Unit 2: Data transmission and networking devices
Computer Networks-I notes · PTU syllabus (UGCC2517)
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Unit summary
Data travels across networks as signals, and devices such as hubs, switches and routers direct it. This unit covers analog and digital signals, transmission modes, bandwidth and latency, and the functions and configuration of networking devices.
After this unit you can
- Distinguish analog and digital signals
- Explain simplex, half-duplex and full-duplex modes
- Define bandwidth, throughput and latency
- Explain the working of hubs, switches, bridges, routers and gateways
PTU syllabus topics
- Analog vs digital signals
- transmission modes (simplex, half-duplex, full-duplex)
- bandwidth and latency
- routers
- switches
- hubs
- bridges
- gateways — functions and configuration
Hub
Layer 1
Repeats signals to every port
Switch
Layer 2
Forwards frames using MAC addresses
Router
Layer 3
Routes packets between networks using IP
Topic 1
Analog and digital signals
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
—
Topic 2
Transmission modes
| 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 3
Bandwidth and latency
- Bandwidth: the maximum data rate of a link, measured in bits per second (bps, Mbps, Gbps).
- Throughput: the actual data rate achieved.
- Latency (delay): time for data to travel from source to destination = propagation + transmission + queuing + processing delay.
- Jitter: variation in delay — harmful to voice and video calls.
Example
Transmission delay = packet size / bandwidth. A 1,000,000-bit file on a 10 Mbps link takes 0.1 seconds to transmit.
Topic 4
Networking devices
Hub
Physical
Repeats incoming data to all ports
Repeater
Physical
Regenerates weak signals
Bridge
Data link
Connects two LAN segments and filters by MAC
Switch
Data link
Sends frames only to the destination port using a MAC table
Router
Network
Forwards packets between networks using IP addresses
Gateway
All layers
Connects networks using different protocols
Basic configuration: a switch learns MAC addresses automatically; a router is configured with IP addresses on its interfaces, a default gateway and routing (static or dynamic, such as RIP or OSPF).
Exam tip
A hub creates one collision domain for all ports; a switch gives each port its own collision domain; a router separates broadcast domains.
Key terms
- Bandwidth
- Maximum data rate of a link
- Latency
- Time taken for data to travel across a network
- Full-duplex
- Two-way simultaneous transmission
- Switch
- A device forwarding frames by MAC address
- Router
- A device forwarding packets between networks by IP address
Quick revision
- Analog = continuous; digital = discrete.
- Simplex one-way; half-duplex alternating; full-duplex simultaneous.
- Hub (L1) broadcasts; switch (L2) uses MAC; router (L3) uses IP.
- Transmission delay = size / bandwidth.
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.Differentiate between analog and digital signals.
- Q2.Give one example each of simplex, half-duplex and full-duplex.
- Q3.Define bandwidth and latency.
- Q4.Differentiate between a hub and a switch.
- Q5.What is a gateway?
Long-answer questions
- Q1.Explain transmission modes and the factors affecting latency.
- Q2.Explain the working of hubs, switches, bridges, routers and gateways with their OSI layers.
- Q3.Compare switching and routing and explain how a switch learns MAC addresses.
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