Question

We discuss the new option of SACKs for TCP on the book website, but for the moment assume that we add an 8-byte NAK option to the end of the TCP segment, which can hold two 32-bit sequence numbers. Show how we can use this 8-byte NAK to define an out-of-order or duplicate range of bytes received.

Answer 1

The 8-byte NAK option in TCP could be used to indicate out-of-order or duplicate byte ranges with two 32-bit sequence numbers, which communicate to the sender the exact range of bytes to be resent.

Step-by-step explanation:

The student's question revolves around an 8-byte NAK option in TCP, which stands for Negative Acknowledgement. This option would presumably serve to inform the sender of packets that have been received out-of-order or are duplicates by specifying the sequence numbers of these packets. In TCP, sequence numbers are used to keep track of the bytes in the data stream, so an 8-byte NAK option can be used to communicate a range of bytes that are not received correctly.

For example, if bytes with sequence numbers 1501 to 1550 are received out-of-order, the NAK option would contain two 32-bit sequence numbers to represent this range: the first number indicates the start of the out-of-order range (1501) and the second indicates the end (1550). This informs the sender that all bytes between and including these sequence numbers need to be resent.