When L2CAP channels are moved from one Controller to another data can be lost. Also, some applications require a residual （殘留的;殘余的）error rate much smaller than some Controllers can deliver. L2CAP provides error checks and retransmissions of L2CAP PDUs. The error checking in L2CAP protects against errors due to Controllers falsely（虛偽，不實地） accepting packets that contain errors but pass Controller-based integrity checks. L2CAP error checking and retransmission also protect against loss of packets due to flushing by the Controller. The error control works in conjunction with（與...協(xié)力 ）flow control in the sense that（也就是說） the flow control mechanism will throttle （調(diào)節(jié)）retransmissions as well as first transmissions

1.l2cap 提供了錯誤檢查和重傳l2cap pdus.

這種錯誤檢查是為了對抗固件接收了那些通過了控制器的crc，hec檢查的負負得正的錯誤包.

2.重傳也用于保護由于控制機flush引起的丟包

（實際controller也有很多其他原因?qū)е聛G包，如檢查到l2cap len 因為負負得正超過正常數(shù)據(jù)包大小，而遭到丟棄；如因為控制器自身buffer管理原因造成丟包；如沒有及時收取hw的內(nèi)存數(shù)據(jù)而hw ack對方后立即使用該buffer）

3.the error control 和flow control的協(xié)作也就是流程控制機制將會調(diào)節(jié)重傳就好像是第一次傳輸一樣.