Presentation Contexts#

Presentation Contexts are used during the negotiation of an association to provide a method for communicating applications to agree on a set of supported services. Each presentation context consists of an Abstract Syntax and one or more Transfer Syntaxes, along with an ID value.

  • The association requestor may propose multiple presentation contexts per association but is limited to a maximum of 128 proposed contexts.

  • Each proposed presentation context contains one Abstract Syntax and one or more Transfer Syntaxes.

  • The requestor may propose multiple contexts with the same Abstract Syntax

  • The association acceptor may accept or reject each presentation context individually, but only one Transfer Syntax may be accepted per presentation context.

  • The acceptor selects a suitable Transfer Syntax for each accepted presentation context.

A more detailed guide to presentation contexts and how to use them with pynetdicom is available here.

Abstract Syntax#

An Abstract Syntax is a specification of a set of data elements and their associated semantics. Each abstract syntax is identified by an Abstract Syntax Name in the form of a UID. Abstract syntax names used with DICOM are usually the officially registered SOP Class UIDs (and the abstract syntax is therefore the SOP class itself), but the standard also allows the use of private abstract syntaxes.

While pynetdicom can handle association negotiation containing private abstract syntaxes the implementation of the associated services is up to the end user and should be specified with the register_uid() function.

Transfer Syntax#

A Transfer Syntax defines a set of encoding rules able to unambiguously represent the data elements defined by one or more abstract syntaxes. In particular, the negotiation of transfer syntaxes allows communicating AEs to agree on the encoding techniques they are able to support (i.e. byte ordering, compression, etc.).

The official DICOM transfer syntaxes are defined in Part 5 of the DICOM Standard and the Standard also allows the use of privately defined transfer syntaxes.