Describe the hardware that is used to support the internet

2.1 Networks – The Internet (Cambridge AS/A‑Level Computer Science)

Learning Objective

Describe the hardware that is used to support the Internet, explain why each device is required, and relate it to the wider networking concepts set out in the Cambridge 9618 syllabus.

1. Core Networking Hardware – Purpose & Benefits

• Network Interface Card (NIC) – Provides the physical (copper/fibre) and data‑link (MAC) connection for every end‑device. Benefit: Enables devices to join a LAN or Wi‑Fi network and be uniquely identified on the link.
• Hub – A multi‑port repeater that copies incoming Ethernet frames to all other ports. Benefit: Simple way to extend a LAN (useful for small, low‑cost setups), but creates collisions.
• Switch – Learns MAC addresses and forwards frames only to the destination port (Layer 2). Benefit: Eliminates collisions, improves bandwidth utilisation and supports VLANs, PoE, and high‑speed links.
• Bridge – Connects two LAN segments and filters traffic based on MAC addresses. Benefit: Reduces broadcast domains and can segment a network without a router.
• Repeater / Extender – Regenerates weakened electrical or optical signals. Benefit: Extends the maximum length of copper or fibre links.
• Wireless Access Point (WAP) – Provides IEEE 802.11 (Wi‑Fi) connectivity and often includes integrated switch ports. Benefit: Gives mobile devices network access without cabling.
• Cabling
  • Twisted‑pair copper (Cat 5e, 6, 6a, 7) – Standard for Ethernet LANs.
  • Coaxial cable – Legacy Ethernet (10BASE‑2/5) and cable broadband.
  • Fiber‑optic (single‑mode, multimode) – High‑speed backbone within and between buildings.
  Benefit: Physical media that carries the bits; choice determines speed, distance, and immunity to interference.

2. LAN vs. WAN – Key Characteristics

3. LAN Topologies & Their Characteristics

4. Router Role, Functions & IP Addressing

• Core Functions (Layer 3)
  • Packet forwarding between different networks.
  • Path selection using routing tables and algorithms (static vs. dynamic routing).
  • Fragmentation/reassembly when a packet exceeds the MTU of the outgoing link.
• IP Addressing
  • IPv4 format: xxx.xxx.xxx.xxx (32 bits) – split into network and host portions.
  • Subnet mask (e.g., 255.255.255.0) defines the network boundary.
  • CIDR notation (e.g., 192.168.1.0/24) provides flexible prefix lengths.
  • 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 global Internet.
  • Network Address Translation (NAT) – maps private IPs to a public IP for outbound traffic.
• Dynamic Host Configuration Protocol (DHCP) – Automatically assigns IP address, subnet mask, default gateway and DNS servers to clients.
• Static vs. Dynamic IP Assignment
  • Static – manually configured; used for servers, printers, routers.
  • Dynamic – allocated by DHCP; simplifies management of large LANs.
• Routing Table Example

  Destination      Subnet Mask      Next Hop        Interface
  0.0.0.0          0.0.0.0          203.0.113.1     eth0   (default route)
  192.168.1.0      255.255.255.0    0.0.0.0         eth1   (directly connected)
  10.0.0.0         255.0.0.0        203.0.113.2     eth0
          

