WA Computer Science ATAR Year 11 — Network Communications Hangman

The 143 key terms

1network

A group of digital systems connected together so they can share data, files, printers and an internet connection. Each connected device is called a node.

2client-server

A client, like your browser, sends a request for data and a server stores that data and sends a response back.

3communication model

How devices share the work of requesting and providing data: client-server uses dedicated servers, while peer-to-peer lets every device do both.

4LAN vs WAN

A LAN connects devices in one small area like a home or school. A WAN connects many LANs over a large distance. The internet is the largest WAN.

5internet

The global network of networks that connects computers worldwide. The World Wide Web is one service that runs on it, alongside email, streaming and online games.

6protocol

An agreed set of rules that devices follow so they can communicate, like HTTP for web pages. Both devices must use the same protocol to understand each other.

7wired transmission

Sending data as signals along a physical cable, such as a USB, Ethernet or fibre optic cable. Wired links are usually fast and reliable.

8Ethernet cable

A cable with an RJ45 plug that carries data as electrical signals along twisted pairs of copper wire between a device and a switch or router.

9fibre optic cable

A cable that carries data as pulses of light along thin glass or plastic strands, giving very fast transfer over long distances with no electrical interference.

10attenuation

The weakening of a signal as it travels along a cable. Copper cables have a length limit because of it, while fibre can go much further. Repeaters boost the signal.

11wireless transmission

Sending data as radio signals through the air with no cables, like Wi-Fi, Bluetooth and mobile data. Range and interference can weaken the signal.

12Wi-Fi

A wireless network technology that uses radio waves to connect devices to a router or access point, usually by joining a network name and password on the 2.4 GHz or 5 GHz band.

13Wi-Fi range

How far a Wi-Fi signal reaches. It gets weaker with distance and walls, and interference from other devices on crowded channels can slow or drop your connection.

14bandwidth

The amount of data a network connection can carry in a given time, usually measured in Mbps. Shared by all users, so more people or video streaming means less speed each.

15latency

The delay between sending data and it arriving, measured in milliseconds (ms). It is not the same as bandwidth, which is how much data can be sent at once. Low latency feels fast.

16serial transmission

Sending data one bit at a time, one after another, down a single wire or channel. The bits arrive in the same order they were sent.

17parallel transmission

Sends several bits at the same time, each down its own wire in the same cable, e.g. 8 bits down 8 wires at once.

18skew

Bits sent together down parallel wires arrive at slightly different times, so data can be received incorrectly. It gets worse as the cable gets longer.

19serial vs parallel

Serial sends 1 bit at a time down one wire: cheaper, reliable, better over long distance. Parallel sends many bits at once down several wires: faster over short distances only.

20simplex

Data transmission in one direction only, from sender to receiver, with no reply possible. Example: a keyboard sending key presses to a computer.

21half-duplex

Data can travel in both directions, but only one direction at a time, so devices take turns, like a walkie-talkie.

22full-duplex

Data is sent in both directions at the same time, so both devices can send and receive at once, for example during a telephone call or over a broadband connection.

23transmission method

Pick the direction (simplex, half-duplex or full-duplex) and the bit arrangement (serial or parallel), then justify both using the scenario's distance, speed and two-way needs.

24network layer model

Splits network communication into layers that each do one job and talk only to the layers above and below, so vendors interoperate, layers change alone and faults are easier to find.

25OSI model

A seven-layer network model: physical, data link, network, transport, session, presentation, application. Layer 1 is physical (bottom) and layer 7 is application (top).

26TCP/IP model

A four-layer plan for network communication: application (HTTP), transport (TCP, UDP), internet (IP) and network access (Ethernet, Wi-Fi). Each layer has its own job.

27TCP/IP to OSI mapping

Each TCP/IP layer covers one or more OSI layers: Application = OSI application, presentation and session; Network Access = physical and data link; Transport and Internet match one each.

28encapsulation

Each layer on the sender adds its own header (and sometimes a trailer) as data moves down the layers. The receiver removes them in reverse order, which is called decapsulation.

