Throughput
The actual amount of data transferred per unit of time. Unlike bandwidth (maximum capacity), throughput is what you really get after accounting for protocol overhead, congestion, and packet loss.
Full Explanation
Bandwidth is the size of the pipe. Throughput is how much water actually flows. A 10 Gbps link might only deliver 6 Gbps of actual data because of TCP overhead, congestion windows, packet retransmissions, and application-layer framing.
For CDN performance, throughput matters more than raw bandwidth. A CDN edge might have 100 Gbps of bandwidth but only deliver 70 Gbps of useful content. The gap comes from TLS encryption overhead (~2-5%), HTTP framing, TCP ACKs, and retransmissions on lossy connections.
Throughput is also affected by distance. TCP's congestion control starts slow (slow start) and ramps up over multiple RTTs. On a high-latency connection, it takes longer to fill the pipe. This is why CDN edges close to users achieve higher throughput even on identical bandwidth links.
Examples
# Measure throughput with curl
$ curl -o /dev/null -w 'Speed: %{speed_download} bytes/sec\n' https://cdn.example.com/bigfile.bin
Speed: 52428800 bytes/sec # ~50 MB/s = ~400 Mbps
# iperf3: measure raw throughput
$ iperf3 -c cdn-edge.example.com
[ ID] Interval Transfer Bitrate
[ 5] 0.00-10.00 1.09 GBytes 938 Mbits/sec
# Compare: bandwidth vs throughput
# Link bandwidth: 1 Gbps
# Measured throughput: 938 Mbps
# Overhead: ~6% (TCP/TLS/framing)Frequently Asked Questions
The actual amount of data transferred per unit of time. Unlike bandwidth (maximum capacity), throughput is what you really get after accounting for protocol overhead, congestion, and packet loss.
# Measure throughput with curl
$ curl -o /dev/null -w 'Speed: %{speed_download} bytes/sec\n' https://cdn.example.com/bigfile.bin
Speed: 52428800 bytes/sec # ~50 MB/s = ~400 Mbps
# iperf3: measure raw throughput
$ iperf3 -c cdn-edge.example.com
[ ID] Interval Transfer Bitrate
[ 5] 0.00-10.00 1.09 GBytes 938 Mbits/sec
# Compare: bandwidth vs throughput
# Link bandwidth: 1 Gbps
# Measured throughput: 938 Mbps
# Overhead: ~6% (TCP/TLS/framing)Related CDN concepts include:
- Bandwidth — The maximum data transfer rate of a network link, measured in bits per second (Mbps, …
- Latency — The time delay between a request and the start of its response. For CDNs, it's …
- RTT (Round-Trip Time) (RTT) — The time it takes for a packet to travel from client to server and back. …
- TCP (TCP) — Transmission Control Protocol. The reliable, ordered, connection-oriented transport protocol underneath HTTP/1.1 and HTTP/2. TCP's three-way …