Callback Control Protocol (CBCP)

Author:

  Narendra C. Gidwani (nareng@microsoft.com)

Presented by:

  Gurdeep S. Pall (gurdeep@microsoft.com)

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How does CallBack CP work?

  o  LCP Option 13, Operation field value 6 used by peers to agree
     to run CBCP after Authentication Phase.

  o  After Authentication Phase, peers enter into CallBack Phase.

     -  All NCP and network layer packets are Silently Discarded.

     -  Peers use CBCP to negotiate CallBack information.

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CallBack Phase

  o  Answerer sends CallBack Request with list of valid CallBack
     Options.

  o  Caller sends CallBack Response, choosing one of the offered
     Options.

  o  Answerer sends CallBack Ack.

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Why LCP extension is not adequate?

  o  Requires callback information to be negotiated before user
     credentials have been authenticated.

     -  Server may not have been configured to allow callback
        for that user.

     -  Callback number that the server has to use depends on 
        user identity.

  o  Current definition not fully defined.

     -  Operations fields can have wide interpretation.

     -  Modem reset delays are not communicated.

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What are the CallBack Scenarios?

  o  No callback - normal dial-in

  o  Server calls back the user at predetermined number for security

  o  Allow user to request callback to user's current location for 
     billing convenience

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Why CallBack?

  o  Security

     -  Dial-in access from predetermined phone numbers only

  o  User Convenience

     -  Server side billing of the phone call