Frequently Asked Question on Stop and Wait ARQ

What is Stop and Wait ARQ?

The Stop and Wait ARQ protocol sends a data frame and then waits for an acknowledgment (ACK) from the receiver. The ACK indicates that the receiver successfully received the data frame. After receiving the ACK from the receiver, the sender delivers the next data frame. So there is a stop before the next data frame is transferred, hence it is known as the Stop and Wait ARQ protocol....

Characteristics of Stop and Wait ARQ

Used in Connection-oriented communication. It offers error and flow control It is used in Data Link and Transport Layers Stop and Wait for ARQ mainly implements the Sliding Window Protocol concept with Window Size 1...

Useful Terms in Stop and Wait Protocol

Propagation Delay: Amount of time taken by a packet to make a physical journey from one router to another router....

Simple Stop and Wait

At Sender...

Problems Associated with Stop and Wait

1. Lost Data...

Stop and Wait for ARQ (Automatic Repeat Request)

The above 3 problems are resolved by Stop and Wait for ARQ (Automatic Repeat Request) that does both error control and flow control....

Working of Stop and Wait for ARQ

Sender A sends a data frame or packet with sequence number 0.  Receiver B, after receiving the data frame, sends an acknowledgement with sequence number 1 (the sequence number of the next expected data frame or packet) There is only a one-bit sequence number that implies that both sender and receiver have a buffer for one frame or packet only....

Characteristics of Stop and Wait ARQ

It uses a link between sender and receiver as a half-duplex link Throughput = 1 Data packet/frame per  RTT If the Bandwidth*Delay product is very high, then they stop and wait for protocol if it is not so useful. The sender has to keep waiting for acknowledgements before sending the processed next packet. It is an example of “Closed Loop OR connection-oriented “ protocols It is a special category of SWP where its window size is 1 Irrespective of the number of packets sender is having stop and wait for protocol  requires only  2 sequence numbers 0 and 1...

Constraints in Stop and Wait ARQ

Stop and Wait ARQ has very less efficiency , it can be improved by increasing the window size. Also , for better efficiency , Go back N and Selective Repeat Protocols are used. The Stop and Wait ARQ solves the main three problems but may cause big performance issues as the sender always waits for acknowledgement even if it has the next packet ready to send. Consider a situation where you have a high bandwidth connection and propagation delay is also high (you are connected to some server in some other country through a high-speed connection). To solve this problem, we can send more than one packet at a time with a larger sequence number. We will be discussing these protocols in the next articles. So Stop and Wait ARQ may work fine where propagation delay is very less for example LAN connections but performs badly for distant connections like satellite connections....

Advantages of Stop and Wait ARQ

Simple Implementation: Stop and Wait ARQ is a simple protocol that is easy to implement in both hardware and software. It does not require complex algorithms or hardware components, making it an inexpensive and efficient option. Error Detection: Stop and Wait ARQ detects errors in the transmitted data by using checksums or cyclic redundancy checks (CRC). If an error is detected, the receiver sends a negative acknowledgment (NAK) to the sender, indicating that the data needs to be retransmitted. Reliable: Stop and Wait ARQ ensures that the data is transmitted reliably and in order. The receiver cannot move on to the next data packet until it receives the current one. This ensures that the data is received in the correct order and eliminates the possibility of data corruption. Flow Control: Stop and Wait ARQ can be used for flow control, where the receiver can control the rate at which the sender transmits data. This is useful in situations where the receiver has limited buffer space or processing power. Backward Compatibility: Stop and Wait ARQ is compatible with many existing systems and protocols, making it a popular choice for communication over unreliable channels....

Disadvantages of Stop and Wait ARQ

Low Efficiency: Stop and Wait ARQ has low efficiency as it requires the sender to wait for an acknowledgment from the receiver before sending the next data packet. This results in a low data transmission rate, especially for large data sets. High Latency: Stop and Wait ARQ introduces additional latency in the transmission of data, as the sender must wait for an acknowledgment before sending the next packet. This can be a problem for real-time applications such as video streaming or online gaming. Limited Bandwidth Utilization: Stop and Wait ARQ does not utilize the available bandwidth efficiently, as the sender can transmit only one data packet at a time. This results in underutilization of the channel, which can be a problem in situations where the available bandwidth is limited. Limited Error Recovery: Stop and Wait ARQ has limited error recovery capabilities. If a data packet is lost or corrupted, the sender must retransmit the entire packet, which can be time-consuming and can result in further delays. Vulnerable to Channel Noise: Stop and Wait ARQ is vulnerable to channel noise, which can cause errors in the transmitted data. This can result in frequent retransmissions and can impact the overall efficiency of the protocol....

Question For Practice

Question: Suppose two hosts are connected by a point-to-point link and they are configured to use Stop and Wait protocol for reliable data transfer. Identify in which one of the following scenarios, the utilization of the link is the lowest. [GATE CS/IT 2023]...

Frequently Asked Question on Stop and Wait ARQ – FAQs

When is Stop-and-Wait ARQ used?...