The Incoming-Call-Reply is a PPTP control message sent by the PNS to the PAC in response to a received Incoming-Call-Request message. The reply indicates the result of the incoming call attempt. It also provides information to allow the PAC to regulate the transmission of data to the PNS for this session.
This message is the second in the three-way handshake used by PPTP for establishing incoming calls. It indicates to the PAC whether the call should be answered or not.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | PPTP Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Magic Cookie |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Control Message Type | Reserved0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Call ID | Peer's Call ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Result Code | Error Code | Packet Recv. Window Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet Transmit Delay | Reserved1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LengthTotal length in octets of this PPTP message, including the entire PPTP header.
PPTP Message Type1 for Control Message.
Magic Cookie0x1A2B3C4D.
Control Message Type10 for Incoming-Call-Reply.
Reserved0This field MUST be 0.
Call IDA unique identifier for this tunnel assigned by the PAC to this session. It is used to multiplex and demultiplex data sent over the tunnel between the PNS and PAC involved in this session.
Peer's Call IDThis field is set to the value received in the Call ID field of the corresponding Incoming-Call-Request message. It is used by the PAC to match the Incoming-Call-Reply with the Incoming-Call-Request it issued. This value is included in the GRE header of transmitted data packets for this session.
Result CodeThis value indicates the result of the Incoming-Call-Request attempt. Current valid Result Code values are:
1 (Connect) - The PAC should answer the incoming call
2 (General Error) - The Incoming Call should not be established due to the reason indicated in Error Code
3 (Do Not Accept) - The PAC should not accept the incoming call. It should hang up or issue a busy indication
Error CodeThis field is set to 0 unless a "General Error" condition exists, in which case Result Code is set to 2 and this field is set to the value corresponding to the general error condition as specified in Section 2.16.
Packet Recv. Window Size The number of received data packets the PAC will buffer for this session.
Packet Transmit DelayA measure of the packet processing delay that might be imposed on data sent to the PAC from the PNS. This value is specified in units of 1/10 seconds. See Appendix A for a description of how this value is determined and used.
Reserved1This field MUST be 0.