PodNet is a research project collaboration between ETH Zürich and KTH Stockholm that started in March 2006. The goal of the project is to develop a mobile distribution system for user-generated broadcast content that uses mobile device-to-device communication.

PodNet expends the traditional podcasting concept for public (i.e., open and unrestricted) peer-to-peer delivery of broadcast contents amongst mobile nodes. The Figure to the right describes the PodNet architecture. Contents are provided in a wireless broadcasting area either through fixed PodNet gateways or by mobile nodes themselves. In the first case, a PodNet server fetches contents from servers across the Internet and forwards them to mobile nodes within the range of PodNet gateways; this is done in the regular podcast mode. In the second case, a mobile node that has contents to share might provide data to another mobile node when they pass within radio range of one another. This is one of the new content distribution mode that we add to the existing one. The other content distribution mode we offer is the possibility for mobile devices to fetch user-generated content to the PodNet server when passing within range of a PodNet gateway. Our ad hoc podcasting mode brings the following advantages. First, it provides nodes with contents when they are not connected to the Internet; second, it provides a new ad hoc broadcasting domain when also the sources of the data are mobile nodes (could be pictures or video/voice recordings from a mobile phone for instance). PodNetSec is a secure version of PodNet.

The sharing of contents is based on a solicitation protocol by which a node asks a peer node for content (a peer node can either be a mobile device or a PodNet gateway). Hence, there is no flooding of contents in the broadcasting area.

Contents are organized into feed channels, and nodes solicit episodes for one or more feed channels. The concept of feed channels allows for a higher hit rate of the queries than if they were for individual episodes of contents. The episodes of a particular feed channel will however reach a node in arbitrary order and the downloads might get interrupted when the nodes move away. We therefore introduce chunks (inspired by BiTtorrent), atomic data units that allow an incomplete episode download to be resumed with the same node or any other node that also has the episode.

PodNet is simple in its protocols, and lightweight in the computational requirements. We allow only pair-wise node associations to increase the chance that downloads eventually succeed when the contact durations are short. As a result, we do not need an explicit multi-hop routing protocol. Dissemination of content is performed implicitly at the application layer, through content distribution by gateways and through node mobility.