DICOM PS3.7 2020a - Message Exchange

D.3.3.3 Asynchronous Operations (And Sub-Operations) Window Negotiation (Current)
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#### D.3.3.3 Asynchronous Operations (And Sub-Operations) Window Negotiation

The Asynchronous Operations Window is used to negotiate the maximum number of outstanding operation or sub-operation requests (i.e., command requests) for each direction. The synchronous operations mode is the default mode and shall be supported by all DICOM AEs. This negotiation is optional.

The Association-requester conveys in the A-ASSOCIATE request:

- when negotiating the SCU role for operations, the maximum number of outstanding operations it may invoke asynchronously; when negotiating the SCP role for operations, the maximum number of outstanding sub-operations it may invoke asynchronously; when negotiating the SCP role for notifications, the maximum number of notifications it may invoke asynchronously

- when negotiating the SCP role for operations, the maximum number of outstanding operations it may invoke asynchronously; when negotiating the SCU role for operations, the maximum number of outstanding sub-operations it may perform asynchronously; when negotiating the SCU role for notifications, the maximum number of notifications it may perform asynchronously when negotiating the SCP role

A value of zero indicates that the above parameters are unlimited. A value of one indicates that there is no Asynchronous Operations support. If the Asynchronous Operations Window is absent the default for the above parameters shall be equal to one.

The Association-acceptor conveys in the A-ASSOCIATE response:

- when negotiating the SCP role for operations, the maximum number of outstanding operations; when negotiating the SCU role for operations, the maximum number of sub-operations it allows the Association-requester to invoke asynchronously; when negotiating the SCU role for notifications, the maximum number of outstanding notifications it allows the Association-requester to invoke asynchronously when negotiating the SCU role. This number shall be equal or less than the number of outstanding notifications, operations and/or sub-operations the Association-requester offers to invoke (by the A-ASSOCIATE indication).

- when negotiating the SCU role for operations, the maximum number of outstanding operations; when negotiating the SCP role for operations, the maximum number of sub-operations it allows the Association-requester to perform asynchronously; when negotiating the SCP role for notifications, the maximum number of outstanding notifications it allows the Association-requester to perform asynchronously. This number shall be equal or less than the number of outstanding notifications, operations and/or sub-operations the Association-requester offers to perform (by the A-ASSOCIATE indication).

A value of zero indicates that the above parameters are unlimited. If the Asynchronous Operations Window is absent the default for the above parameters shall be equal to one. Figures D.3-5 and D.3-6 illustrate examples of Asynchronous Operations Window negotiation.

If this negotiation is not present in the A-ASSOCIATE indication it shall be omitted in the A-ASSOCIATE response.

### Note

The case where the Association-requester offers the value of zero (which indicates unlimited operations), the Association-acceptor may return zero (agreeing to unlimited operations) or negotiate the parameter down by conveying a value other than zero.

Figure D.3-5. Asynchronous Operations Window Negotiation (Window Being Negotiated Down By DICOM Application Entity "B")

Figure D.3-6. Asynchronous Operations Window Negotiation (Window Being Defaulted to 1, 1 By DICOM Application Entity "B")

##### D.3.3.3.1 Asynchronous Operations Window Sub-Item Structure (A-ASSOCIATE-RQ)

The Asynchronous Operations Window Sub-Item shall be made of a sequence of mandatory fixed length fields. This Sub-Item is optional and if supported, only one Asynchronous Operations Window Sub-Item shall be present in the User Data Item of the A-ASSOCIATE-RQ. Table D.3-7 shows the sequence of the mandatory fields.

Table D.3-7. Asynchronous Operations Window Sub-Item Fields (A-ASSOCIATE-RQ)

Item Bytes | Field Name | Description of Field
--- | --- | ---
1 | Item-type | 53H
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 Maximum-number-operations-performed field. In the case of this Sub-Item, it shall have the fixed value of 00000004H encoded as an unsigned binary number.
5 - 6 | Maximum-number-operations-invoked | This field shall contain the Maximum-number-operations-invoked as defined for the Association-requester in Section D.3.3.3. It shall be encoded as an unsigned binary number.
7-8 | Maximum-number-operations-performed | This field shall contain the Maximum-number-operations-performed as defined for the Association-requester in Section D.3.3.3. It shall be encoded as an unsigned binary number.

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