Overlay Convergence Architecture for Legacy Applications

Nov 22, 2006: Website redesigned.


OCALA consists of an Overlay Convergence (OC) layer positioned below the transport layer in the IP stack. The OC layer bridges legacy applications and overlays by presenting an IP-like interface to legacy applications and tunneling the traffic of legacy applications over overlays. The OC layer is decomposed into the overlay dependent sublayer (OC-D), which interacts with the overlays, and the overlay independent (OC-I) sublayer, which interacts with the legacy applications:

The splitting of the OC layer into the OC-I and OC-D sub-layers enables OCALA to support simultaneous access to different overlays. The following figure shows an example in which three applications on host A open connections via IP and two overlays: a web browser (Firefox) uses IP to connect to www.cnn.com , a chat client (IRC) uses i3 to preserve the client's anonymity, and ssh uses RON for improved resilience.

The OC-I OC-D split also enables OCALA to easily support gateways that enable hosts connected to different overlays to communicate with each other. The following figure shows an i3 host communicating with a RON host via a gateway B.

The above figure also illustrates OCALA's notion of paths and tunnels. The OC-I layer creates and maintains an end to end channel, called a path, between two nodes that communicate with each other. A path can span multiple hops (as seen in the above figure), with forwarding information maintained at the OC-I layers of intermediate hops. The communication channel between two hosts at the OC-D layer is called a tunnel. A tunnel can be formed only between two hosts on the same overlay.

A tunnel can be constructed over regular IPv4/IPv6, and not only over new network architectures and overlays. Tunnels over IP enable hosts that do not run the OCALA software to communicate with OCALA-enabled hosts. Special OC-D modules, called legacy-server-IP (LSIP) and legacy-client-IP (LCIP) enable bridging between regular IP and new network architectures. Figure (a) below illustrates an OCALA-enabled host communicating with a legacy server (www.nasa.gov), while Figure (b) shows a legacy client communicating with an OCALA-enabled server.

Last Updated on 11/22/06 15:51:48