<Standard Message Header>

Each message, administrative or application, is preceded by a standard header . The header is used to identify the message type, length, destination, sequence number, origination point and time.

Two fields are provided for use when resending messages. The PossDupFlag (43) is set when resending a message as the result of a session level event (i.e. the retransmission of a message reusing a sequence number). The PossResend (97) is set when reissuing a message with a new sequence number (e.g. resending an order). The receiving application should process these messages as follows:

PossDup - if a message with this sequence number has been previously received, ignore message, if not, process normally.
PossResend - forward message to application and determine if previously received (i.e. verify order id and parameters)

Used in all messages

Tag	Field Name	Req'd	Comments
8	BeginString	Y	FIX.4.0 (Always unencrypted, must be first field in message)
9	BodyLength	Y	(Always unencrypted, must be second field in message)
35	MsgType	Y	(Always unencrypted, must be third field in message)
49	SenderCompID	Y	(Always unencrypted)
56	TargetCompID	Y	(Always unencrypted)
115	OnBehalfOfCompID	N	Trading partner company ID used when sending messages via a third party (Can be embedded within encrypted data section.)
128	DeliverToCompID	N	Trading partner company ID used when sending messages via a third party (Can be embedded within encrypted data section.)
90	SecureDataLen	C	Required to identify length of encrypted section of message. (Always unencrypted)
91	SecureData	C	Required when message body is encrypted. Always immediately follows SecureDataLen (90) field.
34	MsgSeqNum	Y	(Can be embedded within encrypted data section.)
50	SenderSubID	N	(Can be embedded within encrypted data section.)
57	TargetSubID	N	'ADMIN' reserved for administrative messages not intended for a specific user. (Can be embedded within encrypted data section.)
116	OnBehalfOfSubID	N	Trading partner SubID used when delivering messages via a third party. (Can be embedded within encrypted data section.)
129	DeliverToSubID	N	Trading partner SubID used when delivering messages via a third party. (Can be embedded within encrypted data section.)
43	PossDupFlag	N	Always required for retransmissions, whether prompted by the sending system or as the result of a resend request. (Can be embedded within encrypted data section.)
97	PossResend	N	Required when message may be duplicate of another message sent under a different sequence number. (Can be embedded within encrypted data section.)
52	SendingTime	Y	(Can be embedded within encrypted data section.)
122	OrigSendingTime	N	Required for message resends. If data is not available set to same value as SendingTime (52) (Can be embedded within encrypted data section.)