Opportunistic operations are functions carried out by leveraging spare capacity on existing devices. We investigate the performance of implementing distributed RF functions, such as spectrum monitoring, as opportunistic operations on groups of radios and RF sensors. We assume that the primary activities of the devices cannot be fully predicted, and that opportunistic operations on a device may be preempted by its primary functions. Therefore there is uncertainty regarding the ability of RF devices to complete assigned opportunistic operations. Moreover, we assume the communications network is intermittent, lossy and low bandwidth. The network limitations create command and control uncertainty. The primary research challenge addressed in this work is to overcome these sources of uncertainty in order to carry out distributed RF operations with high probability of success, while minimizing resource consumption. The approach we have developed is implemented in a middleware layer called Management of RF Network and Tasking Infrastructure (MARTI). We use an analytic model and experiments with MARTI in a wireless testbed to quantify the impact of various strategies for mitigating uncertainty, the tradeoffs between improved communication reliability and its latency and bandwidth costs, and strategies for trading off between result fidelity and network resource consumption.

In wireless mesh networks, with the standard Optimized Link State Routing (OLSR) metric (i.e. hop count), traffic is routed on the shortest path without considering factors such as traffic distribution and link capacities. Consequently, some nodes may get overloaded from the uneven utilization of network resources. OLSR can be modified to use other link cost metrics, with route selection based on lowest cost path. With delay as the metric, OLSR reduces average round trip time but the load-aware routes may cause wide variance in delay and packet reordering due to route oscillations. We describe a new hybrid routing approach that combines the strength of a) link state routing (e.g. fast convergence), b) load-aware routing (e.g., avoiding congested paths) and c) cognitive routing (e.g. learning to avoid path oscillations). In particular, we investigate the use of Q-learning with OLSR to increase network capacity and reduce congestion delay. We present simulation results for a 36 node dynamic mobile ad hoc network, with standard OLSR, a non-cognitive load-aware OLSR (OLSR-D) and our new hybrid cognitive load-aware OLSR (OLSR-Q). We show that OLSR-Q >; OLSR-D >; OLSR in terms of reducing delay and increasing network capacity. Furthermore, we show that, unlike conventional cognitive Q-routing protocols, our hybrid approach does not reduce performance at low load. Although OLSR-Q can significantly reduce delay and improve capacity, the learning time can reduce connectivity and the distribution of more link state information can reduce raw link capacity. We show how adding OLSR, OLSR-D and OLSR-Q as routing options into the Cognitive Network Engineering Design Analytic Toolset (C-NEDAT), we can select the best routing protocol and parameters (e.g., learning rate) for a given network and its mission. We verify simulation performance improvements by implementing the OLSR-Q in on a 9 node wireless testbed.

We propose a framework for the integration of IEEE 802.21 MIH function with an ad-hoc routing protocol to improve the performances of the ad-hoc routing protocol. In the proposed framework, MIH functions were enabled for the OLSR routing protocol: MIH events were defined and triggered for OLSR, and the OLSR operations responsive to the MIH events were implemented. We analyzed OLSR routing convergence during handover on two ad-hoc network scenarios which can manifest the typical routing behaviors of OLSR. Based on the analysis, we proposed two approaches to improve route convergence of OLSR through MIH. To capture the effects of the proposed framework, we evaluated the performances of OLSR with and without MIH through simulation and compared their performances in terms of packet drop during handover and routing control overhead. The results of the simulations showed that the performance of OLSR was significantly improved through the MIH function.

As future wireless networks become more diverse, there are important performance limits when network conditions become more extreme. An important performance limit in dense networks is the scalability of routing and of topology updates dissemination in particular. In previous work [16], the expected performance of diverse approaches to topology update schemes using flat flooding, Multi-Point relays (MPRs), and Connected Dominating Sets (CDSs), has been modeled and analyzed. Analysis showed that one representative of the analyzed CDS models, the CDS-based Hexagon one, offered order of magnitude less overhead in dense networks with a small increase in routing stretch. To our knowledge, other existing distributed CDS heuristics cannot match the performance of this model. In this work, we are advancing the CDS-HEX topology dissemination approach from the limited-scope centralized scenarios with strict symmetrical relays placement to any general dynamic scenario with totally random placement of nodes. We propose novel heuristics to approximate the theoretically optimal CDS-HEX for dynamic environments. We are showing that: a) although the distributed scheme operates sub-optimally compared to its centralized ancestor, it is still superior to the MPR scheme in key metrics, b) the set-up overhead of the more sophisticated distributed CDS-HEX is not significantly higher than this of MPRs, while the steady state overhead of CDS-HEX turns to be lower, and c) simulations verify all the closed analytical formulae and asymptotic results of previous analysis and provide additional insight on metrics that cannot be analytically measured.

