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HDLC (High-level Data Link Control) is widely used at the data link layer. Which description best characterizes HDLC?

Difficulty: Easy

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.

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