Secondary Secondary ICT

Teaching The Basics Of Computer Networking

Computer networking is something which many ICT teachers shy away from and even some of the most knowledgeable computing teachers have only covered the subject briefly during their degrees, often only covering the theory. There are various places which networking comes into at both GCSE and A level, with various expectations of the students being set. One of the most enjoyable units I have taught at A level is assessed by a ten hour exam, with students designing and costing a network to fit a given problem. This may sound very daunting, but approached in the right way, it leaves students inspired and more importantly with some life skills and knowledge for the future.

When a subject is so different from anything covered before, you have to find an angle to get through to your class. The good thing about networking is they are doing it all the time, hopefully not when they should be listening to you! Mobile phones are the most accessible networking device you have and work in a way that everyone understands, this is a good place to start as the students are the experts.

Networking computers is well documented and many exam boards will point you to either the Seven Layer OSI Model or the TCP/IP Model or indeed both.

The fundamental principle you will need to get across is that, to communicate everyone in the network needs an identity. Mobile phones are not much use if you don’t know someone else’s number, which is unique to that phone (or SIM card). All phone networks have different numbers at the start, this is significant because the system needs to know where to send it (this will become important later in your term when you talk about routing). When you call a number it will only ever call that number and as long as the phone is on and they have a signal the call should go through. So having numbers is an easy way to identify someone, in computing the numbers are called IP addresses and consist of four sets of numbers separated by dots, at this point they don’t need to know about the structure, other than how the numbers are separated into a network identity and a host. In a mobile phone number the first four digits identify the network, this is how the system has been set up, whether for mobile numbers or area codes on the landline structure. In computer networking the computers have to be told which part is the network identity by applying a Subnet Mask. This is another set of numbers which tells the computers to separate off part of the IP Address, again the actual numbers will complicate this so just think of a mask separating off the first three of the four sets (this is the easiest class of network to start with). At this point I like to make it practical, if you have some stickers or sheets to identify different groups this makes it very visual.It would be easy to start at the bottom and work your way through the layers, but the class will probably switch off half way through your explanation of UTP cabling and RJ45s. The excitement of networking comes when things happen, mobile phones become interesting when you get a call, text or BBM and computers are no different. Before the Internet, computers had their uses but they weren’t as exciting as they are now. They will all accept that there are many ways of connecting devices, including wired and wireless. So to grab your students, start at the exciting layer – Network (or Internet in TCP/IP). The objective you have is to introduce IP addresses, Subnet Mask and Default Gateway.

Either split the team into groups or use some students as examples, I wouldn’t go for more than four or five. Give each group a sticker with an IP address on, making sure you have masked off the network portion.

Eg  192.168.0.101             192.168.0.102          192.168.0.103           192.168.0.104

The yellow parts identify the network, leaving a unique number for each group. Now get yourself some envelopes and organise a set of messages to be sent to certain addresses. A message can only be sent in a sealed envelope, with the address of the recipient and the address of who it was sent by labelled on the front and back. Set a strict time limit and let them get on with it. If the activity is successful each group should have a full set of messages, which perhaps make up a whole story (or set of notes). You can also put in spoof messages with incorrect network addresses, which should end up going to no one. As the envelopes are opened teams either get a full set or something goes wrong, in which case you can trouble shoot who sent the wrong messages. The envelopes can actually be referred to as ‘Packets’, which again will be useful later on in the topic.

Hopefully by the end of your session the class should have an idea about network addresses and how this is used to network computers together, the only thing you haven’t covered is the default gateway, which is the door out of your local network. This can be tied up with the envelopes which have the addresses which don’t belong to your groups. You become the default gateway, give yourself the last IP address (if you are using the examples given this would be 192.168.0.254) and say you will deal with those packets as you can contact networks outside the group – walking out of the classroom door often raises an eyebrow!

As an absolute starter for students who have no knowledge of how networking actually happens, this provides lots of different examples for visual, audio and Kinetic learners.

Rob Wilks,

August 2012.

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