Problem 12 - Computer Networks: Global Edition

Question

Consider five wireless stations, \(A, B, C, D\), and \(E\), Station \(A\) can communicate with all other stations. B can communicate with A, C and E. C can communicate with A.B and D. D can communicate with \(A, C\) and \(E\). E can communicate \(A\), D and B. (a) When \(A\) is sending to \(\mathrm{B}\), what other communications are possible? (b) When IB is sending to A what other communications are possible? (c) When \(\mathrm{B}\) is sendiag to \(\mathrm{C}\), what other coenmunications are possible?

Step-by-Step Solution

Answer

(a) C ↔ D, D ↔ E. (b) C ↔ D, D ↔ E. (c) D ↔ E.

Step 1: Understanding Station Communication Possibilities

We need to interpret which stations can communicate with each other based on the given information: 1. Station A communicates with B, C, D, and E. 2. B communicates with A, C, and E. 3. C communicates with A, B, and D. 4. D communicates with A, C, and E. 5. E communicates with A, D, and B.

Step 2: Analyzing when A is communicating with B

Since A is communicating with B, both A and B are occupied. Thus, any communication from or to either A or B cannot occur simultaneously with A sending to B. Possible communications: - C can communicate with D (since neither C nor D involves A or B exclusively). - D can communicate with E (as D → E communication does not depend on A or B). Other than these, no other communications are possible.

Step 3: Analyzing when B is sending to A

When B is sending to A, both are occupied. Hence, communications involving A or B are blocked: Possible communications: - C can communicate with D (since this does not involve A or B). - D can communicate with E. All other direct communications are not possible.

Step 4: Analyzing when B is sending to C

During B sending to C, both B and C are occupied. Communications that do not involve B or C can occur: Possible communications: - D can communicate with E (as this communication does not include B or C). Therefore, only D and E can communicate when B → C is occurring.

Key Concepts

Station Communication

In wireless networks, station communication refers to the ability of different nodes (or stations) to exchange data directly. This involves understanding which stations can effectively communicate with each other based on their range and connectivity.

In the example provided with stations A, B, C, D, and E, each has specific stations they can directly communicate with:

• Station A is particularly powerful, able to communicate with all other stations: B, C, D, and E. This makes A a central communication hub in this network.
• Station B can communicate with A, C, and E, implying it's somewhat less central but connects multiple nodes.
• Station C has connections with A, B, and D, providing a bridge between some stations.
• Station D connects with A, C, and E, making it versatile in its connectivity.
• Station E can communicate with A, D, and B, providing end-to-end connectivity without being directly connected to C.

It is essential to understand these pathways, as they dictate how information can travel across the network, impacting efficiency and latency.

Simultaneous Communication

Simultaneous communication in wireless networks occurs when multiple data streams are exchanged at the same time, provided that they do not interfere with each other.

When station A is sending a message to station B, both stations are occupied:

• This means that other communications cannot involve A or B simultaneously.
• Stations C and D, however, can communicate since they are not using A or B as part of their communication channel.
• Similarly, stations D and E can also communicate in this scenario, as they do not rely on A and B for the communication pathway.

This separation helps manage bandwidth and reduces data collision chances, improving network efficiency.

Network Analysis

Analyzing a network's communication possibilities involves understanding limitations and opportunities for data transfer to maximize efficiency.

When examining the network in different sending scenarios (e.g., B sending to A), key observations are:

• If B sends to A, both are occupied, blocking any data transfer involving these stations.
• Thus, unaffected paths like C-D and D-E become potential communication channels, offering alternative routes for data flow.

Moreover, when examining B sending to C, other paths such as D-E become open, as B-C communication does not affect these paths. Through network analysis, users can understand:

• Conflicting and non-conflicting paths
• Potential bottlenecks and optimal routes

Such analysis helps design more efficient networks, ensuring robust communication and reduced risk of congestion.