Modems are probably ringing and not answering while a terminal server is dumped and rebooting. X9.2.21 has been running on TS6 for six days now without crashing. This isn't long enough to show conclusively that it solves the dumping problem, but it's probably long enough to show that X9.2.21 isn't substantially worse than X9.2.13. PPP negotiations between the terminal server and the remote client sometimes fail in either of two ways. I don't know if we have a reliable way to determine the frequency of this problem.
Users fail to establish a session.
The terminal server port is sometimes left in a hung state, in which case the modem rings without answering until the port is reset. This typically happens about ten times a day. The user is successfully authenticated via PAP, but the two parties get into an infinite loop while negotiating the IP address. This typically happens between two and twelve times a day. Users fail to establish a session and the two sides continue negotiating indefinitely until the user disconnects.