Transmission Delay in Multi-Site Installations
A unique echo problem may occur when different types of video compression technology are interfaced. In the example below,
some sites are connected to each other directly using high bandwidth, low delay MPEG video over ATM. There are other sites, however, that
must connect to the conference via ISDN (H.323), which has low bandwidth and high delay. All sites in the conference use ISDN and an MCU as the
primary connection. (Even the sites that are connected to each other through ATM must connect to the other sites via ISDN). This causes two
signals to arrive from the same site, one delayed by at least 100 milliseconds. In this case, the "echo" is caused by hearing the same site twice.
This type of echo is different from acoustic echo or looped-back echo, where audio from a site is returned to the site (so people hear their own audio
coming back through the system).
The EF1210TEC solves this problem by using the low-delay signal as a reference to identify the high-delay signal. It then removes the redundant audio from the received signal.
Click here for an explanation of looped-back audio.
Click here to download
the EchoFree™ EF1210TEC spec sheet in
Acrobat PDF format. (2 pages, 217K)
