Basically, billing is done only for the encrypted data volume that you have really used. However, each mix-cascade-service demands 3 MB in advance as payment. If you surf over this cascade for some time, this volume is, again and again, "filled" up to 3 MB, even if you disconnect and reconnect in-between. This payment in advance is necessary in each case in order to prevent the mix-services from being used free of charge in a technically reliable manner.

If you encouter data traffic that does not seem to come from you, it may be that JonDo cannot establish a direct connections to info services or to the payment instance, e.g. because they are blocked by a firewall. In this case JonDo is trying to contact these important services over the anonymous connection which amounts to a few MB data traffic per day. However, you may block this behaviour in the advanced settings concerning Infoservice and payment instance any time you want. But remember that this may also block these services altogether.

All the other data traffic is due to external programs, not JonDo. Even your own web-browser can be responsible for generating data traffic unexpectedly, e.g. because it is updating RSS-feeds, certain extensions or itself.