5. Core Internet Hardware (Beyond the LAN)

• Modem – Modulates/demodulates signals for transmission over telephone, cable, DSL, or fibre links.
• ISP / Backbone Router – High‑capacity devices that interconnect autonomous systems and run advanced routing protocols (OSPF, BGP).
• Data‑centre Switch – Layer 2/3 switches operating at 10 GbE, 40 GbE, 100 GbE; aggregate server traffic and provide VLAN, QoS, and link‑aggregation.
• Hardware Firewall – Enforces security policies, performs stateful inspection and can include intrusion‑prevention functions.
• Load Balancer – Distributes incoming client requests across multiple servers (round‑robin, least‑connections, weighted).
• Servers – Host services such as Web (HTTP/HTTPS), Email (SMTP/IMAP), DNS, Cloud storage, Virtualisation.
• Data‑centre Infrastructure
  • Racks, blade enclosures, cable‑management systems.
  • Power Distribution Units (PDUs), UPS, diesel generators.
  • Cooling: CRAC units, liquid‑cooling loops, hot‑aisle/cold‑aisle containment.
  • Environmental monitoring and physical security (CCTV, access control).
• Repeaters / Optical Amplifiers – Boost long‑haul fibre or submarine‑cable signals.
• Satellite Ground Stations & Dishes – Provide broadband where terrestrial infrastructure is unavailable.
• Fiber‑optic Cabling – Single‑mode for long‑distance backbone; multimode for intra‑building links.

6. Client‑Server vs. Peer‑to‑Peer (P2P) Models

Thin‑client vs. Thick‑client (Cambridge wording)

• Thin‑client – Minimal processing power, little or no local storage; relies on a server for applications and data.
• Thick‑client (fat client) – Performs most processing locally, stores data on its own disk, and can operate independently of a server.

7. Internet vs. World Wide Web (WWW)

• Internet – Global network of interconnected routers, switches, servers and end‑devices that use the TCP/IP protocol suite.
• World Wide Web – One of many services that run on the Internet; it uses HTTP/HTTPS to exchange hypertext documents.
• Domain Name System (DNS)
  • Translates human‑readable domain names (e.g., www.example.com) into IP addresses.
  • Hierarchical: root → top‑level domain (TLD) → second‑level domain → sub‑domains.
  • Typical query flow: client → recursive resolver → root server → TLD server → authoritative server.
• URL structure – protocol://host:port/path?query#fragment
  • Protocol: http, https, ftp, …
  • Host: domain name or IP address.
  • Port: optional (default 80 for HTTP, 443 for HTTPS).
  • Path, query string and fragment identify specific resources.

8. Wireless vs. Wired Networks – Key Technical Points

9. Cloud‑Computing Overview (Relevant to the Internet)

• Service models
  • IaaS – Infrastructure as a Service (e.g., Amazon EC2, Microsoft Azure VMs).
  • PaaS – Platform as a Service (e.g., Google App Engine, Heroku).
  • SaaS – Software as a Service (e.g., Google Workspace, Microsoft 365).
• Deployment models
  • Public cloud – Owned by a third‑party provider; resources shared among many customers.
  • Private cloud – Dedicated infrastructure for a single organisation (often in its own data centre).
  • Hybrid cloud – Combination of public and private resources linked via secure connections.
• Key hardware enablers
  • Virtualisation servers (hypervisors), storage arrays, high‑speed Ethernet/fibre switches, and software‑defined networking (SDN) controllers.

10. Typical End‑User to Server Path (Illustrative Example)

1. Desktop PC with a NIC connects to a Wi‑Fi Access Point or an Ethernet Switch (LAN).
2. Switch forwards Ethernet frames to the LAN router (gateway). The router performs NAT, DHCP and forwards packets to the ISP.
3. ISP modem converts digital signals to the appropriate carrier (DSL, cable, or fibre).
4. ISP edge router forwards the packet onto the ISP’s backbone using BGP routing.
5. Backbone routers transmit the packet over single‑mode fibre‑optic links, possibly passing through repeaters/amplifiers and under‑sea cables.
6. At the destination data centre, a load balancer selects a suitable web server (HTTP/HTTPS).
7. The web server processes the request, accesses storage or cloud services, and sends the response back along the reverse path.

11. Supporting Infrastructure (Reliability & Management)

• Power – UPS, diesel generators, redundant power feeds.
• Cooling – CRAC units, liquid cooling, hot‑aisle/cold‑aisle containment.
• Monitoring & Management – SNMP agents, network taps, syslog servers, performance dashboards.
• Physical Security – CCTV, biometric access, man‑traps.
• Disaster Recovery – Geo‑redundant data centres, backup links, fail‑over routing.