Claudiu Danilov

CORE: A real-time network emulator

We present CORE (common open research emulator), a real-time network emulator that allows rapid instantiation of hybrid topologies composed of both real hardware and virtual network nodes. CORE uses FreeBSD network stack virtualization to extend physical networks for planning, testing and development, without the need for expensive hardware deployments. We evaluate CORE in wired and wireless settings, and compare performance results with those obtained on physical network deployments. We show that CORE scales to network topologies consisting of over a hundred virtual nodes emulated on a typical server computer, sending and receiving traffic totaling over 300,000 packets per second. We demonstrate the practical usability of CORE in a hybrid wired-wireless scenario composed of both physical and emulated nodes, carrying live audio and video streams.

Steward: Scaling Byzantine Fault-Tolerant Replication to Wide Area Networks

This paper presents the first hierarchical byzantine fault-tolerant replication architecture suitable to systems that span multiple wide-area sites. The architecture confines the effects of any malicious replica to its local site, reduces message complexity of wide-area communication, and allows read-only queries to be performed locally within a site for the price of additional standard hardware. We present proofs that our algorithm provides safety and liveness properties. A prototype implementation is evaluated over several network topologies and is compared with a flat byzantine fault-tolerant approach. The experimental results show considerable improvement over flat byzantine replication algorithms, bringing the performance of byzantine replication closer to existing benign fault-tolerant replication techniques over wide area networks.

An Inter-domain Routing Protocol for Multi-homed Wireless Mesh Networks

This paper presents an architecture and a hybrid routing protocol for multi-homed wireless mesh networks that provide uninterrupted connectivity and fast handoff. Our approach integrates wireless and wired connectivity, using multicast groups to coordinate decisions and seamlessly transfer connections between several Internet gateways as mobile clients move between access points. The protocol optimizes the use of the wireless medium by short-cutting wireless hops through wired connections, paying a very low overhead during handoffs. The paper demonstrates that inter-domain handoffs occur instantaneously, with virtually no loss or delay, for both TCP and UDP connections.

Experiment and field demonstration of a 802.11-based ground-UAV mobile ad-hoc network

This paper describes a field demonstration and presents the network performance of an 802.11 ground-UAV network composed of 11 ground stations, a mobile vehicle and two fixed wing UAVs, connected by two routing gateways to a legacy wired network. The network effects demonstrated include mobility, network partitions and merges, and gateway failovers. The paper presents experimental results for recorded data traffic and for the state of the routing protocols, with the mobile nodes participating as sources of data traffic.

MANET multicast with multiple gateways

A current challenge in interconnecting mobile ad hoc networks (MANETs) with backbone legacy networks is the lack of compatibility between different multicast routing protocols when using multiple gateways, due to differences in both forwarding semantics and implementations of the different protocols. We present designs and experimental results involving the interconnection of the simplified multicast forwarding (SMF) MANET protocol with the protocol independent multicast (PIM) protocols, both dense- and sparse-mode. We illustrate the types of interconnections and multicast forwarding configurations, evaluate performance issues of existing approaches, and propose solutions to them. We describe techniques for allowing multiple gateways to dynamically detect one another and coordinate the forwarding behavior. We also highlight how the open source implementations of these protocols can be combined. We show that SMF can be connected to both PIM-SM and PIMDM variants, and that policies at the gateways can control the fine-grained forwarding behavior on a per-group basis.

Connecting MANET Multicast

Connecting mobile ad-hoc networks (MANETs) to the legacy layer networks poses numerous challenges that have not been much explored. The internal topology of a MANET and external connectivity to a backbone network will likely vary greatly over time, and MANET nodes need to be able to communicate with nodes in other attached networks as changes occur. Keeping a MANETs multicast routing domain connected to other networks is not well understood and has been under-explored, especially when the MANET has multiple connections to the larger network. In this paper, we describe the challenges for attaching a MANET and delivering multicast between the MANET and other, higher tiered, legacy networks. Most importantly, we provide an efficient simple design solution that addresses the various multicast challenges. Additionally, we analyze the qualitative performance of different design elements and make recommendations for actual deployment.

Elastic multicast for tactical communications

This paper presents a multicast routing mechanism supporting the classical IP multicast service model that can dynamically use redundant forwarding in the parts of the network affected by a high rate of topology changes, while converging to regular multicast distribution trees where or when the network becomes relatively stable. The rationale is that intermittent connectivity directly affects the ability of routers to synchronize on their view of the network, thus making it difficult to converge on efficient distribution trees, while network wide broadcast may be prohibitively expensive for relatively sparse groups. We describe a hybrid approach, called Elastic Multicast, which dynamically expands to limited scope broadcast when needed, and converges single path forwarding if the network is stable, through independent routing decisions made at each node.

Adaptive routing for tactical communications

We present a new approach to performing adaptive, loop-free, destination-based unicast forwarding in an IP-based network. The approach is an integration of several well-known techniques, including broadcast-based flooding, on-demand route discovery, and link state routing. In this approach, routers are not universally in one routing mode, such as a `link-state, for all destinations but instead apply different forwarding strategies depending on the current route availability and quality on a perdestination basis. Furthermore, this approach extends well to traffic prioritized networks, since different forwarding mechanisms can be employed based on the priority of the flow. It also does not require tight coordination between routers on the routing mode being applied for a given destination. This allows parts of the topology to adapt to the local environment as it changes. In this paper we introduce the Adaptive Routing mechanism, evaluate its performance in a thirty-node mobile networking scenario, and discuss its applicability to tactical communications.

Experiment and field demonstration of serverless group communication

This paper presents a field experimentation and demonstration addressing serverless information services that provide both group messaging with ordering guarantees and robust file/media object sharing in a tactical edge communication environment. These serverless information services constitute the main functional components of our real time image and ordered annotation sharing application, called Tactigram. The purpose of Tactigram is to integrate serverless services in useful tool demonstrating the utility of real time information exchange to the warfighter. We show how a Group Communication Service (GCS) framework provides for quick exchange of small data, and tactical torrents (SISTO) provide for file sharing used by Tactigram. The demonstration was conducted as part of the Agile Bloodhound 2014 (AB14) field event. In accordance with AB14 use case scenarios, Android devices were used to exchange images and annotations over Soldier Radio Waveform (SRW) and WiFi MANETs in fully distributed manner. While the results obtained constitute a very preliminary evaluation of serverless group communication, the field test environment was very useful in highlighting critical design points (e.g., on-the-move dynamics) where enhancements of the protocol are needed.