round, in music, a perpetual canon on a tune that returns to its beginning in which all the voices enter at the unison or the octave. An example is Sumer Is Icumen In. Rounds were popular in 17th-century England when the catch reached its height. The catch was originally just a simple round, e.g., Three Blind Mice, written in a single line with the effect gained by having another singer come in ("make the catch") at the right time. Later, comic effects, often quite bawdy, were added, using the interweaving of the parts. The Rounds, Catches and Canons of England (1864) by E. F. Rimbault is a comprehensive collection. The term round was also used to designate a dance performed in a circle and, by extension, to the tunes for such dances.
In telecommunications, the term round-trip delay time or round-trip time (RTT) has the following meanings:

  1. The elapsed time for transit of a signal over a closed circuit, or time elapsed for a message to a remote place and back again.
  2. In primary or secondary radar systems, the time required for a transmitted pulse to reach a target and for the echo or transponder reply to return to the receiver.

Round-trip delay time is significant in systems that require two-way "interactive" communication, such as voice telephony, or ACK/NAK data systems where the round-trip time directly affects the throughput rate, such as the Transmission Control Protocol (TCP). It may range from a very few microseconds for a short line-of-sight (LOS) radio system to many seconds for a multiple-link circuit with one or more satellite links involved. This includes the node delays as well as the media transit time.

In regards to TCP communication the RTT time is calculated from the 3-way handshake by measuring the time between segment transmission and ACK receipt.

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