[Users] OpenSER using TLS / TCP

Hello, I have a problem with OpenSER using TLS / TCP, Clients are MiniSIP and Snom 360 phones. I start the server, the phones connect to it using TCP or TLS over TCP. Calls between all phones are possible. But after some minutes, I think it is the timeout of TLS or TCP, no calls are possible any longer. OpenSER shows the following error message: 8(31121) ERROR: tcp_blocking_connect: SO_ERROR (111) Connection refused 8(31121) ERROR: tcpconn_connect: tcp_blocking_connect failed 8(31121) ERROR: tcp_send: connect failed 8(31121) msg_send: ERROR: tcp_send failed 8(31121) ERROR:tm:t_forward_nonack: sending request failed Has anyone a solution for this problem? Thanks. Torsten