Port 3620: ep-pcp — Epson's Registered-but-Quiet Projector Port

What This Port Is

Port 3620 is registered with the Internet Assigned Numbers Authority (IANA) under the service name ep-pcp, which stands for EPSON Projector Control Port. It is listed for both TCP and UDP.

That's the official story. The practical story is more interesting.

What Actually Happened

Epson registered port 3620 with IANA for projector control, alongside a small cluster of neighboring ports: 3621 (ep-nsp, EPSON Network Screen Port) and 3629 (escvpnet). The idea was presumably a suite of ports for different projector communication functions.

But Epson's actual projector control protocol, ESC/VP.net, runs on port 4352. That's the port users encounter when trying to control an Epson projector over IP, the port that home automation systems query, and the port Epson's own support documentation points to.¹

Port 3620 appears in lists, databases, and IANA's registry. It does not appear in the Epson documentation that matters for people actually connecting to projectors.

This happens. A company files a port registration, product decisions change, and the registered port becomes a permanently reserved-but-idle address in the IANA ledger.

The Registered Port Range

Port 3620 sits in the registered ports range: 1024 through 49151. These ports require formal IANA registration, but registration doesn't guarantee use. It only guarantees that no other service is supposed to use that number.²

The range exists because software authors need stable, predictable port numbers for their applications. Without registration, two unrelated applications might claim the same port and conflict. With registration, Epson's projectors and your accounting software can coexist without negotiating.

The tradeoff: registration requires commitment to a port number before the product ships, which is exactly the moment when requirements change.

Checking What's on This Port

If you see traffic on port 3620 and want to know what's generating it:

On Linux/macOS:

# See what process is listening on port 3620
sudo lsof -i :3620

# Or with ss (Linux):
sudo ss -tlnp | grep 3620

On Windows:

netstat -ano | findstr :3620

If anything is listening, the process ID returned will tell you what application opened the socket.

On most machines, you'll find nothing. Port 3620 is quiet.

Why Unassigned-in-Practice Ports Matter

Even when a registered port sees little official traffic, the registration does real work. It stops other services from squatting the number. If Epson ever ships hardware that uses 3620 as intended, the number is theirs. And security tools flagging port 3620 activity on a network where no Epson equipment exists have a reasonable basis for suspicion — unknown traffic on a quiet registered port deserves attention.

The IANA registry is a reservation system, not a usage ledger. Port 3620 is reserved. What happens on it is another matter.

Related Ports