How do I configure a Point-to-Point Protocol (PPP) dialup server using Red Hat Enterprise Linux?

While dialup modems have become largely obsolete due to broadband Internet connections, there are still situations where dialup access can prove useful. A PPP server in the office can provide employees with an alternative method to access email and the Internet while traveling. Dialup modems can also provide emergency connectivity for system administrators in the event of server or network pro...