The lifetime of dial-up connections must be limitted based on the number of users you expect to establish connection and the kind of services you plan to provide. The mail service provided by the server computer is conceived as a public service so anyone with a modem attached to a computer would be able to have access to it. However, due to hardware limitations, only 100 users will be allowed to be registered in the public mail service. Based on this information, the lifetime of established connections will be of 15 minutes from the established moment on. Once the connection has been established, if the link is idle for 1 minute, the server computer will close the established connection to free the telephone line. This control can be implemented through the maxconnect and idle options inside the pppd's configuration file. Only registered user profiles will be able to establish connections to the server computer. This control can be implemented using the allow-number option in the pppd's configuration file to define a list of all telephone numbers that are allowed to establish connection with the server computer, based on the list of registered user profiles. By default, all telephone numbers are denied from establishing access with the server computer, except those ones explicitly set by allow-number option. If the allow-number option is not present in pppd's configuration file, all telephone numbers are allowed to establish connection with the server computer, so be sure to include the allow-number option in pppd's configuration file if you want to control who can/cannot establish connection with the server computer. ##### centos-pppd-config will overwrite this part!!! (begin) ##### allow-number 12345 allow-number 21345 allow-number 34567 ##### centos-pppd-config will overwrite this part!!! (end) ##### The centos-pppd-admin application must be considered part of user profile registration process inside the server computer. The centos-pppd-admin application would be used to control the list of allowed telephone numbers inside the pppd's configuration file, based on the list of user profiles. The centos-pppd-admin application should be executed after any registration/deletion action against the list of user profiles with root privilages in order to be able of writing the settings on pppd's configuration file. Redialing consecutive connections from the same telephone number without any dealy between call retries must be avoided from client computers. This would reduce the possibilities for other client computers to establish connection with the server computer. To prevent this issue from happening, it would be necessary to provide more telephone lines than users authorized to establish connection with the server computer. Nevertheless, there is only one telephone line available for the server computer to use.