Oftentimes, you (or the remote machine) sit behind a firewall, and your remote access tool wants to work on a fancy port. Accordingly, you might have to open that port on both ends. It presents no difficulty if you have immediate access to network configuration on both ends, which often is *not* the case.
So, a solution that works transparently on any network infrastructure is a desirable option. Here, the connection should be negotiated with a dedicated server provided by the remote access tool vendor. Examples: DeskRoll, SkyFex.