CIS 3210 Lecture Notes - Lecture 16: Checksum

• School: University of Guelph
• Department: Computing and Information Science
• Course: CIS 3210
• Professor: Xiaodong Lin

Document Summary

Negative acknowledgements (naks): receiver explicitly tells the sender that packet had errors. Sender retransmits the packet on receipt of nak. Feedback: control messages (ack, nak) from receiver to sender. Sender gets the data from the application layer, sends it to the receiver and waits for acknowledgement from the receiver. If the receiver gets the data with no errors (according to the checksum) then the receiver extracts the data and delivers it to the application layer, then send s a positive acknowledgement (ack) to the sender. If the receiver get the data with errors (checksum) goes to the top option of the diagram and simply dumps the packet and sends a nak back to the sender. The sender will then retry the transmission rdt2. 0 has a fatal aw! Sender does not know what happened at the receiver. Can"t just simply retransmit (could be duplicate data - which would cause issues when transferred to the application layer)