Unit 3: Data Communication and Networks

CAP1007 — Fundamentals Of Information Technology 7 min read

Data communication is the exchange of data between two devices through a transmission medium, and networking is the practice of interconnecting those devices so they can share resources. Modern computing depends on moving bits reliably across distances ranging from a metre to the whole planet, and this unit builds from the physics of a single link up to the global Internet.

Data: information encoded in a form a device can process, ultimately reduced to binary digits (bits).
Signal: the electrical, optical or electromagnetic representation of data as it travels on a medium.
Medium: the physical path — copper wire, fibre, or free space (wireless).
Protocol: an agreed set of rules governing format, timing, sequencing and error handling.
Bandwidth and data rate: capacity of a link, measured in bits per second (bps, Kbps, Mbps, Gbps).
Latency: delay before a transfer begins, measured in milliseconds (ms).

II. Transmission and Communication Basics

How a single link carries data and how devices are located.

A. local and global search of network

Locating resources or hosts on a network operates at two scales.

Local search: discovery within a single administrative network (LAN). Uses broadcast/multicast — e.g. ARP resolves an IP to a MAC address by broadcasting to all hosts, and mDNS/NetBIOS lets a PC find printers or shared folders on the same subnet.
Global search: locating resources across the whole Internet. Relies on hierarchical naming and directory services — the Domain Name System (DNS) translates www.example.com into an IP address by querying root, top-level and authoritative servers, while search engines index globally distributed content.
Key contrast: local search is fast, connectionless and confined to one subnet; global search is hierarchical, cached and traverses routers.

B. digital and analog transmission

Data can travel as continuous or discrete signals.

Analog transmission: a continuously varying signal (amplitude/frequency over time), as in traditional telephone voice. It weakens with distance and amplifiers boost both signal and accumulated noise.
Digital transmission: discrete voltage levels representing 0s and 1s. Regenerative repeaters rebuild the clean pulse, so noise does not accumulate, giving lower error rates.

Conversion: a modem modulates digital data onto an analog carrier and demodulates it back; a codec digitises analog voice.
Sampling rule: the Nyquist theorem states sampling rate must be at least twice the highest signal frequency to reconstruct it faithfully.

C. components of data communication system

Five elements must be present for communication to occur.

Message: the information to be communicated (text, audio, image, video).
Sender: the device that originates the message (computer, phone, sensor).
Receiver: the device that accepts the message.
Transmission medium: the physical channel carrying it — twisted pair, coaxial, fibre, or radio.
Protocol: the rule set both ends follow so the message is understood; without a shared protocol the other components cannot cooperate.

D. modes of communication (simplex, half duplex, duplex)

Direction of data flow between two devices defines the mode.

Simplex: one direction only; the receiver never transmits back. Example: keyboard to CPU, or a broadcast radio station.
Half duplex: both directions but only one at a time; the link is shared alternately. Example: a walkie-talkie where you press to talk.
Full duplex: both directions simultaneously, effectively two channels or a shared channel split in capacity. Example: a telephone call, or modern Ethernet over separate transmit/receive pairs.

III. Network Structure

How devices are arranged, connected without wires, and classified by scale.

A. network topologies

Topology is the physical or logical layout of connected nodes.

Bus: all nodes share one backbone cable; cheap but a break disables the whole segment and collisions rise with load.
Star: every node connects to a central hub or switch; failure of one link isolates only that node, but the hub is a single point of failure. Dominant in modern LANs.
Ring: nodes form a closed loop and data passes token-by-token in one direction; a single break can halt the ring unless dual-ring redundancy is used.
Mesh: every node links to many others, giving high fault tolerance and multiple paths; a full mesh of n nodes needs n(n-1)/2 links, so it is costly.
Tree/hierarchical: star networks linked to a bus backbone, used for structured campus wiring.

B. wireless networks

Networks that use electromagnetic waves instead of cabling.

Wi-Fi (IEEE 802.11): wireless LAN connecting devices to an access point over 2.4/5/6 GHz bands.
Bluetooth: short-range personal-area links (typically under 10 m) for peripherals.
Cellular (4G LTE, 5G): wide-area mobile data through licensed spectrum and base stations.
Characteristics: mobility and easy deployment, but shared spectrum causes interference, and signals need encryption (WPA2/WPA3) because they radiate openly and are easy to intercept.

C. network types and their features

Networks are classified chiefly by geographic scale.

PAN (Personal Area Network): a few metres around one person — Bluetooth earbuds, smartwatch.
LAN (Local Area Network): a building or campus; high speed (100 Mbps–10 Gbps), privately owned, low latency.
MAN (Metropolitan Area Network): a city-wide network, e.g. a cable-TV or municipal fibre network, often run by a service provider.
WAN (Wide Area Network): spans countries or continents using leased lines and public infrastructure; the Internet is the largest WAN, with higher latency and lower per-link speed than a LAN.

IV. The Internet and Internet Protocol

The global internetwork and the addressing scheme that makes it work.

A. an overview of internet and its working

The Internet is a worldwide network of networks that communicate using the TCP/IP protocol suite.

Packet switching: data is split into packets, each routed independently and reassembled at the destination, sharing links efficiently.
Layered model: application (HTTP, DNS), transport (TCP/UDP), internet (IP), and link layers each handle a defined job.
Working example: loading a page — DNS resolves the domain to an IP, TCP opens a connection, an HTTP request is sent, the server's reply is split into packets that routers forward hop by hop, and the browser reassembles and renders them.
Infrastructure: ISPs, routers, and undersea/backbone fibre interconnect autonomous networks.

B. Internet Protocol (IP)

IP is the internet-layer protocol responsible for delivering packets from source to destination across networks.

Connectionless: each packet (datagram) is handled independently with no prior setup.
Best-effort: IP does not guarantee delivery, order, or freedom from duplication; reliability is left to TCP above it.
Datagram header: carries source and destination IP addresses, a Time To Live (TTL) that decrements at each router to kill looping packets, and a protocol field naming the upper layer.

C. IPv4 and IPv6 addressing

Two versions of IP addressing coexist today.

IPv4: a 32-bit address giving about 4.3 billion (2^32) addresses, written as four dotted decimal octets.

TEXT

192.168.1.10        # dotted-decimal, each octet 0–255

Divided into network and host portions using a subnet mask (e.g. /24 = 255.255.255.0).
Address exhaustion led to workarounds like NAT and private ranges (10.0.0.0/8, 192.168.0.0/16).

IPv6: a 128-bit address giving 2^128 addresses, written as eight groups of four hexadecimal digits.