1. a)UDP and TCP use 1s complement for their checksums. Suppose you have the following three 8 bit bytes: 0101 0011, 0111 0110, 1001 0011. What is the 1s complement of the sum of these 3 8-bit bytes? Show all work. Why is it that the 1s complement is used and not just the sum? What is the sum of the three 8 bit bytes and the checksum you just computed? What is it if you change the first 8 bit byte to 0101 0010 (i.e. we had a single bit error)? What is it if you also change the second 8 bit byte to 0111 0111 (i.e. you have two bit errors)? Does the checksum always catch bit errors?

b. What is the main advantage of the GBN protocol? What can happen with the GBN protocol if an infrequent but regular garble of the data causes packet losses on the order of 1 garble every 1000 packets where the window size is 1000 packets?

c. What is the main advantage of the SR protocol? What can happen if the window size of the SR protocol is greater than half the size of the sequence number space?