Data Communications
Data communications refers to the transmission of digital data between two or more connected devices. A computer network is a telecommunications infrastructure that allows computers to exchange data.
Brief History of Data Communication
| Year | Development |
|---|---|
| 1753 | Proposal to connect villages using 26 parallel wires (one per letter) |
| 1833 | Carl Friedrich Gauss developed a 5×5 matrix system to send messages over a single wire |
| 1832 | Samuel Morse invented the telegraph; also developed Morse code (dots and dashes) |
| 1840 | Morse secured an American patent for the telegraph |
| 1844 | First telegraph line established (Baltimore to Washington D.C.); first message: "What hath God wrought!" |
| 1875 | Alexander Graham Bell invented the telephone |
| 1899 | Guglielmo Marconi transmitted radio (wireless) telegraph messages |
| 1920 | First radio transmission of the human voice |
| 1957 | Launch of Sputnik-1, Earth's first artificial satellite |
| 1963 | Launch of Syncom-1, the first geostationary telecommunications satellite |
Computer Network Elements
The key elements of a computer network are:
- Protocols — rules and agreements governing how devices communicate. A protocol stack is the ordered set of protocols a system uses.
- Data and Messages — the information being transmitted across the network.
- Communications Medium — the physical or wireless channels connecting devices (e.g., copper cables, fiber optic cables, radio waves).
- Devices — the hardware in the network: computers, routers, switches, hubs, bridges.
Network Classification by Geographic Scope
| Type | Coverage | Characteristics |
|---|---|---|
| PAN (Personal Area Network) | ~10 meters around an individual | Short-range device interconnection |
| LAN (Local Area Network) | One building or campus | High speed; usually privately owned |
| MAN (Metropolitan Area Network) | A city or cluster of cities | Often uses telecom provider infrastructure |
| WAN (Wide Area Network) | Between cities or countries | Lower speed; uses public networks |
| GAN (Global Area Network) | Worldwide (e.g., the Internet) | — |
Network Models
Peer-to-Peer — all computers in the network share their resources equally with all other computers. No dedicated server.
Client-Server — one or more powerful machines act as servers, with the rest as clients. The server manages and provides resources; clients request and use those resources.
Network Topologies
A network topology describes how the devices in a network are arranged and connected.
Physical topology — the actual physical layout of devices and cables. Logical topology — how data actually flows through the network, which may differ from the physical arrangement.
Point-to-Point
Two devices connected directly. Simple and always available for those two stations, but only those two can communicate directly.
Star Topology
All devices connect to a central hub or switch.
- Advantages: failure of one link doesn't affect others; easier fault isolation; less cable than mesh.
- Disadvantages: if the central device fails, the entire network goes down; requires more cable than bus.
Bus Topology
All devices share a single cable.
- Advantages: minimal cable; easy installation; no routing needed.
- Disadvantages: cable break disrupts the whole network; collisions occur when multiple devices transmit simultaneously.
Ring Topology
Devices connect in a closed loop — each device connects to exactly two others.
- Advantages: less cable than mesh; relatively easy installation.
- Disadvantages: a break anywhere in the ring disrupts the whole network; slower for non-adjacent stations.
Mesh Topology
Every device has a direct connection to every other device.
- Advantages: no contention for the medium; highly reliable; alternate paths available if one link fails; good security.
- Disadvantages: requires the most cable; most communication ports; most complex installation; highest cost.
Tree Topology
A hierarchical structure with a root node at the top, branching downward through multiple levels via point-to-point links. The root is the only node with nothing above it.
Hybrid Topology
Combines two or more of the topologies above. Inherits both the advantages and disadvantages of the topologies combined.
The Internet
The Internet is a global network of networks that allows any connected device to send and receive data from any other connected device.
Brief Internet History
| Year | Event |
|---|---|
| 1962 | J.C.R. Licklider (MIT) envisioned a globally interconnected computer network |
| 1969 | ARPANET became operational, linking academic and research institutions |
| 1972 | First public demo of ARPANET; email introduced |
| 1983 | ARPANET adopted TCP/IP; LANs and workstations began proliferating |
| 1987 | Nearly 30,000 hosts on the Internet |
| 1995 | SSL encryption developed (enabling secure online transactions); Internet commercialized |
The World Wide Web
The Web is a collection of interlinked multimedia documents stored on the Internet, accessed using HTTP. Each document is a web page; a collection of web pages is a website.
Sir Tim Berners-Lee invented the World Wide Web in 1989 and defined its three core technologies:
- HTML (HyperText Markup Language) — the formatting language for web pages.
- URI/URL (Uniform Resource Identifier/Locator) — a unique address identifying each resource on the web.
- HTTP (HyperText Transfer Protocol) — the protocol for retrieving linked resources across the web.
The World Wide Web Consortium (W3C), with about 350 member organizations, sets standards and guidelines for the web.
Key Internet Concepts
IP Address — a unique numerical label identifying every device on the Internet. IPv4 addresses consist of four groups of numbers (0–255) separated by dots. Example: 72.48.108.101
Domain Name — a human-readable text name for an IP address. The Domain Name System (DNS) translates domain names to their corresponding IP addresses. Example: www.google.com
URL (Uniform Resource Locator) — the complete address of a specific resource on the web. Structure:
https://www.example.com/path/filename
ISP (Internet Service Provider) — a company that provides Internet access using connections such as dial-up, DSL, cable modem, or wireless.
Internet Protocols
TCP/IP (Transmission Control Protocol / Internet Protocol) — the foundational protocols of the Internet; manage how data is packaged, addressed, transmitted, and received.
HTTP (HyperText Transfer Protocol) — the protocol browsers and web servers use to exchange web pages and resources. Operates between client (browser) and server.
HTTPS (HTTP Secure) — an encrypted version of HTTP that protects data in transit from eavesdropping. Used for secure transactions (e.g., online banking, shopping).
FTP (File Transfer Protocol) — used for transferring files between systems interactively.
SMTP (Simple Mail Transfer Protocol) — handles the transmission of email messages and attachments.
Intranet — a private network using the same basic technologies as the Internet, accessible only to authorized members of an organization (e.g., employees).
Practice Exercises — Unit VI
ProReviewer — locked
Drills, code labs, and full solutions.