Speech path switching control apparatus and method for making maintenance of speech possible upon occurrence of fault in echo cancellation

A method of operating a speech path switching control apparatus having time switching means, echo cancellation means, time switching control means and access switching control means, comprising the steps of:

• (a) initializing said time switching means, said echo cancellation means, said time switching control means and said access switching control means, allocating a trunk line to a trunk call through a signalling process and allowing said access switching control means to discriminate whether echo cancellation is required for the trunk call allocated with the trunk line;
• (b) forming under control of said time switching control means a speech path which is not passed through said echo cancellation means, if it is discriminated at said step (a) that the echo cancellation is not required for the trunk call allocated with the trunk line, and discriminating whether said echo cancellation means is normal, if it is discriminated at said step (a) that the echo cancellation is required for the trunk call allocated with the trunk line;
• (c) looping back sub-highway data of TTL levels including a speech channel, if it is discriminated at said step (b) that said echo cancellation means is not normal, and transmitting the looped-back data to said time switching means through subhighways, each of which accommodates PCM 32 channels, to form under the control of said time switching control means the speech path which is not passed through said echo cancellation means;
• and
• (d) forming a speech path which is passed through said echo cancellation means, if it is discriminated at said step (b) that said echo cancellation means is normal.