International bis connections
Buses on international connections are not allowed to carry passengers on inland connections. They also are supposed to refuse boarding without ticket, but sometimes if empty they do. International buses aren't usually faster than an inland connection to the border, walk trough the border and getting an continuing connection on the other side. But they are much more comfortable, usually with toilet and you don't have to carry around your baggage. They are usually more expensive then the same trip with inland connections, and they cost the same independently where you get on and where you get off, therefore it is not very useful to use them to get from the last town before the border to the first town after the border.
If you have an inland connection before you can get on the international bus, always check with a local agent of the international bus company where you can get on the international bus.