Show understanding of the differences between the World Wide Web (WWW) and the internet

2.1 Networks – The Internet, the World Wide Web and Core Networking Concepts

Learning Objective

Show understanding of the differences between the World Wide Web (WWW) and the Internet, and describe the fundamental networking concepts required by the Cambridge AS & A‑Level Computer Science (9618) syllabus.

2.1.1 What is the Internet?

• Definition: A global system of interconnected computer networks that use the Internet protocol suite (TCP/IP) to exchange data.
• Key functions:
  • Packet‑switching – data is broken into packets and routed independently.
  • Routing – routers forward packets toward their destination.
  • Addressing – every device has an IP address (IPv4 or IPv6).
  • Transport – TCP provides reliable, ordered delivery; UDP provides low‑latency, connection‑less delivery.
• Typical services (examples of protocols): Email (SMTP/IMAP/POP3), File Transfer (FTP/SFTP), Voice‑over‑IP (SIP, RTP), Remote login (SSH, Telnet), Streaming (RTSP, MPEG‑DASH), and the World Wide Web (HTTP/HTTPS).

2.1.2 What is the World Wide Web (WWW)?

• Definition: An application‑layer service that runs on the Internet, delivering hypertext documents and multimedia using the HTTP/HTTPS protocols.
• Core components:
  • Web browsers (clients) – render HTML, CSS and JavaScript.
  • Web servers – store and serve resources.
  • Supporting technologies – DNS (for name resolution), CDNs (for content distribution), SSL/TLS (for security).
• Scope: The WWW is a *subset* of Internet services; it is one way of using the underlying network, not the network itself.

2.1.3 Comparison – Internet vs. WWW

2.1.4 Core Networking Concepts (IP, DNS, URLs & Routing)

• IP addressing
  • IPv4 – 32‑bit dotted‑decimal (e.g., 192.168.1.10); supports ~4.3 billion addresses.
  • IPv6 – 128‑bit hexadecimal (e.g., 2001:0db8:85a3::8a2e:0370:7334); virtually unlimited address space.
  • Public vs. private addresses – private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are not routable on the public Internet.
  • Static vs. dynamic allocation – static addresses are manually configured; dynamic addresses are assigned by DHCP.
• Subnetting
  • A subnet mask (e.g., 255.255.255.0 or /24) divides an IP network into smaller logical networks.
  • Subnetting improves security and reduces broadcast traffic; the number of hosts per subnet = 2^(32‑mask) − 2 for IPv4.
• Domain Name System (DNS)
  • Translates human‑readable domain names (e.g., www.example.com) into IP addresses.
  • Typical lookup sequence: client → recursive resolver → root server → TLD server → authoritative server → IP address.
• URL structure
  • General form: protocol://host[:port]/path?query#fragment
  • Example: https://www.example.com:443/articles?id=42#section2
  • Protocol (http/https) tells the browser which application‑layer protocol to use; the host is resolved via DNS.
• Router functions
  • Forward IP packets between different networks based on routing tables.
  • Perform Network Address Translation (NAT) to map private addresses to a public address.
  • Support dynamic routing protocols (e.g., OSPF, BGP) for scalable internetworking.

2.1.5 Networking Devices – Purpose & Benefits

Networking devices enable reliable, efficient communication between computers and other digital devices.

• Network Interface Card (NIC): Provides a physical and data‑link connection to a network; each NIC has a unique MAC address.
• Hub: Simple repeater that broadcasts incoming frames to all ports; inexpensive but creates a single collision domain.
• Switch: Learns MAC addresses and forwards frames only to the intended port; creates separate collision domains for each port, greatly improving bandwidth utilisation.
• Router: Operates at the network layer; forwards IP packets between distinct networks, performs NAT, and selects the best path using routing tables.
• Modem: Modulates digital data into analog signals (and vice‑versa) for transmission over telephone lines, cable, or DSL.
• Access Point (AP): Provides wireless (Wi‑Fi) connectivity; acts as a bridge between a wired LAN and wireless clients.

2.1.6 LAN vs. WAN

2.1.7 Network Topologies

Topologies describe how devices are physically or logically connected.

