To maintain the streaming connection (a better name may have been "session"), both server and clients send heartbeats/PINGs. If the server misses a configured amount of heartbeats from the client, it will close the connection, which also means deleting all non-durable subscriptions. If the client was "network partitioned" from the server when that happened, even after the partition is resolved, the client would not know what happened. Again, to understand how that is possible, see the topology example above: the network partition happened between the two clustered NATS Servers, and no TCP connection between the streaming client and/or streaming server was ever lost.