SLIM: A Session-Layer Intermediary for Enabling Multi-Party and Reconfigurable Communication

Increasingly, communication requires more from the network stack. Due to missing functionality, we see a proliferation of networking libraries that attempt to fill the void (e.g., iOS to OSX Handoff and Google Cast SDK). This leads to considerable duplication of effort. Further, the provisions for extending legacy protocol stacks is largely exhausted (e.g., TCP options space is mostly allocated) making the addition of future extensions much more challenging. We present SLIM, an extensible session-layer intermediary that extracts the duplicate functionality from modern networking libraries and provides the means for future extensibility to the network stack. SLIM enables mobility, multiparty communication, and dynamic reconfiguration of the network stack in a straightforward and elegant way. SLIM includes an out-of-band signaling channel, which not only enables reconfiguration, but also allows for incremental evolution of the stack. To start, we tease out elements of session management which are currently conflated with transport semantics in TCP. Doing so highlights the need for sessions in contemporary use cases. Next, we propose session, flow and endpoint abstractions that allow application developers to describe communication between any number of participants. The abstractions apply to individual or a group communication allowing them to be managed as one. We describe the abstractions and evaluate them in terms of typical communication patterns. We demonstrate the abstractions via a prototype implementation of SLIM.