Bandwidth, Throughput, and Goodput
Bandwidth is the theoretical maximum data transfer rate of a connection, measured in bits per second (bps). It is the capacity of the pipe — a 1 Gbps Ethernet interface has 1 Gbps of bandwidth regardless of actual traffic. Bandwidth is determined by the physical medium and technology standard, not by the amount of data currently flowing.
Throughput is the actual amount of data successfully transferred per unit of time, accounting for protocol overhead, retransmissions, and network conditions. Throughput is always less than or equal to bandwidth. If a 1 Gbps link achieves 800 Mbps throughput, overhead and inefficiency consume the remaining 200 Mbps.
Goodput (application-level throughput) is the useful application data transferred per second — throughput minus protocol headers, retransmissions, and acknowledgments. This is what users and applications actually experience. A VoIP call over a 100 Mbps link consumes about 87.2 kbps of goodput per call.
Latency and Jitter
Latency (delay) is the time it takes for data to travel from source to destination. Measured in milliseconds (ms). Sources of latency: propagation delay (speed of signal through medium), processing delay (router/switch decision time), queuing delay (waiting in buffers), serialization delay (time to transmit bits onto the wire). RTT (Round Trip Time) measures the full path: source → destination → source. Ping measures RTT.
Jitter is the variation in latency over time — inconsistent delay. Low latency with high jitter still causes problems for real-time applications. VoIP and video conferencing are sensitive to both latency and jitter. Acceptable VoIP latency: under 150ms one-way. Acceptable VoIP jitter: under 30ms.
Bandwidth-Related Concepts
Bottleneck: the slowest link in a path determines the maximum throughput. Even if a WAN link is 1 Gbps, if the access link is 100 Mbps, throughput is capped at 100 Mbps. Always check all links in the path when troubleshooting performance.
Full vs half duplex bandwidth: a 100 Mbps full-duplex link can transfer 100 Mbps simultaneously in each direction. A 100 Mbps half-duplex link shares 100 Mbps across all devices in both directions. Duplex directly impacts effective throughput.
Traffic shaping and QoS: bandwidth management techniques that prioritize certain traffic types (VoIP, video) over others (bulk file transfers, backups) to ensure critical applications receive consistent bandwidth and low latency. Network+ tests QoS concepts in both implementation and operations domains.