HDLC Normal Response Mode Explained | Generated by AI
Question: In HDLC, the operation mode where the transmission process is initiated by the primary station, and the secondary station can only transmit information to the primary station as a response after receiving a command frame from the primary station is called
A. Normal Response Mode
B. Asynchronous Response Mode
C. Asynchronous Balanced Mode
D. Synchronous Balanced Mode
Your answer: B
Correct answer: A
Answer:
The correct answer is A. Normal Response Mode (NRM).
Explanation:
HDLC (High-level Data Link Control) defines three main operational modes:
- Normal Response Mode (NRM)
- The primary station (主站) has complete control over the link.
- Only the primary station can initiate data transmission.
- The secondary station (从站) is not allowed to transmit anything unless it is explicitly polled or commanded by the primary station.
- After receiving a command frame (especially with the poll bit set), the secondary may respond with one or more frames.
- If multiple frames are sent in response, the last frame must have the final bit (F-bit) set.
- This mode matches exactly the description in the question:
“传输过程由主站启动，从站只有收到主站某个命令帧后，才能作为响应向主站传输信息。”
- Asynchronous Response Mode (ARM)
- The secondary station can initiate transmission at any time without waiting for permission from the primary (asynchronous means no constant polling is required).
- This is the opposite of the behavior described in the question.
- Asynchronous Balanced Mode (ABM)
- Both stations are equal (balanced configuration).
- Either station can initiate transmission at any time.
- Commonly used in point-to-point full-duplex links (e.g., modem connections, LAPB in X.25).
- Clearly not matching the question.
- Synchronous Balanced Mode
- This is not a standard HDLC mode name.
Therefore, the description given in the question is the textbook definition of Normal Response Mode (NRM).
Your choice of B (Asynchronous Response Mode) is incorrect because in ARM the secondary is allowed to send data spontaneously, without needing a command frame from the primary first.
References:
- HDLC protocol standards (ISO 13239 / ITU-T Recommendation)
- Most computer network textbooks (e.g., Tanenbaum, Kurose & Ross, Forouzan) describe NRM exactly as quoted in the question.