Ethernet scaling behavior: As the number of nodes on a shared Ethernet segment increases, why does overall efficiency decrease in such environments?

Introduction / Context: Legacy shared-media Ethernet (using hubs or coax bus) relies on CSMA/CD (Carrier Sense Multiple Access with Collision Detection). On a shared segment, only one device can successfully transmit at a time. As more stations contend for the channel, collisions increase and net throughput declines.

Given Data / Assumptions:

• Scenario is a shared segment (not modern switched full-duplex per-port).
• Multiple hosts attempt to transmit frames over the same medium.
• CSMA/CD backoff determines retransmission timing after collisions.

Concept / Approach: In CSMA/CD, stations listen before transmitting, but simultaneous sensing or propagation delays mean two stations can still start at nearly the same time, causing a collision. Each collision wastes medium time for jam/abort plus exponential backoff, which grows with congestion, reducing effective throughput as station count and load rise.

Step-by-Step Solution:

Verification / Alternative check: Measurements on busy shared segments show rising collision rates and increasing backoff intervals, aligning with queueing and contention models that predict decreasing throughput at high loads.

Why Other Options Are Wrong:

Common Pitfalls: Applying this logic to switched full-duplex Ethernet (no collisions); assuming signal strength fixes contention; ignoring propagation delay impact on collision windows.

Final Answer: Network collisions occur.