There are two different levels of authentication/connectivity involved.
- Authentication of users in order to connect and access your local network.
- Authentication of users on hosts in order to access specific services.
The user provides a password, based on the selected security protocol (WEP, WPA, WPA2,etc) of your wireless router, in order to become a member of your local network and access various services (e.g. file services on your Ubuntu machine, shell access, or direct outbound Internet access).
This kind of information will be provided directly from your wireless router (probably by a web-based administration page).
The user is already connected to the local network (so the first level of authentication has completed), has a local IP address and can access the various hosts of the network.
When the user connects to your Ubuntu machine through telnet or SSH, a relevant entry will be shown by using the commands
One - possibly - important detail:
The commands above display currently logged on users on your system; that is, users connected remotely or locally to the system through command-line (shell access) or GUI (X session).
Users connected to specific services (such as FTP) will not be visible.
It is up to the specific application/daemon to log/display the users accessing the relevant service.