Policy: Trunks use Erlang B at the entered blocking target; the agent figure uses Erlang C for the selected service level with the average call duration as handling time. SIP trunks = 1 concurrent call per trunk.
E1 = 30 channels. Recording storage = (calls × ratio × size × retention) / 1000.
Design aid only—validate with vendor sizing tools.
PBX & Contact Center Results
Busy Hour Calls
Busy-Hour Traffic
Required Trunks
Agents (entered / Erlang C)
Recording Storage
Growth-Adjusted Trunks
System Complements (Recommended)
IVR with menu & queuing logic
CRM integration (screen pop)
Real-time dashboards & wallboards
Call recording with encryption
Disaster recovery / failover SIP
Quality monitoring & scoring
Mobile extension & softphone support
This tool is a design aid only. Final design must be verified with vendor-specific sizing tools (e.g., Avaya, Cisco, 3CX, Genesys).
Comply with ISO/IEC 27001 for call data security and local telecom regulations.
This summary is a design aid. Final design must be verified with vendor tools and comply with ISO/IEC 27001, GDPR (if applicable),
and local telecom regulations. Recording requires user consent per data privacy laws.
