Ocala: An Architecture For Supporting Legacy Applications Over Overlays

In order for overlays and new network architectures to gain real user acceptance, users should be able to leverage overlay functionality without any modifications to their applications and operating systems. 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. This layer 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, OCALA 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 five overlays, i3 [32], RON [1], HIP [19], DOA [39] and OverDoSe [31] on Linux, Windows XP/2000 and Mac OS X. 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.