Use as an SCU#

Adding requested Presentation Contexts#

If you intend to use your AE as a Service Class User then you need to specify the presentation contexts that will be requested during association negotiation. This can be done in two ways:

You can add requested contexts on a one-by-one basis using the AE.add_requested_context() method.
You can set all the requested contexts at once using the AE.requested_contexts property. Additional contexts can still be added on a one-by-one basis afterwards.

Adding presentation contexts one-by-one:

>>> from pydicom.uid import UID
>>> from pynetdicom import AE
>>> from pynetdicom.sop_class import CTImageStorage
>>> ae = AE()
>>> ae.add_requested_context('1.2.840.10008.1.1')
>>> ae.add_requested_context(UID('1.2.840.10008.5.1.4.1.1.4'))
>>> ae.add_requested_context(CTImageStorage)

Adding presentation contexts all at once:

>>> from pynetdicom import AE, StoragePresentationContexts
>>> ae = AE()
>>> ae.requested_contexts = StoragePresentationContexts

Here StoragePresentationContexts is a prebuilt list of presentation contexts containing 120 of the most commonly used Storage Service Classes’ supported SOP Classes, and there’s a similar list for all the supported service classes. Alternatively you can build your own list of presentation contexts, either through creating new PresentationContext instances or by using the build_context() convenience function:

>>> from pynetdicom import AE, build_context
>>> from pynetdicom.sop_class import CTImageStorage
>>> ae = AE()
>>> contexts = [
...     build_context(CTImageStorage),
...     build_context('1.2.840.10008.1.1')
... ]
>>> ae.requested_contexts = contexts

Combining the all-at-once and one-by-one approaches:

>>> from pynetdicom import AE, StoragePresentationContexts
>>> from pynetdicom.sop_class import Verification
>>> ae = AE()
>>> ae.requested_contexts = StoragePresentationContexts
>>> ae.add_requested_context(Verification)

As the association Requestor you’re limited to a total of 128 requested presentation contexts, so attempting to add more than 128 contexts will raise a ValueError exception. StoragePresentationContexts consists of 120 of most commonly used Storage Service Classes, therefore you are able to add 8 additional presentation contexts without rasing a ValueError exception.

When you add presentation contexts as shown above, the following transfer syntaxes are used by default for each context:

1.2.840.10008.1.2	Implicit VR Little Endian
1.2.840.10008.1.2.1	Explicit VR Little Endian
1.2.840.10008.1.2.1.99	Deflated Explicit VR Little Endian
1.2.840.10008.1.2.2	Explicit VR Big Endian

Specifying your own transfer syntax(es) can be done with the transfer_syntax keyword parameter as either a single str/UID or a list of str/UIDs:

>>> from pydicom.uid import ImplicitVRLittleEndian, ExplicitVRLittleEndian
>>> from pynetdicom import AE
>>> from pynetdicom.sop_class import CTImageStorage, MRImageStorage
>>> ae = AE()
>>> ae.add_requested_context(CTImageStorage, transfer_syntax='1.2.840.10008.1.2')
>>> ae.add_requested_context(
...     MRImageStorage, [ImplicitVRLittleEndian, ExplicitVRLittleEndian]
... )

>>> from pydicom.uid import ImplicitVRLittleEndian, ExplicitVRBigEndian
>>> from pynetdicom import AE, build_context
>>> from pynetdicom.sop_class import CTImageStorage
>>> ae = AE()
>>> context_a = build_context(CTImageStorage, ImplicitVRLittleEndian)
>>> context_b = build_context(
...     '1.2.840.10008.1.1', [ImplicitVRLittleEndian, ExplicitVRBigEndian]
... )
>>> ae.requested_contexts = [context_a, context_b]

The requested presentation contexts can be accessed with the AE.requested_contexts property and are returned in the order they were added.

>>> from pynetdicom import AE
>>> from pynetdicom.sop_class import Verification
>>> ae = AE()
>>> len(ae.requested_contexts)
0
>>> ae.add_requested_context(Verification)
>>> len(ae.requested_contexts)
1
>>> print(ae.requested_contexts[0])
Abstract Syntax: Verification SOP Class
Transfer Syntax(es):
    =Implicit VR Little Endian
    =Explicit VR Little Endian
    =Explicit VR Big Endian

It’s also possible to have multiple requested presentation contexts for the same abstract syntax.

>>> from pydicom.uid import ImplicitVRLittleEndian
>>> from pynetdicom import AE
>>> from pynetdicom.sop_class import CTImageStorage
>>> ae = AE()
>>> ae.add_requested_context(CTImageStorage)
>>> ae.add_requested_context(CTImageStorage, ImplicitVRLittleEndian)
>>> len(ae.requested_contexts)
2
>>> print(ae.requested_contexts[0])
Abstract Syntax: CT Image Storage
Transfer Syntax(es):
    =Implicit VR Little Endian
    =Explicit VR Little Endian
    =Explicit VR Big Endian
>>> print(ae.requested_contexts[1])
Abstract Syntax: CT Image Storage
Transfer Syntax(es):
    =Implicit VR Little Endian

All the above examples set the requested presentation contexts on the Application Entity level, i.e. the same contexts will be used for all association requests. To set the requested presentation contexts on a per-association basis (i.e. each association request can have different requested contexts) you can use the contexts keyword parameter when calling AE.associate() (see the Association page for more information).

Specifying the network port#

In general it shouldn’t be necessary to specify the port when acting as an SCU, as by default pynetdicom will use the first port available. To specify the port number manually you can use the bind_address keyword parameter when requesting an association, which takes:

For IPv4 or IPv6 a 2-tuple of (str host, int port), with the flowinfo and scope_id defaulting to 0 for IPv6, or,
For IPv6 a 4-tuple of (str host, int port, int flowinfo, int scope_id)

>>> from pynetdicom import AE
>>> ae = AE()
>>> ae.add_requested_context('1.2.840.10008.1.1')
>>> assoc = ae.associate("127.0.0.1", 11112, bind_address=("127.0.0.1", 11113))  
>>> assoc.release()
>>> assoc = ae.associate("::1", 11112, bind_address=("::1", 11113))  
>>> assoc.release()

Note

When using bind_address you may sometimes be unable to immediately reconnect with the same bound address and port due to an exception about the socket or address already being in use. This occurs because the previous TCP connection using the bound socket remains in a TIME_WAIT state which must expire before you are able to re-use the socket.