Telecommunications systems are used to provide telecommunications services between two or more user interfaces. User interfaces may include telephone handsets, facsimile machines, computers and other equipment, and may be connected to the switching system by fixed land-based conductors or wireless services. Telecommunications services are provided by establishing a telecommunications channel between two user interfaces, such that encoded analog or digital data may be transmitted between the user interfaces until a state of completion is reached.
An undesired characteristic of telecommunications channels is the generation of echo. Echo may be inadvertently created, and is usually a function of the physical parameters of a telecommunications channel. For example, when a telecommunications channel includes a two wire conductor in series with a four wire conductor, echo may be generated at the interface between the two wire conductor and the four wire conductor. Other sources of echo are also known. Echo is one of the primary factors affecting the perceived quality of voice connections. Echo canceller devices are routinely used to prevent echo from degrading telecommunications channels.
Although echo cancellation is a useful technique in processing telecommunications, echo cancellation is not always required. If an echo canceller is enabled on a given telecommunications channel when echo cancellation is not required, the resulting signal may have degraded quality such that voice data is unintelligible. Moreover, enabling an echo canceller typically consumes resources that may be better utilized to carry out other functions rather than unneeded echo cancellation. Accordingly, it is highly desirable to not enable, or disable if already enabled, echo cancellation with respect to a telecommunications channel that does not require echo cancellation, such as when a call is directed to a radio based subscriber unit, such as a hand held mobile telephone.
One method of simulating the activation of an echo canceller is to increase the rate of attack of an echo canceller upon detection of off-hook signaling. This method has the drawback of requiring the echo canceller to remain active, even though echo cancellation is not performed. Thus, increasing the rate of attack of echo cancellation upon detection of off-hook signaling may still result in allocation of system resources to perform echo cancellation when not required. Increasing the rate of attack of echo cancellation to simulate turning the echo canceller on may also result in additional processing delay if the echo canceller is located in an external bank and the signal is routed to the echo canceller regardless of the rate of attack of echo cancellation.