C1, also known as New Punter, was developed in 1984 by Steve Punter as a successor to PTP. C1 was the standard protocol for use on Commodore BBSes, and was rarely supported by terminal or BBS software for other operating systems.
The C1 specification was rife with inaccuracies and ambiguities, making it difficult to implement from scratch. Nevertheless, the protocol came into widespread use because Punter released the source code for the original implementation into the public domain.
Read more about this topic: Punter (protocol)