• Bus: All devices share a single communication line; simple but prone to collisions and difficult to extend.
• Star: Each device connects to a central hub or switch; most common in modern LANs because a failure affects only the linked device.
• Mesh: Multiple redundant paths between devices; provides high reliability and is often used in WAN backbones and data‑centre fabrics.
• Hybrid: Combination of two or more basic topologies (e.g., star‑bus in a campus network).

2.1.8 Client‑Server and Peer‑to‑Peer (P2P) Models

• Client‑Server: Centralised servers provide resources or services to multiple clients.
  Example: An email server (SMTP/IMAP) stores mail; users’ mail clients retrieve it.
• Peer‑to‑Peer (P2P): Each node can act as both client and server, sharing resources directly.
  Example: BitTorrent – users download and upload file pieces simultaneously.

Understanding these models helps analyse computational problems (AO2) and design appropriate networked solutions.

2.1.9 Thin‑Client vs. Thick‑Client

2.1.10 Wired vs. Wireless Networks & Hardware

2.1.11 Ethernet, CSMA/CD and “Why Ethernet?”

• Ethernet: Dominant LAN technology that uses MAC addresses and frames. Modern implementations support 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps, 40 Gbps and 100 Gbps.
• CSMA/CD (Carrier Sense Multiple Access with Collision Detection): The original half‑duplex access method. Devices listen to the medium, transmit when idle, and if a collision occurs they back‑off and retry.
• Why Ethernet?
  • Separate collision domains – each switch port operates in full‑duplex, eliminating collisions.
  • Scalability – easy to add ports, upgrade speed, and integrate with fibre‑optic uplinks.
  • Cost‑effectiveness – inexpensive NICs and cabling compared with alternatives such as Token Ring.
  • Standardisation – IEEE 802.3 defines a clear, widely‑supported set of physical and data‑link specifications.
• Although CSMA/CD is now mainly of historical interest, it remains in the syllabus to illustrate how early Ethernet dealt with shared media.

2.1.12 Cloud Computing Concepts (Networking Perspective)

Cloud services are delivered over the Internet; understanding the networking layer clarifies how they operate.

• IaaS (Infrastructure as a Service): Provides virtualised hardware (e.g., Amazon EC2). Users access VMs via SSH or RDP over TCP/IP; bandwidth and latency are determined by the underlying network.
• PaaS (Platform as a Service): Supplies a development platform (e.g., Google App Engine). Applications communicate with databases and other services through HTTP/HTTPS APIs, relying on DNS for service discovery.
• SaaS (Software as a Service): Delivers complete applications via a browser (e.g., Google Docs). The WWW is the transport mechanism; performance depends on CDN placement, TCP congestion control, and TLS encryption.

2.1.13 Common Misconceptions

1. Thinking the WWW *is* the Internet – the WWW is just one of many services that run on the Internet.
2. Assuming every Internet‑connected device can display web pages – only devices with a web browser and HTTP capability can access the WWW.
3. Believing the Internet and the WWW use the same protocols – the Internet relies on TCP/IP, while the WWW adds HTTP/HTTPS on top.
4. Confusing LAN and WAN speeds – LANs are usually much faster because they cover smaller distances and use higher‑grade media.
5. Assuming a hub is as efficient as a switch – hubs broadcast to all ports causing collisions; switches forward frames intelligently, creating separate collision domains.
6. Over‑looking the role of DNS and URLs – without DNS a user cannot translate a domain name to an IP address, and a URL defines the exact resource requested.

2.1.14 Summary

The Internet is the global packet‑switching infrastructure that carries all digital data. The World Wide Web is an application‑layer service that uses this infrastructure to deliver hypertext and multimedia via browsers. Mastery of IP addressing, subnetting, DNS, URL structure, routing, networking devices, LAN/WAN characteristics, topologies, client‑server models, thin/thick clients, wired and wireless media, Ethernet (including CSMA/CD), and cloud‑computing models equips students to meet the Cambridge AS & A‑Level Computer Science (9618) requirements for Section 2.1.