For login-like services (those that create an entry in the utmp file), the session management facilities of PAM are invoked as well as the account management facilities if both are configured in /etc/pam.conf.
The Solaris Resource Manager product's session management handles charging for devices. It looks to see if the user has exceeded the connect-time limit, or has the onelogin flag evaluate to set and is already logged in, and if so, prevents login.
Otherwise, it generates a message to the limdaemon process to inform it of the login and the configured cost for the terminal being used. It then informs the kernel that the current process is a login header process, and that the limdaemon process must be notified when it expires.
The limdaemon process then tracks connect-time limits and issues warnings if they are about to be exceeded.