The present document specifies the architecture and protocols for discovering TV Devices in the home that implement@ interfaces defined in the other parts of this multi-part deliverable. The discovery protocol is used by the Companion Screen Application to detect TV Devices. The discovery protocol supplies the information so that the following interfaces can be used over the established link: the interfaces between the TV Device and the Companion Screen Application: - interface for metadata exchange@ including content identification (CSS-CII); - interface for Wall Clock synchronization (CSS-WC); - interface for Timeline Synchronization (CSS-TS); - interface for notification of Trigger Events (CSS_TE). The interfaces themselves are described in clauses 6@ 8@ 9 and 10 of ETSI TS 103 286-2 [4]. Note that Wall Clock synchronization and Timeline Synchronization interfaces are (currently) discovered indirectly. The present document defines the means to discover the CSS-CII interface. The other interfaces are then discovered by means of the established connection for the CSS-CII interface and this is defined in ETSI TS 103 286-2 [4]. The present document does not describe: The UPnP? Device Architecture [1]. The UPnP? Application Management service [2]. How to establish communication through a web socket [3].