Port 1853: VIDS-AVTP — Assigned, Abandoned

Port 1853 sits in a peculiar position: officially claimed, practically empty.

IANA assigned it to VIDS-AVTP, a protocol registered by Sascha Kuemmel at VidSoft, a company that developed IP-based visual communication software. The registration covers both TCP and UDP. Beyond that, the trail goes cold. VIDS-AVTP left no RFC, no public specification, no community of implementers. The port number is taken; the protocol never arrived.¹

The Registered Port Range

Port 1853 falls in the registered port range (1024–49151). This range works differently from the well-known ports below 1024:

• Well-known ports (0–1023): Reserved for foundational protocols. Using them requires root or administrator privileges. HTTP, SSH, DNS — these live here.
• Registered ports (1024–49151): Any vendor or developer can apply to IANA to claim a number for their service. No privilege required to use them. IANA records the assignment but doesn't enforce it — nothing stops another application from using port 1853 on your machine.
• Dynamic/ephemeral ports (49152–65535): Assigned on the fly by the operating system for outbound connections.

Registration is intent, not enforcement. A port in this range is "claimed" the same way a domain name is claimed: on record, but only meaningful if someone actually uses it.

What VIDS-AVTP Was

VidSoft built visual communication tools — essentially video conferencing infrastructure for enterprises. AVTP (Audio/Video Transport Protocol) is a real class of protocols for streaming time-sensitive audio and video data across networks. The IEEE standardized its own AVTP (IEEE 1722) for use in automotive and professional AV networks.

VIDS-AVTP appears to have been VidSoft's own variant or application layer built atop similar concepts. It never saw wide adoption, and VidSoft itself has faded from prominence. What remains is a name in a registry.²

What's Actually on Port 1853

Almost certainly nothing, unless you put something there yourself.

Because the port has no dominant unofficial use and no active protocol implementation, you may encounter it claimed by:

• Custom or internal enterprise applications
• Development servers and local tooling
• Malware or unexpected software (always worth checking)

How to Check What's Listening

macOS/Linux:

# Show what process is listening on port 1853
sudo lsof -i :1853

# Or with ss (Linux):
ss -tlnp | grep 1853

Windows:

# Show listening ports and owning process IDs
netstat -ano | findstr :1853

# Then look up the PID
tasklist | findstr <PID>

If something is listening on this port and you don't recognize it, that's worth investigating.

Why Unassigned Ports Matter

The port registry is not just bureaucracy. When every application picks its own port arbitrarily, conflicts happen — two services fighting over the same number, firewalls blocking legitimate traffic, security tools raising false alarms. The registry is a coordination mechanism: a way for developers to say "this number is ours" and for everyone else to know to route around it.

The tragedy of ports like 1853 is the reservation that locked up a number without ever delivering a protocol. There are 65,535 ports, which sounds like plenty until you realize that thousands are similarly claimed by services that never shipped, vendors that dissolved, or protocols that lost the adoption race. The registry is littered with good intentions.

Port 1853 is reserved. It is not busy. If you need it, you can use it — just know that somewhere in IANA's records, VidSoft got there first.