Elementary Data Link Protocols

Introduction

Data link protocols are fundamental to the efficient & reliable transmission of data across communication networks. These protocols define the rules & procedures for data transfer between network nodes, ensuring accurate & orderly communication.

As a coding student, this article will equip you with an understanding of different types of data link protocols, their functions, & practical applications. You'll learn to distinguish between these types, allowing you to grasp their roles in various networking scenarios better.

Types of Data Link Protocols

Data Link Protocols are a set of rules that determine how data is formatted, controlled, and transmitted over a network. 

These protocols ensure the safe and efficient transfer of data between connected devices. They mainly handle framing, error control, flow control, and the physical addressing of frames.

Stop-and-Wait Protocol

Stop-and-Wait Protocol is a fundamental data link protocol where the sender transmits a frame and waits for an acknowledgment (ACK) from the receiver before sending the next frame.

Process

 After sending a frame, the sender stops and waits until it receives an acknowledgment from the receiver. Only upon receiving the ACK for the current frame does the sender transmit the next frame.

Drawback

The major drawback of this protocol is its inefficiency, especially over long distances or in high-speed networks, as the wait time can significantly reduce the network's throughput.

Stop-and-Wait Automatic Repeat reQuest (ARQ)

Stop-and-Wait ARQ improves upon the basic Stop-and-Wait Protocol by adding error control. It involves error detection and retransmission of lost or damaged frames.

Error Detection 

It uses acknowledgment packets (ACKs) and negative acknowledgment packets (NAKs). If the sender receives a NAK or no acknowledgment within a certain time frame, it retransmits the data frame.

Efficiency

More efficient than the basic Stop-and-Wait protocol due to its error-handling capabilities, but still suffers from lower throughput in high-latency networks.

Go-Back-N Automatic Repeat reQuest (ARQ)

Go-Back-N ARQ is a more sophisticated protocol that allows multiple frames to be in transit at the same time, increasing the efficiency of data transmission.

Sliding Window

This protocol uses a 'sliding window' technique. The sender can send multiple frames before needing an acknowledgment, but it maintains a window of frames that have been sent and not yet acknowledged.

Retransmission Strategy

If an error is detected or an acknowledgment is not received, the sender goes back and retransmits all frames starting from the problematic frame. This can lead to the retransmission of frames that were correctly received, hence potentially reducing efficiency.

Selective Repeat ARQ

Selective Repeat ARQ is a refined version of the Go-Back-N ARQ, designed to improve efficiency by avoiding unnecessary retransmissions.

Selective Acknowledgments 

Unlike Go-Back-N, Selective Repeat ARQ allows the receiver to accept and acknowledge frames out of order. It only requests the retransmission of the actual erroneous or lost frames.

Complexity & Efficiency

It is more complex to implement but significantly increases the efficiency of the network, especially in environments with higher error rates, as it minimizes the number of retransmissions.

Simplex Protocol

Simplex protocol, as the name suggests, is the most basic form of data link protocol. It operates in a one-way communication mode, where data can only be sent in a single direction. This type of protocol is typically used in environments where the communication needs are straightforward & unidirectional. For example, a keyboard transmitting keystrokes to a computer.

Half-Duplex Protocol

Half-duplex protocols allow data transmission in both directions, but not simultaneously. Here, each end of the connection can both send & receive data, but only one at a time. This type of protocol is useful in systems where two-way communication is needed, but the simultaneous transmission is not critical. Walkie-talkies are a classic example of half-duplex communication.

Full-Duplex Protocol

In full-duplex protocols, simultaneous data transmission & reception occur, allowing two-way communication in real-time. This protocol is used in most modern networks, including the internet, because of its efficiency & speed. Ethernet is a common example of a full-duplex data link protocol.