What is SIP Trunk & Extension Capacity Planner?
The SIP Trunk & Extension Capacity Planner is a planning utility that estimates the number of concurrent call paths (SIP Trunks or channels) your business needs based on your team size and average phone traffic. Sizing your SIP trunk capacity incorrectly leads to busy tones for incoming clients or blocked outbound calls for agents. This calculator uses traffic engineering principles to ensure your office has the exact capacity needed for seamless calling.
How to Use SIP Trunk & Extension Capacity Planner
- Enter the total number of phone users (extensions) in your office or call center.
- Select your business type/call frequency (e.g., standard office, busy sales team, or active call center).
- Input your target grade of service (blocking probability) — standard practice is 1% to 2% blocking.
- The tool calculates the required number of concurrent SIP channels (trunks) to support your call volume.
- Review the recommended internet bandwidth required to support these concurrent calls without quality degradation.
Common Use Cases
- Telecom network engineers designing SIP Trunk trunks for corporate offices and enterprise buildings.
- Call center managers determining how many SIP channels to purchase from service providers like PTCL or Transworld.
- IT managers auditing telephone system capacity to reduce unused channel rentals.
Pro Tips & Best Practices
- A standard office typically has a 4:1 or 5:1 ratio of employees to lines, while a call center needs a 1:1 ratio.
- Ensure your firewall has Session Border Controller (SBC) capabilities or SIP ALG disabled, which often interferes with packet routing.
- If you experience busy signals during seasonal peaks, temporarily expand your SIP trunk capacity if your provider supports elastic SIP trunking.