Multi-Path TCP (MPTCP) is a new standardized transport protocol that enables devices to utilize multiple network interfaces. The default MPTCP path scheduler prioritizes paths with the smallest round trip time (RTT).In this work, we examine whether the default MPTCP path scheduler can provide applications the ideal aggregate bandwidth, i.e., the sum of available bandwidths of every paths. Our experimental results show that heterogeneous paths cause underutilization of the fast path, resulting in undesirable application behaviors such as lower streaming quality in a video than can be obtained using the available aggregate bandwidth. To solve this problem, we propose and implement a new MPTCP path scheduler, ECF (Earliest Completion First), that utilizes all relevant information about a path, not just RTT. We compare ECF with both the default and other MPTCP path schedulers, using both an experimental testbed and in-the-wild measurements. Our results show that ECF consistently utilizes all available paths more efficiently than other approaches under path heterogeneity, particularly for streaming video. In Web browsing workloads, ECF also does better in some scenarios and never does worse.

Multi-Path TCP (MPTCP) is a new transport protocol that enables systems to exploit available paths through multiple network interfaces. MPTCP is particularly useful for mobile devices, which usually have multiple wireless interfaces. However, these devices have limited power capacity and thus judicious use of these interfaces is required.

With the popularity of mobile devices and the pervasive use of cellular technology, there is widespread interest in hybrid networks and on how to achieve robustness and good performance from them. As most smart phones and mobile devices are equipped with dual interfaces (WiFi and 3G/4G), a promising approach is through the use of multi-path TCP, which leverages path diversity to improve performance and provide robust data transfers. In this paper we explore the performance of multi-path TCP in the wild, focusing on simple 2-path multi-path TCP scenarios. We seek to answer the following questions: How much can a user benefit from using multi-path TCP over cellular and WiFi relative to using the either interface alone? What is the impact of flow size on average latency? What is the effect of the rate/route control algorithm on performance? We are especially interested in understanding how application level performance is affected when path characteristics (e.g., round trip times and loss rates) are diverse. We address these questions by conducting measurements using one commercial Internet service provider and three major cellular carriers in the US.

A recent topic of research in the network science community is combined or composite networks - these are two or more interacting networks that must be characterized jointly rather than individually. For example, a social network and a communication network sharing some nodes (corresponding to users) may be modeled together as a composite network. This may be useful since the aggregate performance of a composite network may often depend on how the individual networks influence each other. Information may travel faster or slower through composite networks depending on how they are coupled. The above vision was captured in the Call for Papers for this special issue in the IEEE Journal On Selected Areas In Communications, and it was published in June 2012. As a result of this solicitation, we received 62 submissions by the deadline of August 15, 2012. Papers were selected after two rigorous rounds of review. The first round of notifications were sent out on December 17, 2012 to the authors whose papers passed the first round of review. Revised versions of the papers were submitted on January 31, 2013. Finally, after a second round of review, the Guest Editorial board decided on March 12, 2013 to accept 16 high quality papers for publication in this competitive special issue. Papers appearing in this special issue belong to five broad themes, which are not necessarily mutually exclusive: (1) fundamental principles in network science, (2) information propagation models in networks, (3) bringing insights from other genres of networks, (4) economic and game theoretic models, and (5) application of network science principles to communications networking problems.

In multi-hop wireless networks, per-hop forwarding strategies that optimize local transmissions can have a subtle impact on network performance. Motivated by a number of scenarios for improving signal strength or mitigating interference, we study a fundamental problem that arises in a wireless ad hoc network with directional transmission (e.g., using directional antennas), where nodes are randomly placed with their transmission footprints (each as a sector) aligned toward the destinations. Only the nodes located in the transmission footprint of a transmitter act as forwarders. Our study addresses connectivity of this setting. We first examine through simulation the percolation probability and the number of cross-area paths available to directional transmission, at different spread angles of transmission footprints. We observe that there is a critical spread angle, above which there is little impact on these properties. Analytically, we derive upper and lower bounds for the critical spread angle. Moreover, we show that with high probability there exist at least Ω(n/ log n) number of disjoint paths across a strip area of n × Θ(n), when the critical spread angle lies above the threshold. Our results provide insights on optimizing directional transmission in wireless ad hoc networks.

