9.3.3 A-ASSOCIATE-AC PDU STRUCTURE

An A-ASSOCIATE-AC PDU shall be made of a sequence of mandatory fields followed by a variable length field. Table 9-17 shows the sequence of the mandatory fields.

The variable field consist of one Application Context Item, one or more Presentation Context Items, and one User Information Item. Sub-Items shall exist for the Presentation Context and User Information Items.

Table 9-17 ASSOCIATE-AC PDU fields

PDU bytes Field name Description of field
1 PDU-type 02H
2 Reserved This reserved field shall be sent with a value 00H but not tested to this value when received.
3-6 PDU-length This PDU-length shall be the number of bytes from the first byte of the following field to the last byte of the variable field. It shall be encoded as an unsigned binary number.
7-8 Protocol- version This two byte field shall use one bit to identify each version of the DICOM UL protocol supported by the calling end-system. This is Version 1 and shall be identified with bit 0 set. A receiver of this PDU implementing only this version of the DICOM UL protocol shall only test that bit 0 is set.
9-10 Reserved This reserved field shall be sent with a value 0000H but not tested to this value when received.
11-26 Reserved This reserved field shall be sent with a value identical to the value received in the same field of the A-ASSOCIATE-RQ PDU, but its value shall not be tested when received.
27-42 Reserved This reserved field shall be sent with a value identical to the value received in the same field of the A-ASSOCIATE-RQ PDU, but its value shall not be tested when received.
43-74 Reserved This reserved field shall be sent with a value identical to the value received in the same field of the A-ASSOCIATE-RQ PDU, but its value shall not be tested when received.
75-xxx Variable items This variable field shall contain the following items: one Application Context Item, one or more Presentation Context Item(s) and one User Information Item. For a complete description of these items see Sections 7.1.1.2, 7.1.1.14, and 7.1.1.6.

9.3.3.1 Application context item structure

An Application Context Item shall be made of a sequence of mandatory fields followed by a variable length field. Table 9-12 shows the sequence of mandatory fields.

9.3.3.2 Presentation context item structure

The Presentation Context Item shall be made of a sequence of mandatory fixed length fields followed by a variable field. Table 9-18 shows the sequence of the mandatory fields.

The variable field shall consist of one Transfer Syntax Sub-Item.

Table 9-18 PRESENTATION CONTEXT ITEM FIELDS

Item bytes Field name Description of field
1 Item-type 21H
2 Reserved This reserved field shall be sent with a value 00H but not tested to this value when received.
3-4 Item-length This Item-length shall be the number of bytes from the first byte of the following field to the last byte of the Transfer Syntax Sub-Item. It shall be encoded as an unsigned binary number.
5 Presentation- context-ID Presentation-context-ID values shall be odd integers between 1 and 255, encoded as an unsigned binary number. For a complete description of the use of this field see Section 7.1.1.13.
6 Reserved This reserved field shall be sent with a value 00H but not tested to this value when received.
7 Result/Reason This Result/Reason field shall contain an integer value encoded as an unsigned binary number. One of the following values shall be used: 0 - acceptance 1 - user-rejection 2 - no-reason (provider rejection) 3 - abstract-syntax-not-supported (provider rejection) 4 - transfer-syntaxes-not-supported (provider rejection)
8 Reserved This reserved field shall be sent with a value 00H but not tested to this value when received.
9-xxx Transfer syntax sub-item This variable field shall contain one Transfer Syntax Sub-Item. When the Result/Reason field has a value other than acceptance(0), this field shall not be significant and its value shall not be tested when received. For a complete description of the use and encoding of this item see Section 9.3.3.2.1.

9.3.3.2.1 Transfer syntax sub-item structure

The Transfer Syntax Sub-Item shall be made of a sequence of mandatory fixed length fields followed by a variable field. Table 9-19 shows the sequence of the mandatory fields.

Table 9-19 TRANSFER SYNTAX SUB-ITEM FIELDS

Item bytes Field name Description of field
1 Item-type 40H
2 Reserved This reserved field shall be sent with a value 00H but not tested to this value when received.
3-4 Item-length This Item-length shall be the number of bytes from the first byte of the following field to the last byte of the Transfer-syntax-name field. It shall be encoded as an unsigned binary number.
5-xxx Transfer-syntax-name This variable field shall contain the Transfer-syntax-name proposed for this presentation context. A valid Transfer-syntax-name shall be encoded as defined in Annex F. For a description of the use of this field see Section 7.1.1.14. Transfer-syntax-names are structured as UIDs as defined in PS 3.5 (see Annex B for an overview of this concept). DICOM Transfer-syntax-names are registered in PS 3.5.

9.3.3.3 User information item structure

The User Information Item shall be made of a sequence of mandatory length fields followed by a variable field. Table 9-20 shows the sequence of the mandatory fields.

The variable field shall consist of one or more User-Data Sub-Items.

Note: The User-Data Sub-Items may be present in any order within the User-Information Item. No significance should be placed on the order of User-Data Sub-Items within the User Information Item. Sending applications should be aware that some older applications might expect Sub-Items to be encoded in ascending order of Item-type within the enclosing Item.

Table 9-20 USER INFORMATION ITEM FIELDS

Item bytes Field name Description of field
1 Item-type 50H
2 Reserved This reserved field shall be sent with a value 00H but not tested to this value when received.
3-4 Item-length This Item-length shall be the number of bytes from the first byte of the following field to the last byte of the User-data-information field(s). It shall be encoded as an unsigned binary number.
5-xxx User-data This variable field shall contain User-data sub-items as defined by the DICOM Application Entity. The structure and content of these sub-items is defined in Annex D.