OSI-licensed open source
A session border controller (SBC) sits at the edge of a VoIP network to handle SIP signaling and media: topology hiding, NAT traversal, security, load balancing and interoperability between carriers and PBXs. There is no single dominant open-source SBC product; instead, teams assemble one from SIP proxies, media relays and B2BUA components.
This page lists the open-source projects commonly used to build that edge: SIP servers (Kamailio, OpenSIPS), media and B2BUA platforms (FreeSWITCH, Asterisk), a SIP application server (drachtio) and a media proxy (RTPengine). Expect configuration work rather than a turnkey appliance. Licences were read from each repository or licence file.
Tools, licences and pricing checked against vendor and repository pages on November 7, 2026.
| Tool | Best for | Pricing | Licence |
|---|---|---|---|
| Kamailio | High-volume SIP routing and edge proxying | Free, open source | GPL-2.0 |
| OpenSIPS | SIP proxy and B2BUA with routing logic | Free, open source | GPL-2.0 |
| RTPengine | Media relay behind Kamailio or OpenSIPS | Free, open source | GPL-3.0 |
| FreeSWITCH | B2BUA and media server in a custom SBC stack | Free, open source | MPL-1.1 |
| Asterisk | PBX and applications | Free, open source | GPL-2.0 |
| drachtio | Node.js developers building custom SIP logic | Free, open source | MIT |
Best for: High-volume SIP routing and edge proxying · Free, open source
Open-source SIP server for large-scale VoIP platforms handling signaling, routing, registration and load balancing, with a flexible configuration language.
Best for: SIP proxy and B2BUA with routing logic · Free, open source
Multi-functional open-source SIP server for voice, video and IM, usable as proxy, registrar, load balancer and B2BUA with a scripting language.
Best for: Media relay behind Kamailio or OpenSIPS · Free, open source
Proxy for RTP and other media streams developed by Sipwise, controlled by SIP proxies such as Kamailio and OpenSIPS; supports WebRTC and transcoding.
Best for: B2BUA and media server in a custom SBC stack · Free, open source
Open-source telephony platform acting as a softswitch, media server and B2BUA, with extensive codec and WebRTC support.
Best for: PBX and applications · Free, open source
Open-source PBX and telephony toolkit with SIP, WebRTC and many applications, often used behind a dedicated SBC or in a B2BUA role.
Best for: Node.js developers building custom SIP logic · Free, open source
Open-source SIP application server framework with Node.js integration, used to build SIP proxies, B2BUAs and call control apps.
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| If you need… | Start with |
|---|---|
| High-volume SIP routing and security | Kamailio or OpenSIPS |
| Media relay and NAT traversal | RTPengine |
| B2BUA and transcoding | FreeSWITCH |
| Custom call logic in JavaScript | drachtio |
| PBX features behind the edge | Asterisk |
Quick answers to common questions
Not a single turnkey one. Most teams combine Kamailio or OpenSIPS for signaling with RTPengine for media.
Both are mature SIP servers with scripting; the choice usually comes down to team familiarity and specific modules.
If you must proxy media for NAT or bridging, yes; Kamailio and OpenSIPS handle signaling only.
It can bridge calls, but it is built as a PBX; a SIP proxy plus media relay is more usual for edge duty.
Yes; this page covers open-source options only.
List it on TechLogHub and we'll review it for this guide.
