FreeSWITCH15 min readJune 16, 2026

Asterisk to FreeSWITCH Migration Guide: Step-by-Step (2026)

Practitioner guide to migrating from Asterisk to FreeSWITCH — compatibility reality check, dialplan rewriting, AGI to ESL conversion, 5-phase process, zero-downtime parallel-run cutover with Kamailio, timeline, and risks.

Kaushik Parmar

Founder & VoIP Architect, CelloIP Technologies

Should You Even Migrate?

Migrate only with a concrete driver: hitting Asterisk's concurrency ceiling (>2,000–3,000 calls), needing FreeSWITCH's MPL licence for proprietary SaaS, or requiring FreeSWITCH-specific media features. A working Asterisk system has no business case to rebuild.

5-Phase Migration Process

Phase 1: audit & inventory. Phase 2: feature mapping. Phase 3: rebuild dialplan as XML and AGI as ESL applications (the bulk of effort). Phase 4: parallel run with Kamailio dispatcher shifting traffic gradually. Phase 5: cutover and decommission. Medium deployment: 4–8 weeks.

Zero-Downtime Parallel-Run Cutover

Place Kamailio/OpenSIPS in front of both platforms and shift traffic using the dispatcher module with weighted routing (95/5 → 50/50 → 0/100). If FreeSWITCH misbehaves, revert weights instantly with no dropped calls.

MigrationAsteriskFreeSWITCHAGI to ESLZero DowntimeKamailio

Frequently Asked Questions

Can you automatically convert Asterisk dialplan to FreeSWITCH?

No. There's no reliable automatic converter. Asterisk dialplan and FreeSWITCH XML are different paradigms, and AGI scripts must be rewritten as ESL applications. It's re-engineering, not translation — plan 4–8 weeks for a medium deployment.

How long does the migration take?

Small (basic PBX/IVR): 2–4 weeks. Medium (call center): 4–8 weeks. Large carrier/CPaaS: 12–24 weeks. The biggest cost is rewriting AGI/AMI logic as ESL.

Can both run in parallel during migration?

Yes — recommended. Deploy FreeSWITCH alongside Asterisk, place Kamailio/OpenSIPS in front as a dispatcher, and shift traffic gradually while comparing behavior. Enables zero-downtime cutover and instant rollback.