What Is Throughput?
Throughput — the actual amount of data successfully transferred per second — what you really get, as opposed to bandwidth, which is what the link is rated for.
How it works
Throughput is always at or below bandwidth. Protocol overhead (headers, acknowledgments), retransmissions, congestion and the weakest link in the path all shave it down. A 100 Mbps link commonly delivers 90-something Mbps of useful TCP throughput under good conditions.
Why it matters
When users say "the network is slow," engineers verify throughput (speed tests, interface counters) against expected bandwidth and then hunt the bottleneck — duplex mismatches, saturated uplinks, errors. The bandwidth/throughput/latency trio is core CCNA vocabulary.
Frequently asked questions
What is the difference between bandwidth and throughput?
Bandwidth is the rated capacity; throughput is the real, measured transfer rate after overhead and congestion.
Why is my throughput lower than my bandwidth?
Header overhead, acknowledgments, retransmissions, congestion and slower devices along the path all reduce it.
How is throughput measured?
With transfer or speed tests, or by reading interface traffic counters over time.
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