Summary of stop and wait protocols

| rdt version | network layer channel | new features | | 1.0 | no error | nothing | | 2.0 | bit error in data | sender-side checksum, receiver-side ACK/NAK | | 2.1 | bit error in data/feedback | receiver-side checksum, sender-side sequence number | | 2.2 | same as 2.1 | receiver-side seq no. | | 3.0 | bit error/pkt loss in data/feedback | timeout/re-transmission |