29network interface

The internal part of a device that lets it send and receive data on a network, using an Ethernet port for wired links or a wireless adapter for Wi-Fi.

30network switch

A device that connects computers on the same network and sends data only to the device it is meant for, using its ports. A router links different networks.

31router

A device that directs data between networks, such as joining a home LAN to the internet and choosing the path data packets take. A home Wi-Fi router also shares the connection wirelessly.

32wireless access point

A device that connects to a wired network and broadcasts a Wi-Fi signal so wireless devices can join the network.

33modem

A device that converts signals so a local network can connect to an internet service provider (ISP), such as over an NBN connection. A router then shares that connection.

34device layer

The OSI layer a device works at: hubs at layer 1, NICs and access points at layers 1-2, switches at 2, routers at 3, and firewalls and proxies at layers 3 to 7.

35MAC address

A unique hardware address given to one network interface card (NIC). Each NIC has its own, so a device with Wi-Fi and Ethernet has two. It identifies the hardware, not the network.

3600:1A:2B:3C:4D:5E

A MAC address is six pairs of hex digits (two digits per pair, 48 bits in total), separated by colons or hyphens, such as 00:1A:2B:3C:4D:5E.

37IP address

A unique number that identifies a device on a network, like a postal address, so data knows where to go. IPv4 looks like 192.168.1.5.

38IPv4 address

32 bits written as four denary numbers from 0 to 255 separated by full stops, such as 190.0.5.20. Each number is a group of 8 bits.

39invalid IPv4 address

An address without exactly four groups, or with a group outside 0 to 255. Examples: 256.1.1.1 (too big), 192.168.1 (too few groups), 10.-5.2.1 (negative) and 10.a.2.1 (letter).

41IPv6 address

A 128-bit address written as eight groups of four hex digits separated by colons, e.g. 2001:0DB8:0000:0000:0000:FF00:0042:8329

43static IP address

An IP address that is set once, usually by hand, and stays the same every time the device connects, so the device always has a predictable address.

44dynamic IP address

An IP address given to a device automatically by the network each time it connects, so it may change and can later be reused by another device.

45DHCP

Dynamic Host Configuration Protocol: a router service that automatically gives each joining device an IP address, subnet mask and default gateway, so no manual set-up is needed.

46MAC address vs IP address

MAC is fixed by the manufacturer and stays the same, written in hex. IP is given by the network and can change, written in denary (IPv4) or hex (IPv6).

47private IP address

An address like 192.168.1.5 that works only inside a local network. The internet sees the router's public IP instead, and NAT translates between the two so many devices can share it.

48subnet mask

A number like 255.255.255.0 that splits an IP address into a network part and a device (host) part. With 255.255.255.0, the first three groups name the network.

49same network

Two devices are on the same network when their IP addresses have the same network part under the subnet mask. If the network part differs, data must go via the router.

50default gateway

The router address a device sends data to when the destination is not on its own network. It is usually the router's LAN address. With no gateway set, a device cannot reach the internet.

51Internet Protocol (IP)

The protocol that puts source and destination IP addresses on each packet so routers can deliver it. It is best-effort: it does not guarantee a packet arrives.

52TCP

Transmission Control Protocol. It sets up a connection, numbers packets, checks each one arrived and resends any missing, so data arrives complete and in order. Web pages and email use it.

53UDP

User Datagram Protocol: sends packets with no connection and no resending. It is faster than TCP but data may be lost, so it suits live video, voice calls and online games.

55HTTP

Hypertext Transfer Protocol: the set of rules a browser and web server use to request and send web pages. It is the default protocol for the web and is used only for web pages.

56HTTP request and response

The browser sends an HTTP request asking for a page. The web server sends back an HTTP response with the page's HTML, or an error such as 404 page not found.

57SMTP and IMAP

SMTP sends email from a client to a mail server and between servers. IMAP (or POP3) lets a client read email stored on the server. Each protocol has a different job.

58https://www.example.com/shop/index.html

A URL splits into protocol (https), domain name (www.example.com) and web page or file name (shop/index.html). Each part can be labelled.

