In SNA, a set of related request/response units(RUs) that are consecutively transmitted on a particular normal or expedited data flow. The request RU chain is the unit of recovery: if one of the RUs in the chain cannot be processed, the entire chain must be discarded.; 在系統(tǒng)網絡體系結構(SNA)中，一組相互有關的請求應答單元(RU)，它們在一種特定的常規(guī)數(shù)據(jù)流或加急數(shù)據(jù)流中連續(xù)傳送。請求RU鏈是恢復單位：若 鏈中有一個RU不能被處理，則整個鏈就得放棄。