Goughy's Guide to Networking - Part 1

[goughy000]

Welcome to the first part of "Goughy's Guide to Networking"

In this part:
The basics of networking
Network topologies



The basics of networking

Most of you will know this already but i'll try and throw in some of the new words for you.

A computer network is a way for computers (or nodes) to be linked so they can communicate and share information/resources e.g. Files/Printers.
There are 2 main categories of network, p2p (peer to peer) and Client-Server.

In a peer to peer network all the nodes are more or less equal and files/resources are spread accross all the nodes, this is useful when one of the nodes is unreachable then a lot of the processes on the other nodes will still be able to continue if there files are available on the other nodes however in this type of network it can be harder to locate problems and the speed can often be much slower.

In a client-server network there will be 2 main types of machine, a client and a server of course, all the network applications will have 2 parts. The server side, there will usually be one of these, and a client side, there can be several of these but sometimes only 1 aswell. The server hosts the resources and the client(s) connect to the server to ask for the resources, the server can then decide on permissions and processor load to if and how it gives access to the resources.

That's enough for the very basic section


Network topologies

There are many network topologies, i am going to talk about 3 of them.

A network topology is the way that the (traditionally) hardware of the network is organised.

The 3 topologies i'll go through are Bus, Ring and Star

Firstly BUS:

In a bus network all the nodes share a common line as shown in the following diagram:


The main line through the middle is shared between all nodes. In this type of network only one node may transmit at once and therefore before transmitting then the node must listen on the line to see if it is being used before transmitting itself however if 2 nodes listen at the same time then transmit the signals will mix together, this is called a collision.

To fix this each node will always listen to its own message as its transmitting, if it hears something different to what it knows it's transmitting then it knows the message has been mixed with a message from another node. Each node will detect this and resend, to lower the chance of each nodes message then resending and colliding again they each choose a random time to wait before listening then transmitting. Once a large amount of nodes have been added to this type of network collisions are very common and the network can slow down and stop completely in bad situations so a better method had to be designed.

A hub is basically just a bus network, the long shared line in the diagram is inside the hub with each of the ports connected to the main line. A hub is said to have no intelligence.

Next, Ring:
In a ring network each node is connected to 2 others in a ring untill all nodes are connected in a circuit.

This is how a ring network should be drawn:


THIS IS NOT HOW TO DRAW A RING NETWORK and is a common mistake seen in diagrams


The collision problem is removed in a ring network as all messages will go in one direction in the ring. And rules are set that a node may only transmit a message if it has just received an empty message. If a node has just received a message addressed to it it cannot then send a message straight back, it must add an empty message to the ring. This is to stop 2 nodes communicating directly with each other and tieing up the network from other nodes.

However there is one obvious problem here... if one node was to crash then the whole network would go down as the messages would not be able to complete their circuit.


This brings me onto the 3rd basic topology:

Star

In a star network all nodes are connected to a single device called a switch (or a router but we'll come onto those in part 2)

Messages are sent from nodes to the switch and the switch then creates a virtual connection between the ports on the switch so that the message goes in the right direction. As the switch in the middle has inteligence and a small amount of memory it can reduce the collisions by holding back messages in a buffer if the line it needs to send messages down is busy.

Example of a star network:


As i said before if the device in the middle is a hub it is a bus network not a star network, this is also a common misconception!

[darkfate]

I always like to think of a Token Ring network as having a train going around the circle. It can only have one token at a time and continues to travel around until it can find a place to drop it off. Then it picks up another token and continues.

Most consumer switches allow only one vlan. Enterprise is different in that respect.

I just want to say a little about collisions on the network. A hub is dumb. The hub takes any incoming frame and pushes it out to all the ports it has and asks if the MAC address on packet matches theirs. A switch on the other hand is a bit smarter. The switch has Content-addressable memory or CAM because it's a lot faster than a flash rom or even RAM. The switch updates an internal table with the frame's source MAC address and the port it was received on. It then looks up the destination MAC address in the table to determine what port the frame needs to be forwarded to, and sends it out that port. As it adds to this table, the switching gets a whole lot faster. This increases the latency from just a dumb hub, but it reduces the number of collisions and jams that happen on a high traffic network. Also CSMA/CD is a useful protocol that was developed to help detect collisions and sense when another packet is in the way. It uses holddown timers and jam signals to keep the collisions to a minimum.

EDIT: I don't know if you want to save it for later, but mesh networks are how the internet works. There is also tree, and star-bus which are popular.

[goughy000]

Thanks for that darkfate, your token-ring explanation is easy to picture.

I'll come onto mesh in a later issue, next up i'll do the "Protocols" and the OSI model, then move onto the IP protocol in particular

[progogre]

Lol sorry goughy, two words to describe this, Poor formatting. The rest itself, which would be the content, terrifically awesome.

[MoNsTeReNeRgY22]

Very good read, thanks!

[goughy000]

i'll try get part 2 done later today.

[Clarkii]

Awesome. but im pretty sure that were learning this in Alevel computing ey gough , great guide