Port 3715: Anoto Rendezvous — A Digital Pen's Forgotten Door

What This Port Is

Port 3715 is officially registered with IANA as anoto-rendezv — the Anoto Rendezvous Port, registered in March 2003.¹ It supports both TCP and UDP. It is not unassigned; it belongs to a specific technology from a specific company at a specific moment in computing history.

You almost certainly have never used it.

Anoto and the Digital Pen

Anoto Group AB is a Swedish company founded in 1996 (originally as C Technologies) by Christer Fåhræus, who was writing his doctorate and imagined a pen that could capture handwriting digitally without abandoning paper.²

The technology they built is genuinely clever. Anoto paper is printed with a nearly invisible pattern of tiny dots, arranged in a non-repeating grid so vast it can uniquely identify every point on paper equivalent to the surface area of Europe. A digital pen contains a small infrared camera that reads this pattern 70+ times per second. The pen always knows which document it's on and exactly where on that document it's writing.³

The rendezvous port was part of the infrastructure connecting these pens to backend services — the handshake mechanism that let a pen announce itself and synchronize captured data.

What Happened

Anoto licensed their technology to Nokia, Ericsson, Logitech, and others in the early 2000s. The vision was a world where paper and digital coexisted seamlessly — you write on paper, the data flows instantly into your computer.

It didn't take over the world. Smartphones arrived. Touchscreens got good. The friction of specially printed paper proved too high for mass adoption.

Anoto still exists. They still ship digital pens, primarily into healthcare, field data collection, and specialized enterprise workflows where paper truly isn't going away. But port 3715 is largely a fossil — reserved for infrastructure that runs in a small corner of the world.⁴

What Range This Port Belongs To

Port 3715 sits in the registered ports range (1024–49151). These ports are not reserved by the operating system for privileged use (that's ports 0–1023), but they are registered with IANA so that applications can claim a consistent, documented home.

Registration means: IANA recognizes the assignment. It does not mean the port is in active widespread use.

Checking What's Actually on Port 3715

If you see traffic on port 3715 on your network and you're not running Anoto infrastructure, investigate.

On Linux/macOS:

# See what process is listening on port 3715
sudo lsof -i :3715

# Or with ss
ss -tlnp | grep 3715

On Windows:

netstat -ano | findstr :3715

Capture traffic:

# Watch actual traffic on the port
sudo tcpdump -i any port 3715 -v

If something unexpected appears here, it's worth identifying. Unrecognized listeners on registered ports occasionally indicate software using a port opportunistically — or something you didn't install.