Data is conveyed as a stream of bits across a point-to-point wire connection called framing between two devices. In a computer network, framing employs frames to convey and receive data. Each frame may be distinguished from the others, because of the way that the data connection layer packs bits into each frame.
In this article, we will look more into the Framing in Data Link Layer according to the GATE Syllabus for (Computer Science Engineering) CSE. We will read ahead to find out more about it.
Table of Contents
What is Framing in a Data Link Layer?
Data transmission in the physical layer involves synchronised bit transfer from the source to the destination. These bits are bundled into frames by the data link layer.
Particularly in computer networks and telecommunications, frames are the basic building blocks of digital transmission. Energy packets called photons are used to transmit frames, just like the light energy. In the process of time division multiplexing, the frame is continuously used.
The frames are created by the data-link layer by encapsulating the packets coming from a network layer. The packet may be split into smaller frames in case the frame size grows to be too large. Flow control and error control are more effectively controlled with smaller frames. These frames are transmitted bit by bit by the hardware. The data link layer gathers signals from hardware at the receiver’s end and puts them together into frames.
Parts of a Frame
Here are the components of a frame:
- Frame Header − It includes the frame’s source and destination addresses.
- Payload field − It includes the message that needs to be spread.
- Trailer − The bits for error detection and repair are present.
- Flag − It designates the start and finish of the frame.
Framing
A point-to-point connection called framing uses a wire to send data as a stream of bits between two computers or other devices. These pieces must be organised into comprehensible informational units. Data link layer functionality includes framing, and it offers a method for a sender to deliver a group of bits that are significant to the receiver. Each data link layer technology has its unique frame structure, including Ethernet, Frame Relay, Token Ring, and others. The headers of frames contain data like error-checking codes.
Types of Framing
There are two different forms of framing: fixed size framing and variable size framing.
Fixed-sized Framing
Since the frame’s size is constant in the fixed-sized framing, its length serves as its boundary. As a result, it is not necessary to use additional boundary bits to specify the beginning and end of the frame. ATM cells are an example of this.
Variable-sized Framing
Each frame that needs to be transferred in this case may have a variable size. Therefore, additional processes are maintained to indicate when one frame ends and the next one begins. Local area networks employ it.
In variable-sized framing, there are two techniques to define frame delimiters:
- Length Field − Here, the size of the frame is decided by a length field. It is used in Ethernet (IEEE 802.3).
- End Delimiter − Here, the size of the frame is defined by a pattern that serves as a delimiter. In Token Rings, it is used. The following two methods are employed to prevent the problem if the pattern is present in the message.
- Byte Stuffing − To distinguish the message from the delimiter, a byte is added. This technique is also known as character-oriented framing.
- Bit Stuffing − To distinguish the message from the delimiter, a byte is added. This technique is also known as character-oriented framing.
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