A coding technique in which a command to read or write is initiated as the need for a new block of data occurs,thus eliminating the need to store data. 需求，当发生对新数据块的需求时，产生一个读或写命令的，它可以减少数据存贮的需求。
The trap command is used by managed devices to asynchronously report events to the NMS. 网络管理系统使用写命令控制被管理设备。
