A method of determining when there has been a change in the modem power state of a modem connected to a digital subscriber line. An Uncalibrated Echo Response (UER) trace is obtained from the digital subscriber line by running a Single Ended Line Test (SELT) on the line. This UER trace is compared to a historical (baseline) UER trace from the same line. A difference in the two traces in a higher frequency range (for example, DS3 for a VDSL line), is indicative of a possible modem power state change.

Systems and methods of testing call quality and control devices are provided according to examples of the present disclosure. In one aspect, the system includes a simulation base station, a tested communication device, a control device configured to transmit a call instruction such that a call between the tested communication device and the simulation base station is established, and a testing device configured to provide a standard audio, where the standard audio becomes a test audio after it is processed by the tested communication device during a transmission process via the call and the test audio is sent back to the testing device, and perform a similarity comparison between the test audio and the standard audio to obtain a similarity comparison result, where the similarity comparison result shows the call quality of the tested communication device.

A transmission system includes a transmission terminal locally reproducing video and voice data and transmitting and receiving the video and voice data via a network; a relay apparatus transmitting the video data and voice data to another transmission terminal or the transmission terminal; and a transmission management apparatus managing a session for a single transmission terminal. Further, the transmission terminal sends a request for establishing a session for a single site to the relay apparatus via the transmission management apparatus, and the relay apparatus establishes the session for the single site related to the transmission terminal so that a connection check process is performed on the transmission terminal within the single site only.