what is encapsulating security payload (esp)
IPsec The IP Encapsulating Security Payload (ESP)[19] was researched at the Naval Research Laboratory starting in 1992 as part of a DARPA-sponsored research project, and was openly published by IETF SIPP[20] Working Group drafted in December 1993 as a security extension for SIPP. This ESP was originally derived from the US Department of Defense SP3D protocol, rather than being derived from the ISO Network-Layer Security Protocol (NLSP). The SP3D protocol specification was published by NIST in the late 1980s, but designed by the Secure Data Network System project of the US Department of Defense. Encapsulating Security Payload (ESP) is a member of the IPsec protocol suite. It provides origin authenticity through source authentication, data integrity through hash functions and confidentiality through encryption protection for IP packets. ESP also supports encryption-only and authentication-only configurations, but using encryption without authentication is strongly discouraged because it is insecure.[21][22][23]
Transport layer In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet Protocol Suite and the OSI model. The protocols of the transport layer provide host-to-host communication services for applications.[1] It provides services such as connection-oriented communication, reliability, flow control, and multiplexing.