Describe network components (routers, switches, hubs)

14 Communications Technology

Objective

Describe the main network components (routers, switches, hubs) and relate them to the Cambridge AS & A‑Level IT syllabus – network types, topologies, additional hardware, servers, cloud computing, data transmission, protocols, wireless and mobile technologies.

14.1 Networks – Types & Topologies

Network Types (with one key advantage and disadvantage)

Type	Typical Use	Advantage	Disadvantage
Local Area Network (LAN)	Home, office, school	High speed, low latency	Limited geographic coverage
Wide Area Network (WAN)	Connecting multiple LANs across cities/countries	Large geographic reach	Higher cost and latency
Client‑Server	File, web, mail services	Centralised management & security	Server is a single point of failure (unless redundant)
Peer‑to‑Peer (P2P)	File‑sharing, small collaborative groups	Simple, no dedicated server required	Limited control, security risks
Virtual Private Network (VPN)	Secure remote access to a corporate LAN	Encrypted traffic over public infrastructure	Requires additional configuration & bandwidth
Mobile / Wireless Networks	Wi‑Fi in cafés, campuses; cellular data	Mobility and ease of deployment	Signal interference & security concerns

Physical vs. Logical Topologies

• Physical topology – the actual layout of cables and devices (star, bus, ring, mesh, extended‑star).
• Logical topology – how data flows over the physical layout (e.g., a star physical layout may use a logical bus protocol such as Ethernet).

Common Physical Topologies

Topology	Typical Use	Key Feature
Star	Office LANs, schools	All devices connect to a central switch/hub; easy to manage.
Extended Star	Large campuses, data‑centres	Multiple switches inter‑connected, preserving star benefits.
Bus	Legacy Ethernet, some industrial links	All devices share a single cable; collisions possible.
Ring	Token Ring, some fibre deployments	Frames travel in one direction; dual rings add fault tolerance.
Mesh	Backbone WAN, data‑centre fabrics	Redundant paths give high reliability and load‑balancing.

14.2 Components in a Network

All components listed in the Cambridge syllabus (14.2) are shown below with the OSI layer they primarily operate on, their main role and a typical example.

Component	OSI Layer(s)	Role	Typical Example
Network Interface Card (NIC)	1 & 2 (Physical & Data Link)	Provides the physical/electrical link between a device and the network.	Ethernet card in a desktop PC.
Repeater	1 (Physical)	Regenerates and amplifies signals to extend cable length.	Extending a 100 m Ethernet run to 200 m.
Hub	1 (Physical)	Broadcasts incoming electrical signals to every port; creates a single collision domain.	Classroom demo of Ethernet collisions.
Switch	2 (Data Link) – some 3 (Network)	Forwards frames to the correct port using MAC addresses; each port is a separate collision domain.	48‑port Gigabit Ethernet switch in an office.
Router	3 (Network)	Routes packets between different networks using IP addresses and routing tables.	Home broadband router linking LAN to ISP.
Access Point (AP)	2 & 3 (Data Link & Network)	Provides wireless connectivity to a wired LAN; may include basic routing/NAT.	Wi‑Fi AP in a café.
Bridge	2 (Data Link)	Connects two LAN segments and forwards frames based on MAC addresses; reduces collisions compared with a hub.	Linking two Ethernet labs.
Gateway	3 & 7 (Network & Application)	Translates between different network protocols or architectures (e.g., LAN ↔ Internet, IPv4 ↔ IPv6, email formats).	Email gateway converting SMTP to an internal messaging format.

Key Switch Features

• MAC address table – learns source MACs and forwards frames only to the appropriate port.
• Port security & VLANs – managed switches can restrict which MACs may use a port and segment a LAN into virtual LANs.
• Full‑duplex operation – each port has its own collision domain, eliminating collisions.
• Managed vs. unmanaged – managed switches add configuration options (QoS, STP, monitoring).

Bridge vs. Switch

• Both operate at Layer 2, but a bridge connects only two network segments, whereas a switch connects many ports and typically includes advanced features (VLANs, QoS).

Gateway vs. Router

• A router forwards packets between IP networks (Layer 3).
• A gateway performs protocol conversion that may involve higher‑layer (Application) processing – for example, translating between IPv4 and IPv6 or between different email formats.

14.3 Network Servers

Servers provide specialised services to client devices. The syllabus expects eight common types.

