Echo canceller
From Wikipedia, the free encyclopedia
An Echo canceller is a telecommunications device used to remove the echo that can result from delay on a telecommunications circuit. This delay can be the result of the length of the circuit or due to packetization or queuing delay. As a result, echo cancellers are used on all Voice over IP and mobile telephone calls and essentially all long-distance calls.
The functionality of echo cancellers in public networks is standardised by ITU-T Recommendation G.165. For digital networks, recommendation G.168 defines the standard.
[edit] History
Echo cancellers are the replacement for earlier echo suppressors that were initially developed in the 1950s to control echo caused by the long delay on satellite telcommunications circuits. Initial echo canceller theory was developed at AT&T Bell Labs in the early 1960s, but the first commercial echo cancellers were not deployed until the late 1970s owing to the limited capability of the electronics of the era.
Rapid advances in the implementation of digital signal processing allowed echo cancellers to get smaller and more cost-effective. In the 1990s, echo cancellers were implemented within voice switches for the first time (in the Northern Telecom DMS-250) rather than as standalone devices. The integration of echo cancellation directly into the switch meant that echo cancellers could be reliably turned on or off on a call-by-call basis, removing the need for separate trunk groups for voice and data calls.
