HDLC (High-level Data Link Control) is widely used at the data link layer. Which description best characterizes HDLC?
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AA method of determining which device has access to the transmission medium at any time
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BAn access control technique for multiple-access transmission media
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CA very common bit-oriented data link protocol issued by ISO.
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DA network access standard for connecting stations to a circuit-switched network
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ENone of the above
Answer
Correct Answer: A very common bit-oriented data link protocol issued by ISO.
Explanation
Introduction / Context: HDLC is a foundational, bit-oriented data link protocol used for point-to-point and multipoint links, influencing protocols such as PPP and LAPB.
Given Data / Assumptions:
- Layer focus: Data Link (Layer 2).
- ISO standardization.
- Frame-based communication with control fields.
Concept / Approach: HDLC defines framing, error detection, and control mechanisms (I/S/U frames). Being bit-oriented means control is defined at the bit level (flags, bit stuffing) rather than fixed byte boundaries for characters.
Step-by-Step Solution:
1) Frames are delimited by flag 01111110.2) Bit-stuffing prevents accidental flag patterns in payload.3) CRC provides error detection.4) Control field supports reliable data transfer and link management.Verification / Alternative check: Compare with PPP, which borrows HDLC framing style for serial links.
Why Other Options Are Wrong:
Medium access control schemes (options A and B) describe contention/token systems, not HDLC's role.Circuit-switched access standards (option D) describe network access, not a data link framing protocol.“None of the above” is wrong since option C is correct.Common Pitfalls: Confusing HDLC with MAC methods like CSMA/CD or token passing; assuming byte-oriented protocols like PPP are unrelated.
Final Answer: A very common bit-oriented data link protocol issued by ISO.