单项选择题
A. Optional authentication phase, link establishment phase, network layer protocol phase.
B. Network layer protocol phase, link establishment phase, optional authentication phase.
C. Network layer protocol phase, optional authentication phase, link establishment phase.
D. Link establishment phase, network layer protocol phase, optional authentication phase.
E. Link establishment phase, optional authentication phase, network layer protocol phase.
F. Optional authentication phase, network layer protocol phase, link establishment phase.
单项选择题 Which Frame Relay feature is responsible for transmitting keepalives to ensure that the PVC does not shut down because of inactivity?（）
多项选择题 Which characteristics are representative of a link-state routing protocol?（）
多项选择题 Which of the following contribute to congestion on an Ethernet network?（）