59domain name

An easy-to-remember name, like example.com, that stands in for a numeric IP address. It must be converted into the IP address before the computer can find the web server.

60DNS

Domain name server: stores a list of domain names with their matching IP addresses. Give it a domain name and it returns the IP address. Many DNS servers exist across the internet.

61DNS lookup

The browser sends a domain name to a DNS server, which searches for it and returns the matching IP address. If it has no match, it passes the request to another DNS server.

62URL -> DNS -> IP -> server -> HTML -> render

The ordered steps after you enter a URL: the browser asks DNS for the IP address, sends a request to the web server, gets HTML back, then renders the page.

63packet

A small piece of a larger file. Data is split into numbered packets so they share the network and a lost packet can be resent instead of the whole file.

64header, payload, trailer

The three parts of a packet, in order: the header (start) holds addresses and packet number, the payload (middle) holds the data, the trailer (end) marks the packet's end.

65packet header

The first part of a packet. It holds control information: the destination address, the originator's address and the packet number, used to deliver and reassemble the packet.

66packet switching

Data is split into packets that are sent separately, each routed on its own from router to router, then joined back together in the right order at the destination.

67routing

A router reads each packet's destination address in its header and picks the next router to send it to, so every packet's route is decided one step at a time.

68routing table

A list a router uses to pick where to send each packet. Each row has a destination network and a next hop. The default route 0.0.0.0 is used when no other row matches.

69packets arrive out of order

Packets take different routes, so they may reach the destination in a different order from the one sent, e.g. packet 5 before packet 4. Order is not guaranteed.

70reordering packets

After the last packet arrives, the receiving device uses the packet numbers in the headers to put the packets in the right order and joins the payloads to rebuild the message.

71TTL

Time to live: a number in a packet that drops by 1 at each router hop. When it reaches 0 the packet is discarded, so a packet stuck in a loop cannot circle forever.

72ping address

A command that sends a small test message to another device and reports whether it replied and how long the reply took in milliseconds. Example: ping 8.8.8.8

73nslookup example.com

A command that asks a DNS server for the IP address that matches a domain name. The reply shows which DNS server answered and the Address line with the site's IP.

74tracert example.com

Windows command (traceroute on Mac and Linux) that lists each router hop between your device and a site, with the time taken to reach each one. Stars (*) mean no reply.

75error detection

Checking received data, because it can be damaged in transit and the receiver cannot see the original. Spotting the error is the first step to fixing it.

76interference

Unwanted disturbance to a signal, such as electrical noise or crosstalk, that damages data as it travels and can cause bits to be lost, gained or changed.

77parity bit

One extra bit added to a group of bits (such as 7 data bits) so the total number of 1s follows a rule, even or odd, agreed by sender and receiver. It is used to detect errors.

78checksum

A value calculated from a block of data by a set rule and sent with it. The receiver repeats the calculation and compares the results. If they differ, an error occurred.

79echo check

The receiver sends a copy of the received data back to the sender, who compares it with the original. A match means no error was detected; a mismatch means the data is sent again.

80ARQ

Sender sends data and starts a timer. Receiver checks it and replies ACK or NAK. Sender resends on a NAK or a timeout until an ACK arrives.

81split, send, check, resend, reassemble

Data is split into numbered packets, sent over wired or wireless links, checked for errors, resent if needed, then reassembled in order so it arrives complete and correct.

82star topology

A network layout where each device has its own cable to a central switch or router, so one broken cable cuts off only that device. If the central device fails, the whole network goes down.

83topology

The layout of a network: bus shares one cable, ring passes data around a loop, and mesh links devices by many paths.

84network diagram

A drawing that shows each device as a labelled symbol and each connection as a line, so you can see how data can travel between devices.

85network design factors

The needs and limits, such as cost, performance, reliability, security, scalability and user needs, that decide which devices, cables and layout a network should use.

86scalability

A scalable network can grow in users, devices and traffic without a major redesign, for example by planning for growth, keeping spare switch ports and having an upgrade path.

