SBC (Session Border Controller)
What is SBC (Session Border Controller)?
An SBC (Session Border Controller) is the network appliance or software layer that sits at the edge of a VoIP network, controlling and securing every SIP call and its media as it crosses from one network to another — for example, between a business's PBX and a carrier's SIP trunk. An SBC handles NAT traversal, protocol normalization between slightly different SIP implementations, encryption, and protects the network behind it from toll fraud and denial-of-service attacks.
More detail
Because SIP implementations vary slightly between vendors, an SBC commonly normalizes signaling differences so a PBX and a carrier's trunk can interoperate cleanly despite not being from the same vendor.
SBCs are a standard chokepoint for encrypting media (SRTP) and signaling (TLS) on calls crossing the public internet, and for rate-limiting or blocking suspicious call patterns associated with toll fraud.
Frequently asked
- Why does a business need an SBC if it already has a firewall?
- A standard firewall isn't built to inspect and manage real-time SIP signaling and media the way an SBC is — an SBC understands the call-control protocol itself, handling NAT traversal, encryption, and toll-fraud protection that a generic firewall doesn't provide.
- What's the difference between an SBC and a softswitch?
- An SBC secures and normalizes SIP signaling and media at the network edge; a softswitch makes the actual routing decision — which network or carrier a call should go to next. Many production deployments use both together.
See also
Build it on Orbit
Voice, messaging, email, video, and AI agents on one platform and one pay-as-you-go bill. Start free — no credit card required.