Port 787: QSC — The professional audio control channel

Port 787 is officially assigned to QSC, a protocol used for controlling professional audio equipment manufactured by QSC Audio and related systems.

What Port 787 Does

Port 787 operates in the well-known ports range (0-1023), which contains ports assigned by the Internet Assigned Numbers Authority (IANA) for specific protocols and services. This port carries control commands for professional audio systems—the kind found in conference centers, concert halls, houses of worship, and other venues where audio quality and remote control matter.

Unlike web servers or email, you won't encounter port 787 in everyday Internet use. It's specialized infrastructure, speaking a protocol designed for a specific purpose: managing sound systems that professionals depend on.

The QSC Protocol

QSC Audio manufactures professional audio equipment and networking solutions. The company's Q-SYS platform provides networked audio, video, and control for large installations. While Q-SYS uses several ports for different purposes—audio streaming, discovery protocols, web interfaces—port 787 appears to be designated for QSC control traffic.

The protocol itself is proprietary. There's no public RFC documenting its operation. This is common for specialized industrial protocols where the manufacturer controls both ends of the communication.

The Well-Known Range

Port 787 sits in the well-known ports range (0-1023). Historically, these ports were restricted to privileged processes on Unix systems—you needed root access to listen on them. The idea was that important, system-level services would occupy this space, and the operating system would prevent random programs from impersonating them.

Today, that security model feels quaint. But the well-known range still serves as a registry of officially assigned ports, managed by IANA through a formal process requiring documentation and review.

Port 787's presence here means someone at QSC submitted an application, provided documentation of the protocol, and received official assignment. It's a small claim on the Internet's namespace, but a legitimate one.

Security Considerations

If you're not running QSC audio equipment, nothing should be listening on port 787. You can check what's listening with:

# On Linux or macOS
sudo lsof -i :787

# On Windows
netstat -an | findstr :787

If you see unexpected traffic on this port, investigate. It could be legitimate QSC equipment you forgot about, or it could be something pretending to be.

Like any specialized industrial protocol, QSC traffic shouldn't be exposed to the public Internet unless absolutely necessary. These protocols were designed for controlled environments—corporate networks, venue installations—not the hostile environment of the open Internet.

Why Specialized Ports Matter

The Internet has thousands of ports like 787—assigned to specialized equipment, industrial protocols, proprietary systems that most users never encounter. They represent the hidden infrastructure that makes the physical world work.

Port 787 isn't glamorous. It won't help you browse websites or send email. But in a conference center somewhere, it's carrying the commands that route microphones to speakers, adjust volume levels, and ensure the presenter's voice reaches the back row.

That's the Internet's real superpower: it's not just web pages and social media. It's the nervous system for everything that needs to communicate. Even professional audio equipment.

Related Ports

QSC's Q-SYS platform uses several other ports for different purposes:

• Port 2467-2470 — Q-SYS Discovery Protocol
• Port 3702 — Web Services Discovery
• Port 6516-6517 — Audio streaming (UDP)

Each port serves a different function in the ecosystem of networked audio control.