Proxy routing was an interim routing solution that Session used at launch while we worked to implement onion requests. Onion requests are now active and functioning on Session.
When proxy routing was in use, instead of connecting directly to an Oxen Service Node to send or receive messages, Session clients connected to a service node which then connects to a second service node on behalf of the Session client. The first service node then sends or requests messages from the second node on behalf of the mobile device.
This proxy routing system ensured that the client device’s IP address was never known by the service node which fetches or sends the messages. However, proxy routing did provide weaker privacy than the onion request system Session now uses. Proxy routing still provided a high level of security for minimising metadata leakage in the interim. The proxy routing system has now been replaced by onion requests.