4. UDP and TCP use 1's complement for their checksums. Suppose you have the following two 16-bit words:

0101 0101 0101 0101 and 1010 1010 1010 1011.

4.a. (2 pts.) What is the 1's complement of the sum of these words? Show all work.

4.b. (2 pts.) With the 1's complement scheme, how does the receiver detect errors?

4.c. (2 pts.) Is it possible that a 4-bit error will go undetected? If so, provide an example.

4.d. (2 pts.) Is it possible that a 1-bit error will go undetected? If so, provide an example.4.