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CAIE 9618 · Paper 1 · Topic 1.2.3

MAC Addresses, IP Addresses
& Wireless Networking

MAC vs IP · IPv4 vs IPv6 · SSID · WPA2 · CSMA/CA

CSZone Cambridge International AS & A Level Computer Science 9618
MAC Addresses

Physical Hardware Address

A MAC (Media Access Control) address is a unique identifier assigned to a NIC (Network Interface Card) by the manufacturer. It is used to identify devices on a local network (Layer 2).
FORMAT
00:1A:2B:3C:4D:5E
48 bits · 12 hex digits · 6 bytes
First 3 bytes = manufacturer ID (OUI)
KEY FACTS
Permanently assigned at manufacture (burned in)
Used within a LAN — not routable across the internet
Used by switches to forward frames
IP Addresses

Logical Network Address

FeatureIPv4IPv6
Length32 bits (4 bytes)128 bits (16 bytes)
Format192.168.1.12001:0db8:85a3::8a2e
Addresses~4.3 billion (2³²)~340 undecillion (2¹²⁸)
StatusRunning outDesigned to replace IPv4
IP vs MAC: IP = logical address, can change (assigned by DHCP). MAC = physical address, fixed to hardware. IP addresses enable routing across the internet.
Wireless Networking

WLAN Standards and Security

SSID
Service Set Identifier — the name of a wireless network (e.g. "HomeNetwork")
Broadcast by the access point (AP)
Can be hidden (SSID broadcast disabled) for security
WIRELESS SECURITY
WEP — old, now broken (deprecated)
WPA — improved, but vulnerabilities found
WPA2 — current standard, AES encryption
WPA3 — latest, stronger protection
CSMA/CA

Collision Avoidance in Wireless

CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) — wireless devices cannot detect collisions while transmitting (as wired Ethernet can with CSMA/CD), so they avoid collisions before they occur.
Sense the channel — listen before transmitting. If busy, wait.
Random back-off — wait a random time before retrying to reduce simultaneous retransmission
RTS/CTS — optional Request-to-Send / Clear-to-Send handshake to reserve the channel
Acknowledgement — sender waits for ACK before assuming successful delivery
Exam Practice

Cambridge-style questions

Question 1
Describe two differences between a MAC address and an IP address.
4 marks
✓ MARK SCHEME
1 mark
MAC: permanently assigned by manufacturer / IP: assigned dynamically (DHCP) or statically, can change
1 mark
MAC: used within a local network (LAN) to identify hardware / IP: used to route data across networks including the internet
1 mark
MAC: 48-bit hexadecimal address / IP (IPv4): 32-bit dotted decimal notation
1 mark
MAC: unique globally to hardware / IP: same IP can be reassigned to different devices
Exam Practice
Question 2
Explain why CSMA/CA is used in wireless networks rather than CSMA/CD.
3 marks
✓ MARK SCHEME
1 mark
CSMA/CD detects collisions during transmission, which requires a device to "hear" its own signal
1 mark
Wireless devices cannot detect collisions while transmitting (cannot listen and transmit simultaneously on same frequency)
1 mark
CSMA/CA avoids collisions before they occur by listening before transmitting and using random back-off
Common Mistakes

Don't lose easy marks

1
Saying MAC addresses can be easily changed — technically they can be spoofed in software, but for 9618, MAC addresses are described as permanently assigned by the manufacturer and burned into the NIC.
2
Confusing CSMA/CA with CSMA/CD — CD = collision detection (wired Ethernet). CA = collision avoidance (wireless). Wireless uses CA because it cannot detect collisions mid-transmission.
3
Saying IPv6 is "faster" than IPv4 — IPv6 is not faster. The main reasons for IPv6 are: more addresses (address exhaustion), improved routing efficiency, and built-in security features.
Topic Summary — 1.2.3

What You Need to Know

MAC ADDRESS
48-bit hardware address (12 hex digits)
Burned in by manufacturer, permanent
Used within LAN by switches
Format: 00:1A:2B:3C:4D:5E
IP ADDRESS
IPv4: 32-bit, ~4.3B addresses, exhausted
IPv6: 128-bit, virtually unlimited
Assigned by DHCP, can change
Used for routing across networks
WIRELESS
SSID: wireless network name
WPA2: current encryption standard (AES)
CSMA/CA: avoid collisions before they happen
Listen → random wait → transmit → await ACK
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1.2.4
Internet Protocols
HTTP · HTTPS · FTP · SMTP · POP3 · IMAP
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