Data Link Layer: Identifying the Task That Is Not Performed
In the OSI model, the data link layer is responsible for creating frames from the incoming data stream, and for managing reliable hop-by-hop delivery. Commonly cited responsibilities include framing, error control, and flow control. Meanwhile, channel coding is typically associated with the physical layer, where signals are prepared for transmission over a channel.
Therefore, among the given options, the task not done by the data link layer is (iv) Channel coding.
Below is a structured way to see why this mapping is standard in layered networking descriptions, and how each option aligns to the OSI responsibilities.
A high-level view:
Key conclusion: (iv) Channel coding is not performed by the data link layer; it belongs to the physical layer.
From Options → OSI Responsibilities
- 1Step 1
Frame formatting and delimiting are classic duties of the data link layer.
- 2Step 2
Link-level reliability features (e.g., detecting/correcting errors or retransmitting) are placed in the data link layer.
- 3Step 3
Rate matching between a sender and receiver on a single hop is handled by data link layer mechanisms.
- 4Step 4
Channel coding is about preparing data for transmission on the communication channel (signal resilience), which is tied to the physical layer.
- 5Step 5
Since channel coding is under physical-layer processing, choose (iv) Channel coding.
Exam Shortcut
If an option mentions coding for the channel (e.g., channel coding, modulation coding, FEC-like coding tied to the physical medium), it’s usually physical layer, not data link.
Common Confusion
People sometimes say “error control” in general and assume coding—however, link error control in data link layer is about reliable delivery between adjacent nodes (often using ARQ/CRC at the frame level), while channel coding is physical-layer redundancy for the transmission medium.
Where Each Task Typically Lives in Layered Networking
Framing & Link Management
Data preparation (logic)Data link layer creates frames and manages hop-by-hop delivery policies."
Error control & Flow control
Delivery reliability (per hop)Link-level mechanisms provide reliability and prevent receiver overload."
Channel coding (physical layer)
Transmission over the mediumPhysical layer adds redundancy for robust communication over the channel."
Option-to-Layer Mapping (Correctness Heuristic)
Scores indicate which OSI layer the task is typically associated with.
How to Justify the Correct Choice Quickly
OSI Model Explained (Data Link vs Physical Layer)
Knowledge Check
Which one of the following tasks is NOT done by the data link layer?