The Quote Of The Day service was a method used by mainframe sysadmins to broadcast a daily quote on request by a user. It was formally codified both for prior purposes as well as for testing and measurement purposes in Internet protocol

Internet Protocol

The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...

 RFC 865.

A host may connect to a server that supports the RFC 865 QOTD protocol, on either TCP

Transmission Control Protocol

The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...

 or UDP

User Datagram Protocol

The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...

 port 17. In order to keep the quotes at a reasonable length, RFC 865 specified a maximum length of 512 characters for the quote.

Although some sources indicate that the QOTD service is rarely enabled, and is in any case often firewalled

Firewall (computing)

A firewall is a device or set of devices designed to permit or deny network transmissions based upon a set of rules and is frequently used to protect networks from unauthorized access while permitting legitimate communications to pass....

 to avoid 'pingpong'

Denial-of-service attack

A denial-of-service attack or distributed denial-of-service attack is an attempt to make a computer resource unavailable to its intended users...

 attacks., interest continues in the pre-existing purpose of serving quotes as can be seen with web engine searches. As is indicated in RFC 865, the QOTD concept predated the testing and measurement purposes ascribed to QOTD in that protocol.

Current testing and measurement of IP networks is more commonly done with ping

Ping

Ping is a computer network administration utility used to test the reachability of a host on an Internet Protocol network and to measure the round-trip time for messages sent from the originating host to a destination computer...

 and traceroute

Traceroute

traceroute is a computer network diagnostic tool for displaying the route and measuring transit delays of packets across an Internet Protocol network. Traceroute is available on most operating systems....

, which are more robust adaptations of the echo protocol, specified in RFC 862 which predated the attempt at QOTD standardization.