Port 1113: LTP-DeepSpace — The Protocol for Talking Across Planets

Port 1113 carries something most Internet protocols never have to think about: planetary distances.

What Runs on Port 1113

Licklider Transmission Protocol (LTP-DeepSpace) operates on port 1113 for both TCP and UDP. LTP is a point-to-point protocol designed specifically for deep space communications—the kind where your message takes 20 minutes to reach Mars and another 20 minutes for a response to come back.¹

This is the protocol that helps NASA communicate with rovers, orbiters, and deep space probes. Every command sent to a spacecraft millions of miles away, every photo transmitted back from another planet—this is the infrastructure that makes it possible.

Why Deep Space Needs Its Own Protocol

TCP was designed for networks where round-trip time is measured in milliseconds. It assumes if you don't get a response quickly, something went wrong and you should try again.

Deep space communications operate under completely different constraints:²

• Extremely long round-trip times — Light takes 3 minutes to reach Mars at closest approach, 22 minutes at farthest. Double that for a round trip.
• Frequent interruptions — Links disappear when planets rotate, when spacecraft go behind celestial bodies, or when solar conjunction blocks the signal path.
• Limited bandwidth — You're transmitting across hundreds of millions of miles. Every bit counts.

TCP would interpret these delays as failures and constantly retransmit. It would waste precious bandwidth trying to "fix" conditions that are actually normal in space.

LTP was designed from the ground up to handle these realities. It provides reliable transmission without the assumptions that make TCP unsuitable for interplanetary distances.

How LTP Works

LTP operates as a reliable convergence layer over deep space radio frequency links. It's commonly used with the Bundle Protocol (defined in RFC 5050) to create what's known as Delay-Tolerant Networking (DTN)—networks that can store messages and forward them when links become available again.³

The protocol uses:

• Red segments — Reliable data that requires acknowledgment
• Green segments — Unreliable data that doesn't require acknowledgment
• Checkpoints and reports — For acknowledging received data across massive delays

This design allows a spacecraft to receive a large file in pieces, acknowledge what arrived, and request retransmission of only the segments that failed—all while accounting for the fact that responses take minutes or hours to arrive.

Named After a Pioneer

The Licklider Transmission Protocol is named after J.C.R. Licklider—an American computer scientist who envisioned networks of computers communicating long before the Internet existed. In the 1960s, he described an "Intergalactic Computer Network."⁴

Sixty years later, we're building exactly that. And we named the protocol after him.

CCSDS and Standards

LTP is standardized by the Consultative Committee for Space Data Systems (CCSDS), an international organization that develops communications standards for space agencies worldwide. The protocol is defined in:

• RFC 5325 — Licklider Transmission Protocol - Motivation¹
• RFC 5326 — Licklider Transmission Protocol - Specification²
• CCSDS 734.1-B-1 — LTP specification for CCSDS missions⁵
• ISO 21080:2016 — International standard for LTP in space environments⁶

These standards ensure that different space agencies can communicate reliably, even across systems built by different countries and organizations.

Security Considerations

LTP itself focuses on reliable transmission rather than security. For secure space communications, LTP is typically paired with:

• Bundle Protocol Security (BPSec) — For end-to-end security in delay-tolerant networks
• CCSDS Space Data Link Security Protocol — For link-level security

Space communications also benefit from physical security—it's hard to intercept a signal traveling through the vacuum of space, though not impossible for well-resourced adversaries with large antennas pointed at the right part of the sky.

Checking What's Listening

On most systems, you won't find anything listening on port 1113 unless you're working with deep space communications equipment or delay-tolerant networking research.

To check what's using port 1113:

# Linux/macOS
sudo lsof -i :1113
sudo netstat -tulpn | grep 1113

# Windows
netstat -ano | findstr :1113

If you see something listening on this port and you're not running space communications software, investigate—it could be legitimate research software or something unexpected.

Related Ports

• Port 4556 — DTN2 Bundle Protocol (another delay-tolerant networking protocol)
• Port 2628 — DICT Protocol (dictionary lookups, also named after a computing pioneer)

The Bigger Picture

Port 1113 exists because the Internet assumptions—fast responses, always-on links, short distances—break down when you're talking to something on another planet.

We needed protocols that could handle delays longer than most TCP sessions stay open. We needed reliability without the assumption of quick feedback. We needed to store and forward when links disappeared for hours or days.

LTP is one answer to that impossible problem. It's how we turn the Deep Space Network into something that feels connected, even when messages travel for minutes and links vanish with the rotation of worlds.

Every photo from Mars. Every command to a probe near Jupiter. Every scientific measurement transmitted across the solar system. Port 1113 is part of what makes that conversation possible.