In SNA, the layer within a half-session that controls whether the half-session can send, receive, or concurrently send and receive, request units (RUs); group related RUs into RU chains; delimits transactions via the bracket protocol; controls the interlocking of requests and responses in accordance with control modes specified at session activation; generates sequence numbers; and correlates requests and responses.; 在系統(tǒng)網(wǎng)絡(luò)體系結(jié)構(gòu)(SNA)半話路期中的層,它控制半話路期是否能發(fā)送、接收或同時(shí)發(fā) 送和接收請求單元,將相關(guān)的請求單元組合為請求單元鏈,通過分層協(xié)議定界事務(wù),根據(jù)激活 話路時(shí)所規(guī)定的控制方式控制請求和應(yīng)答的連鎖,生成序號并使請求和應(yīng)答相互關(guān)聯(lián)。