What are the two protocols used in the transport layer?

TCP and UDP

Correct:

UDP (User Data-gram Protocol) is a communications protocol that offers a limited amount of service when messages are exchanged between computers in a network that uses the internet Protocol.

UDP provides two services not provided by the IP layer. It provides port numbers to help distinguish different user requests and, optionally, a checksum capability to verify that the data arrived intact.

TCP (Transmission Control Protocol) is a set of rules (protocol) used along with the Internet Protocol (IP) to send data in the form of message units between computers over the Internet. While IP takes care of handling the actual delivery of the data, TCP takes care of keeping track of the individual units of data (called packets) that a message is divided into for efficient routing through the Internet. (TCP/IP) is the know definition by most.