TCP/IP Model
Transmission Control Protocol (TCP) helps make host-to-host communication more reliable. Packets are constructed in a secure connection. TCP makes up part of the Transport layer along with UDP, sitting between the Internet IP layer below and passing constructed packets to the Application layers via port connections to applications like Telnet, FTP, SSH, HTTP or SMTP.
User Datagram Protocol (UDP) also makes up the Transport Layer in TCP/IP protocols along with TCP. UDP is used for transmission with "best effort" and no checking for lost segments. Domain Name Systems receive UDP segments.