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What is the purpose of framing in the data-link layer?
What is the purpose of framing in the data-link layer?
- To guarantee error-free transmission.
- To compress data for faster transmission.
- To pack bits into frames to distinguish them from each other. (correct)
- To handle flow control efficiently.
In fixed-size framing, delimiter needs to be defined for the frames.
In fixed-size framing, delimiter needs to be defined for the frames.
False (B)
What is bit stuffing in bit-oriented framing?
What is bit stuffing in bit-oriented framing?
adding one extra 0 whenever five consecutive 1s follow a 0 in the data
Flow control refers to a set of procedures used to restrict the amount of data that the sender can send before __________ for acknowledgment.
Flow control refers to a set of procedures used to restrict the amount of data that the sender can send before __________ for acknowledgment.
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Match the error control methods with their descriptions:
Match the error control methods with their descriptions:
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Study Notes
Framing
- In the data-link layer, framing separates messages from different sources to destinations by adding sender and destination addresses.
- Framing is necessary to distinguish one frame from another.
- Frames can be of fixed size or variable size.
Fixed-Size Framing
- Fixed-size framing does not require defining boundaries, as the frame size can be used as a delimiter.
- An example of fixed-size framing is the ATM WAN, which uses fixed-size cells.
Variable-Size Framing
- Variable-size framing requires a way to define the end of one frame and the beginning of the next.
- There are two approaches: character-oriented framing and bit-oriented framing.
Character-Oriented Framing
- In character-oriented framing, a header and trailer are added to the frame, carrying source and destination addresses and control information.
- A flag (special character) is added at the beginning and end of a frame to signal the start or end of a frame.
- Byte-stuffing is used to avoid flags being mistaken for data in the middle of a frame.
Bit-Oriented Framing
- In bit-oriented framing, the data section of a frame is a sequence of bits interpreted by the upper layer as text, graphics, audio, video, etc.
- Bit-stuffing is used to avoid flags being mistaken for data in the middle of a frame.
Flow Control
- Flow control restricts the amount of data that the sender can send before waiting for acknowledgment.
- Flow control is necessary to prevent the receiving node from becoming overwhelmed with frames.
- Flow control can be achieved through feedback from the receiving node to the sending node to stop or slow down pushing frames.
Error Control
- Error control at the data link layer is based on automatic repeat request (ARQ), which involves retransmission of data.
- There are two common methods of error control:
- Frames are silently discarded if corrupted, and packets are delivered to the network layer if not corrupted.
- Frames are silently discarded if corrupted, and acknowledgments are sent to the sender if not corrupted.
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