Transmission delay and echo suppression

We are all aware that radio communication is not instantaneous. With the coming of satellite communication we have fallen prey to some of the consequences of telephony with long propagation time. So it is that when one person speaks to another via satellite link, he must wait perhaps 600 ms for a rejoinder. Such a delay, of itself, may not be too disconcerting, but in combination with echo it can contribute to poorer quality transmission. This is an account of how echo is produced, how it can affect a telephone conversation, and what steps are being taken to overcome the problems.