This property enable applications to share or negotiate extended information about themselves.
The exact meanings of the various values and byte positions used for extended negotiation vary from one service class to another, and they are all detailed in part 4 of DICOM. e.g. for C-STORE operations, byte 1 represents the "storage level", byte 3 the level of digital signature support and byte 5 controls the coercion of data elements (2,4, & 6 are reserved). However, for C-FIND operations, only 1 byte is specified, indicating whether the SCP supports relational queries. In all cases, support is optional, and default values exist if extended negotiation is not performed.
If this property is set to true, then any extended negotiation items set up before Open are proposed. When incoming associations are received, then incoming values are automatically sent out again (i.e. accepted) unless altered using the ExtendedNegotiationValues property in the AssociationRequest event.
Once an association is established, this property becomes read-only, but still reflects the arrangement negotiated.
Please note that this property is shared between all contexts with the same AbstractSyntax (SOP class), so changing one will change the value for any other matching contexts.