2.2.15 Call Disconnect Acknowledge (SSTP_MSG_CALL_DISCONNECT_ACK), Echo Request (SSTP_MSG_ECHO_REQUEST), and Echo Response (SSTP_MSG_ECHO_RESPONSE) Messages
These messages are identical in wire format except for the message type field.
A Call Disconnect Acknowledge message can be sent by both the SSTP client and the SSTP server to each other (that is, to the SSTP far end) in response to a Call Disconnect message that is received from the SSTP far end.
The Echo Request message is sent by both the SSTP client and the SSTP server when they do not receive an SSTP packet (either an SSTP control packet or SSTP data packet) in a specified amount of time. See Hello Timer (section 3.1.2.3) for details.
The Echo Response message is sent by both the SSTP client and the SSTP server to each other in response to an Echo Request packet that is received from one another.
The fields of the structure MUST be transmitted in network byte order from left to right.
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Version |
Reserved |
C |
LengthPacket |
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Num Attributes |
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Version (1 byte): An 8-bit (1-byte) field that is used to communicate and negotiate the version of SSTP that is used. The upper 4 bits are the MAJOR version, which MUST be 0x1, and the lower 4 bits are the MINOR version, which MUST be set to 0x0. This means that the 8-bit value of the Version field MUST be 0x10.
Reserved (7 bits): This 7-bit field is reserved for future use. MUST be set to zero when sent and MUST be ignored on receipt.
C (1 bit): A 1-bit field that is used to indicate whether the packet is an SSTP control packet or SSTP data packet. The value MUST be set to 1.
LengthPacket (2 bytes): A 16-bit unsigned integer in network byte order that packs data for two fields, configured in the following format.
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0
1
2
3
4
5
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7
8
9
1
0
1
2
3
4
5
R
Length
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R (4 bits): This 4-bit field is reserved for future use. MUST be set to zero when sent and MUST be ignored on receipt.
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Length (12 bits): A 12-bit unsigned integer in network byte order that MUST specify the length of the Call Disconnect Acknowledge, Echo Request, or Echo Response message. This field MUST be set to 8 (0x008).
Message Type (2 bytes): A 16-bit field in network byte order that specifies the type of message. This field MUST be one of the following values.
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Name
Value
SSTP_MSG_CALL_DISCONNECT_ACK
0x0007
SSTP_MSG_ECHO_REQUEST
0x0008
SSTP_MSG_ECHO_RESPONSE
0x0009
Num Attributes (2 bytes): A 16-bit field in network byte order that specifies the number of attributes in the message. This value MUST be zero for these messages because they do not support any attribute.