Chapter 10 — Introduction to Computer Networks: Exercise Solutions Guide
How to Use This Page
1. Attempt every exercise on your own before reading the solutions. 2. Compare your method with the answer shown — focus on the concept, not just memorising terms. 3. Draw diagrams (topologies, OSI layers) by hand — the exam often includes diagram-based questions.
Key Concepts (Quick Recap)
- A computer network is a group of interconnected computers that share data, resources, and communication.
- LAN (Local Area Network) — covers a small area (room, building, campus); high speed, low cost.
- MAN (Metropolitan Area Network) — covers a city or town; connects multiple LANs.
- WAN (Wide Area Network) — covers a large geographic area (countries, continents); uses public or leased lines.
- PAN (Personal Area Network) — connects devices within an individual's reach (Bluetooth, USB).
- Topology — the arrangement/layout of nodes and connections in a network.
- Star topology — all devices connect to a central hub/switch; failure of one device doesn't affect others.
- Bus topology — all devices share a single cable (bus); failure of the backbone cable affects all.
- Ring topology — devices form a circular loop; data travels in one direction; one node failure can disrupt the network.
- Mesh topology — every device connects to every other device; high redundancy, expensive.
- OSI Model — 7 layers: Physical, Data Link, Network, Transport, Session, Presentation, Application.
- TCP/IP Model — 4 layers: Network Access, Internet, Transport, Application.
- Network devices — Hub (broadcasts to all), Switch (directs to specific device), Router (connects different networks), Gateway (translates between different network architectures).
I. Choose the Best Answer (MCQs)
1. Which type of network covers the largest geographical area?
Answer
(a) PAN (b) LAN (c) MAN (d) WAN
Answer(d) WAN
Explanation: WAN (Wide Area Network) spans countries or continents, making it the largest in geographical coverage. LAN is limited to a building, and MAN to a city.
2. In which topology do all devices connect to a single central device?
Answer
(a) Bus (b) Ring (c) Star (d) Mesh
Answer(c) Star
Explanation: In star topology, each device has a dedicated connection to a central hub or switch. If one cable fails, only that device is affected.
3. Which OSI layer is responsible for routing?
Answer
(a) Physical (b) Data Link (c) Network (d) Transport
Answer(c) Network
Explanation: The Network layer (Layer 3) handles logical addressing (IP addresses) and routing packets across networks using routers.
4. A hub sends data to:
Answer
(a) Only the intended recipient (b) All connected devices (c) Devices in the same subnet (d) The router only
Answer(b) All connected devices
Explanation: A hub is a dumb device that broadcasts every frame to all ports. A switch, in contrast, sends data only to the intended device.
5. Which topology uses a single backbone cable?
Answer
(a) Star (b) Bus (c) Ring (d) Mesh
Answer(b) Bus
Explanation: In bus topology, all devices tap into a single central cable (backbone). If the backbone fails, the entire network goes down.
6. The Transport layer of the OSI model operates at layer number:
Answer
(a) 2 (b) 3 (c) 4 (d) 7
Answer(c) 4
Explanation: The 7 layers from bottom to top are: 1-Physical, 2-Data Link, 3-Network, 4-Transport, 5-Session, 6-Presentation, 7-Application.
7. Which device connects two different networks and uses IP addresses for forwarding?
Answer
(a) Hub (b) Switch (c) Router (d) Repeater
Answer(c) Router
Explanation: A router operates at the Network layer and uses IP addresses to determine the best path for forwarding packets between different networks.
8. In a ring topology, if one node fails, what happens?
Answer
(a) Network continues normally (b) Only that node is affected (c) The entire network may be disrupted (d) Data speeds increase
Answer(c) The entire network may be disrupted
Explanation: In a basic ring, data passes through each node. If one node fails, the ring is broken and communication stops. Dual ring topologies provide redundancy.
9. Which TCP/IP layer corresponds to the OSI Session, Presentation, and Application layers?
Answer
(a) Network Access (b) Internet (c) Transport (d) Application
Answer(d) Application
Explanation: The TCP/IP Application layer combines the functions of the top three OSI layers (Session, Presentation, Application).
10. A switch operates at which OSI layer?
Answer
(a) Physical (b) Data Link (c) Network (d) Transport
Answer(b) Data Link
Explanation: A switch operates at Layer 2 (Data Link) and uses MAC addresses to forward frames to the correct device. (Some managed switches also work at Layer 3.)
