återutsändningsstrategier

återutsändningsstrategier, or retransmission strategies, are methods used in computer networking to ensure reliable data transfer. When a data packet is sent from a source to a destination, it may be lost or corrupted during transmission. Retransmission strategies are employed to detect these errors and resend the lost or corrupted packets.

The most common approach is automatic repeat request (ARQ). ARQ protocols use acknowledgments (ACKs) and negative acknowledgments (NACKs) to signal the status of received packets. If the sender receives an ACK for a packet, it knows the packet was received correctly and can send the next one. If it receives a NACK, or if a certain time limit (timeout) passes without an ACK, the sender assumes the packet was lost and retransmits it.

There are several variations of ARQ. Stop-and-wait ARQ is the simplest, where the sender waits for an acknowledgment before sending the next packet. This is reliable but inefficient due to the waiting time. Go-back-N ARQ allows the sender to send multiple packets without waiting for individual acknowledgments, but if an error is detected, it retransmits all packets from the point of error onwards. Selective repeat ARQ is more efficient, as it only retransmits the specific packets that were lost or corrupted, allowing other correctly received packets to be buffered.

Another concept related to retransmission is probabilistic retransmission. In some scenarios, especially in wireless networks where packet loss can be frequent, retransmission might be triggered based on a probability rather than a strict timeout or NACK. This can help avoid congestion and adapt to changing network conditions. The choice of retransmission strategy depends on factors such as network reliability, latency requirements, and the complexity the application can handle.