In recent years, there has been increasing interest in the US Department of Defense to build an on-demand airborne network for communications relay utilizing high-capacity, long-range military radio systems. While these systems operate well in a network of homogeneous systems, platforms generally employ multiple heterogeneous radio systems making internetworking difficult due to varying radio characteristics and lack of interoperability. Although simulations and emulation tests can provide a baseline for how systems will perform in a controlled environment, field tests are crucial to demonstrate capabilities in real-world operating environments. In this paper, we present measurement results from a field test involving two airborne platforms forming a dynamically routed aerial IP backbone over 200 nautical miles with various radio systems as part of the C4ISR on-the-move 2010 exercise. We present measurement results on per link performance, radio-to-router interface performance, and multihop network performance results with prototype software on open source platforms. Additionally, key lessons learned and recommendations are given.

The desire to increase bandwidth efficiency in an all-IP infrastructure in the presence of reduced spectrum and increasing demand for connectivity has led to several developments in IP header compression techniques. In recent years, there have been several IP header compression schemes developed in industry specifically for wireless networks including RObust Header Compression (ROHC) and IP Header Compression (RFC 2507). ROHC and IPHC (RFC 2507) have been adopted by several commercial cellular networks and military networks as one of the techniques for implementing IP header compression. In addition to ROHC and IPHC which were designed primarily for one-hop wireless networks, MANET IP Header Compression (MIPHC) was defined to help bridge the gap to multi-hop MANETs. To evaluate the effectiveness of IP header compression schemes on multi-hop MANETs and other networks, we implement simulation models of ROHC, IPHC, and MIPHC and evaluate their performance under various conditions in a mobile ad hoc network. The results show that although ROHC was designed specifically for one-hop cellular networks and context is required to be maintained per hop per IP flow, its performance is fairly good in multi-hop MANETs.

The current generation of long-range, high capacity, military radios are stove-piped systems that work well in a homogeneous environment, but lack interoperability with other radio systems. Each radio provides a subset of disparate link information in non-standard interfaces and has built-in home-grown routers running different routing protocols. In a heterogeneous radio system airborne environment, wireless link characteristics change rapidly, often requiring direct link feedback from the radio to make routing decisions. In recent years, much work has been done in developing a common radio-to-router interface (R2RI) that standardizes a subset of per-link information to pass to the network layer for use in dynamic MANET routing. While simulations and emulation tests can provide a baseline for how systems might perform, field-tests are crucial to demonstrate capabilities in real-world operating environments. In this paper, we present measurement results from a field test involving several air and ground assets with various radio systems that test an implementation of RFC4938, a radio-to-router interface protocol, and its interaction with a dynamic MANET routing protocol. The assets formed a high capacity, dynamically routed aerial IP backbone made of heterogeneous radio technologies over 250 nautical miles (Nm), allowing the passing of military traffic.

The enormous interest for peer-to-peer systems in recent years has prompted research into finding scalable and robust seeding and searching methods to support these overlay networks. Routing and search in these overlay networks have ranged from flooding-based unstructured techniques to structured ones mainly for popular and rate items respectively. In this paper, we propose a new method of establishing a virtual structure and introduce a technique to scalably route packets through an unstructured overlay network. We introduce virtual direction routing (VDR). VDR is a lightweight and scalable overlay network routing protocol that uses the concept of virtual directions to efficiently perform node information seeding and lookup. State information is replicated at nodes along virtual orthogonal lines originating from each node and periodically updated. When a path lookup is initiated, instead of flooding the network, query packets are also forwarded along virtual orthogonal lines until an intersection with the seeded state occurs. We show that VDR achieves high reachability with relatively low seed and search packet TTL even under high network churn. We also show that VDR scales well without imposing DHT-like graph structures (e.g., trees, rings, torus, coordinate-space) and the path stretch compared to random-walk protocols is very good. The tradeoff is added latency by choosing suboptimal paths.

