$(1)$ Utility of checksums $(2+2=4$ points$).$ Consider the TCP$/$UDP checksum algorithm discussed in class.

a$.$ If the TCP$/$UDP checksum algorithm at the receiver computes a checksum value that isnon$-$zero, can the receiver conclude that the received data contains an error? Why or why not? $(1+1=2$ points$)$

b$.$ If the TCP$/$UDP checksum algorithm at the receiver computes a checksum value that is zero,can the receiver conclude that the received data is correct, i$.$e$.,$ the same as the data transmitted by the sender$?$ Why or why not? $(1+1=2$ points$)$