connection problem with T-Online

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I can't get a stable connection with my T-Online provider. I use pppconfig to create an account. When I create an account to Mobilcom's Freenet provider all is working fine. I can connect to it and surf in the Internet without any problems. But when I wanna connect with my t-online configuration it disconnects after 4-5 secs later. Both are configured with the PAP authorization method. I know how to build my login-name and don't think thats the problem. I've heard something about to prelogin to the provider within the chat-script. I haven't figured out how to set up such a prelogin.   It would be very nice if somebody could help me. Thnx in advance :)