Networks Exam Practice

This lesson brings together all the topics from OCR J277 Section 1.3 (Computer Networks) and provides exam-style questions with model answers. Use this to consolidate your knowledge and practise the skills needed for Paper 1.

---

Key Topics to Revise

Topic	Key Points
LAN vs WAN	LAN: small area, single owner; WAN: large area, third-party infrastructure
Client-server vs P2P	Client-server: central server; P2P: all devices are equal
Topologies	Star (central switch), mesh (multiple paths), bus (shared backbone)
Network hardware	NIC (MAC address), switch (LAN, MAC), router (between networks, IP), WAP (wireless)
Internet, DNS, hosting	DNS resolves domain names to IPs; hosting stores websites on servers
Protocols	TCP/IP, HTTP/S, FTP, SMTP, IMAP
TCP/IP layers	Application, Transport, Internet, Network Interface
Packet switching	Data split into packets, different routes, reassembled at destination
Wired vs wireless	Ethernet/fibre (fast, reliable) vs WiFi/Bluetooth (mobile, convenient)

mindmap
  root((OCR 1.3 Networks))
    Network types
      LAN small area single owner
      WAN large area third party
    Models
      Client server central
      Peer to peer equal
    Topologies
      Star central switch
      Mesh many paths
      Bus shared backbone
    Hardware
      NIC MAC
      Switch LAN
      Router between networks IP
      WAP wireless
    Internet
      DNS name to IP
      Hosting servers
    Protocols and stack
      Application HTTP HTTPS FTP SMTP IMAP
      Transport TCP UDP
      Internet IP
      Network Interface
    Transmission
      Packet switching
      Wired vs wireless

---

Practice Question 1: LAN and WAN (3 marks)

Question: Explain the difference between a LAN and a WAN.

Model Answer:

A LAN (Local Area Network) covers a small geographical area such as a single building or school campus, and is owned and managed by one organisation. [1 mark]

A WAN (Wide Area Network) covers a large geographical area such as multiple cities or countries, and typically uses infrastructure owned by third-party telecommunications companies. [1 mark]

The internet is the largest example of a WAN, connecting millions of LANs worldwide. [1 mark]

---

Practice Question 2: Network Topologies (4 marks)

Question: Compare star and bus network topologies, explaining one advantage and one disadvantage of each.

Model Answer:

Star topology:

• Advantage: If one device or cable fails, only that device is affected; the rest of the network continues working. [1 mark]
• Disadvantage: If the central switch fails, the entire network goes down — it is a single point of failure. [1 mark]

Bus topology:

• Advantage: Requires less cabling than a star topology, making it cheaper to set up. [1 mark]
• Disadvantage: If the backbone cable fails, the entire network fails, and as more devices are added, collisions increase, slowing the network. [1 mark]

---

Practice Question 3: Network Hardware (4 marks)

Question: Describe the purpose of each of the following network devices: (a) Switch (b) Router

Model Answer:

(a) Switch: A switch connects devices within a LAN and directs data to the specific device it is intended for. It does this by reading the MAC address in the data frame and forwarding it only to the port connected to that device. This is more efficient than a hub, which broadcasts data to all devices. [2 marks]

(b) Router: A router connects different networks together (e.g. a LAN to the internet/WAN). It reads the IP address in each data packet and determines the best route to forward the packet to the destination network. Routers also perform NAT (Network Address Translation) to translate between private and public IP addresses. [2 marks]

---

Practice Question 4: Protocols (3 marks)

Question: State the protocol used for each of the following tasks: (a) Sending an email (b) Retrieving an email from a mail server (c) Securely browsing a website

Model Answer:

(a) SMTP (Simple Mail Transfer Protocol) [1 mark] (b) IMAP (Internet Message Access Protocol) [1 mark] (c) HTTPS (HyperText Transfer Protocol Secure) [1 mark]

---

Practice Question 5: Packet Switching (4 marks)

Question: Explain how data is transmitted across the internet using packet switching.

Model Answer:

Data is broken into small packets, each with a header containing the source IP address, destination IP address, and a sequence number. [1 mark]

Each packet is sent independently across the network. Routers read the destination IP address and forward each packet along the best available route. Different packets may take different routes. [1 mark]

At the destination, TCP uses the sequence numbers to reassemble the packets in the correct order. [1 mark]

If any packets are missing or corrupted, TCP requests retransmission from the sender. [1 mark]

---

Practice Question 6: DNS (3 marks)

Question: Explain the role of DNS when a user types a website address into their browser.

Model Answer:

DNS (Domain Name System) translates the domain name (e.g. www.bbc.co.uk) that the user typed into the corresponding IP address (e.g. 151.101.0.81) of the web server. [1 mark]

The browser sends a request to a DNS server, which looks up the IP address associated with the domain name. [1 mark]

The browser then uses the returned IP address to connect to the web server and request the web page. [1 mark]

---

Practice Question 7: Wired vs Wireless (4 marks)

Question: A school is deciding between wired (Ethernet) and wireless (WiFi) connections for a new computer lab. Discuss the advantages and disadvantages of each option.

Model Answer:

Wired (Ethernet):

• Advantage: Provides faster and more consistent speeds, which is beneficial for tasks like downloading large files or streaming educational videos.
• Advantage: More secure because physical access to the cable is needed to intercept data.
• Disadvantage: Limits mobility — computers must remain at fixed positions near Ethernet ports.

Wireless (WiFi):

• Advantage: Provides mobility — students with laptops or tablets can move freely around the room.
• Disadvantage: Speeds can fluctuate due to interference from walls, other devices, and distance from the WAP.
• Disadvantage: Less secure by default — wireless signals can be intercepted, so WPA2/WPA3 encryption must be used.

[4 marks — 1 mark per valid point with explanation]

---

Common Exam Mistakes

Mistake	Correction
Confusing a switch and a router	Switch: within a LAN, uses MAC addresses. Router: between networks, uses IP addresses
Saying the internet is the World Wide Web	The internet is the network infrastructure; the web is a service that runs on it
Not mentioning reassembly in packet switching	Always mention that packets are reassembled using sequence numbers at the destination
Forgetting to mention encryption for WiFi	Always state that WiFi should use WPA2/WPA3 encryption
Confusing SMTP and IMAP	SMTP sends emails; IMAP retrieves emails

---

Summary