Unit 1: Data communication fundamentals
Computer Networks notes · PTU syllabus (BSIT404/BSBC603)
On this page
- Unit summary
- Data communication and networks
- Digital and analog transmission
- Parallel and serial transmission
- Synchronous and asynchronous transmission
- Simplex, half-duplex and full-duplex communication
- Multiplexing: an introduction
- LAN, MAN and WAN
- Network topologies: bus, star, ring, mesh, tree and hybrid
- Wired communication channels
- Key terms
- Quick revision
- Important questions
Unit summary
Data communication moves bits reliably from one device to another. This unit covers digital and analog transmission, parallel and serial, synchronous and asynchronous modes, simplex, half-duplex and full-duplex communication, multiplexing, LAN, MAN and WAN, network topologies, and wired communication channels.
After this unit you can
- Distinguish digital and analog transmission
- Compare parallel, serial, synchronous and asynchronous transmission
- Explain communication modes, network types and topologies
- Compare wired transmission media
PTU syllabus topics
- Digital and analog transmission
- parallel/serial and synchronous/asynchronous modes
- simplex/half-duplex/full-duplex communication
- multiplexing
- LAN/MAN/WAN types
- network topologies (bus, star, ring, mesh, tree, hybrid)
- wired communication channels
Simplex
One way only
Keyboard to computer, TV broadcast
Half-duplex
Both ways, one at a time
Walkie-talkie
Full-duplex
Both ways at once
Telephone call
Topic 1
Data communication and networks
A computer network is a set of interconnected autonomous computers and devices that exchange data and share resources. Objectives: resource sharing (printers, files, internet), communication (email, chat), reliability (backups and alternatives), cost reduction and scalability. Components: end devices (computers, phones), network interface cards, transmission media (cables, wireless), networking devices (switches, routers) and protocols (rules for communication). Types by size: PAN (personal), LAN (building/campus), MAN (city) and WAN (country or world).
- 1Message
The data to be sent
- 2Sender
Device that sends
- 3Transmission medium
Cable or wireless path
- 4Receiver
Device that receives
- 5Protocol
Rules both sides follow
Topic 2
Digital and analog transmission
Form
Continuous wave
Discrete values (0 and 1)
Noise
Affected easily
More resistant
Example
Human voice, radio
Computer data
Conversion
Modem converts digital to analog and back
—
- Digital-to-digital (line coding)
- NRZ, Manchester — data on a LAN cable
- Analog-to-digital
- PCM sampling — voice in a mobile phone
- Digital-to-analog (modulation)
- ASK, FSK, PSK, QAM — modems
- Analog-to-analog
- AM, FM — radio broadcasting
Topic 3
Parallel and serial transmission
Bits sent
Several bits at once on separate wires
One bit at a time on one line
Speed over short distance
High
Lower per clock, but very fast links today
Cost and cabling
Many wires, expensive
Fewer wires, cheaper
Distance
Short (skew problems)
Long
Examples
Old printer port, internal buses
USB, SATA, Ethernet, PCIe lanes
Topic 4
Synchronous and asynchronous transmission
Unit
One character at a time with start and stop bits
Blocks or frames of data
Timing
No shared clock; gaps allowed between characters
Sender and receiver clocks synchronised
Overhead
High (2–3 extra bits per byte)
Low
Speed
Slower
Faster
Examples
Keyboard, RS-232 serial port
Ethernet, SONET, video streaming
- Isochronous transmission: data at a fixed, guaranteed rate for real-time audio and video.
Topic 5
Simplex, half-duplex and full-duplex communication
| Mode | Direction | Example |
|---|---|---|
| Simplex | One way only | Keyboard to computer, TV broadcast |
| Half-duplex | Both ways, one at a time | Walkie-talkie |
| Full-duplex | Both ways at the same time | Telephone call |
Topic 6
Multiplexing: an introduction
- Multiplexing lets several signals share one link, using a multiplexer (MUX) at the sender and a demultiplexer (DEMUX) at the receiver — making best use of expensive bandwidth. FDM, TDM and CDMA are covered in Unit 3.
Topic 7
LAN, MAN and WAN
LAN
Building or campus; privately owned
100 Mbps–10 Gbps; college computer lab
MAN
City; often a company or government
Moderate–high; cable TV network, city Wi-Fi
WAN
Country or world; telecom carriers
Lower per user, long delays; the internet, bank networks
- PAN covers a few metres (Bluetooth earphones); CAN (campus area network) connects buildings in one campus.
Topic 8
Network topologies: bus, star, ring, mesh, tree and hybrid
Physical topology is the actual layout of cables and devices; logical topology is how data actually flows.
Bus
Cheap, little cable
A cable break stops the network
Star
Easy to add devices and find faults
Hub/switch failure stops everything
Ring
Orderly access, no collisions
One break can stop the ring
Mesh
Highly reliable, many paths
Costly cabling: n(n − 1)/2 links
Hybrid
Flexible, combines strengths
Complex to design
Example
A full mesh of 5 devices needs 5 × 4 / 2 = 10 links.
- Tree topology: star networks connected in a hierarchy to a central backbone — easy to expand, but the backbone is a single point of failure.
Topic 9
Wired communication channels
Twisted pair (UTP, STP)
Pairs of insulated copper wires twisted to reduce interference
Telephone lines and Ethernet LANs (Cat 5e, Cat 6); cheap; up to 100 m
Coaxial cable
Central conductor, insulation, braided shield
Cable TV and broadband; better shielding than twisted pair
Optical fibre
Glass core and cladding carrying light by total internal reflection
Backbones, FTTH; very high bandwidth, immune to EMI, long distance
- Fibre types: single-mode (one ray, long distance) and multimode (many rays, shorter distance).
Key terms
- Data communication
- Exchange of data between devices over a medium
- Serial transmission
- Sending bits one after another on one line
- Asynchronous transmission
- Character-wise transmission with start and stop bits
- Topology
- Arrangement of devices and links in a network
- Optical fibre
- Glass medium carrying data as light
Quick revision
- Five components of data communication.
- Analog vs digital; line coding and modulation.
- Parallel vs serial; synchronous vs asynchronous.
- Simplex, half-duplex, full-duplex; LAN, MAN, WAN.
- Bus, star, ring, mesh, tree, hybrid; twisted pair, coaxial, fibre.
Important exam questions
Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).
Short-answer questions
- Q1.Distinguish analog and digital signals.
- Q2.Why is serial transmission preferred for long distances?
- Q3.What are start and stop bits?
- Q4.Give an example of half-duplex communication.
- Q5.How many links does a full mesh of 6 nodes need?
- Q6.State two advantages of optical fibre.
Long-answer questions
- Q1.Explain digital and analog transmission.
- Q2.Compare parallel and serial, and synchronous and asynchronous transmission.
- Q3.Explain network topologies with their merits and demerits.
- Q4.Explain wired communication media.
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