Differences

Short Answers to Differences (Including Advantages and Disadvantages) Between:

 Mesh, Bus, Ring, and Star topologies

 Ethernet, Token Ring, FDDI, and wireless

 Use a short answer to explain at what levels of the OSI model does TCP/IP

function?

Mesh

A mesh topology has a point-to-point connection to every other device (node) within the topology. The point-to-point link is dedicated between each device so it will only carry traffic to the two devices that is connected by that link.

The advantage of a mesh topology is it works on the concept of routes, which means that traffic can take one of several paths between the source and destination. The network is also robust in that it will not be crippled if one path becomes unavailable or unstable due to each device being connected to every other device. The Internet uses a mesh topology to operate efficiently.

The main disadvantage to a mesh topology is the fact that it requires a large number of cables, which is very expensive.

Bus

A bus topology is a multipoint topology that entails each device being connected to a common link or path. The common link can be thought of as the backbone to the network. All devices typically connect to the backbone with a T-connector and coax cable.

The main advantages of a bus topology are that it is easy to install and is not expensive (cost effective) because it uses very little cable to build.

The main disadvantage is if there is a problem with the one backbone cable, then the entire network will no longer have the ability to communicate. These networks are also very difficult to troubleshoot because any small problem such as a cable break, loose connector, or cable short can cause the outage. The entire length of cable and each connector must be inspected during troubleshooting. Another disadvantage is the lack of amplification of the signal, which results in a limited network size based on the characteristics of the cable because of how far a signal can travel down that cable.

Ring

A ring topology means that each device is connected in a ring, or daisy-chain fashion, one after another. A dedicated connection only exists between a device and the device on each side of it. Data flows around the ring in one direction. Each device contains a repeater that regenerates the signal before passing it to the next device.

The main advantage of a ring topology is that it is easy to install.

One disadvantage includes difficulty to troubleshoot because data flows in one direction and it could take time to find the faulty device when there are problems. The entire network could be taken off line if there is a faulty device or cable break within the ring.

Star

The star topology has each device in the network connected to a central device called a hub, which can actually be a hub or switch. All traffic must pass through the hub in order to communicate with any other device on the network. There is no direct communication between devices like in a mesh topology.

One advantage to a star topology is any failure to one cable or device connected to the hub will not bring the entire network down. Repairs can be done to individual nodes without disrupting traffic flow. Another advantage is expandability of the network. Additional devices can be added to the network without disrupting any of the current users. All that is required is an additional cable run from the device to the hub.

One disadvantage includes cable costs because each device must have its own cable connected back to the hub. The other disadvantage is the hub itself. Since all traffic runs through one device, it becomes the single point of failure. If the hub goes down, so does the entire network.

Ethernet

Ethernet is a Local Area Network (LAN) technology with a transmission rate of 10 Mbps and has a typical star topology. Computers and devices must wait-and-listen for transmission time on the network as only one device can transmit at any one time. In order to operate with this network strategy, Ethernet incorporates CSMA/CD (Carrie Sense Multiple Access with Collision Detection). Each device on the network "listens" for the network to be "clear" before transmitting data. If more than one computer or device transmits data at the same time, then collisions occur. Once collisions are detected, all devices stop transmitting for a period of time until one of the devices senses the line is free and will then gain control of the line to transmit its data. Receiving devices just sit there waiting and listening for transmissions that are meant for them, which are determined by an IP (Internet Protocol) address.

The main advantage to Ethernet is it is one of the cheapest networks to put into service. Compared to other hardware for Token Ring, Ethernet equipment such as hubs, switches, network interface cards, and cable (Cat5 common) is inexpensive.

The main disadvantage to Ethernet is related to the collisions that occur on the network. Even though Ethernet cable (Cat5) is fairly inexpensive, it can become a cost issue if designing a large network as each device or computer requires its own cable connection to the central hub. Another disadvantage is distance limitation for node connections. The longest connection that can occur within an Ethernet network without a repeater is 100 meters.

Today's Ethernet standards, 100 Mbps and 1000 Mbps, incorporate switched technology, which for the most part, eliminates collisions on the network. The IEEE's (Institute of Electrical and Electronics Engineers) specification for Ethernet is 802.3 with three-part names designating the different types. For example, 10BASE-T is for 10 Mbps, and 100BASE-TX is for 100 Mbps.

Token Ring

Token was developed by IBM as an alternative to Ethernet. The network is physically wired in star topology, but is arranged in a logical ring. Instead of a hub or switch like in an Ethernet network, a MAU (Multistation Access Unit) is used. Access to the network is controlled by possession of a token that is passed around the ring from computer to computer as data can only travel in one direction at a time. A computer that wishes to transmit data on the network takes possession of the token and replaces the token frame with data. The data goes around the ring and returns to