Many applications need routing paths with diverse Quality of Service (QoS) objectives and constraints based on multiple metrics, including delay, bandwidth, and error rate. Since most multi-metric path selection problems are NP complete heuristics are used. However, current heuristics tend to be specific to a problem, computationally complex, or amalgamate metrics into one cost (which limit the allowable solution space). This paper investigates: (a) an approximation that can quickly find a 'good' path subject to flexible objectives and constraints, without amalgamating link metrics, and (b) the application of simulated annealing to improve path quality. Results for networks of 100 to 1000 nodes show the new approximation reduces min-max path cost by 28% over existing multi-metric heuristics (and by 40% over single metric heuristics); simulated annealing, however, could only provide a further 3% improvement.

Networks of portable devices are very popular due to the technological evolution in the area of electronics. The devices are becoming smaller, more compact and getting more processing power and flexible communication capabilities. Furthermore, portable devices constitute the core of sensor networks, which is one of the more attractive areas of research. The portability that makes these devices popular, however, creates the inherent limitation of finite energy. If the energy of a critical node is depleted then the network gets disconnected. Such a phenomenon is usually referred to as the termination of the network lifetime. For prolonging the network lifetime we need to preserve and utilize the finite energy of the node in the most efficient way. Efficient utilization of energy requires the elimination of unnecessary energy usage wherever possible. For a portable - communication enabled - device, a significant part of energy is consumed for communications and more specifically for transmissions. As the transmission power is directly related to the transmission range achieved, we focus on optimizing the transmission range assignments; to reduce the corresponding energy consumed while sufficient network connectivity is preserved. In a typical 100 node network, for example, we show that lowering the transmission range of all nodes can reduce the power over 30% while still keeping all nodes reachable from all other nodes. Furthermore, by adjusting each node's range individually, we reduce transmit power another 30%. The developed heuristics are very efficient in this matter, as it is highlighted by their performance evaluation.

Creating a hierarchy to meet certain constraints and optimize objective functions can greatly improve scalability, performance and robustness of large networks. However, as constant optimization would result in excessive reconfiguration and signaling overhead, existing hierarchy maintenance protocols are only invoked after detecting constraint violations (e.g., when a node cannot directly reach other nodes in its part of the hierarchy). This passive approach minimizes overhead, but will, over time, result in declining network optimality, particularly in dynamic MANET networks. This paper investigates a new active approach to maintaining a hierarchy, which maintains better network optimality, while balancing the reconfiguration and signaling overhead. Our active approach is performed only at border routers that, at random intervals, perform a local optimization based on the objective functions globally optimized during the hierarchy generation. Using an example of creating balanced size domains (clusters), our simulation results show that active localized decisions can maintain the hierarchy close to the optimal value even after much network dynamics; this is in marked contrast to passive local maintenance which allows the network to deteriorate dramatically.

To build ad-hoc networks with hundreds or even thousands of nodes, the network must be split into relatively independent layer 3 clusters. There are currently no general approaches or methodologies for the creation of domains that take into account the following important engineering constraints: balanced domains, minimal inter-domain traffic, robust network design. Moreover, there is also no contribution that specifically addresses the problem of area formation for OSPF-based ad hoc networks. By assuming that the creation of layer 3 clusters is done after layer 2 topology management has set local radio parameters, we have re-formulated the problem at hand in a graph theoretic framework and found a strong connection between the problem of area design and a classical problem in graph theory, the graph partitioning (GP) problem. The limitation of GP algorithms (GPAs) is that they are OSPF-agnostic and, therefore, are not capable of solving the problem of robust backbone network (Area 0) design. We here propose a two-step approach for OSPF area design: the first step consists of an efficient GPA that will create areas (including a rough Area 0 design), and the second step consists of ad-hoc heuristics that are able to ameliorate the Area 0 design as well as factoring in OSPF specific metrics.

