OCALA: An Architecture for Supporting Legacy Applications over Overlays

The ever increasing demand of new applications has led researchers to propose new network architectures that address limitations of the current Internet. Given the rigidity of the Internet today, overlay networks are used to implement such architectures, in the hope of gaining a large user base. Despite sustained efforts to test and deploy new network architectures (on testbeds such as Planetlab), few of these efforts have attracted a significant number of users. We believe that chances of user acceptance of overlays, and eventually new network architectures, will be substantially improved by enabling users to leverage their functionality without any modifications to their applications and operating systems. In this paper, we present our design, implementation, and experience with OCALA, an overlay convergence architecture that achieves this goal. OCALA interposes an overlay convergence layer below the transport layer, that is composed of an overlay independent sub-layer that interfaces with legacy applications, and an overlay dependent sub-layer that delivers packets to the overlay. Unlike previous efforts, this design enables: (a) simultaneous access to multiple overlays (b) communication between hosts in different overlays (c) communication between overlay hosts and legacy hosts (d) extensibility, allowing researchers to incorporate their overlays into OCALA. We currently support three overlays, i3 [29], RON [1] and HIP [17], on Linux and Windows XP/2000. We (and a few other research groups and end-users) have used OCALA for over a year with many legacy applications ranging from web browsers to remote desktop applications.