ARQN (Automatic Retransmission Request Notification)

Last updated on 28 Feb 2023

Introduction

ARQN (Automatic Retransmission Request Notification) is a mechanism used in the communication between two devices in a wireless network. It is primarily used in wireless local area networks (WLANs), which are commonly used in today's workplaces, homes, and public spaces. ARQN is a part of the medium access control (MAC) protocol of the IEEE 802.11 standard, which is the standard for wireless communication in WLANs. This protocol uses a technique called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) to access the wireless channel and avoid collisions.

ARQN Mechanism

ARQN is a mechanism that provides reliability to the wireless communication by requesting the retransmission of a data frame if it is not received correctly by the receiver. This mechanism uses an acknowledgement (ACK) frame to indicate the successful reception of a data frame. If the sender does not receive an ACK frame from the receiver after a certain period, it assumes that the data frame was not received correctly, and it retransmits the data frame.

The ARQN mechanism uses two parameters: the sequence number and the acknowledgement number. The sequence number is a unique identifier assigned to each data frame by the sender, and it is used to identify the data frame. The acknowledgement number is a unique identifier assigned to each ACK frame by the receiver, and it is used to acknowledge the reception of the data frame.

When a sender transmits a data frame, it waits for an ACK frame from the receiver. If the sender does not receive an ACK frame within a specified time, it assumes that the data frame was not received correctly, and it retransmits the data frame. The receiver uses the sequence number of the data frame to identify the data frame and sends an ACK frame with the acknowledgement number equal to the sequence number of the received data frame.

If the receiver does not receive the data frame correctly, it sends a negative acknowledgement (NAK) frame instead of an ACK frame. The sender receives the NAK frame and retransmits the data frame. This process continues until the sender receives an ACK frame or the maximum number of retransmissions is reached. If the maximum number of retransmissions is reached, the sender assumes that the data frame is lost, and it discards the data frame.

ARQN is a simple and effective mechanism that provides reliability to the wireless communication. It ensures that the data frames are received correctly by the receiver and avoids the loss of data frames due to collisions, interference, or other reasons. ARQN is widely used in WLANs and is a critical component of the IEEE 802.11 standard.

ARQN in IEEE 802.11 Standard

ARQN is a part of the MAC protocol of the IEEE 802.11 standard. This protocol uses the CSMA/CA technique to access the wireless channel and avoid collisions. CSMA/CA is a contention-based protocol in which the devices contend for the use of the wireless channel.

The CSMA/CA protocol uses a mechanism called the Distributed Coordination Function (DCF) to access the wireless channel. DCF is a contention-based access method in which the devices contend for the use of the wireless channel by sensing the channel and waiting for a random backoff time before transmitting data frames.

ARQN is used in the DCF mechanism to provide reliability to the wireless communication. When a sender transmits a data frame, it waits for an ACK frame from the receiver. If the sender does not receive an ACK frame within a specified time, it assumes that the data frame was not received correctly, and it retransmits the data frame. The receiver uses the sequence number of the data frame to identify the data frame and sends an ACK frame with the acknowledgement number equal to the sequence number of the received data frame.

ARQN uses a sliding window protocol to manage the transmission of data frames. The sliding window protocol is used to control the flow of data frames between the sender and receiver. The sender maintains a window of data frames that it can transmit, and the receiver maintains a window of data frames that it expects to receive.

The sliding window protocol uses two parameters: the send window size and the receive window size. The send window size is the maximum number of data frames that the sender can transmit without receiving an ACK frame from the receiver. The receive window size is the maximum number of data frames that the receiver can expect to receive without sending an ACK frame to the sender.

ARQN uses a selective repeat algorithm to manage the retransmission of data frames. The selective repeat algorithm is used to retransmit only the lost or damaged data frames and not the entire window of data frames. This algorithm improves the efficiency of the transmission and reduces the delay in the transmission of data frames.

ARQN also uses a mechanism called the Fragmentation/Reassembly (F/R) mechanism to handle large data frames. The F/R mechanism divides large data frames into smaller fragments and transmits them separately. The receiver reassembles the fragments to reconstruct the original data frame. This mechanism reduces the likelihood of collisions and improves the reliability of the transmission.

ARQN also uses a mechanism called the Request-to-Send/Clear-to-Send (RTS/CTS) mechanism to reduce collisions in the wireless channel. The RTS/CTS mechanism is used to reserve the wireless channel for the transmission of a data frame. When a sender wants to transmit a data frame, it sends an RTS frame to the receiver requesting permission to transmit. The receiver sends a CTS frame to the sender, indicating that the wireless channel is available for transmission. This mechanism reduces collisions and improves the efficiency of the transmission.

Conclusion

ARQN is a critical mechanism used in wireless communication to provide reliability and ensure the successful transmission of data frames. It is a part of the MAC protocol of the IEEE 802.11 standard and is widely used in WLANs. ARQN uses a sliding window protocol to manage the transmission of data frames and a selective repeat algorithm to manage the retransmission of lost or damaged data frames. ARQN also uses the F/R mechanism to handle large data frames and the RTS/CTS mechanism to reduce collisions in the wireless channel. ARQN is a simple and effective mechanism that provides reliability to the wireless communication and ensures the successful transmission of data frames.