1. 1.4 Wired and Wireless Networks
In this unit you will cover…

2. 3. Performance This lesson you will know:
Factors that affect the performance of a network

3. Performance We want fast networks, right?
Otherwise how will you stream the World Beard Championships live and in 4k to your TV? Poor network performance would make this impossible
Think of the transmission media like roads – small little country lanes can’t handle much traffic at once and the speeds are fairly slow
Dual carriageways can handle a fair amount of traffic at a reasonable speed
The Autobahn can handle loads of traffic at crazy speeds

4. Bandwidth
We call the rate that data can be carried over a network, bandwidth
A measure of how much traffic can flow in a given time frame
It is NOT necessarily a measure of speed!
Measured in bits per second (bps) but often we see MBPS (megabits per second)
This is how internet connections are sold/rated

5. Bits per second A “10 mbps” internet connection has a bandwidth of:
10mb/ps (duh)
1.25 MB/ps (megabytes)
Er… that’s a hell of a difference. This means the maximum theoretical download speed on a 10mb connection is actually 1.25megabytes of data per second.
1 kilobyte = 8 kilobits

6. Bandwidth Depends on media used:
Copper
Fibre
Wifi
Which is has the most bandwidth and why?

7. Performance Another factor affecting performance is duplex
Duplex = data can be sent and received at the same time
In computing there are different types:
Simplex – can only go one direction, ever
Half Duplex – only send or receive at one time
Full Duplex – send and receive at the same time

8. Ethernet and fibre are full duplex – they can both send and receive packets of data at the same time
Wireless is not! A single wireless radio can only send or receive at one time
This drastically slows down performance as it has to keep alternating between send and receive

9. Distance Copper cables transmit electronic signals:
Electricity is affected by resistance
Metal has a natural resistance
Therefore cable = resistance
Longer cable = more resistance
Eventually you get loss or degradation of the signal quality (and therefore data)
Data loss/Degradation = longer transmit times

10. Distance
Fibre optic uses light, this is much faster than electricity and can be carried much further although it still has length limits
Speed of light: 299,792,458 meters per second

11. Latency
Latency - The time taken for a packet to get from a source to destination
Think about lag in online games – usually down to long latency between you and the opponents’ devices
Measured in milliseconds
Can be seen using the PING command.

12. Reliability
If a transmission media is unreliable (weak Wi-Fi signal, long Ethernet cable etc) data may be lost or damaged in transit
In this case, the recipient device must request the damaged/missing packets from the sender again – this adds to time taken!

13. Routes

14. Routes Imagine you want to get from town A to town B
There’s two ways of getting there
Route 1: 12 miles, small roads and towns
Route 2: 20 miles, motorway
There’d be different times it’d be sensible to use any of these – why?
Distance, type of roads, traffic on the roads
The router decides which route packets will take depending on distance, transmission media and traffic
Related packets may take completely different routes to their destination (which is why that sequence number is so important if they all arrive from different routes at different times)