Protocol layering forms the basis of protocol design. Bootstrap Protocol is a similar protocol and predecessor to DHCP. The UPnP discovery protocol is known as the Simple Service Discovery Protocol (SSDP). The Simple Mail Transfer Protocol (SMTP) protocol was introduced in 1981. MQTT relies on the TCP protocol for data transmission. Implementations send and receive timestamps using the User Datagram Protocol (UDP) on port number 123. STUN messages are sent in User Datagram Protocol (UDP) packets. This stands for Protected Extensible Authentication Protocol. All SNMP messages are transported via User Datagram Protocol (UDP). This stands for the Lightweight Extensible Authentication Protocol. It uses UDP as the underlying transport protocol. RTP typically runs over User Datagram Protocol (UDP). This table is also accessible via Simple Network Management Protocol (SNMP). Enhanced Interior Gateway Routing Protocol (EIGRP). Requests initiate a functionality of the protocol.