Multi-point data distribution for synchronous multimedia communication poses interesting problem for networking environment and it is usually implemented by either native or virtual multicast. We describe and evaluate a scalable network of Active Elements (AE) that implements user-empowered virtual-multicast overlay network for synchronous data distribution and processing in the network. The AE network is based on strict separation of control plane and data plane. The control plane is organized as peer-to-peer network in order to achieve robustness and user-empowered approach while sacrificing efficiency to some extent. The data plane which handles the actual data distribution is optimized for efficiency and allows pluggable implementation of different distribution models. Each plane solves robustness and scalability by own.
We present a prototype implementation with control plane based on JXTA peer-to-peer substrate. Control plane is responsible for managing and controlling AEs in the AE network and also to gather information about state of AE network for the data distribution schemes. Prototype consists of stand-alone modular application which implements server side and also client side. We have evaluated control plane behavior, scalability, robustness, and efficiency. In order to achieve better results in robustness and scalability of control plane, we have had to do specific changes into the JXTA peer-to-peer substrate. The results show that AE network can grow significantly without any restriction because there is linear dependency between number of exchanged messages and number of AEs in the network. Growing number of the AEs in the network does not have influence on the number of messages send and receive by each single AE. Robustness of the AE network also reaches very high level. As a consequence to our changes in JXTA, the latency when AE recognizes failure of the neighbor AE decreased from 60 s to about 1 s. Both attributes can be adjusted to better fit host environment and needs.
Generally AE network is used for any multimedia applications, that rely on RTP/UDP data transmission like MBone videoconferencing tools (RAT, VIC) and shared whiteboard (WB/WBD). Also unidirectional ”broadcasting” applications like VideoLAN Client can utilize AE networks for distribution of their data.