Inter-Session Network Coding in Delay Tolerant Mobile Social Networks: An empirical study

Delay Tolerant Mobile Social Networks (DTMSNs) are networks made of human-carried wireless devices with intermittent connections, and whose physical meeting patterns make cluster into social communities. In such environments, routing is a challenge as the limited resources (like memory and contact opportunities) must be efficiently used and shared between the sessions (or users, contents). To handle several unicast sessions, Inter-Session Network Coding (ISNC) has been proven necessary for optimal throughput in general networks, but is a delicate problem as it can quickly get detrimental. This paper investigates empirically whether ISNC can be beneficial in DTMSNs. We first show that on a simple chain topology, without or with a hub node, no gain can be generally obtained when contacts are bidirectional. We then show that if non-directionality impedes ISNC gain, it can be due to greedy replication, and on the same DTMSN operated with a social-aware routing algorithm, the set of chosen routes turns ISNC into beneficial. On a butterfly topology, we investigate the impact, on ISNC gain, of key network parameters such as buffer management, copy (memory) budget and network load. This allows to determine what parameters to take into account when designing a decentralized ISNC criterion for general topologies.