One of the challenges of wireless networks is to provide a reliable end-to-end path between two end hosts in the face of link and node outages. These can occur due to fluctuations in channel quality, node movement, or node failure. One mechanism that has been proposed is based on multipath routing, the idea being to establish two or more paths between the end hosts so that they always have a path between them with high probability in the face of outages. This naturally raises the question of how to discover these paths in an unknown, random wireless network to enable robust multipath routing. In order to answer this question, we model a random wireless network as a 2D spatial Poisson process. Based on the results of percolation highways in Franceschetti, et al., we present accurate conditions that enable robust multipath routing. If the number of hops of a path between the end hosts is n, then there exists a path between them in a strip of width proportional to log n. More precisely, there exist C log n disjoint paths in a strip of width a(C, p) · log n, where p is the probability that characterizes the availability of an individual wireless communication link. We derive tight bounds for the function a(C, p). This provides a useful guideline for the establishment of multiple paths in a real wireless network, namely that the width should grow logarithmically in the number of hops on the path between the hosts.

Duty cycling or periodic sleep scheduling of RF transceivers of nodes in a wireless ad hoc or sensor network can significantly reduce energy consumption. This paper sheds light on the fundamental limits of the end-to-end data delivery latency and the per-flow throughput in a wireless network with multiple interfering flows, in the presence of "coordinated" duty cycling. We propose green wave sleep scheduling (GWSS) - inspired by synchronized traffic lights - for scheduling sleep-wake slots and routing data in a duty cycling wireless network, whose performance can approach the aforementioned limits. Particularly, we derive a general latency lower bound and show that GWSS is latency optimal on various structured topologies, such as the line, grid and the tree, at low traffic load. For an arbitrary network, finding a solution to the delay-efficient sleep scheduling problem is NP-hard. But for the 2D grid topology, we show that a non-interfering construction of GWSS is optimal in the sense of scaling laws of latency and capacity. Finally, using results from percolation theory, we extend GWSS to random wireless networks, where nodes are placed in a square area according to the Poisson point process. Aided by strong numerical evidence for a new conjecture on percolation on a semi-directed lattice that we propose, we demonstrate the latency optimality of GWSS on a random extended network, i.e., for an area-n random network with unit-density-Poisson distributed nodes, and a node-active (duty-cycling) rate p, GWSS can achieve a per-flow throughput scaling of T(n, p) = Ω(p/√n) bits/sec and latency D(n, p) scaling of O(√n) + O(1/p) hops/packet/flow.

One of the major concerns of IPTV network deployment is channel switching (or zapping) delay. This delay can add up to two seconds or more, and its main culprits are synchronisation and buffering. By analysing an extensive dataset - comprising 255 thousand users, 150 TV channels, and covering a 6-month period - we have observed that most channel switching events are linear: it is very common the user switching up or down to the next TV channel. This fact led us to the proposal, in this paper, of a simple mechanism to reduce channel switching delay. Our proposal is to send the neighbouring channels (i.e., channels adjacent to the requested one) to the Set Top Box (STB) during zapping periods. If the user switches to any of these channels the switching latency is virtually eliminated, not affecting therefore user's experience. Notwithstanding the simplicity of this scheme, trace-driven simulations show that the zapping delay can be virtually eliminated for a significant percentage of channel switching requests. As an example, by sending the previous and the next channel concurrently with the requested one, for only one minute after a zapping event, switching delay is eliminated for around 45% of all channel switching requests. Furthermore, this simple scheme has a performance close to that of an ideal predictor, while the increase of bandwidth utilisation in the access link is negligible.