Server Type	Primary Function	Real‑World Example
File Server	Stores and shares files across the network.	Company shared‑drive for documents.
Web Server	Hosts web pages and serves HTTP/HTTPS requests.	Corporate website on Apache or IIS.
Mail Server	Handles sending, receiving and storing email (SMTP, POP3/IMAP).	Microsoft Exchange for corporate mail.
Application Server	Runs business applications and provides APIs.	Java EE server for an inventory system.
Print Server	Manages network printers and queues print jobs.	Central print server for office printers.
FTP Server	Facilitates file transfer using the FTP protocol.	File‑transfer hub for large media files.
Proxy Server	Acts as an intermediary for client requests; provides caching and security.	Web proxy that filters Internet access.
Virtual Server / Server Farm	Multiple virtual machines or physical servers delivering the same service for load‑balancing and redundancy.	Cloud‑based virtual web servers behind a load balancer.

14.4 Cloud Computing

Service Models

• IaaS – Infrastructure as a Service: virtualised hardware (e.g., Amazon EC2).
• PaaS – Platform as a Service: development platform and runtime (e.g., Google App Engine).
• SaaS – Software as a Service: complete applications delivered over the Internet (e.g., Microsoft 365).

Deployment Models

• Public cloud – services owned by a third‑party provider and shared among many organisations.
• Private cloud – dedicated infrastructure for a single organisation, often on‑premises.
• Hybrid cloud – combination of public and private clouds, allowing data and applications to move between them.

Advantages

• Scalability – resources can be increased or decreased on demand.
• Cost‑effectiveness – pay‑as‑you‑go, reduced capital expenditure.
• Accessibility – services available from any Internet‑connected device.
• Rapid provisioning – new servers or services can be created in minutes.

Disadvantages

• Dependence on reliable Internet connectivity.
• Security and privacy concerns (data stored off‑site).
• Limited control over underlying hardware and sometimes software versions.
• Potential vendor lock‑in.

14.5 Data Transmission Across Networks

Key Concepts

• Bandwidth – maximum data rate a link can carry (e.g., 100 Mbps, 1 Gbps).
• Bit‑rate – actual number of bits transmitted per second.
• Latency – time taken for a single bit or packet to travel from source to destination.
• Throughput – effective data rate after accounting for protocol overhead, collisions and errors.

Transmission Media

Medium	Typical Bandwidth	Maximum Length (per segment)	Common Use
Twisted‑pair copper (Cat 5e)	Up to 1 Gbps	100 m	Office LANs.
Twisted‑pair copper (Cat 6a/7)	10 Gbps	100 m	Data‑centre uplinks.
Coaxial cable	10 Mbps – 10 Gbps (depends on standard)	500 m	Older cable TV, some broadband.
Fibre‑optic (single‑mode)	10 Gbps – 100 Gbps+	10 km+ (with repeaters)	WAN backbones, metro networks.
Fibre‑optic (multimode)	1 Gbps – 40 Gbps	550 m (OM4)	Data‑centre intra‑rack links.
Wireless (Wi‑Fi 6/6E)	Up to 9.6 Gbps (theoretical)	~30 m indoor	Mobile devices, hot‑desks.
Microwave / Radio (point‑to‑point)	Up to 1 Gbps	Several kilometres	Rural backhaul.

Latency vs. Bandwidth Trade‑off (Streaming & Real‑Time Transfer)

• High‑definition video needs large bandwidth** but can tolerate modest latency.
• Real‑time applications (VoIP, online gaming) require low latency** even if bandwidth is modest.
• Adaptive‑bitrate streaming (DASH, HLS) adjusts video quality to match the current bandwidth, helping maintain smooth playback.

14.6 Network Protocols

Protocol	Purpose	OSI Layer(s)
TCP (Transmission Control Protocol)	Reliable, connection‑oriented transport; ensures ordered delivery.	4 (Transport)
UDP (User Datagram Protocol)	Connection‑less transport; low overhead, used for streaming, DNS.	4 (Transport)
IP (Internet Protocol)	Logical addressing and routing of packets.	3 (Network)
ICMP (Internet Control Message Protocol)	Network diagnostics (e.g., ping, traceroute).	3 (Network)
ARP (Address Resolution Protocol)	Maps IP addresses to MAC addresses on a LAN.	2 (Data Link)
DHCP (Dynamic Host Configuration Protocol)	Automatically assigns IP addresses and other network parameters.	7 (Application)
HTTP / HTTPS	Web page request/response; HTTPS adds TLS encryption.	7 (Application)
FTP	File transfer between client and server.	7 (Application)
SMTP	Sending email messages.	7 (Application)
POP3 / IMAP	Retrieving email from a server.	7 (Application)
TLS / SSL	Encrypts data for secure communications (used by HTTPS, FTPS, etc.).	6 (Presentation)

14.7 Wireless Technology

Common Wireless Methods

• Wi‑Fi (IEEE 802.11) – radio waves, typical range 30 m indoor.
• Bluetooth – short‑range (≤10 m), low power, used for peripherals.
• Infrared (IR) – line‑of‑sight, low data rates, remote controls.
• Microwave / Radio – point‑to‑point links, up to several kilometres.
• NFC (Near Field Communication) – ≤4 cm, used for contactless payments.