The integrated networking technology prototype demonstrates the capability of several emerging networking technologies to operate together seamlessly to enhance network services targeted for dynamic mobile environments such as those found in the battlefield. The prototype consists of four technologies: (1) autoconfiguration technology supports autonomous and rapid network deployment and configuration; (2) self-managed virtual network (SMVN) technology provides virtual networking capabilities for networks which do not natively support these functions; (3) integrated mobility management technology supports session continuity in the presence of node mobility; (4) assured IP QoS technology supports guarantees for mission-critical applications. The prototype is capable of operating over the various types of equipment and protocols to be utilized in battlefield networks. The prototype is designed such that network services and functions are survivable and reconfigurable. In this paper, we describe the four technologies as well as the integrated prototype in the laboratory environment.

If heterogeneous ad hoc battlefield networks are to scale to hundreds or thousands of nodes, then they must be automatically split into separate network domains. Domains allow routing, QoS and other networking protocols to operate on the fewer nodes. This division greatly reduces the overall overhead (e.g., routing overhead with n nodes that goes from O(n/sup 2/) to O(nlogn) and allows protocols to be tuned to more homogenous conditions (K. Manousakis et al., 2002). Domain generation (or clustering) can be done using either the local or global information. The two approaches are complementary since local domain generation reacts faster, requires less overhead, and is more robust while the global domain generation provides better overall domains. While the most existing work has concentrated on the local distributed solutions, this paper reports on the new global domain generation techniques. In particular we concentrate on the design of good cost functions and efficient optimization algorithms. We show that the simple "intuitive" cost functions do not produce good domains; rather we need complex functions with multiple parameters depending on the design goals (e.g., low overhead or low delay). Although existing optimization algorithms are too slow to be useful in a large dynamic network, we show that a modified simulated annealing algorithm with well chosen cooling schedule, state transition probabilities, and stop criteria produces good quality domains in acceptable time.

Although there are a plethora of mobility management solutions proposed in the literature, there is no method for analytical comparison that helps identify optimal solutions in a specific scenario. Since simulations and implementations can provide only limited information, we propose an analytical approach for the comparative analysis of mobility protocols. By decomposing existing protocols into their building blocks, we obtain general cost functions for different mobility mechanisms. Our analysis allows us to identify network and topology conditions under which a certain protocol performs better than another, according to specific criteria. We present results for the signaling and overhead case, whereas the handoff delay case is addressed in S. Galli et al. (2004).

This paper presents the design principles of dynamic service negotiation protocol (DSNP). DSNP is a protocol to negotiate the SLS (service level specification) in the IP layer. It can be used for service negotiation from host to network, network to host, and network to network. The automated negotiation makes service negotiation efficient in terms of time, cost, and correctness. The dynamic negotiation not only allows users to adapt their needs dynamically, but also lets providers utilize the network better. DSNP can be used in both wireline and wireless networks. It is, however, particularly useful in the mobile environment. To demonstrate the usefulness of DSNP, a reference wireless QoS architecture based on DiffServ is presented. Example applications and experimental results are illustrated.

In an effort to realize wireless Internet telephony and multimedia streaming in a highly mobile environment a testbed emulating a wireless Internet has been built. This allows the setting up of multimedia calls between IP mobiles and integration between IP and PSTN end-points in a wireless environment. Different functionalities and components involved with the wireless Internet streaming multimedia have been prototyped and experimented in the testbed. These include signaling, registration, dynamic binding, location management as well as supporting the QoS features for the mobile users. This paper describes some of the components of the testbed and highlights the experiences while building this testbed which could be beneficial to some who plan to build a similar testbed to realize several features and capabilities of Mobile Wireless Internet, before actually bringing to the market.

We present our implementation of TeleMIP, a two-level architecture for IP-based mobility management. TeleMIP essentially uses an intra-domain mobility management protocol (IDMP) for managing mobility within a domain, and mobile IP for supporting inter-domain (global) mobility. Unlike other proposed schemes for intra-domain mobility management, IDMP uses two care-of addresses for mobility management. The global care-of address is relatively stable and identifies the mobile node's current domain, while the local care-of address changes every time the mobile changes subnets and identifies the mobile's current point of attachment. The paper describes our TeleMIP implementation based on enhancements to the Stanford University mobile IP Linux code and presents performance results obtained through experiments on our test-bed. Finally, we use analysis to accurately quantify the savings in signaling overhead obtained when TeleMIP is used in environments where mobiles change subnets relatively rapidly.

