Scaling and selectivity: from NSTP to SGAP

Abstract

We previously designed the Notification Service Transfer Protocol (NSTP) as a general-purpose coordination mechanism for building synchronous groupware applications. We initially thought that a colleague awareness tool (colloquially, a "buddy list") was just another synchronous groupware application. However, as users requested more capabilities, we discovered that awareness applications have an underlying model of interaction that differs from our other, quasi-meeting, applications. In particular, we ran into problems of scaling (NSTP's model required too much unnecessary information to be distributed) and selectivity (NSTP's model did not allow fine enough control of the way information was exposed). Accordingly, we designed the Simple General Awareness Protocol (SGAP) to address the problems that arise in sophisticated awareness applications. The problem is broader than NSTP alone: the international standard T. 120 suffers from the same limitations, as does any other infrastructure built around a quasi-meeting model.