State information exchange among connected devices

A system comprising a plurality of playback devices, wherein each playback device comprises:

• one or more processors;
• and
• one or more storage devices that comprise instruction code that is executable by at least one of the one or more processors,
• wherein instruction code executed by one or more processors of a particular primary playback device (PPD) causes the particular PPD to:
• receive state information from a particular secondary playback device (SPD), wherein the state information specifies a state associated with at least one aspect of the particular SPD, and
• after receiving a subscription from one or more other PPDs for the state of the particular aspect of the particular SPD, communicate the state information that specifies the state of the particular aspect of the particular SPD to the one or more other PPDs.

A system comprising a plurality of playback devices, wherein each playback device comprises:

• one or more processors;
• and
• one or more storage devices that comprise instruction code that is executable by at least one of the one or more processors,
• wherein instruction code executed by one or more processors of a particular primary playback device (PPD) causes the particular PPD to:
• receive state information from a particular secondary playback device (SPD), wherein the state information specifies a state associated with at least one aspect of the particular SPD, and
• after receiving a subscription from one or more global state aggregation devices (GSADs) for the state of the particular aspect of the particular SPD, communicate the state information that specifies the state of the particular aspect of the particular SPD to the one or more GSADs,
• wherein instruction code executed by one or more processors of the one or more GSADs causes the one or more GSADs to:
• after receiving a subscription from one or more other GSADs for the state of the particular aspect of the particular SPD, communicate the state information to the one or more other GSADS.

A playback device comprising:

• one or more processors;
• and
• one or more storage devices that comprise instruction code that is executable by at least one of the one or more processors,
• wherein the playback device corresponds to a primary playback device (PPD) and wherein instruction code executed by one or more processors of the playback device causes the playback device to:
• receive state information from a particular secondary playback device (SPD), wherein the state information specifies a state associated with at least one aspect of the particular SPD, and
• after receiving a subscription from one or more other PPDs for the state of the particular aspect of the particular SPD, communicate the state information that specifies the state of the particular aspect of the particular SPD to the one or more other PPDs.