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2.2.9 Call Connect Request Message (SSTP_MSG_CALL_CONNECT_REQUEST)

The following diagram specifies the format that MUST be used for the Call Connect Request message. This message MUST be the first message that is sent by the SSTP client after it establishes an HTTPS connection with the server. The client uses this message to request the establishment of an SSTP connection with the server. Note that this message follows the format of an SSTP control packet.

The fields of the structure MUST be transmitted in network byte order from left to right.


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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 and corresponds to Version 1.0.

 

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 an SSTP data packet. The value MUST be 1 for a Call Connect Request message that is a control packet.

 

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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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.

 

Length (12 bits): A 12-bit unsigned integer in network byte order that MUST specify the length, in bytes, of the entire Call Connect Request message.

Message Type (2 bytes): A 16-bit field in network byte order that specifies the type of message. It MUST be 0x0001 (SSTP_MSG_CALL_CONNECT_REQUEST).

 

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 0x0001 because SSTP Version 1 supports only the Encapsulated Protocol ID attribute by using a Protocol ID value of PPP. For more information, see [RFC1661].

 

Reserved1 (1 byte): This 8-bit field is reserved for future use. MUST be set to zero when sent and MUST be ignored on receipt.

 

Attribute ID (1 byte): An 8-bit (1-byte) field that is used to specify the type of attribute; its value MUST be 0x01 for the Encapsulated Protocol ID attribute.

 

LengthPacket1 (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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R1 (4 bits): This 4-bit field is reserved for future use. MUST be set to zero when sent and MUST be ignored on receipt.

 

Length1 (12 bits): A 12-bit unsigned integer in network byte order that contains the value 0x006 for the Encapsulated Protocol ID attribute length.

Protocol ID (2 bytes): A 2-byte field in network byte order that contains the value 0x0001 (that is, SSTP_ENCAPSULATED_PROTOCOL_PPP ). Note that SSTP Version 1 supports only the transport of PPP frames. For more information, see [RFC1661].

 
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