II. Fill in the Blanks
1. A LAN (Local Area Network) covers a small geographical area such as a room, building, or campus.
2. The star topology connects all devices to a central hub or switch.
3. The Network layer of the OSI model is responsible for routing packets across networks.
4. A router connects two or more different networks and forwards data packets based on IP addresses.
5. In bus topology, all devices share a single communication cable.
6. The TCP/IP model has 4 layers.
7. The Physical layer (Layer 1) deals with the transmission of raw bits over a medium.
8. A hub broadcasts data to all connected devices, while a switch sends data only to the intended device.
9. MAN stands for Metropolitan Area Network and covers a city-sized area.
10. In mesh topology, every device is connected to every other device, providing maximum redundancy.
III. True or False
1. A LAN typically covers a city. — False. A LAN covers a small area like a building or campus. A MAN covers a city.
2. In star topology, failure of the central device brings down the entire network. — True. The central hub/switch is a single point of failure.
3. The OSI model has 7 layers. — True. Physical, Data Link, Network, Transport, Session, Presentation, Application.
4. A switch uses IP addresses to forward data. — False. A switch uses MAC addresses (Data Link layer). Routers use IP addresses (Network layer).
5. A gateway can connect networks with different architectures. — True. A gateway translates between different protocol suites, acting as an interpreter.
6. In bus topology, adding a new device requires reconfiguring the entire network. — False. Bus topology makes it easy to add devices by tapping into the backbone cable.
7. The Transport layer ensures reliable data delivery through error checking and flow control. — True. TCP at the Transport layer provides reliable, ordered delivery.
8. TCP/IP model's Internet layer corresponds to the OSI Network layer. — True. Both handle addressing and routing.
9. A repeater operates at the Network layer. — False. A repeater operates at the Physical layer; it amplifies and regenerates signals.
10. Mesh topology is the most cost-effective for large networks. — False. Mesh is the most expensive due to the large number of connections required (n(n-1)/2 links for n nodes).
IV. Match the Following
Set A
| No. | Column A | No. | Column B |
|---|
| 1 | LAN | d | Small area (building/campus) |
| 2 | MAN | e | City-sized area |
| 3 | WAN | a | Large geographic area |
| 4 | PAN | c | Personal area (Bluetooth) |
| 5 | VPN | b | Secure tunnel over public network |
Set B
| No. | Column A | No. | Column B |
|---|
| 1 | Hub | d | Broadcasts to all devices |
| 2 | Switch | e | Forwards using MAC addresses |
| 3 | Router | a | Forwards using IP addresses |
| 4 | Gateway | c | Translates between protocols |
| 5 | Repeater | b | Amplifies signals (Physical layer) |
V. Short Answer Questions
1. Differentiate between LAN, MAN, and WAN.
Answer
| Feature | LAN | MAN | WAN |
|---|
| Full form | Local Area Network | Metropolitan Area Network | Wide Area Network |
| Coverage | Room/building/campus | City/town | Country/continent |
| Speed | High (100 Mbps–10 Gbps) | Moderate | Low to moderate |
| Cost | Low | Moderate | High |
| Ownership | Private | Private or public | Usually public/ISP |
| Error rate | Low | Moderate | Higher |
| Example | Office network, school lab | Cable TV network, city WiFi | Internet |
2. Explain star topology with advantages and disadvantages.
Answer
In star topology, all devices connect to a central hub or switch via separate cables.
Advantages:
- Easy to install and manage.
- If one cable fails, only that device is affected.
- Adding or removing devices is simple.
- Fault detection is easy.
Disadvantages:
- If the central hub/switch fails, the entire network goes down.
- Requires more cable than bus topology.
- The central device is a single point of failure.
3. List the seven layers of the OSI model from bottom to top.
Answer
| Layer | Name | Function |
|---|
| 7 | Application | Network services to applications (HTTP, FTP, SMTP) |
| 6 | Presentation | Data formatting, encryption, compression |
| 5 | Session | Establishes, manages, and terminates sessions |
| 4 | Transport | Reliable data delivery, error checking (TCP, UDP) |
| 3 | Network | Routing and logical addressing (IP) |
| 2 | Data Link | Framing, MAC addressing, error detection |
| 1 | Physical | Transmission of raw bits over medium (cables, signals) |
4. What is the difference between a hub and a switch?
Answer
| Feature | Hub | Switch |
|---|
| Layer | Physical (Layer 1) | Data Link (Layer 2) |
| Operation | Broadcasts to all ports | Forwards to specific port |
| Addressing | None (no intelligence) | Uses MAC addresses |
| Collision | High (single collision domain) | Low (separate collision domains per port) |
| Performance | Lower (bandwidth shared) | Higher (dedicated bandwidth) |
| Cost | Cheaper | More expensive |
| Security | Low (all data sent everywhere) | Higher (data sent only to recipient) |
5. Explain bus topology with a diagram description.
Answer
In bus topology, all devices connect to a single central cable called the backbone or bus. Terminators at both ends prevent signal reflection.
