Ping pong communication methods, which are well known in the prior art, are used to provide full duplex communications over a communications channel, which channel requires amplification. Full duplex allows each station that is on the communications channel to transmit and receive with apparent simultaneity. For example, an ordinary telephone is duplexed; a user can talk and listen at the same time.
With ping pong methods, only one communications channel is required. This channel may be a light fiber, a radio link or a multiplexed telephone pair. The ping pong method converts the data to be transmitted into digital data by sampling. Sampling is done at a frequency that is much higher than the Nyquist frequency of the sampled data. The sample data is then transmitted over the communications channel in bursts.
Some prior art methods operate in the following manner: a first station transmits a data burst on the channel, which is received by a second station. Upon receipt of the data burst, the second station transmits its own data burst, which is received by the first station. Upon receipt of the second station's data burst, the first station transmits another data burst, and so on. Thus, the stations take turns transmitting and receiving so that data bursts are transmitted in a ping pong fashion. This transmitting arrangement is ineffective at long ranges (over 10 kilometers). The transmitted data bursts suffer a propagation delay, which is the time of travel between the two stations. At long ranges, the propagation delay is significantly long, slowing the transmission rate to unacceptable levels.
Another prior art ping pong method transmits large bursts of data in order to compress the effective transmission rate. Each large burst is made up of several single data bursts. Unfortunately, this prior art approach is difficult and expensive to implement.
One way to achieve ping pong communication at long ranges in a simple and economical manner is to provide a master station and a slave station as the first and second stations. The master stations transmits single data bursts at fixed intervals of time. The slave station only transmits upon receipt of a master station data burst.
When the distance between stations is such that the propagation delay results in data from the slave station arriving at the master station while the master station is transmitting, the data is lost. Thus, the slave station is located in a type of "dead zone" along the communications channel, wherein communication with the master station is unobtainable.
Service personnel frequently encounter this problem when tapping into a channel to communicate, for example, with a central station. When tapping into the channel with a test set, they may tap into a "dead zone", wherein communication with the central station is unachievable. It may be inconvenient or impossible to move to another location that is along the communications channel to relocate the tap out of the dead zone. What is needed is a simple and economical approach to provide communication at all locations along a ping pong communications channel.