| Publisher | ADT - Adaptive Digital Technologies | ||
|---|---|---|---|
| Format | HTML | Date added | 27 Oct 2000 |
| Topics | Voice - Data Integration, Modems | ||
| Downloads | 125 | ||
The Public Switched Telephone Network (PSTN) uses both 4-wire circuits and 2-wire circuits to carry full duplex voice circuits. The 2-wire circuits tend to be used in the local loop portion of the network, which is the connection between the end user (home or business) and the telephone central office. Hybrid circuits are used to convert between 2-wire and 4-wire circuits. Since the hybrid circuits are not perfect, they reflect a portion of the signal received on the 4-wire circuit back to the transmitted signal. This causes an echo to be heard at the far end of the network. In order to combat this problem, the PSTN employs echo cancellers and echo suppressors. The introduction of voiceband fax and data modems brought a new set of requirements to the PSTN. The echo suppressors and cancellers can interfere with the transmission of modem signals. Many modem standards have been adopted over the years and they are not all affected in the same way by echo cancellers and suppressors.
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