OCR J277 · Component 01 · §1.3 · Paper 1

§1.3 Computer Networks, Connections and Protocols

How do computers communicate, and what rules govern data transfer across networks?

A network is two or more computers connected to share resources and communicate. A LAN (Local Area Network) is confined to one building or site and uses hardware owned by the organisation; a WAN (Wide Area Network) spans large geographical distances and typically uses infrastructure owned by a third party (the Internet is the world's largest WAN). Networks can be arranged so that one central server provides services to client computers (client-server) or so that all computers share equal roles and resources directly (peer-to-peer).

Protocols are the rules that govern how data is packaged, addressed, and delivered. TCP/IP handles the overall routing of data across the Internet; HTTP and HTTPS govern web page transfer; FTP is for file transfers; SMTP/POP/IMAP handle email (send, retrieve-download, retrieve-leave-on-server). A DNS (Domain Name Server) converts human-readable URLs into IP addresses — without it you would need to remember a number like 142.250.185.68 instead of google.com. The concept of layers allows different parts of the protocol stack to be changed independently, like swapping one part of a machine without rebuilding the whole thing.

A small primary school wants to connect 20 computers, a printer, and a central file server. (a) Should they use a star or mesh topology? Justify your choice. (b) Name the hardware items needed to build this LAN. (c) A student types "https://school.ac.uk" in a browser. Describe the role of DNS in this process.

Key terms

LAN — Local Area Network: confined to one site; typically fast, owned infrastructure
WAN — Wide Area Network: spans large distances; uses third-party infrastructure
DNS — Domain Name System: converts URL → IP address
Star topology — all devices connect to a central switch; single point of failure
Mesh topology — every device connects to every other; resilient but expensive cabling

What students must understand

Diagrams

Star topology diagram: eight computers each cabled to one central switch
Star topology. Every device connects to a central switch, so one failed cable isolates only one device.
Two mesh network diagrams, a partial mesh on the left and a fully connected mesh on the right
Mesh topologies, partial on the left and full on the right. Every node has more than one route to the others.
Diagram of nine routers between a sender and receiver, showing the many routes a packet can take
Packet switching. Routers pass packets from sender to receiver, and each packet can take a different route.
The four network layers stacked: application, transport, internet and link
Protocol layers. Each layer has one job and passes data only to the layer above or below it.

Diagrams: PG Online (Paul Long), OCR J277 textbook. Used under the school site licence.

Linking questions

Practice

Video Support

Craig'n'Dave — OCR J277
1.3 Computer networks, connections and protocols — unit playlist