Software & Stacks

FreeSWITCH

FreeSWITCH is an open-source telephony engine started by Anthony Minessale in 2006 (originally as a multi-threaded successor to Asterisk). It is more flexible than Asterisk — it can be used as a Class 5 PBX, a Class 4 softswitch, an SBC, a media server, or any combination — and scales to tens of thousands of concurrent calls per box.

Architecture differences vs Asterisk

• Multi-threaded core: calls are not pinned to a single thread. Scales linearly with CPU cores.
• Modular at every layer: SIP (mod_sofia), media (mod_dptools), apps (mod_voicemail) are all swappable.
• Strong B2BUA support: natively designed as a back-to-back user agent; cleaner than Asterisk's bridge model.
• Lua / JS / Python / C scripting: mod_lua, mod_v8, mod_python — pick your scripting language.

When to pick FreeSWITCH over Asterisk

• You need >2000 concurrent calls per box.
• You're building a hosted PBX SaaS (multi-tenant out of the box).
• You need an SBC (FreeSWITCH is a credible SBC; Asterisk is a stretch as one).
• You need a Class 4/5 hybrid in one box.

When to pick Asterisk instead

• You want FreePBX's polished web UI for end-customers (FreePBX is Asterisk-only).
• You're following a tutorial — the Asterisk ecosystem has 10x more docs.
• You need vendor support — Sangoma sells commercial Asterisk (PBXact). Commercial FreeSWITCH (SignalWire) exists but is smaller.

Common usage patterns

• Hosted PBX SaaS: FreeSWITCH cluster + database + provisioning UI. The base of products like FusionPBX (FreeSWITCH-based, Class 5) and many other FreeSWITCH-powered hosted offerings.
• Anchored SBC: media gets anchored at FreeSWITCH for transcoding, signaling at Kamailio in front.
• WebRTC gateway: mod_verto + mod_sofia bridge browser WebRTC to PSTN SIP.

Related terms

Related glossary terms

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