Two-way
In a two-way time transfer system, the two peers will both transmit, and will also receive each others' messages, thus performing two one-way time transfers to determine the difference between the remote clock and the local clock. The sum of these time differences is the round trip delay between the two nodes. It is often assumed that this delay is evenly distributed between the directions between the peers. Under this assumption, half the round-trip delay is the propagation delay to be compensated. A drawback is that the two-way propagation delay must be measured and used to calculate a delay correction. That function can be implemented in the reference source, in which case the source capacity limits the number of slaves that can be served, or by software in each slave. The NIST provides a time reference service to computer users on the Internet, based on Java applets loaded by each slave. The two-way satellite time and frequency transfer (TWSTFT) system being used in comparison among some time laboratories uses a satellite for a common link between the laboratories. The Network Time Protocol uses packet based messages over an IP network.
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Famous quotes containing the word two-way:
“Think of the child’s question as the start of a two-way conversation rather than a question-and-answer session. Sometimes it may be necessary to learn what children think about the subject and what misconceptions they may have before providing an answer.”
—Ruth Formanek (20th century)