Andrew Gideon wrote:
I understand that mode S transponders have unique identifiers, thus
eliminating the need for beacon "codes" as we use them today. Is that
right?


No.


Do people flying with mode S today still need to use beacon codes
for compatibility reasons?

Not for compatibility reasons. Take your average Boeing 757 used by an
airline. The mode S transponder is registered to the N number. The
airline will never use that N number in flight and that aircraft will
fly under a different identification every day.



TIS travels via the mode S data link. TIS-B uses ADS-B's data link. So
no mode S transponder is required.

Right but the transponder will allow others to see you.