KS3 Computing · A network is computers joined up to share. The internet is a network of networks. Data crosses it in small numbered packets, following agreed rules called protocols.
Networks and Digital CommunicationCambridge Lower Secondary Computing 0860
You will learn to
Explain why a file is split into numbered packets before it travels.
Describe what a packet holds: who it is from, who it is to, a sequence number and some data.
Explain what happens when a packet is lost or arrives out of order.
Identify an IPv4 address and explain why each part stops at 255.
Success criteria
I can put packets back in order using their numbers.
I can say what happened when our class lost a packet.
I can explain why an IP address is like a postal address.
Key words
Say each word, then read what it means. Every one is in the glossary too.
IP address
A device's address on a network. IPv4 = 4 bytes.
packets
A small numbered chunk of data sent across a network.
LAN / WAN
Local Area Network: a network over a small area.
Router
Connects different networks and forwards packets.
MAC address
Fixed unique ID of a network card. 48 bits in hex.
DNS
Domain Name System: turns website names into IP addresses.
Packet
A small numbered chunk of data sent across a network.
Protocol
A set of agreed rules for communication.
Bandwidth / latency
How much data a connection can carry per second.
The explanation
Read it here, or open the study page below to go one step at a time with things to try.
Addresses
IP address: a device's address on a network. It can change, like a postal address when you move.
IPv4 looks like 192.168.1.25.
Each part stops at 255 because each part is one byte.
4 bytes = 32 bits ≈ 4.3 billion addresses. Not enough, so IPv6 uses 128 bits.
MAC address: the fixed ID of the network card itself. 48 bits, written in hex: 3C:22:FB:7A:1E:90.
Packets
A photo is split into thousands of packets. Each has a header (from, to, sequence number), a slice of the data, and a check value.
Split the file into numbered packets.
Send each one separately.
Routers send each packet on whatever route is least busy.
Packets arrive at different times, out of order.
The receiver puts them back in order by number.
Anything missing gets asked for again.
?Why?
Why chop it up? Many people share the cables at once. A broken link just means another route. A lost packet is a small resend, not the whole file.