单项选择题
What is the function of the AJB bits on DS1 using Extended Super Frame （ESF）？（）
A.It is used for signaling on-hook and off-hook status B.It carries CRC information for error detection C.It is used for a control and performance information D.It is used for a frame’s synchronization and alignment
单项选择题 Duringthemodembootprocess，howdoesthemodemacquirethedownstreamchannel？（）
单项选择题 WhatprotocoldoesanIPphoneusetolearnthevoiceVLANIDitshoulduseforvoicetraffic？（）
单项选择题 WhatistheeffectofchangingDMTinterleaveddelayfrom3millisecondsto15milliseconds？（）
