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

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

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

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

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

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

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

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

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

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

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.

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!

Routes

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)