Network Latency Budget Calculator

Frequently Asked Questions

Why is the speed of light in fiber slower than in vacuum?

Glass has a refractive index of ~1.5, so light travels at about 2/3 of vacuum speed (roughly 200,000 km/s). This is a fundamental physical property that cannot be engineered away, only minimized by routing more directly.

What is a reasonable per-hop processing delay?

Modern routers process packets in 0.05-0.2 ms under normal conditions. 0.5 ms is a conservative planning number that accounts for typical enterprise and carrier routers including some queuing.

Why do trading firms pay millions for dedicated fiber?

Microseconds matter for high-frequency trading. A dedicated straight-line fiber path cuts RTT by 1-2 ms versus public internet paths, which compounds across millions of daily transactions.

Is this calculator suitable for satellite link planning?

For GEO satellites the RTT is around 600 ms. For LEO constellations like Starlink at 550-600 km altitude, one-way propagation is 3-5 ms. Enter the actual distance and hop count for your specific architecture.

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Estimates for informational purposes only.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How It Works

End-to-end latency is the sum of three independent components. Propagation delay is distance divided by signal speed: light in fiber travels about 200 km/ms (~5 microseconds/km), copper approximately 182 km/ms, and free-space radio near the speed of light at ~300 km/ms. Processing and queuing delay is the per-hop delay each router adds, multiplied by the hop count. Serialization delay is the time to clock the packet onto the wire: (packet bits) divided by (link bits per second), incurred at each hop.

One-way latency is the sum of all three components. Round-trip time (RTT) is approximately twice the one-way latency, which is what ping and TCP handshakes actually measure. Note that distance dominates on long-haul paths: serialization on fast links is nearly negligible, which is why physics, not bandwidth, sets the floor for intercontinental latency.

Use Cases

Network architects and application designers use this calculator to:

Determine where to place database replicas, CDN edge nodes, or application servers to meet latency SLAs for a given user population.

Justify the cost of a lower-latency path (direct fiber vs. multi-hop transit) by quantifying the exact latency savings.

Calculate the maximum sustainable distance for synchronous database replication given a write-commit latency budget.

Design VoIP and real-time gaming infrastructure by confirming RTT budgets stay under 150 ms for acceptable quality.

Identify whether a slow application path is a physics problem (must move closer) or a congestion problem (must add capacity).

Tips

Use 200 km/ms for fiber, not 300 - fiber carries light at roughly 67% of the speed of light in vacuum due to refractive index; using 300 km/ms will make your estimates optimistic by 50%.

Always double one-way for RTT - applications wait on round-trip time; a one-way estimate is useless for planning TCP, HTTP, or RPC behavior.

Measure actual RTT under load with ping or iperf - per-hop queuing delay balloons under congestion; this calculator models nominal, uncongested conditions.

Actual fiber routes are longer than great-circle distance - cables follow coastlines and rights-of-way; add 30-50% to great-circle distance for realistic terrestrial fiber estimates.

Serialization matters most on slow links - a 64-byte packet on a 1 Mbps link takes 0.5 ms; on 1 Gbps it is 0.0005 ms; only slow or saturated links have meaningful serialization delay.

FAQ

Why is the speed of light in fiber slower than in vacuum?

Glass has a refractive index of approximately 1.5, which means light travels through it at about 2/3 of its vacuum speed (roughly 200,000 km/s in fiber vs 299,792 km/s in vacuum). This is a fundamental physical property of the medium that cannot be engineered around, only minimized by routing more directly.

What is a reasonable per-hop processing delay to use?

Modern high-performance routers process packets in 50-200 microseconds (0.05-0.2 ms) under normal conditions. 0.5 ms is a conservative but realistic number for planning that accounts for typical enterprise and carrier routers including some queuing. Congested links can add tens of milliseconds of queuing delay.

Why do trading firms pay millions for dedicated fiber?

For high-frequency trading, microseconds matter. A dedicated straight-line fiber path between Chicago and New York cuts the RTT to around 13 ms versus 14+ ms on public internet paths due to more direct routing. That 1 ms advantage compounds across millions of transactions per day.

Is this calculator suitable for satellite link planning?

For geostationary satellites (GEO), the one-way propagation to the satellite and back is about 600 ms each way, giving an RTT of around 600 ms plus ground processing. Low-Earth orbit (LEO) constellations like Starlink have altitudes of 550-600 km and one-way propagation of about 3-5 ms, but routing through multiple LEO hops adds more. Enter the actual distance and hop count for the specific LEO architecture.

Network Latency Budget Calculator

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