In the Open System interconnection network architecture model, the Data Link Layer is the second layer for error-free data transmission. It is also responsible for encoding, decoding, and organizing the incoming and outgoing data. It is the most complex layer of the OSI model because it hides all the underlying complexities of the hardware from the above layers.
The error detection bits are used by the Data Link Layer. It corrects the errors and outgoing messages are assembled into frames. It is reliable to send messages.
Brief Introduction to OSI Model
The OSI model was conceptualized to standardize the characteristics of communication of computing systems without any regard to their underlying technology and internal structure. It aims to provide inter-operability between diverse systems of communication using standard protocols.
- In the early 1970’s, the OSI model was proposed and in the year 1984, this was published by the International Organization of Standardization (ISO).
- With the help of this model, troubleshooting has become very easy as the error can be detected at various levels.
- This model also helps in understanding the relationship and function of the software and hardware of a computer network.
- The OSI model’s seven – layer structure was proposed by Charles Bachman at Honeywell Information Systems.
- Initially this model did not gain much fame as it could not support the Internet protocol suite that was not acceptable to a lot of IT companies.
- The seven layers of the structure are classified into two parts – the upper layer or the host layer and lower layer or the media layer.
Read More About OSI LayersSeven Layers of OSI Model
Here, are the seven layers of the OSI Model explained below:
Physical Layer
It is the first layer of the OSI model. It consists of the raw data which is later transmitted to the higher layers of the structure. The conversion of the digital bits into electrical, radio or optical signals are taken care by this layer.
Data Link Layer
This layer makes sure the data received is free from any errors. It controls the flow of data in the given time duration and along with a set speed of transmission. It accesses to get the data that is achieved at this layer.
Network Layer
This layer acts as a network controller. It transfers variable data from one node to another, connected in a network. Every node has a specific address and the network layer make sure that the data is sent to its destination address.
Transport Layer
This transport layer manages the delivery of data packets. It also manages flow of data, segmentation and de-segmentation and error control.
Session Layer
It manages the connection between the computers connected in a network. This layer can also terminate a session or transmission which is complete.
Presentation Layer
This layer is converted into the syntax which an application can understands. The data is formatted prior to passing on the data. It serves as a data translator for the network.
Application Layer
In this stage, the interaction with the user or the user application takes place. It checks the identity and the available partners which are communicating for an application with data to transmit.
Read More about OSI Layers
What is Data Link Layer?
The Data Link Layer is the second layer of the OSI (Open Systems Interconnection) model and the TCP/IP (Transmission Control Protocol/Internet Protocol) model. It is responsible for the reliable transmission of data frames between adjacent nodes over a physical network link. The primary functions of the this layer include framing, physical addressing, error detection and correction, flow control, and media access control.
Characteristics of Data Layer Link
Below mentioned are some of the main characteristics:–
Transfer Data
Transfer the datagram across an individual link is the responsibility of data link layer.
Position
In the OSI model, data link layer is 2nd layer from bottom and 4th layer from the top.
Communication Channel
A link is a communication channel which connects the adjacent nodes. In order to move the datagram from the source to destination, it should be moved across an individual link.
Data Format
The format of the packet exchanged across the nodes along with the actions like error detection, retransmission, flow control and random-access has been defined by the data link layer.
Protocol
The datagram can be managed by various data link layer protocols on various links in a path. Example, the datagram is handled by ethernet on the first link, point to point protocol on the second link. Moreover, the data link layer protocols are ethernet, token ring, point to point protocol (PPP) and Fibre Distributed Data Interface (FDDI).
Services of Data Link Layer
Below are some of the services offered:
Framing and Link Access
The data link layer protocol summarizes every network frame within a link layer frame prior the transmission across the link. A frame contains a data field (where network layer datagram is inserted) and a header of data fields. It describes the structure of the frame along with channel access protocol through which the frame is to be transmitted over a link.
Reliable Delivery
The data link layer transmits the network layer datagram without any error and hence it is referred to as reliable delivery service. A reliable delivery service is skilled with transmissions and acknowledgements. Since, the rate of errors are high and they can be corrected locally, link at which an error occurs apart from forcing to retransmit the data.
Flow Control
A receiving node is capable of receiving the frames much faster rate when compared to processing the frame. Without the help of flow control, the receiver’s buffer can overflow and thus, there are frame loss. In order to overcome this concern, the data link layer uses the flow control to prevent sending node on one side of the link from immense receiving node on the other side of the link.
Error Detection
The purpose of error detection in the data link layer is to detect transmission errors that may occur due to noise, interference, or other factors during data transmission. The error detection techniques generate a checksum or FCS value that is appended to the data frame. The receiver then performs the same calculation and compares the received value with the calculated one. If they match, it indicates that the data frame is likely error-free. If there is a mismatch, it suggests that errors have occurred during transmission.
Error Correction
It is same to error detection. Here, receiving node detect the errors and also determines the place where the errors have occurred in the frame.
Half Duplex and Full Duplex
In full duplex mode, both the nodes can transmit the data at once. However, in Half duplex mode, only one node can transmit the data at once.
Data Link Layer Sub-Layers
This layer is classified into two sub layers like –
Logical Link Control (LLC)
It deals with multiplexing, the data flow among the applications and other services. Logical Link control is mainly responsible for providing error messages and acknowledgements too.
Media Access Control (MAC)
It manages the interaction of the device, responsible for addressing the frames, and also controls the physical media access. Basically, the data link layer receives the information like packets from the network layer, where it divides packets into frames and then sends those frames bit-by-bit to the underlying physical layer.
Protocols in Data Link Layer
There are different protocols that are as follows –
- Synchronous Data Link Protocol
- High-level Data Link Protocol
- Serial Line Interface Protocol
- Point to Point Protocol
- Link Access Procedure
- Link Control Protocol
- Network Control Protocol
Data Link Layer Design Issues
Here, are the following issues:
How to keep a fast transmitter?
Some specific issues triggered in the data link layer i.e., how to keep a fast transmitter from drowning to a slow receiver in data. A particular type of traffic regulation mechanism is needed on frequent basis to allow the transmitter to know buffer space, required by the receiver at the moment. Very often, the regulation flow and the error handling are segregated.
How to Control Access to Shared Channel?
Another issue in the data link layer i.e., the broadcast networks have is ‘how to control access to the shared channel’. The sublayer of the data link layer, the medium access control (MAC) deals with the problem.
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