer then backs off and waits a random amount of time before attempting to re-transmit.

Hub - Hubs are commonly used to connect segments of a network. A hub contains multiple ports. They are usually connect to other nodes, through a ethernet cable. When a block of data (a packet) arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets. Hubs repeat everything they receive and can be used to extend the network. However, this can result in a lot of unnecessary traffic being sent to all devices on the network.

Switch – A switch acts very much as a hub, however a switch can interpret the destination of data packets and will route packets only to their intended destination. This increases the capacity of the network because the incoming data is not repeated to every node. A switch also has a lot more ports than a hub, meaning more computers can be connected to the network.

Router - Route-r for Michael , Is a device which forwards data packets along networks. It is normally connected to at least two networks, often two LANs or WANs or a LAN and an internet service provider’s network. Routers are located at gateways, the places where two or more networks connect.

So with the hardware cleared up, I will now move onto the topologies. After at least all of us got hired and fired by Mcgivern as his network manager, we did get to the bottom of the topologies and what each network consists of.

Star Topology

A star topology is designed with each node connected directly to a central node. The central node can be a network hub or switch. The central node offers a common connection for all nodes on the network. Each network device has its own direct cable connection to the central node. In most cases, this means more cable is required than a bus topology. However, this makes adding or moving computers a relatively easy task: simply plug them into a cable outlet on the wall.

Advantages of a Star Topology

∙ It is relatively easy to install and wire a star network because the construction of the network only revolves running a cable from each network device to the central node.

∙ It is easy to detect faults and to remove parts because if an error occurs it should only affect one node on the network, therefore making fault finding easier.

Disadvantages of a Star Topology

∙Significantly more network cabling must be used to create a star network in comparison with a bus network.

∙If the central node fails, all other nodes attached to it are disabled and unable to communicate with any other node on the network.

∙Star networks are more expensive than bus topologies because of the cost of the hub or switch that is needed to function as the central node.

Tree Topology

A tree topology is like a series of interconnected star topology networks. Tree Topologies allow for the expansion of an existing network, and enable organisations to configure new networking to meet their needs.

Advantages of a Tree Topology

∙ Additional nodes can be added easily to individual segments, and segments can be added easily to the main central node.

∙ It is relatively easy to install and wire a tree network. Construction of the network involves simply running a cable from each network device to the central node in each segment, and then connecting the segments.

∙ Each device on the network has its own connection to the central node in the segment, and therefore there are no disruptions to the network when connecting or removing devices.

∙ It is relatively easy to detect faults and to remove parts. This is because if an error occurs it should only affect one node or segment on the network.

Disadvantages of a Tree Topology

∙The overall length of each segment is limited by the type of cabling used. If the central node fails the network fails.

∙Overall, the tree topology is more difficult to configure and wire than other topologies.

Hub/Switch





Ring Topology

A ring topology consists of a set of nodes connected serially by cable. In other words, it is a circle or ring of computers. There are no terminated end to the cable; the signal travels around the circle in a clockwise direction.

Under the ring concept, a signal is transferred sequentially via a `token’ from one station to the next. When a station wants to transmit, it `grabs’ the token, attaches data and an address to it, and then sends it around the ring.

Advantages of a Ring Topology

∙Networks based on a ring topology can grow without significantly impacting on the performance of the system.

∙All stations on the network have equal access to communication because of the use of the token.

Disadvantages of a Ring Topology

∙Ring networks require specialist hardware to function which makes them one of the most expensive topologies to implement.

∙It is possible that the failure of one computer may impact on others in a clockwise direction around the ring.

Mesh Topology

Mesh is a network topology in which devices are connected with many redundant interconnections between network nodes. In a true mesh topology every node has a connection to every node in the network; this is called a fully connected mesh. In a partially connected mesh, there are still multiple connections but all nodes are not connected.

Advantages of a Mesh Topology

∙ Mesh topologies provide multiple physical paths along which data can travel. If one of the network connections is cut there will normally be another route available along which can travel to reach its destination.

Disadvantages of a Mesh Topology

∙Mesh topologies are expensive to implement because of the multiple physical connections required to link each node on the network. These physical connections are difficult to install because of the sheer number involved.

∙The complexity of the mesh makes it difficult to manage. Keeping track of the network data cables and their connections and routes becomes a very difficult task with such a complicated network.

∙If an error occurs it can be difficult to detect, five the sheer number of network cables involved.

Advertisement