DICOM PS3.7 2018a - Message Exchange

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