Rdt2.0: channel with bit errors O underlying channel may flip bits in packet o recall: UdP checksum to detect bit errors o the question: how to recover from errors o acknowledgements(ACKs): receiver explicitly tells sender that pkt received oK o negative acknowledgements(NAKs ): receiver explicitly tells sender that pkt had errors o sender retransmits pkt on receipt of nak o human scenarios using ACKs, NAKs O new mechanisms in rdt2 o(beyond rdtl. o) o error detection o receiver feedback: control msgs(ACk, NAKrcvr->sender 3: Transport Layer 3a-143: Transport Layer 3a-14 Rdt2.0: channel with bit errors  underlying channel may flip bits in packet  recall: UDP checksum to detect bit errors  the question: how to recover from errors:  acknowledgements (ACKs): receiver explicitly tells sender that pkt received OK  negative acknowledgements (NAKs): receiver explicitly tells sender that pkt had errors  sender retransmits pkt on receipt of NAK  human scenarios using ACKs, NAKs?  new mechanisms in rdt2.0 (beyond rdt1.0):  error detection  receiver feedback: control msgs (ACK,NAK) rcvr->sender