The time taken for this round-trip of request and acknowledgment determines the network's latency.
就是因为这种往返的要求和回应，导致了网络的延迟。
2
Although unlikely, it is possible that the RPC server will die just after sending us the answer, but before sending an acknowledgment message for the request.
尽管几率很小，可还是有可能??RPC服务在给我们发送完响应后宕掉，但还没来得进行消息确认。
3
However, you can request that an acknowledgment message be sent if a delivery failure prevents a message from arriving in the queue.