Testing the connection and the ISDN callback

The connection is set up by the head office, for example, with a ping. You can follow the set-up of the connection and the ISDN callback by entering the command debug ipsec in the command line.

This debug extract shows how the IPSec tunnel is initiated from head office. The system first attempts to transmit the IP address over the D-channel. However, this attempt fails as it is not supported by the PBX or the provider. Next, the IP address is transmitted in the B-channel and the tunnel is set up.