Understanding Types of Hubs and Their Operation

Types of Hubs

Passive Hubs

Passive hubs simply connect devices by propagating electrical signals without any modification. They neither amplify nor regenerate signals.

Example: Simple wire-based connectors used in older Ethernet networks.

Active Hubs

Active hubs amplify and regenerate incoming signals before broadcasting them to all ports, allowing signals to travel longer distances. These hubs require a power supply.

Example: Used to extend network segments beyond standard Ethernet distance limits.

Intelligent Hubs

Intelligent hubs include basic management functions such as SNMP monitoring. They can report traffic statistics or port status and are sometimes found in early managed environments.

Note: Intelligent hubs are rare in modern networks due to advances in switches.

Hub Operation

Broadcasting: Any data received on one port is rebroadcast to all other ports.
No Filtering: Hubs do not check MAC addresses; thus, all devices “hear” all transmissions, increasing unnecessary traffic.
Half-Duplex: Hubs cannot send and receive data simultaneously, which limits performance.

Hub vs. Switch

Feature	Hub	Switch
OSI Layer	Layer 1 (Physical)	Layer 2 (Data Link)
Traffic Handling	Broadcasts to all ports	Forwards only to destination MAC address
Collision Domain	All ports share a single collision domain	Each port has its own collision domain
Efficiency	Low (more collisions, shared bandwidth)	High (less collisions, dedicated bandwidth)

Example: In a hub-based network with 5 PCs, if two PCs transmit simultaneously, a collision occurs, forcing retransmissions and slowing the network. In a switch-based network, each port is isolated, preventing collisions.

Physical Characteristics of Hubs

Common port counts: 4, 8, 12, or 24 ports.
Speeds: Typically 10 Mbps (Ethernet); some support 100 Mbps (Fast Ethernet).
Use twisted-pair cables with RJ45 connectors.

Network Topologies Involving Hubs

Hubs are commonly used in star topologies physically but functionally behave like bus topologies because all devices share the same collision domain.

They have limited scalability due to high collision rates and low performance under load.

Advantages and Limitations of Hubs

Advantages	Limitations
Simple and easy to set up. Low cost compared to switches. No configuration required.	All ports share a single collision domain, leading to frequent collisions. Bandwidth is shared among all devices. No security or traffic filtering capabilities. Obsolete for most modern networks; replaced by switches.

Collision and Network Performance Issues

Hubs rely on CSMA/CD (Carrier Sense Multiple Access with Collision Detection) to manage access to the network medium.

As the number of connected devices and traffic increase, collisions become more frequent, leading to decreased throughput and network slowdown.

Example: If John’s PC and printer transmit data simultaneously through a hub, a collision occurs. Both devices must stop and retransmit later, resulting in slower communication.

Use Cases and Relevance Today

Legacy Networks: Present in older Ethernet installations.
Educational/Lab Environments: Useful for demonstrating collision domains and basic networking concepts.
Network Troubleshooting: Sometimes used for traffic sniffing since all packets are broadcasted to every port.

Despite these niche uses, hubs are not recommended for production networks today; switches offer better performance, security, and manageability.

Troubleshooting Hubs

No power to the hub can cause complete network failure.
Faulty ports may fail to broadcast signals.
Cabling issues such as bad cables or connectors.

Diagnostics:

Check LED indicators for activity and link status.
Use a cable tester to verify correct wiring and signal integrity.
Replace the hub if it fails to broadcast signals to all ports.

Key Points & Exam Tips

Hubs operate at OSI Layer 1 (Physical Layer) with no traffic filtering or intelligence.
All devices connected to a hub share the same collision domain, resulting in performance bottlenecks.
Understand the differences between hubs, switches, and routers.
Active hubs amplify signals; passive hubs do not.
Due to their limitations, hubs are largely obsolete and replaced by switches in modern networks.
Hubs increase the likelihood of network congestion and collisions.

Hub Quiz

1. At which OSI layer does a hub operate?

A. Layer 2 (Data Link) B. Layer 3 (Network) C. Layer 4 (Transport) D. Layer 1 (Physical)

Correct answer is D. Hubs operate at the Physical Layer (Layer 1), handling only electrical signals without any filtering.

2. What is the main difference between passive and active hubs?

A. Passive hubs amplify signals; active hubs do not B. Active hubs amplify and regenerate signals; passive hubs do not C. Passive hubs support management; active hubs do not D. Active hubs require no power supply; passive hubs do

Correct answer is B. Active hubs regenerate and amplify signals to extend transmission distance, requiring power, unlike passive hubs.

3. Which statement best describes the broadcasting behavior of a hub?

A. It rebroadcasts incoming data on one port to all other ports B. It forwards data only to the intended destination port C. It filters traffic based on MAC addresses D. It routes data between different networks

Correct answer is A. Hubs broadcast incoming signals to all ports, causing all devices to receive the data.

4. What is a major limitation of hubs compared to switches?

A. They provide better security B. They have multiple collision domains C. All ports share a single collision domain, increasing collisions D. They forward data based on IP addresses

Correct answer is C. Hubs have one collision domain, so simultaneous transmissions cause collisions and slow down the network.

5. Why are hubs considered obsolete in modern networks?

A. Because they require complex configuration B. Because they only work with fiber optic cables C. Because they are too expensive D. Because switches offer better performance, security, and management

Correct answer is D. Switches have replaced hubs due to their improved efficiency and security features.

6. What happens when two devices connected to a hub transmit data simultaneously?

A. A collision occurs, requiring retransmission B. Data is prioritized to avoid loss C. The hub switches to full-duplex mode D. The hub buffers the data and forwards sequentially

Correct answer is A. Collisions happen because hubs operate in half-duplex and broadcast all signals.

7. What type of cables do hubs typically use?

A. Coaxial cables B. Twisted-pair cables with RJ45 connectors C. Fiber optic cables only D. USB cables

Correct answer is B. Hubs commonly use twisted-pair cables with RJ45 connectors for Ethernet connections.

8. What is an intelligent hub?

A. A hub with advanced routing capabilities B. A hub with built-in firewall C. A wireless hub D. A hub with basic management features like SNMP monitoring

Correct answer is D. Intelligent hubs can monitor traffic and port status but are largely outdated.

9. In which network topology are hubs often used, despite their functional similarity to a bus?

A. Mesh topology B. Ring topology C. Star topology D. Hybrid topology

Correct answer is C. Hubs are used in star physical topology but behave like a bus logically.

10. Why might hubs still be used in educational or lab environments?

A. To demonstrate collision domains and basic network behavior B. Because they provide better performance than switches C. For secure communication D. To increase network bandwidth

Correct answer is A. Hubs are useful in labs to show how collisions occur and to teach network fundamentals.

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