Wi‑Fi Security Protocols

Standard	Encryption	Strength / Note
WEP	RC4 (40/104‑bit key)	Very weak; easily cracked.
WPA	TKIP	Improved over WEP but still vulnerable.
WPA2	AES‑CCMP	Current baseline security for most networks.
WPA3	SAE (Simultaneous Authentication of Equals)	Stronger protection against password‑guessing attacks.

Advantages & Disadvantages of Wireless Methods

Method	Advantage	Disadvantage
Wi‑Fi	High data rates, easy to deploy.	Interference, limited range, security concerns.
Bluetooth	Very low power consumption.	Short range, lower throughput.
Infrared	Secure (line‑of‑sight).	Requires direct line‑of‑sight, very low speed.
Microwave / Radio	Long distance, can bypass physical obstacles.	Requires line‑of‑sight, licensing for some bands.
NFC	Instant connection, very low power.	Extremely short range, minimal data rate.

14.8 Mobile Communication Systems

Cellular Generations

Generation	Typical Speed	Key Features	Advantages	Disadvantages
3G	0.5–5 Mbps	Packet‑switched data, video calls.	Broad coverage, good voice quality.	Limited bandwidth for high‑definition video.
4G (LTE)	10–100 Mbps (up), 50 Mbps (down)	All‑IP core, low latency.	Fast mobile internet, supports streaming.	Higher power consumption, coverage gaps in rural areas.
5G	100 Mbps – 10 Gbps	Massive MIMO, network slicing, ultra‑low latency (<1 ms).	Enables IoT, AR/VR, autonomous vehicles.	Requires dense infrastructure, still rolling out.

Cellular Network Architecture

• Base Transceiver Station (BTS) – the radio antenna that communicates with mobile devices.
• Base Station Controller (BSC) / Radio Access Network (RAN) – manages multiple BTSs, handles handovers.
• Core Network (EPC for 4G, 5GC for 5G) – provides routing, authentication, and connection to external networks (Internet, PSTN).

14.9 Comparison of Routers, Switches and Hubs

Feature	Router	Switch	Hub
OSI Layer	3 (Network)	2 (Data Link) – some 3	1 (Physical)
Decision Basis	IP address & routing table	MAC address table	None (broadcast)
Collision Domain	One per interface	One per port (full‑duplex)	All ports share one
Typical Use	Connecting different networks (LAN ↔ WAN, VPN)	Connecting devices within a LAN	Simple network extension, teaching demos
Intelligence	High – routing protocols, NAT, ACLs, QoS	Medium – MAC learning, VLANs, QoS (managed)	None
Bandwidth Efficiency	High – selective forwarding	High – point‑to‑point frames	Low – all traffic repeats

14.10 Practical Example – Small Office Network

1. Each workstation connects to a **managed 48‑port Gigabit Ethernet switch** via Cat 6 cable.
2. The switch forwards frames directly to the destination port using its MAC address table.
3. An uplink from the switch connects to a **router** that provides Internet access, NAT, a built‑in firewall and VPN support.
4. A **wireless access point** is attached to the switch to give Wi‑Fi coverage for laptops, tablets and smartphones.
5. A **hub** is placed on a lab bench solely for demonstration of collision domains; it is **not** part of the production network.
6. Servers (file, web, mail) reside on the LAN behind the router. A **cloud‑based SaaS** (e.g., CRM) is accessed over the Internet.

14.11 Key Points to Remember

• Routers operate at Layer 3, routing between different networks (LAN, WAN, VPN) using IP addresses.
• Switches operate at Layer 2, creating a separate collision domain for each port and forwarding frames by MAC address; managed switches add VLANs, QoS and port security.
• Hubs operate at Layer 1, broadcasting incoming signals to all ports and sharing a single collision domain; they are now largely obsolete except for teaching.
• Additional components – NIC, repeater, bridge, access point, gateway – each fulfil a specific role in the OSI model.
• Choosing the appropriate device (router, switch, hub, etc.) directly impacts performance, security and scalability.
• Understanding network types, topologies, servers, cloud models, protocols, wireless and mobile technologies is essential for designing, implementing and troubleshooting modern IT systems.