Supported control messages

• control connection management

  The following messages are used to maintain the control connection:

  • Start-Control-Connection-Request

  • Start-Control-Connection-Reply

  • Stop-Control-Connection-Request

  • Stop-Control-Connection-Reply

  • Echo-Request

  • Echo-Reply

  The remaining control message types are sent over the established TCP session to open/maintain sessions and to convey information about the link state:

• call management

  Call management messages are used to establish/terminate a session/call and to exchange information about the multiplexing field (Call-id). Call-IDs must be captured and translated by the NAT. The call management messages are:

  • Outgoing-Call-Request (contains Call ID)

  • Outgoing-Call-Reply (contains Call ID and peer’s Call-ID)

  • Call-Clear-Request (contains Call ID)

  • Call-Disconnect-Notify (contains Call ID)

• error reporting

  This message is sent by the client to indicate WAN error conditions that occur on the interface supporting PPP.

  Wan-Error-Notify contains Call ID and Peer’s Call ID.

• PPP session control

  This message is sent in both directions to setup PPP-negotiated options.

  Set-Link-Info contains Call ID and Peer’s Call ID.

After Call-ID is negotiated by both endpoints, it is inserted in GRE header and used as multiplexing field in the tunnel that carries data traffic.