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Abstract-Packet forwarding in Public TransportNetworks is particularly challenging due to the high mobility, rapidly changing topology and intermittent connectivity observed in these networks. Though clustering of nodes can aid forwarding decision in these Delay Tolerant Networks (DTNs), the clustering process is extremely costly in a large network. In this paper, we introduce a generic efficient clustering method which is suitable for grouping the nodes of large networks. We also demonstrated how encounter frequencies of public transport networks can be fed to that clustering algorithm in order to build clusters of nodes. And finally, our large scale extensive simulation study on real bus traces shows the efficacy of clustering in packet forwarding.

SUMMARYThis paper presents the results of performance tests carried out for a file delivery system based on the file delivery over unidirectional transport (FLUTE) protocol. FLUTE is a file transport protocol used to deliver files over IP networks, including the Internet and unidirectional systems, from a sender to one or more receivers. FLUTE uses UDP, an unreliable transport protocol, and so reliable delivery must be guaranteed by other means. This paper shows how FLUTE manages to recover from packet losses using forward path redundancy (forward error correction (FEC) and repeat transmissions in a data carousel), and a simple HTTP-based point-to-point file repair scheme which is specified in 3GPP and DVB standards. The results presented in this paper show that careful optimization of FEC overhead, and the number of repeat transmissions, gives the best system performance in most cases. Based on the simplified error reception and distribution model depicted in this study, it is illustrated that the simple client-server pointto-point file repair is optimal only for small groups. Several options to improve the configuration of FLUTE senders are provided, to deliver reception guarantees with optimal data expense from the system point of view.

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SUMMARYIn this paper, we propose an analytical cross-layer model for a Transmission Control Protocol (TCP) connection running over a covariance-stationary wireless channel with a completely reliable Automatic Repeat reQuest scheme combined with Forward Error Correction (FEC) coding. Since backbone networks today are highly overprovisioned, we assume that the wireless channel is the only one bottleneck in the system which causes packets to be buffered at the wired/wireless interface and dropped as a result of buffer overflow. We develop the model in two steps. At the first step, we consider the service process of the wireless channel and derive the probability distribution of the time required to successfully transmit an IP packet over the wireless channel. This distribution is used at the next step of the modeling, where we derive expressions for the TCP long-term steady-state throughput, the mean round-trip time, and the spurious timeout probability. The developed model allows to quantify the joint effect of many implementationspecific parameters on the TCP performance over both correlated and non-correlated wireless channels. We also demonstrate that TCP spurious timeouts, reported in some empirical studies, do not occur when wireless channel conditions are covariance-stationary and their presence in those measurements should be attributed to non-stationary behavior of the wireless channel characteristics.