Core Requirements of an Outbound Call Center
International outbound call centers have unique voice system requirements: high concurrency, multi-country coverage, cost sensitivity, strict call quality standards, and caller ID localization.
| Requirement | Description | Recommended Solution |
|---|---|---|
| High Concurrency | 100-1,000+ simultaneous outbound calls | Elastic SIP trunk concurrency |
| Multi-Country Coverage | Outbound calls to multiple destination countries | Global SIP trunk + local POPs |
| Caller ID Localization | Display local numbers in destination countries | Country-specific DID numbers + CLI pass-through |
| Cost Optimization | Cost control for large-scale outbound calling | LCR routing + tiered routes |
| Quality Assurance | Ensure clear, uninterrupted calls | Quality monitoring + automatic failover |
Recommended Architecture: SIP Trunk + Predictive Dialer
For international outbound call centers, we recommend the following architecture:
- PBX / Softswitch: FreeSWITCH (recommended for high-concurrency performance) or Asterisk
- Predictive Dialer Engine: Built-in or third-party (e.g., VICIdial, OSDial)
- SIP Trunk: Cainiao Voice (coverage in 200+ countries, elastic concurrency)
- DID Number Pool: Local numbers configured per destination country
- CRM Integration: API-based integration with enterprise CRM systems
Multi-Country Number Strategy
The caller ID displayed on outbound calls significantly impacts answer rates:
| Strategy | Impact on Answer Rate | Implementation Effort |
|---|---|---|
| Display international number (e.g., +86) | Baseline (lowest) | No additional configuration needed |
| Display destination country number (local DID) | +30-50% improvement | Requires procuring DIDs in each country |
| Number rotation (multiple DIDs rotating) | Prevents numbers from being flagged as spam | Requires PBX number pool configuration |
| Destination number + local area code matching | Highest answer rate | Requires per-city number provisioning |
Route Quality Tiering
Different outbound scenarios have different route quality requirements. We recommend a tiered approach:
| Call Type | Recommended Route Tier | Rationale |
|---|---|---|
| Key account follow-up | Premium | Call quality directly affects client impression |
| Daily telemarketing | Standard | Best value for money |
| Notification reminders | Economy | Short calls, cost is the priority |
| Voice verification (OTP) | Standard | Must ensure delivery rate, though calls are very short |
Concurrency Planning & Bandwidth Calculation
Agents vs. Concurrent Channels: When using a predictive dialer, concurrent channels are typically 1.5-3x the number of agents (depending on dialing strategy and answer rates).
| Agents | Recommended Concurrency | G.729 Bandwidth | G.711 Bandwidth |
|---|---|---|---|
| 50 | 75-150 | 2.3-4.7 Mbps | 6.5-13 Mbps |
| 100 | 150-300 | 4.7-9.4 Mbps | 13-26 Mbps |
| 200 | 300-600 | 9.4-18.7 Mbps | 26-52 Mbps |
| 500 | 750-1500 | 23-47 Mbps | 65-131 Mbps |
We recommend reserving 30% bandwidth overhead and using the G.729 codec to conserve bandwidth.
Cost Optimization Strategies
- LCR (Least Cost Routing): Configure the PBX to automatically select the cheapest available route per destination country
- Quality-threshold routing: Set minimum quality standards (MOS >3.8), then choose the cheapest route among those that qualify
- Volume commitments: Negotiate monthly traffic commitments with SIP providers for lower per-minute rates
- Off-peak dialing: Some countries have higher answer rates and lower rates during off-peak hours
- Number sharing: Use the same DID number across multiple agents (SIP trunk model — not tied to physical lines)
Case Study: 100-Agent Southeast Asia Outbound Center
Business Requirements: 100 agents, covering Thailand, Vietnam, Malaysia, Indonesia, and the Philippines, with 250K monthly call minutes.
| Configuration | Solution |
|---|---|
| PBX | FreeSWITCH cluster (2 servers, active-passive) |
| SIP Trunk | Cainiao Voice, 200 concurrent channels |
| Codec | G.729 (bandwidth savings) |
| DID Numbers | 10 local numbers per country (5 countries), with number pool rotation |
| Bandwidth | 20 Mbps dedicated (G.729, including 30% overhead) |
| Routing Strategy | Standard routes as primary, Premium for VIP clients |
| Monthly Cost | Approximately $3,500 (including routes + numbers + call charges) |
Planning an International Call Center?
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