问题
单项选择题
SDLC was invented by IBM to replace the older Bisynchronous protocol for wide area connections between IBM equipment. A varietion of the (71) protocol called NRM is essentially the same as SDLC. SDLC is (72) protocol like HDLC, Frame Relay or X.25.An SDLC network is made up of (73) that controls all communications, and (74) . It is capable of (75) operation, but almost all practical applications are strictly half duplex.
A．half duplex
B．full duplex
C．half or full duplex
D．half and full duplex
答案
参考答案：B
解析： SDLC由IBM发明用来取代老的双同步协议(用于大范围内IBM设备之间的连接)。各种叫做NRM的(71)协议本质上与SDLC是相同的。SDLC是一种类似HDLC，贞中继或X.25的(72)协议。一个SDLC网络是由(73)组成的，用来控制所有的通信和(74)。他有能力进行(75)操作，但几乎所有的实际应用是严格的半双工。