| 单词 | echo |
| 释义 | echo 1. Also known as the rain-barrel effect, echo is signal reflection. At any point in a circuit where an electromagnetic wave meets a discontinuity, a portion of the wave is reflected back in the direction of the transmitter. Such discontinuities can be caused by impedance mismatches, mismatches between line and balancing networks, and irregular spacing of loading coils. Echo is imperceptible in human-to-human conversations as long as the echo return is weak and the total roundtrip delay is not longer than 30–40 milliseconds (ms). Echo generally is not an issue, except in very long haul copper circuits or over satellite circuits. Contemporary networks are designed with echo cancellers, which remove a portion of the delayed transmitted signal from the received signal.There are also devices known as echo suppressors, which often convert full duplex (FDX) phone connections into half duplex (HDX). See also echo canceller, echo suppressor, FDX, HDX, impedance, and loading coil. 2. A signal intentionally returned to the transmitter by the receiver for purposes of primitive error control. See also echo checking. 3. A packet intentionally returned to the transmitter by the receiver for purposes of testing an end-to-end path.The ping utility is an application of the Internet Control Message Protocol (ICMP) used to test a path from one host computer to another across an IP-based network in what is essentially a command to echo the packet from the remote host back to the originating host. See also host, ICMP, IP, ping, and utility. |
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