Call Setup Delay Calculator
Add up signalling hops, processing time and radio setup to get post-dial delay and check it against the ITU target.
About Call Setup Delay Calculator
Every proxy, border controller and application server in the path adds both propagation time and its own processing time, and both scale with the hop count. Radio bearer establishment and name resolution are one-off costs added on top. Users abandon calls that take more than a couple of seconds to ring, and each extra SBC or application server inserted 'just for policy' quietly spends hundreds of milliseconds of that budget.
Formula
Call Setup Delay
post-dial delay = hops × per-hop RTT + hops × per-element processing + radio bearer setup + DNS/ENUM resolution.
- hops
- Signalling elements the INVITE traverses
- per-hop RTT
- Round-trip network latency between adjacent elements
Worked example
With the default values below, Call Setup Delay Calculator returns Post-Dial Delay of 270. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Signalling hops end to endaccepts 1–40 hops
- 6 hops
- Round-trip latency per hopaccepts 0.1–500 ms
- 12 ms
- Processing time per network elementaccepts 0–500 ms
- 8 ms
- Radio bearer setup timeaccepts 0–3,000 ms
- 120 ms
- DNS/ENUM resolutionaccepts 0–2,000 ms
- 30 ms
- Target post-dial delayaccepts 100–20,000 ms
- 2,000 ms
Results
- Post-Dial Delay
- 270 ms
- Signalling Transport Time
- 72 ms
- Element Processing Time
- 48 ms
- Margin Against Target
- 1,730 ms
- Verdict
- Within target — 1730 ms of margin
Step by step
- 1Values used
- 2Call Setup Delay
- 3Post-Dial Delay= 270 ms
- 4Signalling Transport Time= 72 ms
- 5Element Processing Time= 48 ms
- 6Margin Against Target= 1,730 ms
- 7Verdict= Within target — 1730 ms of margin
Assumptions and limits
- The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Call Setup Delay calculated?
post-dial delay = hops × per-hop RTT + hops × per-element processing + radio bearer setup + DNS/ENUM resolution. Every proxy, border controller and application server in the path adds both propagation time and its own processing time, and both scale with the hop count. Radio bearer establishment and name resolution are one-off costs added on top.
Why does Call Setup Delay matter?
Users abandon calls that take more than a couple of seconds to ring, and each extra SBC or application server inserted 'just for policy' quietly spends hundreds of milliseconds of that budget.
What values do I need to enter?
This calculator takes 6 inputs: Signalling hops end to end, Round-trip latency per hop, Processing time per network element, Radio bearer setup time, DNS/ENUM resolution, Target post-dial delay. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.