Dealing With User Heterogeneity in P2P Multi-Party Video Conferencing: Layered Distribution Versus Partitioned Simulcast

Abstract

We consider peer-to-peer multi-party video conferencing (P2P-MPVC), where users with different uplink -downlink capacities send their videos using multicast trees. One way to deal with user bandwidth heterogeneity is employing layered video coding, generating multiple layers with different rates, whereas an alternative is partitioning the receivers of each source and disseminating a different non-layered video version within each group. In this paper, we aim to maximize the received video quality for both systems under uplink-downlink capacity constraints, while constraining the number of hops the packets traverse to two. We first show any multicast tree is equivalent to a collection of 1-hop and 2-hop trees, under user uplink-downlink capacity constraints. This reveals that the packet overlay hop count can be limited to two without sacrificing the achievable rate performance. Assuming a fine granularity scalable stream that can be truncated at any rate, we propose an algorithm that solves for the number of video layers, layer rates, and distribution trees for the layered system. For the partitioned simulcast system, we develop an algorithm to determine the receiver partitions along with the video rate and the distribution trees for each group. Through numerical comparison, we show that the partitioned simulcast system achieves the same average receiving quality as the ideal layered system without any coding overhead for the four-user systems simulated, and better quality than the layered system when the layered coding overhead is only 20%. The two systems perform similarly for the six-user case if the layered coding overhead is 10%.