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.
Inputs
Post-Dial Delay
270ms
Signalling Transport Time
72ms
Element Processing Time
48ms
Margin Against Target
1,730ms
Verdict
Within target — 1730 ms of margin
Step by step
Values used
Signalling hops end to end = 6 hops; Round-trip latency per hop = 12 ms; Processing time per network element = 8 ms; Radio bearer setup time = 120 ms; DNS/ENUM resolution = 30 ms; Target post-dial delay = 2,000 ms
Call Setup Delay
post-dial delay = hops × per-hop RTT + hops × per-element processing + radio bearer setup + DNS/ENUM resolution.
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
How it works
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
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.