单项选择题 Which WAN service utilizes two different encapsulation types (one for data and one for signaling) on its data link layer?（）

单项选择题 A router receives a packet on interface 172.16.45.66/26. The source IP of the packet is 172.16.45.127/26 and the destination is 172.16.46.191/26.How will the router handle the packet?（）

单项选择题 Network equipment supporting the use of flow control mechanisms has been recently installed. What is the purpose of flow control in a data network?（）