单项选择题
Which frame field do error detection schemes view to perform their function?（）
A. ERR B. Flag C. FCS D. MTU E. MAC F. PDU
单项选择题 Which of one the following fields is contained within an IEEE Ethernet frame header?（）
单项选择题 Which device enables a router serial interface to connect to the ISDN BRI?（）
多项选择题 What functions do routers perform in a network?（）
