DICOM PS3.8 2021b - Network Communication Support for Message Exchange

E.2 Message Control Header Encoding (Current)
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## 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:

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

2. 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:

1. 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.

2. 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.

Figure E.2-1. Presentation Data Value and the Message Control Header

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DICOM PS3.8 2021b - Network Communication Support for Message Exchange