A Presentation Context may be considered as a negotiated “sub-channel” with a DICOM Association through which the Application Entities have agreed to exchange information.

A proposed presentation context consists of

• A presentation context ID (an odd integer <= 255, and unique within the association)
• A SOP Class or Meta SOP Class
• A list of proposed Transfer Syntaxes

This is considered by the requesting Application Entity which either rejects it completely or accepts, in which case the list of proposed transfer syntaxes is replaced by a single accepted transfer syntax which is then used for all communications using that presentation context.

Such subsequent communications only quote the presentation context ID, and so applications must retain copy of the agreed information in order to determine the SOP class and transfer syntax used.