How it works:
- A device sends a signal along the backbone.
- The signal travels in both directions to all devices.
- Only the intended recipient processes the data.
- Other devices ignore it.
Advantages: Easy to install, requires less cable, low cost. Disadvantages: Backbone failure brings down the entire network, performance degrades with more devices, difficult to troubleshoot.
6. Compare the OSI model and TCP/IP model.
Answer
| Feature | OSI Model | TCP/IP Model |
|---|
| Layers | 7 | 4 |
| Approach | Theoretical/reference model | Practical/implementation model |
| Top layer | Application | Application (combines Session + Presentation + Application) |
| Transport | Transport | Transport |
| Network | Network | Internet |
| Lower layers | Data Link + Physical | Network Access (combines both) |
| Developed by | ISO | DARPA (US Dept. of Defense) |
| Protocol-specific | No (generic) | Yes (built around TCP/IP) |
VI. Detailed Answer Questions
1. Explain all four network topologies — star, bus, ring, and mesh — with advantages and disadvantages.
Answer
Star Topology: All devices connect to a central hub or switch.
- Advantages: Easy to install/manage, one device failure doesn't affect others.
- Disadvantages: Central device failure brings down the whole network; more cable needed.
Bus Topology: All devices connect to a single backbone cable with terminators at both ends.
- Advantages: Easy to install, requires least cable, inexpensive.
- Disadvantages: Backbone failure disables the entire network; performance degrades with more devices; difficult to troubleshoot.
Ring Topology: Devices form a closed loop; data travels in one direction (or both in dual ring).
- Advantages: No collisions, orderly data transfer, equal access to all devices.
- Disadvantages: One device failure can disrupt the network; adding/removing devices is difficult; slower than star.
Mesh Topology: Every device connects to every other device (full mesh) or to multiple devices (partial mesh).
- Advantages: High redundancy — multiple paths for data; reliable; no single point of failure.
- Disadvantages: Very expensive; complex to install; requires many cables (n(n-1)/2 connections for n nodes).
2. Describe the OSI model with the function of each layer.
Answer
The OSI (Open Systems Interconnection) model is a 7-layer reference model that standardises network communication.
Layer 1 — Physical Layer:
- Transmits raw bits over a physical medium (cables, wireless signals).
- Deals with voltage levels, data rates, and physical connectors.
- Devices: hubs, repeaters, cables.
Layer 2 — Data Link Layer:
- Provides error-free transfer of frames between two directly connected nodes.
- Handles MAC addressing, framing, and error detection.
- Devices: switches, bridges.
Layer 3 — Network Layer:
- Handles routing and forwarding of packets across networks.
- Provides logical addressing (IP addresses).
- Devices: routers.
Layer 4 — Transport Layer:
- Ensures reliable end-to-end data delivery.
- Protocols: TCP (reliable, connection-oriented), UDP (fast, connectionless).
- Handles flow control and error recovery.
Layer 5 — Session Layer:
- Establishes, manages, and terminates communication sessions.
- Handles session checkpoints and recovery.
Layer 6 — Presentation Layer:
- Translates data formats between applications.
- Handles encryption, decryption, compression, and data formatting.
Layer 7 — Application Layer:
- Provides network services directly to user applications.
- Protocols: HTTP, FTP, SMTP, DNS, Telnet.
3. Explain the TCP/IP model and compare it with the OSI model.
Answer
The TCP/IP model has 4 layers:
Network Access Layer (combines OSI Physical + Data Link):
- Handles hardware, physical addressing, and local network delivery.
- Protocols: Ethernet, Wi-Fi, ARP.
Internet Layer (corresponds to OSI Network):
- Handles logical addressing and routing.
- Protocols: IP, ICMP.
Transport Layer (corresponds to OSI Transport):
- Provides end-to-end communication.
- Protocols: TCP (reliable), UDP (fast).
