4.1.1 Creating the MESSAGE_PACKETs
To start the connection the initiator allocates the next free connection identifier; in this instance, it is 0x00000001. The initiator then creates a MESSAGE_PACKET, with the MsgTag field set to MTAG_CONNECTION_REQ (0x00000005) (section 3.1.5.5) and with the dwUserMsgType field set to 0x00000101 (which is CONNTYPE_PARTNERTM_PROPAGATE as specified in [MS-DTCO]. By definition, the instance that creates the connection always sets the fIsMaster field to 0x00000001, and as this MESSAGE_PACKET structure contains no extra data, the dwcbVarLenData is set to 0x00000000.
The following table displays the first MESSAGE_PACKET structure that the initiator creates (all values are 32-bits wide).
|
Field |
Value |
Value description |
|---|---|---|
|
MsgTag |
0x00000005 |
MTAG_CONNECTION_REQ |
|
fIsMaster |
0x00000001 |
1 |
|
dwConnectionId |
0x00000001 |
1 |
|
dwUserMsgType |
0x00000101 |
CONNTYPE_PARTNERTM_PROPAGATE |
|
dwcbVarLenData |
0x00000000 |
0 |
|
dwReserved1 |
0xcd64cd64 |
dwReserved1: 0xcd64cd64 |
The initiator then creates a second MESSAGE_PACKET to contain the user message. It sets the MsgTag field to MTAG_USER_MESSAGE (0x00000FFF) (section 3.1.5.6) and the dwUserMsgType field to 0x00002001 (which is PARTNERTM_PROPAGATE_MTAG_PROPAGATE as specified in [MS-DTCO]).
The MESSAGE_PACKET also contains an extra 64 bytes of data for the message body, so it sets the dwcbVarLenData field to 0x00000040. The message body that follows is specific to the message; in this instance, it specifies a transaction ID (guidTx, set to 9fa8a337-eaf7-4230-9232-b57379d65077), a transaction isolation level (isoLevel, set to 0x00100000, which is ISOLATIONLEVEL_SERIALIZABLE), and a transaction description (szDesc, set to the string "Example Transaction - 39 chars long...."). The following table is the second MESSAGE_PACKET structure that the initiator creates.
|
Field |
Value |
Value description |
|---|---|---|
|
MsgTag |
0x00000FFF |
MTAG_USER_MESSAGE |
|
fIsMaster |
0x00000001 |
1 |
|
dwConnectionId |
0x00000001 |
1 |
|
dwUserMsgType |
0x00002001 |
PARTNERTM_PROPAGATE_MTAG_PROPAGATE |
|
dwcbVarLenData |
0x00000040 |
64 |
|
dwReserved1 |
0xcd64cd64 |
dwReserved1: 0xcd64cd64 |
|
|
|
|
isoLevel |
0x00100000 |
ISOLATIONLEVEL_SERIALIZABLE |
|
|
|
To send these MESSAGE_PACKETs, the initiator wraps the two messages into a single boxcar, which is in turn passed to the instance of the underlying transports protocol specified in [MS-CMPO], as specified in sections 2.1.1.3 and 3.1.7.1.