Complex sentence: Previously, Ottawa and Hull also had exchange protection in place to preserve seven-digit dialing between the two cities, implemented in such a way that if a number was in use in Ottawa the equivalent 819 number could not be assigned anywhere in western Quebec.
Split into simpler sentences: Previously, Ottawa and Hull also had exchange protection in place to preserve seven-digit dialing between the two cities. However, it was implemented in such a way that if a number was in use in Ottawa, the equivalent 819 number could not be assigned anywhere in western Quebec.