Here is the protocol stack for I2P. See also the Index to Technical Documentation.

Each of the layers in the stack provides extra capabilities. The capabilities are listed below, starting at the bottom of the protocol stack.

• Уровень интернета
  IP: Internet Protocol, allow addressing hosts on the regular internet and routing packets across the internet using best-effort delivery.
• Транспортный уровень:
  TCP: протокол управления передачей, обеспечивает надежную, с сохранением порядка, доставку пакетов в сети
  UDP: протокол пользовательских датаграмм, обеспечивает ненадежную, неупорядоченную доставку пакетов в сети
• I2P Transport Layer: provide encrypted connections between 2 I2P routers. These are not anonymous yet, this is strictly a hop-to-hop connection. Two protocols are implemented to provide these capabilities. NTCP2 builds on top of TCP, while SSU uses UDP.
  NTCP2: TCP на основе NIO
  SSU: Secure Semi-reliable UDP
• I2P Tunnel Layer: provide full encrypted tunnel connections.
  Tunnel messages: tunnel messages are large messages containing encrypted I2NP (see below) messages and encrypted instructions for their delivery. The encryption is layered. The first hop will decrypt the tunnel message and read a part. Another part can still be encrypted (with another key), so it will be forwarded.
  I2NP messages: сообщения I2P Network Protocol используются для прохода сообщений через несколько маршрутизаторов. Эти сообщения I2NP совмещаются с сообщениями туннелей.
• I2P Garlic Layer: предоставляет зашифрованную и анонимную сквозную доставку I2P сообщений.
  I2NP messages: I2P Network Protocol messages are wrapped in each other and used to ensure encryption between two tunnels and are passed along from source to destination, keeping both anonymous.

The following layers are strictly speaking no longer part of the I2P Protocol stack, they are not part of the core 'I2P router' functionality. However, each of these layers adds additional functionality, to allow applications simple and convenient I2P usage.

• I2P Client Layer: позволяет любому клиенту использовать функциональность I2P без необходимости прямого использования API маршрутизатора.
  I2CP: I2P Client Protocol позволяет защищенный и асинхронный обмен сообщениями через I2P отправкой сообщений через TCP сокет I2CP.
• I2P End-to-end Transport Layer: позволяет TCP- или UDP-подобную функциональность поверх I2P.
  Streaming Library: an implementation of TCP-like streams over I2P. This allows easier porting of existing applications to I2P.
  Datagram Library: an implementation of UDP-like messages over I2P. This allows easier porting of existing applications to I2P.
• I2P Application Interface Layer: additional (optional) libraries allowing easier implementations on top of I2P.
  I2PTunnel
  SAMv3
• I2P Application Proxy Layer: прокси системы.
  HTTP Client/Server, IRC Client, SOCKS, Streamr

Finally, what could be considered the 'I2P application layer', is a large number of applications on top of I2P. We can order this based on the I2P stack layer they use.

• Потоковые/приложения дейтаграмм: i2psnark, Syndie, i2phex...
• SAM applications: IMule, i2p-bt...
• Другие приложения I2P: Syndie, EepGet, плагины...
• Regular applications: Jetty, Apache, Git, browsers, e-mail...

Figure 1: The layers in the I2P Network stack.

* Note: SAM can use both the streaming lib and datagrams.