Question

Suppose a 10-Mbps Ethernet hub (repeater) is replaced by a 10-Mbps switch, in an environment where all traffic is between a single server and \(N\) "clients." Because all traffic must still traverse the server-switch link, nominally there is no improvement in bandwidth. (a) Would you expect any improvement in bandwidth? If so, why? (b) What would your answer be if the original hub were token ring rather than Ethernet? (c) What other advantages and drawbacks might a switch offer versus a hub?

Short answer

(a) Yes, because a switch reduces collisions. (b) No significant improvement because token ring already minimizes collisions. (c) Switches offer better performance and manage collisions, but are more expensive and complex.

Step-by-step solution

- Understanding Bandwidth Improvement with a Switch

When a switch replaces a hub, collision domains are segmented. This means each client-server connection is its own collision domain, reducing collisions and improving efficiency. Therefore, even though the nominal bandwidth remains the same (10-Mbps), effective bandwidth utilization might improve.

- Comparing Hub and Token Ring

If the original hub operates on a token ring network, the scenario changes. Token ring is more efficient in collision handling as it uses token passing. Replacing it with a switch might not show significant improvements in bandwidth, as token ring already minimizes collisions better than Ethernet hubs.

- Evaluating Switch versus Hub

Switches have several advantages over hubs, including reduced collisions, better bandwidth management, and the ability to handle full-duplex communication. Drawbacks might include higher cost and increased complexity in network setup and maintenance.

Key concepts

collision domains

In a network, a collision domain is a segment where data packets can collide with each other when being sent on a shared medium. When multiple devices send data simultaneously, collisions occur, causing data to be resent and leading to inefficiency. Hubs connect all devices into a single collision domain, increasing the likelihood of collisions. However, switches operate differently. Instead of broadcasting data to all ports, a switch creates a unique collision domain for each connected device, allowing data to pass through without interference. This segmentation significantly reduces collisions and enhances network performance. Therefore, even with the same nominal bandwidth, using a switch can improve the effective utilization due to reduced collisions.

Ethernet switch

An Ethernet switch is a network device that channels data frames between devices by using MAC addresses to forward data only to the specific port it is intended for. This targeted traffic flow provides several benefits over hubs, which broadcast data to all ports indiscriminately. Here are some key points about Ethernet switches:

• **Collision Reduction:** By assigning individual collision domains, an Ethernet switch minimizes data collisions, leading to more effective bandwidth utilization.
• **Full-Duplex Communication:** Switches allow full-duplex communication, meaning data can be sent and received simultaneously, doubling the potential communication capacity.
• **Efficient Bandwidth Allocation:** Switches manage bandwidth more effectively, as each port on a switch can handle its own dedicated bandwidth without interference from other devices.

In conclusion, an Ethernet switch is more efficient than a hub, especially in reducing collisions and managing network traffic.

token ring network

Token ring networks operate differently from Ethernet networks by using a token-passing mechanism to control data transmission. In a token ring network, a token circulates around the network, and only the device holding the token can send data. This method inherently avoids collisions, as it ensures that only one device transmits at a time. Here is why a token ring network is collision-free:

• **Token Control:** The token ensures that only one device can send data at a time, eliminating the possibility of collisions.
• **Predictable Performance:** Network performance is predictable, as devices must wait for the token to send data, avoiding random access delays.

If a hub in a token ring network is replaced by a switch, the improvement in bandwidth might not be as substantial as in an Ethernet network, because token ring networks already manage collisions effectively.

bandwidth utilization

Bandwidth utilization refers to how effectively the available bandwidth is used in a network. Higher utilization means more efficient use of the available capacity, leading to better network performance. Here are some factors affecting bandwidth utilization:

• **Collision Reduction:** As mentioned, reducing collisions through devices like switches can significantly improve utilization.
• **Full-Duplex Communication:** Utilizing full-duplex communication, where devices can send and receive data simultaneously, also enhances bandwidth efficiency.
• **Traffic Management:** Proper traffic management ensures data is directed efficiently, minimizing delays and congestion.

Replacing a hub with a switch can improve bandwidth utilization by reducing collisions, enabling full-duplex communication, and better managing network traffic. This leads to more efficient use of the 10-Mbps bandwidth, improving overall network performance.