E.2 Message control header encoding

The Message Control Header is located in front of each DICOM message fragment (see Figure E.2-1). Its presence is mandatory for all DICOM Abstract Syntaxes (see Annex B for further discussion on Abstract Syntaxes).

The Message Control Header shall be made of one byte with the least significant bit (bit 0) taking one of the following values:

a) If bit 0 is set to 1, the following fragment shall contain Message Command information.

b) If bit 0 is set to 0, the following fragment shall contain Message Data Set information.

The next least significant bit (bit 1) shall be defined by the following rules:

a) If bit 1 is set to 1, the following fragment shall contain the last fragment of a Message Data Set or of a Message Command.

b) If bit 1 is set to 0, the following fragment does not contain the last fragment of a Message Data Set or of a Message Command.

Bits 2 through 7 are always set to 0 by the sender and never checked by the receiver.

Note: The Message Control Header, in the Transport data flow, is the 1st byte in each PDV. The Transfer Syntax, negotiated at association establishment, defines the encoding for the Command/Data fragment.

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Figure E.2-1 PRESENTATION DATA VALUE AND THE MESSAGE CONTROL HEADER