When direct communication, such as via Bluetooth, is unavailable, a communication protocol is used by an initiating communication device and/or a recipient communication device to establish a communication session via a cloud-based relay server. Establishing the communication session, such as a phone call or video streaming, includes setting up at least a first connection or link between the initiating communication device and the relay server, and at least a second connection or link between the relay server and the recipient communication device. Transports and interfaces for the first link and the second link may be selected independently of each other, and at least one of transports and interfaces for the first link and the second link may differ, e.g., the communication session may include asymmetric transport.