Application Layer (combines OSI Session + Presentation + Application):
- Provides user-level network services.
- Protocols: HTTP, FTP, SMTP, DNS, SSH.
Comparison:
| OSI Model | TCP/IP Model |
|---|
| Application | Application |
| Presentation | Application |
| Session | Application |
| Transport | Transport |
| Network | Internet |
| Data Link | Network Access |
| Physical | Network Access |
Key differences:
- OSI is a theoretical reference model; TCP/IP is a practical implementation.
- OSI has 7 layers; TCP/IP has 4 layers.
- OSI developed the model first, then protocols; TCP/IP developed protocols first.
- OSI is protocol-independent; TCP/IP is built around the TCP/IP protocol suite.
4. Explain the functions of network devices: hub, switch, router, and gateway.
Answer
Hub:
- Operates at Layer 1 (Physical).
- Broadcasts every incoming frame to all connected devices.
- No intelligence — cannot filter traffic.
- Creates a single collision domain.
- Cheap but inefficient for larger networks.
Switch:
- Operates at Layer 2 (Data Link).
- Uses MAC addresses to forward frames only to the intended port.
- Creates separate collision domains per port.
- More efficient than a hub — reduces unnecessary traffic.
- Builds a MAC address table to learn which device is on which port.
Router:
- Operates at Layer 3 (Network).
- Connects different networks and routes packets between them.
- Uses IP addresses to determine the best path.
- Can perform NAT, firewall filtering, and traffic management.
- Essential for Internet connectivity.
Gateway:
- Operates at multiple layers (typically Application layer).
- Translates between different network architectures or protocols.
- Acts as the entry/exit point of a network.
- Example: an email gateway translating between different email protocols.
- Most complex and expensive network device.
5. Write a note on PAN (Personal Area Network) and VPN (Virtual Private Network).
Answer
PAN — Personal Area Network:
- Covers a very small area (typically within 10 metres).
- Connects personal devices like phones, laptops, tablets, and peripherals.
- Technologies: Bluetooth, Infrared, USB.
- Can be wired (USB) or wireless (Bluetooth).
- Example: connecting wireless headphones to a phone, or a smartwatch to a laptop.
VPN — Virtual Private Network:
- Creates a secure, encrypted tunnel over a public network (Internet).
- Allows remote users to access a private network securely.
- Encrypts all data between the user and the VPN server.
- Types: Remote Access VPN (individual users), Site-to-Site VPN (connecting offices).
- Uses protocols like IPSec, SSL/TLS, PPTP, L2TP.
- Benefits: security, privacy, bypassing geo-restrictions, remote access.
Common Mistakes
1. Confusing LAN, MAN, and WAN boundaries — LAN is within a building/campus, MAN is city-sized, and WAN spans countries. Don't mix them up.
2. Mixing up hub and switch — A hub broadcasts to all (Layer 1); a switch uses MAC addresses to target specific devices (Layer 2).
3. Forgetting the OSI layer order — Remember: "Please Do Not Throw Sausage Pizza Away" (Physical, Data Link, Network, Transport, Session, Presentation, Application) — from bottom to top.
4. Confusing router and gateway — A router connects networks using IP; a gateway translates between different protocol architectures. All gateways are routers but not all routers are gateways.
5. Stating that ring topology is fault-tolerant — A basic ring is vulnerable to single node failure. Only a dual-ring or token ring with bypass is more resilient.
6. Mixing up OSI and TCP/IP layer numbering — OSI Transport is Layer 4, not Layer 2. TCP/IP has only 4 layers, so its Transport is Layer 3 (counting from bottom).
7. Saying bus topology has no disadvantages — Bus topology has serious limitations: single point of failure (backbone), performance degrades with more nodes, and difficult troubleshooting.
Exam Checklist
- [ ] Can define computer network and state its purpose
- [ ] Can differentiate LAN, MAN, WAN (area, speed, cost, examples)
- [ ] Can explain star, bus, ring, and mesh topologies with pros and cons
- [ ] Can list all 7 OSI layers with functions and protocols
- [ ] Can list all 4 TCP/IP layers and map them to OSI layers
- [ ] Can compare OSI and TCP/IP models
- [ ] Can explain hub, switch, router, and gateway with the layer they operate on
- [ ] Can draw topology diagrams (star, bus, ring, mesh)
- [ ] Can describe PAN and VPN with examples
- [ ] Can answer comparison questions (hub vs switch, OSI vs TCP/IP, LAN vs WAN)
