monero-site/knowledge-base/moneropedia/ssu.md

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---
layout: moneropedia
entry: "SSU"
tags: ["kovri"]
terms: ["SSU"]
summary: "I2P's Secure Semi-reliable UDP layer"
---
### The Basics
*Secure Semi-reliable UDP* (SSU) is one of two encrypted @transport layers for @Kovri/@I2P.
SSU's *primary* purpose is to securely transmit @in-net @I2NP messages through @tunnels over encrypted [UDP](https://en.wikipedia.org/wiki/User_Datagram_Protocol).
### In-depth information
- Much like its @NTCP counterpart, SSU is a connection-oriented, point-to-point data transport
- Termed *semi-reliable* because SSU will repeatedly retransmit *unacknowledged* messages (up to maximum number then dropped)
- SSU also provides several unique services (in addition to its function as a @transport layer):
- IP detection (local inspection + peer testing)
- NAT traversal (using introducers)
- Firewall status
- If implemented, SSU can notify NTCP if the external address or firewall status changes
### Notes
For further details, read @Java-I2P's [SSU](https://geti2p.net/en/docs/transport/ssu)