Computer Network Notes for Computer Science: Core Concepts & Models

Reviewed 21 October 2026. These computer network notes organize core concepts for computer science students. Use them as a revision guide and compare terminology with your course syllabus.

What is a computer network?

A computer network is a group of connected devices that exchange data using agreed communication rules. Networks can also let users share resources such as storage, printers, applications, and internet access.

Computer Network

Components of data communication

A basic data communication system has five parts: a sender, a receiver, a message, a transmission medium, and a protocol. The sender creates the information; the receiver gets it; the medium carries it; and protocols define how devices format, transmit, and interpret it.

Components of Data Communication

Types of data flow

Simplex is one-way communication, such as a one-way broadcast. Half-duplex allows both sides to transmit, but only one side at a time, as with a walkie-talkie. Full-duplex allows both sides to transmit at the same time, as in a phone call.

Simplex

Half Duplex

Full-Duplex:

Network types by coverage

A PAN connects devices around one person; a LAN covers a limited area such as a home, office, or campus; a MAN spans a town or metropolitan area; and a WAN connects networks across larger geographic areas. The internet is a global network of interconnected networks.

LAN and WAN

A LAN usually serves a smaller area and is managed by one organization or household. A WAN connects sites across larger distances and often relies on multiple network operators and communication links. Size, ownership, technologies, and latency can all differ; no single distance threshold defines every network.

Point-to-point and broadcast transmission

Point-to-point transmission connects a sender to one receiver over a link. Broadcast sends a frame or message to multiple devices within the applicable network or broadcast domain. Modern networks also use unicast and multicast, so the delivery method depends on the protocol and network design.

point to point

Broadcast

Common network topologies

Topology describes how devices and links are arranged. A physical layout and the logical path that data follows do not always match.

1. Bus topology

Devices share a main communication backbone. It uses less cabling in a simple design, but a backbone fault can affect the connected segment.

2. Star topology

Each device connects to a central hub or switch. It is easy to manage and expand, but failure of the central device can disrupt connected devices.

3. Ring topology

Each device connects to neighboring devices to form a loop. Data follows the ring according to the network design; a link or device failure can affect communication unless the system has a recovery path.

4. Mesh topology

Devices have multiple links to other devices. Redundant paths can improve resilience, but mesh designs require more links and are more complex to maintain.

5. Hybrid topology

A hybrid topology combines layouts, such as star segments joined by a backbone. It can fit an organization's needs, but design and troubleshooting depend on how the parts connect.

Network devices and protocols

Common devices include network interface cards, switches, routers, wireless access points, modems, and firewalls. A switch connects devices within a local network; a router forwards traffic between networks; an access point provides wireless connectivity.

A protocol is a set of rules for communication. Internet Protocol (IP) addresses and routes packets; TCP provides a reliable, ordered byte stream; UDP sends datagrams without TCP's delivery guarantees; DNS maps domain names to records; DHCP helps configure network addresses; and HTTPS protects web traffic using TLS.

The OSI reference model

The seven-layer OSI model is a teaching and troubleshooting framework. Real internet protocols do not always map one-to-one to these layers.

7. Application — network services used by applications, such as HTTP, DNS, and SMTP.

6. Presentation — data representation, encoding, compression, and encryption concepts.

5. Session — starting, coordinating, and ending communication sessions.

4. Transport — end-to-end data delivery using protocols such as TCP or UDP.

3. Network — logical addressing and routing, including IP.

2. Data Link — local-link framing and delivery, such as Ethernet or Wi-Fi link functions.

1. Physical — signals and the physical or radio transmission medium.

TCP/IP model

The TCP/IP model commonly groups networking into link, internet, transport, and application layers. Link handles the local network; IP works at the internet layer; TCP and UDP operate at the transport layer; and application protocols such as HTTP, DNS, and SMTP sit at the top. Course texts may show a five-layer model by separating the physical layer from the link layer.

Network performance, reliability, and security

Performance includes throughput, latency, and how well a network handles load. Reliability concerns availability and recovery from failures. Security protects confidentiality, integrity, and availability through measures such as access control, updates, encryption, monitoring, and segmentation.

Quick revision questions

• What are the five components of a data communication system? Sender, receiver, message, transmission medium, and protocol.

• How do half-duplex and full-duplex differ? Half-duplex sends in both directions one direction at a time; full-duplex supports simultaneous two-way communication.

• What is the main difference between a switch and a router? A switch forwards traffic within a local network; a router forwards traffic between networks.

• What does the OSI model provide? A seven-layer reference for describing and troubleshooting network functions.