Some access-restricted services of the university or the "Staats- und Universitätsbibliothek Bremen" (SuUB) can only be used if you are on campus, so that the computer you are using has an IP address from the area assigned to the university.
If you want to access these services from home or on the road with an account from the "Zentrum für Netze" (ZfN), you must install a so-called VPN client software (AnyConnect or OpenConnect) once on your computer and establish a connection to the campus with the VPN client before you can get access to the restricted services. This way you are "virtually" on campus and can use the usual services.
Only active university employees and students may use the VPN service. For licensing reasons, use by alumni is excluded.