Nortel Networks Corp., the Canadian maker of telecom equipment, filed a lawsuit on Dec. 14 against Vonage — claiming that it violated nine patents related to Internet phone services and related features such as 911 and 411 calling and click to call.

Nortel spokesman Mohammed Nakhooda said the lawsuit, filed in U.S. District Court in Delaware, countered claims made by Vonage that Nortel had violated three of its patents.