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An interface for streamed media channels that can indicate call progress or call states. The presence of this interface is no guarantee that call states will actually be signalled (for instance, SIP implementations are not guaranteed to generate status 180 Ringing, so a call can be accepted without the Ringing flag ever having been set). Get the current call states for all contacts involved in this call. The current call states. Participants where the call state flags would be 0 (all unset) may be omitted from this mapping. Emitted when the state of a member of the channel has changed. An integer handle for the contact. The new state for this contact. A map from contacts to call states. A contact involved in this call. State flags for the given contact. A set of flags representing call states. The contact has been alerted about the call but has not responded (e.g. 180 Ringing in SIP). The contact is temporarily unavailable, and the call has been placed in a queue (e.g. 182 Queued in SIP, or call-waiting in telephony). The contact has placed the call on hold, and will not receive media from the local user or any other participants until they unhold the call again. The initiator of the call originally called a contact other than the current recipient of the call, but the call was then forwarded or diverted.