In this paper, we propose a scheme for implementing multiparty videoconferencing service on SONET/ATM rings. We focus on the architectural design and bandwidth demand analysis. Different multicasting methods on SONET/ATM rings are discussed and compared. A new multicast virtual path (VP) called "Multidrop VP" which is particularly suitable for SONET/ATM rings is proposed. An add-drop multiplexer (ADM) structure for rings capable of multidropping is also presented. Several VP assignment schemes are proposed and their bandwidth utilizations are compared.