The increased usage of directional methods of communications has prompted research into leveraging directionality in every layer of the network stack. In this paper, we explore the use of directionality in layer 3 to facilitate routing in highly mobile environments. We introduce mobile orthogonal rendezvous routing protocol (MORRP), a lightweight, but scalable routing protocol utilizing directional communications (such as directional antennas or free-space-optical transceivers) to relax information requirements such as coordinate space embedding, node localization, and mobility. This relaxation is done by introducing a novel concept called the directional routing table (DRT) which maps a set-of-IDs to each directional interface to provide probabilistic routing information based on interface direction. We show that MORRP achieves connectivity with high probability even in highly mobile environments while maintaining only probabilistic information about destinations. We also compare MORRP with various proactive, reactive, and position-based routing protocols using single omni-directional interfaces and 8 directional interfaces and show that MORRP gains over 10-14X additional goodput vs. traditional protocols and 15-20% additional goodput vs. traditional protocols using multiple interfaces.

The increased usage of directional methods of communications to improve medium reuse, network capacity, and bandwidth has prompted research into leveraging directionality in every layer of the network stack. Recently, there has been work on bringing the apparent capacity gains on layer 2 using directional communications methods to layer 3 by using directionality to route packets scalably in unstructured, flat networks. In their protocol, Orthogonal Rendezvous Routing Protocol, Cheng et al. [1] showed that by ”drawing” two lines orthogonal to each other at each node, it is possible to provide over 98% connectivity while maintaining only O(N3/2) evenly distributed states at a cost of only 1.2 path stretch. In this paper, we seek to provide more in-depth performance analysis by tuning additional factors such as the number of directions to transmit, the number of interfaces per node, among others, to understand its affect on varying network densities, topologies, connections, and traffic patterns. We show that by sending packets out in more directions, increased connectivity, smaller average path length, better goodput results only up to a point as compared to other routing protocols. The trade-off, however, is added state information maintained at each node and additional control packets received. We also show that the addition of more interfaces generally yields better packet delivery success, average path length, and goodput.

Routing in multi-hop wireless networks involves the indirection from a persistent name (or ID) to a locator. One of the biggest issues in routing is providing adequate connectivity while scaling the network. Recently, Bow-Nan Cheng et al., (2006) has attempted to mitigate this issue by using directional communication methods to find intersections between source-rendezvous and rendezvous-destination paths, providing effective routing in unstructured, flat networks. Cheng et al. showed that by "drawing" two lines orthogonal to each other at each node, it is possible to provide over 98% connectivity while maintaining only order O(N3/2) states. It is interesting, however to investigate what happens when additional lines are "drawn" and how that affects connectivity, path length and state complexity. In this paper, we examine how transmitting along one, two, three, and four lines affects routing and provide both analytical bounds for connectivity as well as packetized simulations on how these methods stack up in a more realistic environment. We show that by sending packets out in more directions, increased connectivity and smaller average path length results only up to a point. The trade-off, however, is added state information maintained at each node. We also show that in mobile environments, adding additional lines increases the chances for successful packet delivery only marginally.

Routing in multi-hop wireless networks involves the indirection from a persistent name (or ID) to a locator. Concepts such as coordinate space embedding help reduce the number and dynamism complexity of bindings and state needed for this indirection. Routing protocols which do not use such concepts often tend to flood packets during route discovery or dissemination, and hence have limited scalability. In this paper, we introduce orthogonal rendezvous routing protocol (ORRP) for meshed wireless networks. ORRP is a lightweight, but scalable routing protocol utilizing directional communications (such as directional antennas or free-space-optical transceivers) to relax information requirements such as coordinate space embedding and node localization. The ORRP source and ORRP destination send route discovery and route dissemination packets respectively in locally-chosen orthogonal directions. Connectivity happens when these paths intersect (i.e. rendezvous). We show that ORRP achieves connectivity with high probability even in sparse networks with voids. ORRP scales well without imposing DHT-like graph structures (eg: trees, rings, torus etc). The total state information required is O(N3/2) for N-node networks, and the state is uniformly distributed. ORRP does not resort to flooding either in route discovery or dissemination. The price paid by ORRP is suboptimality in terms of path stretch compared to the shortest path; however we characterize the average penalty and find that it is not severe.