why tcp is reliable but udp not

tcp in data transmission, data is transmitted to the transmitting side first its own cache, then the data in the cache control protocol sent to the peer, the peer returns an ack = 1, a transmitting side data buffer is clean, the peer returns ack = 0, the re-transmission data, so reliable tcp

Udp and transmitting data, the peer returns an acknowledgment message is not therefore unreliable

https://www.cnblogs.com/sui776265233/p/9289858.html