(1) In the strength of the carrier signal is varied to represent binary 1 or 0.

(2) is a system that can map a name to an address and conversely an address to an name.

(3) is a three-way handshaking authentication protocol that it’s packets are encapsulated in the point-to-point protocol

(4) is an approach that enables an ATM Switch to behave like a LAN switch.

(5) is an guided media which is made of glass or plastic and transmits signals in the form of light.

2（）

A．NAT

B．NCP

C．DDN

D．DNS

春季的夜晚有哪些著名的星座、亮星？