87wired speed

Wired connections are usually faster and steadier than wireless, because the signal travels in its own cable and is not shared through the air.

88reliability

How steadily a connection stays working. Wired is usually more reliable as interference affects it less, while wireless signals can drop out.

89wireless security

Wired data stays in the cable, but wireless signals travel through the air where anyone in range can try to pick them up, so they need a password and encryption.

90cost and installation

Wired networks need cables, ports and installation work, while wireless needs less cabling but may need more access points to cover a large area.

91choose a network type

Name the needs (speed, reliability, security, cost, mobility), match them to wired, wireless or mobile, then justify the choice using the word because.

92redundant route

A spare path between devices. If one link or router fails, packets are sent another way so data keeps flowing. It costs more because extra cables and routers are needed.

93network design

Turning user requirements into a plan by choosing devices, media, topology, IP addressing and security controls, then justifying each choice.

94network simulator

Software like Filius where you place devices, set each IP address and subnet mask, connect them with cables, then send a ping to test they can reach each other.

95ISM segmentation guideline

A rule that tells organisations to divide their network into separate zones and limit access between them, so a breach stays contained.

96trust boundary

A line on a diagram where data passes between parts of a system with different levels of trust, such as from a user's device to a server. Threats often cluster here.

97man-in-the-middle attack

An attack where someone secretly sits between two parties and can read or change the data passing between them, such as logins, session tokens or code sent over an unsecured network.

98Unsecured Wi-Fi

A network with no encryption, letting attackers intercept the data sent across it.

99DDoS attack

A botnet of infected computers floods one server with requests at the same time, so it cannot respond to real users and the website goes offline.

100STRIDE

A memory aid for six threat types: Spoofing, Tampering, Repudiation, Information disclosure, Denial of service and Elevation of privilege. Use it to ask what could go wrong in a system.

101threat model table

A table with one row per threat. Columns record the asset, threat, vulnerability, risk rating and chosen control, e.g. a school app storing student data.

102encrypt

To scramble data so nobody can read it without the key. This keeps private things like messages, passwords and bank details safe if someone steals or intercepts them.

103symmetric encryption

The sender encrypts plaintext into ciphertext with a key; the receiver decrypts it back to plaintext using the same key. A wrong key gives unreadable output.

104public key

The half of a key pair that the owner shares openly. Anyone can use it to encrypt data sent to the owner, but it cannot decrypt that data. Only the matching private key can.

105private key

The secret half of a key pair. Only the owner keeps it, never sends it, and uses it to decrypt data that was encrypted with their public key.

106HTTPS

HTTP plus SSL/TLS encryption. Plain HTTP sends readable text that can be intercepted; HTTPS scrambles data so intercepted data can't be read, and a certificate shows the site is genuine.

107SSL handshake

Browser asks the server for its digital certificate, checks it is genuine, then both agree an encryption key to begin a secure session.

108VPN

A virtual private network creates an encrypted tunnel across a public network so a remote user can access a private network securely.

109WPA3

The newest Wi-Fi security standard. With a strong password it scrambles data in the air so outsiders can't read it. WPA2 is the older version. Open networks have no protection at all.

110MAC filtering

A router setting that only lets devices with MAC addresses on an allowed list join. It is easy to set up but weak, because a MAC address can be copied (spoofed).

111Firewall

A device or program that monitors and controls incoming and outgoing network traffic according to defined security rules.

112Firewall software

A program installed on a single device that filters its incoming and outgoing traffic using security rules.

113network firewall

A device or router feature between a local network and the internet that filters inbound and outbound traffic for every device behind it, not just one.

114allow inbound TCP 443

A firewall rule with an action (allow), a direction (inbound) and a port (TCP 443). It lets incoming web traffic through. A deny rule on a port, such as 23, blocks it.

115deny from 192.168.1.50

A firewall rule that blocks traffic from one IP address. Use a range like 192.168.1.0/24 to match a whole network, and allow to let only trusted addresses, such as the school network, in.

116default deny

A firewall checks rules from the top and uses the first match. A final default deny rule blocks anything not allowed by an earlier rule.