This paper describes a robust method of improving TCP performance for terrestrial and satellite wireless networks without modification to TCP or change in its semantics. Tools to transparently improve performance have been around for many years and many work even when the TCP header information is encrypted (e.g., IPSEC) or TCP acknowledgments do not go through the reverse path. Little work has been done; however, to quantiy how beneficial these techniques are. Using protocol boosters we show that reducing the packet size is critical as bit error rates get worse than 10/sup -5/. We also show that over two orders of magnitude improvement in throughput can be achieved by adding redundant FEC packets, with well-chosen parameters for the number of data (k) and parity (h) packets in a block, and a small maximum encode time (t). It is important to note that we are looking strictly at enhancement techniques that do not require modifications at the end hosts as this can be a difficult task for the typical end user.

We compare various existing approaches for locating roaming users and providing continuous connectivity in quasi-dynamic networks in which the movement is much more restricted than in ad-hoc networks. However, there are frequent host movements combined with occasional major topology changes (e.g., whole network is changing their point of attachment or getting disconnected). The higher dynamics causes many proposed mobility solutions including basic Mobile IP (which work well in environments limited to host mobility), perform poorly. Based on some qualitative comparisons, we suggest which approaches are the best to handle mobility in quasi-dynamic networks.

This paper describes a new methodology for protocol design, using incremental construction of the protocol from elements called "protocol boosters" on an as-needed basis. Protocol boosters allow: (1) dynamic protocol customization to heterogeneous environments and (2) rapid protocol evolution. Unlike alternative adaptation approaches, such as link layer, conversion, and termination protocols, protocol boosters are both robust (end-to-end protocol messages are not modified) and efficient (do not replicate the functionality of the end-to-end protocol). We give examples of error and congestion control boosters, and give initial results from booster implementations.

The paper investigates error control mechanisms for mobile messaging applications, such as e-mail, fax, and credit card verification. Although existing protocols provide efficient error control over conventional networks, wireless networks present significant new challenges. The radio link introduces noise and multipath interference causing long periods of increased error rate, while host motion requires changing communication paths that can cause packet delay, misordering, duplication, and loss. Furthermore, scarce radio resources make bandwidth efficiency desirable. Using measurements from a field-deployed PCS system in Boulder Colorado, the authors identify two types of reception area. They highlight the benefits of powerful error control mechanisms in the fringe reception areas, especially selective acknowledgments and combining data from multiple transmissions.

Describes a new family of error detection codes called weighted sum codes. These codes are preferred over four existing codes (CRC, Fletcher checksum, Internet checksum, and XTP CXOR), because they combine powerful error detection properties (as good as the CRC) with attractive implementation properties. One variant, WSC-1, has efficient software and hardware implementations; while a second variant, WSC-2, is almost as efficient in software (still significantly better than CRC) and offers commutative processing (that enables efficient out-of-order, parallel, and incremental update processing).>

The authors investigate fast routing table lookup techniques, where the table is composed of hierarchical addresses such as those found in a national telephone network. The hierarchical addresses provide important benefits in large networks, but existing fast routing table lookup techniques, based on hardware such as content addressable memory (CAM), work only with flat addresses. Several fast routing table lookup solutions for hierarchical address based on binary and ternary CAMs are presented, and their advantages and drawbacks are analyzed.>

An approach is presented to high-performance asynchronous architectures offering significant advantages over conventional clocked systems, without some of the drawbacks normally associated with asynchronous techniques. As the level of integration increases, an asynchronous wavefront array designed using the techniques described will have three important advantages over the equivalent synchronous systolic array: faster throughput (rate at which data are clocked through a system), reduced design complexity, and greater reliability. The benefits and drawbacks of using the asynchronous technique are highlighted using three wavefront arrays: two one-dimensional multipliers, and a two-dimensional sorter. All three can be built using just one basic building block.>

Traditionally, a transport protocol corrects errors in a computer communication network using a simple ARQ protocol. With the arrival of broadband networks, forward error correction is desirable as a complement to ARQ. This paper describes a simplified Reed-Solomon erasure correction coder architecture, adapted for congestion loss in a broadband network. Simulations predict it can both encode and decode at rates up to 1 gigabit per second in a custom 1 micron CMOS VLSI chip.