Nortel Networks VT100 - Manual (Page 13)

1-6 About the VT100 Gateway
555-9001-316 Standard 1.0 February 1996
ATTENTION!
The TRS process for managing calls is restricted to handling one active
line at a time (single threaded mode).
Therefore, you should add a loop to applications that interact with the
TRS so that customers who call at peak hours are informed on the
status of their call. For example, you can allow callers to hear a
recurring message that an operator will assist them as soon as possible.