When I first moved from England to the US in 2005, I discovered something rather unexpected: I had become mysteriously interesting.
Back home, I was just a regular guy — polite, a bit nerdy, nothing special. But in the US, I suddenly found that people were delighted to talk to me. The moment I opened my mouth, there was this spark of enthusiasm — “Where are you from?” “What brought you here?” “Say something again — I love your accent!” It was like having a cheat code for small talk.
Even my wife, who won’t admit it now, may have been a little more intrigued by the accent than she’s letting on.
One of the curious things I noticed early on was how the letter R behaves very differently depending on which side of the Atlantic you’re on. In British English, we tend to drop it — so butter becomes butta. In American English, you go the other way — the T gets softened, but the R comes out loud and proud: budder.
This came to mind a few years later when I was working with Metaswitch, who had just released a new Session Border Controller. They decided to give it a clever name: Perimeta.
It was a classic bit of British wordplay — a mashup of perimeter (i.e. border) and Meta (as in Metaswitch). In British English, Perimeta and Perimeter sound nearly identical. But in American English? Not so much. The pun doesn’t quite land when you’re putting that bold American R in there.
Still, name confusion aside, the Session Border Controller (SBC) is a vital part of any VoIP network — no matter how you pronounce it.
So what does an SBC actually do?
If you’re running a voice network, your SBC is kind of like the customs and immigration checkpoint at your network’s borders. It’s standing at the edge of your domain, inspecting all the traffic that comes in and out, and making sure everything is safe, valid, and properly formatted.
Let’s break down the main roles an SBC plays:
🔐 Security
An SBC acts as a firewall for VoIP, blocking malicious traffic, validating SIP headers, and preventing denial-of-service (DoS) attacks or toll fraud. Without one, your SIP servers are just sitting there exposed, ready to be exploited.
🤝 Interoperability
Not all SIP devices speak the same dialect — much like Americans and Brits discussing aluminium. The SBC can manipulate SIP headers, reformat SDP, or add/remove fields so that different vendors and devices can interoperate cleanly. This is especially useful when integrating with new carriers or application servers.
🚦 Routing
SBCs often sit at the center of your SIP routing logic — acting as a traffic cop to determine which SIP trunk or network path to use for a given call. This gives you flexibility, redundancy, and control.
🌐 NAT Traversal
When subscribers are behind a NAT (e.g., using home routers or business firewalls), direct SIP communication can be tricky. An SBC can help ensure media and signaling flow properly, even when devices are hidden behind private IP addresses.
SBCs in the Real World
At Award Consulting, we’ve worked extensively with Metaswitch’s Perimeta, and we continue to see it as a powerful, feature-rich SBC for complex environments.
But we also understand that not every network needs the full bells-and-whistles enterprise model. For simpler deployments, we often recommend TelcoBridges ProSBC — a cost-effective, reliable SBC that still offers great security and flexibility. We’re proud to have a close partnership with TelcoBridges, and can help design, configure, and manage their SBC solutions as part of your overall voice architecture.
And of course, SBCs often serve as the go-between with application servers. One of our favorite tools for STIR/SHAKEN is ClearIP from TransNexus. In fact, we recently completed a large project integrating ClearIP with Perimeta for Least Cost Routing, allowing calls to be dynamically routed based on real-time pricing and performance metrics. The SBC was the essential glue that made the whole system work.
Need help with your SBC?
We genuinely enjoy this work. There’s something satisfying about untangling SIP headers, tweaking call routing logic, and watching a formerly-broken interop call sail through cleanly. Whether you’re using Perimeta, ProSBC, or something else entirely — we’d be happy to lend a hand.
From design and deployment, to SIP debugging and STIR/SHAKEN integration, we’ve seen it all. And while we can’t promise you’ll become more interesting overnight (unless you happen to have a British accent in America), we can help you secure and optimize your voice network — and that’s almost as good.
