# Basic questions about network topologies

I have just started learning about network topologies, but there are a lot of confusion about different types of network topologies i have learnt so far.

First of all, BUS topology. If i have like 100 PCs in the same wire connected using BUS topology, and the network connection speed is 100Mbps, then each PC will have a connection of 1Mbps, right ?

With the same scenario, if i connect those 100 PCs using STAR topology, then each PC will have a connection of 100Mbps ?

Then with the TREE topology, i divide the system into 10 sub-system (10 tree branches) , each branch has 10 PCs, then i will have other 10 small "BUS-topology" networks each one will have a connection of 10Mbps and therefore each PC will also have 10Mbps ?

And the last one is RING topology, 100 PCs, each PC will have 100Mbps connection ?

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There are about 10 gazillion books and Internet articles on this topic. I suggest you take some time to read some of those, as the topic is a bit too large for a simple Q&A format. – John Gardeniers Dec 22 '10 at 21:24

When you talk about the speed of the network you are usually talking about the speed that two clients could theoretically get using a perfectly efficient protocol, and no other communication on the network.

When you are talking about only the network topologies you are talking about an abstract concept. The abstract concepts doesn't really tell you anything about how bandwidth is split. You need to know a lot more about the connecting equipment, and protocols in use to actually know how bandwidth is split amongst the end nodes in a network that is setup using a given topology.

First of all, BUS topology. If i have like 100 PCs in the same wire connected using BUS topology, and the network connection speed is 100Mbps, then each PC will have a connection of 1Mbps, right ?

If only two nodes are trying to communicate they will communicate at 100Mbps. If more then two nodes are trying to communicate then what happens depends on the network. In a CSMA/CD network they will each try to talk when nobody else is talking. The maximum capacity will still only be 100Mbps, but client a may get 80Mbps and client b only 20 Mbps.

Think of a bus network like a typical street with a speed limit. Just because everyone's driveway is connected to the street doesn't mean the speed limit is divided by the total number of driveways.

With the same scenario, if i connect those 100 PCs using STAR topology, then each PC will have a connection of 100Mbps ?

It depends on what happens at the point of your star. Is your start connected with an Ethernet Hub? If so, then the bandwidth you get will be like that of a bus, is the point an Ethernet Switch? If you have a switch then you will get a much higher bandwidth.

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Thanks so much, i am now having a clearer idea of network topologies – laoshanlung Dec 23 '10 at 15:06

For a bus topology I believe you are right. Bus topologies are very rarely used nowadays.

For a star, you are also right. However, limiting factors here are the total bandwidth of the so-called backplane of the switch in the center of the star. In your example, it would have to support 100*100*2 (full duplex) Mbps, a total of about 20 Gbps, to have every PC to utilize the maximum bandwidth. This is a very common topology in real life.

For the tree, the maximum bandwidth between PCs depends on where they are in the tree. Each subset of the tree has a shared bandwidth to the rest of the tree. So within a sub-system, you can reach higher bandwidths than between PCs in different sub-systems. Commonly, tree networks are basically built out of multiple stars, with one spoke of the star going to a higher level of the tree.

I don't know ring networks well enough to know the last answer.

When looking at topologies, also do not forget the mesh network, which can be full or partial. The internet is mostly basically a partial mesh network.

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Actually busses ARE rare, you know. PCI: bus. PCI-e: star, with a controller in the center. LAN networks - only EXTREMELY cheap people buy a hub anymore, switches are already very cheap. – TomTom Dec 22 '10 at 21:24