It is important to note that potential problems related to data segment transmission can happen. The image next shows the last message-transmitting failure scenario: So, the sender will receive a duplicate ACK message, ignoring it.

The other entity will receive a duplicate packet, ignore it, and send a new ACK.

At this point, the sender entity can already send the following segment. In such a scenario, the sender retransmits the data segment, receiving the ack from the first transmission after that. We can check the described scenario in the following image:įinally, the third scenario we’ll study is when the ACK messages arrive after the timeout. Thus, the receiver will get a duplicate segment, ignore it, and send the corresponding ack message again. So, a timeout occurs on the sender side, which retransmits the data segment. We can see this scenario in the image next:Ī second case is when the data segment reaches the destination, but there is a failure in the ACK message transmission. In such a case, this entity will send the message again. If a data segment does not reach the destination, a timeout event will occur in the sender entity, thus indicating that the ACK message never arrived. We have three main message-transmitting failure types: (i) not receiving a data segment in the destination (ii) not receiving the ACK message in the source, and (iii) receiving an ACK message after the timeout event. The stop-and-wait mechanism infers that a transmission failed based on timeouts. In such cases, the sender transmits the same message again to the receiver entity. Of course, both the transmissions of data segments and ACK can fail. By employing the stop-and-wait protocol, the process occurs as depicted in the following image: So, let’s consider an entity that should send three data segments to another one. To do that, the sender waits for the acknowledgment message of the last sent data segment before sending a new one. The stop-and-wait uses the acknowledgment strategy to ensure the receiver has all the already sent segments. So, the sender only has the guarantee that a data segment reaches its destination after receiving an ACK message.

This strategy is pretty simple: for each segment sent, the receiver (destination) sends an acknowledgment message, typically called ACK, to the sender (origin).

The stop-and-wait mechanism employs a strategy to confirm the receiving of each sent data segment. It is the simplest protocol of a category called Automatic Repeat-Request (ARQ). As we studied in the previous section, connection-based transport protocols can use the stop-and-wait mechanism to manage transmission errors in communication.

Stop and wait arq protocol program in c