117proxy server

A server between a user's device and the internet. It receives the user's web requests, passes them to the web server for the user, then returns the response. Used in schools and companies.

119Intrusion detection system (IDS)

A system that monitors network traffic for suspicious activity and raises an alert when it finds it.

120Intrusion prevention system (IPS)

A system that sits inline in the traffic path, detects threats, and automatically blocks them before they reach the network.

121Antivirus software

A program that detects, blocks and removes malicious programs from a device.

122Operating system update

Installing the latest patches for the OS, fixing known security vulnerabilities and bugs.

123Authentication vs authorisation

Authentication checks who you are, like logging in. Authorisation decides what you can do once you are known, like which files you can open. Authentication always comes first.

124authentication factor

A type of proof that you are who you say you are: something you know (password, PIN), something you have (phone, key), or something you are (fingerprint, face).

125Multi-factor authentication

A login method that requires two or more independent proofs of identity, such as a password plus a one-time code.

126user account management

An OS function that creates, stores and controls user accounts, so each user logs in with a username and password and gets their own settings, files and access rights.

127access levels

Settings that give each user different rights to data: no access, read only, read/write or full control. Users only see and change what their role needs, protecting confidentiality and integrity.

128rwxr-x---

Three groups of three letters for owner, group and others: r is read, w is write, x is execute and - means not allowed. Here the owner has rwx, group r-x, others nothing.

129principle of least privilege

Give every user, program and device only the minimum access it needs to do its job. This limits the damage if an account is stolen, and unneeded access should be removed.

130Role-based access control (RBAC)

A way to manage access by giving permissions to roles, like student, teacher or admin, then assigning each user a role. Changing a user's role changes what they can access.

131access control list (ACL)

A table attached to a resource, like a file or router, that lists which users or groups may access it and what they can do. If you are not listed, access is denied.

132access log

An automatic record of who accessed a system or file, what they did and when. It helps spot failed logins and misuse, and holds users accountable for their actions.

133log analysis

Reading a log in time order for patterns, like many failed logins then one success, odd times or unfamiliar places, to spot an attack.

134ISM access controls guideline

A rule that tells organisations to only give people access to the parts of the network they actually need, after checking who they are.

135access control

Naming the data to protect, then choosing controls like login, permissions, a firewall or encryption, and justifying each one with the risk it reduces.

136countermeasure

A solution chosen to stop a specific threat, such as a firewall for hacking, SSL for interception or anti-malware for malware, plus an explanation of how it works.

138file management

An OS function that keeps track of files and folders, lets users create, name, open, copy, move and delete them, and records where each file is stored.

139file path

The location of a file in the folder tree, written from the root (absolute, e.g. /home/sam/file.txt) or from the current folder (relative).

140Version history

A tool in a shared folder that records who changed a file and when, so you can view earlier versions and restore one. Clear names with dates or version numbers help too, like Plan_v2_2025-03-14.

141Backup strategy

A plan for how and when backups are taken and stored, such as scheduling regular backups and keeping copies in multiple locations.

142full vs incremental vs differential

They differ in size, time and restore steps: full copies all data, incremental saves changes since the last backup, differential saves changes since the last full backup.

1433-2-1 rule

Keep 3 copies of data on 2 different types of media, with 1 copy stored offsite (such as cloud storage), so one disaster cannot destroy both the data and its backups.

144archive

Moving data no longer in everyday use to long-term storage so it is kept safely for a set retention period and can be retrieved later. It is not the same as a backup copy.

145disposal

Permanently destroying files and storage media no longer needed (e.g. secure deletion, shredding old drives) so data cannot be recovered, once any retention period ends.

146cron

A scheduler that runs a command or script at set times without a person starting it, such as a nightly backup. Windows Task Scheduler does the same job.

147shell script

A text file of shell commands, such as cp, mv or rm, that run in order each time the script is run, so file tasks like backups can be automated.

150shutil.copy(src, dst)

Python call that copies a file to a backup folder. Put a datetime timestamp in the new name so old backups are not overwritten, and a scheduler can then run the script.