Final answer:
In a protocol using ARQ, a message is sent (S1) and the ACK is corrupted (X1). The sender retransmits the message (X3) after not receiving a proper ACK (X2), which is then correctly received and acknowledged (X4). Subsequently, the next message is sent (X5) and received (S6), concluding the communication cycle.
Step-by-step explanation:
The scenario presented is typical in communications that use automatic repeat request (ARQ) protocols, which provide error control in data transmission by using acknowledgments (ACK) and retransmissions. The steps in the sequence provided are part of a typical interaction in a data communication protocol where proper receipt of messages needs to be confirmed, and any errors are handled through retransmissions.
Here is the explanation of the sequence:
1. S1: Sender transmits the initial message.
2. X1: The receiver correctly receives the message and sends an acknowledgment (ACK) message, but this ACK is corrupted.
3. X2: The sender waits for an ACK, but since the ACK is corrupted, it does not receive a proper acknowledgment within the expected time frame.
4. X3: Sender retransmits the initial message.
5. X4: The receiver correctly receives the retransmission of the message and sends an ACK, which this time is not corrupted.
6. S4: The Sender correctly receives the ACK and knows that the initial message was properly received.
7. X5: Sender transmits the next message.
8. S6: The receiver correctly receives the next message and both the sender and receiver return to their starting positions, ready for the next message transmission cycle.
This process ensures that two messages get successfully received and that both the sender and receiver are synchronized in their communication.