Which TCP/IP Internet layer protocol is in charge of sending error messages when two computers' communication fails?

Internet Protocol (IP) is the main Internet layer protocol and the workhorse of TCP/IP. Another important protocol at this layer is Internet Control Message Protocol (ICMP), which is in charge of sending error messages. If you're familiar with the ping utility, you'll know that it sends and receives packets using ICMP. Both the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) are communication protocols; however, TCP ensures delivery while UDP does not.