Academy Computer Science Networks, connections and protocols

Course map 1.4 →

Paper 1 · J277/01 · unit 1.3

Networks, connections and protocols

LAN/WAN, switches and routers, star and mesh, DNS and the cloud, IP vs MAC, protocols and layers. Exercises and quiz, no locks.

Everything on this course is open. Skip, jump, retry. Nothing is locked and there is no required order.

How machines share a room, share a planet, and agree the rules of a conversation. Skip to protocols if hardware bores you today — it is all open.

1.3.1 Networks and topologies

A network is two or more devices connected to share data, hardware, or an internet connection.

LAN and WAN

LAN (Local Area Network) WAN (Wide Area Network)
Coverage One site: home, school, office Large area: cities, countries
Ownership Usually one organisation Often many networks joined (the internet is the biggest WAN)
Speed / latency Typically faster, lower delay Typically slower / more hops
Example School computers and printers Connecting all the school’s sites, or the internet

Hardware

Device Job
NIC Network Interface Controller/Card — the device’s connection (wired or wireless)
Switch Connects devices on a LAN; sends frames to the right port using MAC addresses (smarter than an old hub, which shouted at everyone)
Router Connects different networks (e.g. LAN to the internet); uses IP addresses; path finding
WAP Wireless Access Point — Wi-Fi onto the wired LAN
Transmission media Copper (Ethernet), fibre (light, long distance, high bandwidth), radio (Wi-Fi, 4G/5G)

A home “router” is often a router + switch + WAP in one box. In the exam, keep the roles separate.

Topologies

Star — every device links to a central switch.

    • One cable failure usually takes down one device
    • Easy to add devices
  • − If the switch dies, the LAN dies
  • − More cable than a daisy-chain

Mesh — many (or all) devices have multiple paths.

    • Very fault tolerant (another route exists)
  • − Expensive, complex to wire and manage
  • Used in parts of the internet and some wireless meshes

OCR may still mention bus historically; star and mesh are the ones to draw cleanly.

The internet, DNS, hosting, cloud

  • Internet: a worldwide WAN of networks using standard protocols (TCP/IP)
  • DNS (Domain Name System): translates a human name (tyneside.academy) into an IP address. Without DNS you would type numbers
  • Hosting: a company runs servers that store and serve your website/files 24/7
  • The cloud: using someone else’s servers (storage, software, processing) over the internet, billed as a service
  • Client asks; server answers. A web server sends pages; your browser is the client

Advantages of cloud: access anywhere, someone else handles backups/hardware, scales up. Risks: needs connectivity, you trust the provider with data, ongoing cost, less direct control.

1.3.2 Wired and wireless, protocols and layers

Connections

Wired (Ethernet, fibre) Wireless (Wi-Fi, Bluetooth)
Speed / reliability Usually higher, more stable Convenient, more interference
Security Harder to snoop without physical access Radio can be intercepted if not encrypted (use WPA2/WPA3)
Mobility Cable length Roam within range
Bluetooth — Short range, low power (controllers, earbuds)

Encryption on Wi-Fi is not optional in a serious answer: it stops casual interception.

Addressing

  • MAC address: burned into the NIC, 48-bit hex, identifies the hardware on a LAN. Example style A4:5E:60:C2:1F:09
  • IP address: identifies a device on a network / the internet. IPv4 is four denary numbers 192.168.0.14. Can change (DHCP)

Switching on a LAN cares about MAC. Routing between networks cares about IP.

Standards

Standards (IEEE, IETF, …) mean a Dell NIC talks to a Cisco switch. Without them, every vendor would invent a private plug.

Protocols you must recognise

A protocol is an agreed set of rules for communication (format, order, error handling).

Protocol Use
TCP Reliable delivery: connections, acknowledgements, retransmission, order
IP Addressing and routing packets across networks
HTTP Fetching web pages (not encrypted)
HTTPS HTTP inside encryption (TLS) — the S is the point
FTP Copying files to/from a server
SMTP Sending email between servers
POP / IMAP Receiving email. POP often downloads and may remove from server; IMAP keeps mail on the server and syncs devices

Layers

Networks are split into layers so one job can change without rewriting everything.

OCR’s TCP/IP-style stack (learn four layers and an example protocol at each):

  1. Application — HTTP, HTTPS, FTP, SMTP, DNS
  2. Transport — TCP (reliable), UDP (fast, no fuss)
  3. Internet — IP
  4. Network access / link — Ethernet, Wi-Fi (frames, MAC)

Why layers? Specialists can work on one layer; you can swap Wi-Fi for Ethernet without rewriting HTTPS.

Practice below includes a “which box does this job?” drill and a protocol match.

Practice · optional · answers on this page

Exercises

Do as many or as few as you like, in any order. Hints and a model answer sit under each task.

1.3.1 · e1 paper

LAN or WAN?

1. All PCs on one school site, sharing a printer. 2. The school’s three campuses in different towns, linked together. 3. A phone using 4G to reach tyneside.academy. For each: LAN or WAN, and one justification.
Hint
One site / one organisation vs wide area / many networks.
Show a model answer
1. LAN — single site, school-owned 2. WAN — multiple sites over a large area 3. WAN (the internet) — public wide-area networks
1.3.1 · e2 paper

Switch vs router

Write two differences between a switch and a router that would score on OCR (role + address type is a strong pair).
Hint
Same network vs different networks. MAC vs IP.
Show a model answer
A switch connects devices on the same LAN and forwards using MAC addresses. A router connects different networks (e.g. LAN to internet) and forwards using IP addresses.
1.3.1 · e3 paper

Star topology — two plus, two minus

A new classroom LAN will be a star. Give two advantages and two disadvantages compared with a mesh.
Hint
Cost and simplicity vs what happens when the centre dies.
Show a model answer
+ Cheaper/simpler cabling than a full mesh + A single end-device cable fault usually isolates only that device − Central switch is a single point of failure − Less redundant than mesh (no alternative path if the hub/switch fails)
1.3.2 · e4 paper

Protocol match

Which protocol? 1. Load a web page with encryption 2. Send an email from your mail server to the recipient’s server 3. Read the same inbox on phone and laptop, leaving mail on the server 4. Split a file into packets and make sure they all arrive in order 5. Turn tyneside.academy into an IP address
Hint
HTTPS vs HTTP. SMTP sends. IMAP syncs. TCP is reliable transport. DNS names.
Show a model answer
1. HTTPS 2. SMTP 3. IMAP 4. TCP 5. DNS
1.3.2 · e5 think

IP or MAC?

1. A switch deciding which port to send a frame to. 2. A router deciding the next network hop to reach 8.8.8.8. 3. Identifying a specific USB Wi-Fi dongle on the LAN.
Hint
Local hardware identity vs worldwide routing identity.
Show a model answer
1. MAC 2. IP 3. MAC

Check yourself · not a gateway

Quiz

Mark it, reveal it, or skip it. A low score does not close anything. Try again as often as you want.

1 1.3.1 Which device connects a home LAN to the internet?
2 1.3.1 DNS is used to…
3 1.3.1 A disadvantage of star topology is that…
4 1.3.2 Which protocol is used to send email between mail servers?
5 1.3.2 HTTPS is preferred over HTTP because…
6 1.3.2 Which statements about layers are true? (Select all that apply)
7 1.3.2 A MAC address identifies…