3.4.1 Abstract Data Model
This section describes a conceptual model of possible data organization that an implementation maintains to participate in this protocol. The described organization is provided to facilitate the explanation of how the protocol behaves. This document does not mandate that implementations adhere to this model as long as their external behavior is consistent with the behavior that is described in this document.
The server role MUST maintain the following data elements:
Endpoint Reference Store: A data element that is capable of holding an instance of an endpoint reference or an empty value.
State: An enumeration that identifies the current state of the server role with the following possible values:
WAIT_CM
ENDED
The following figure shows the relationship between server role states.

Figure 10: State diagram for the callback context exchange server role