We use the term policy-based routing to refer collec- tively to the Stable Paths Problem, Sobrinho's Routing Algebras, and to classical Path Algebras (semi-rings used to generalise minimum-weight routing). These theories all contain sufficient conditions that ensure the existence of solutions (stable routings) for labelled graphs. We attempt to provide a unified theory from which all of these seemingly disparate sufficient conditions can be derived. Our theory is based purely on abstract relations and their properties and not on the syntactic or axiomatic details of the policy-based theories.

This paper analyzes competition between two Internet service providers (ISPs), either or both of which may choose to offer multiple service classes. In the model analyzed, a social planner who maximizes the total benefit from network usage and a profit maximizing monopolist will both form multiple service classes; but two networks competing to maximize profits will not. The reason is that a competition effect always outweighs a segmentation effect. Networks wish to offer multiple service classes in order to increase user benefits and hence charge higher prices. In doing so, however, they effectively increase the number of points in the service quality range at which they compete. Consequently, in any equilibrium competitive outcome, both ISPs offer a single service class. The analysis has particular implications for the Paris Metro pricing (PMP) proposal, which is considered in depth in this paper, since it suggests that PMP may not be viable under competition.

This paper describes how some of the insights available from the stochastic analysis of dynamic routing may be incorporated into the classical mathematical programming approach to the design of networks. In particular, we present the results of a number of numerical investigations into network architectures for circuit-switched communication networks. Our investigations use recent theoretical results integrating network flow optimization and Markov decision processes to provide performance bounds for dynamic routing strategies. Following a tutorial introduction of the above mentioned topics we develop a sequence of network examples. Our first examples are familiar ones, such as symmetric fully connected networks and networks with moderate amounts of asymmetry, and we describe how network programming methods complement earlier work on dynamic routing. We then consider a variety of example networks which have a more sparse collection of links. These examples indicate the potential applicability of the methods to a variety of areas, including studies of the design, performance and resilience of future communication networks.>

This paper describes a simple and robust ATM call admission control, and develops the theoretical background for its analysis. Acceptance decisions are based on whether the current load is less than a precalculated threshold, and Bayesian decision theory provides the framework for the choice of thresholds. This methodology allows an explicit treatment of the trade-off between cell loss and call rejection, and of the consequences of estimation error. Further topics discussed include the robustness of the control to departures from model assumptions, its performance relative to a control possessing precise knowledge of all unknown parameters, the relationship between leaky bucket depths and buffer requirements, and the treatment of multiple call types.>

The aggregated-least-busy-alternative (ALBA), a distributed, state-dependent, dynamic routing strategy for circuit-switched loss networks is discussed. The networks considered are symmetric and fully connected. The offered calls form Poisson streams, and routes have at most two links. In ALBA(K), the states of each link are lumped into K (K>or=2) aggregates, and the route of each call is determined by local information on the aggregate states of the links of the alternate routes at the time of the call's arrival. The last aggregate is always the set of states reserved for direct traffic. A fixed-point model for ALBA(K) for general K is presented. The particular case of ALBA in which there is no aggregation is least busy alternative (LBA); ALBA(2) represents the other extreme of aggregation. Simulation and analytic results for LBA are compared. An asymptotic scaling based on the fixed-point models is also discussed. It is shown that there is a dichotomy in network behavior: if the offered traffic is below a threshold, then the network loss probability decreases exponentially with increasing network size, and above the threshold, performance is poor.>

The authors investigate some of the consequences for dynamic routing schemes of dual- and multiparented networks, in which a call can enter (or leave) the network at two or more points. In particular, they compare bounds on the performance of optimal dynamic routing strategies which respectively ignore and utilize the multiparented structure, and show that simple schemes, easily implemented and analyzed, are able to achieve most of the additional advantages allowed to dynamic routing schemes by multiparenting. The robust behavior of these schemes under traffic mismatches as well as multiple link or node failure events is illustrated.>