适配器中的Vc状态表 *记录当前存在哪些VC、哪些VC有信元要发送、每条v℃拥有 多少cred等 *既有信元又有ced的vC称为就绪的VC(可调度发送的VC Active Active Active has credits Inactive no credits has credits VC VC 5 7 FIGURE 4.3 An ATM virtual circuit is eligible to send data if it is active(has some outstanding cells to send in the queue shown below the vC)and has credits(shown by black dots above the vC). the problem is to select the next eligible vC in some fair manner without stepping through VCs that are ineligible适配器中的VC状态表  记录当前存在哪些VC、哪些VC有信元要发送、每条VC拥有 多少credit等  既有信元又有credit的VC称为就绪的VC（可调度发送的VC ）