Carlos Ruizbal focused on restoring backward compatibility for legacy STUN clients in the coturn/coturn repository, addressing a regression that affected interoperability with older clients. He analyzed and corrected logic errors in C within ns_turn_server.c and dtls_listener.c, removing a stray negation and adding a missing compatibility branch to ensure proper packet validation. By applying targeted changes across both TCP and UDP code paths, Carlos enabled the stun_backward_compatibility flag to function as intended. His work in C programming and protocol implementation improved network stability and compliance, reducing support overhead and ensuring that legacy clients could reliably communicate with updated coturn servers.