TCP over geo-routing for high mobility: vehicle grids and airborne swarms

Ad hoc wireless networks have become the architecture of choice for peer to peer communications in areas where the telecommunications infrastructure is inadequate or has failed. A major challenge is the reliable delivery of data when nodes move. The reliable Internet protocol is TCP. However, TCP performs poorly in mobile ad hoc networks, mainly because of route breakage. To overcome this problem, a robust routing protocol must be used. To this effect, Geo-routing has recently received attention in large scale, mobile systems as it does not require end- to-end path establishment and pre-computed packet forwarding routing structure at nodes. These properties make Geo-routing robust to highly dynamic route changes. For best performance, however, several parameters must be carefully tuned. In this paper we study the joint optimization of TCP and Geo-routing parame- ters to handle high speeds. We first introduce two highly mobile ad hoc scenarios that require reliable delivery, namely the vehicle urban grid and the airborne swarms. Then, we study the impact of critical system parameters (e.g., hello message ex- change rate, delay timer in TCP for out-of-order delivery, etc) on the performance of both UDP and TCP. We improve hello message effciency in Geo-routing by using an adaptive hello exchange scheme. Then, we fix the out-of-order problem in TCP by using a receiver-side out-of-order detection and delayed ack strategy. We show that these parameter adjustments are critical for effcient TCP over Geo-routing in highly mobile applications. With these enhancements our TCP with Geo-routing solution easily outperforms TCP over traditional ad hoc routing schemes, such as AODV.1st IFIP International Conference on Ad-Hoc NetWorkingRed de Universidades con Carreras en Informática (RedUNCI

TCP over geo-routing for high mobility: vehicle grids and airborne swarms

Ad hoc wireless networks have become the architecture of choice for peer to peer communications in areas where the telecommunications infrastructure is inadequate or has failed. A major challenge is the reliable delivery of data when nodes move. The reliable Internet protocol is TCP. However, TCP performs poorly in mobile ad hoc networks, mainly because of route breakage. To overcome this problem, a robust routing protocol must be used. To this effect, Geo-routing has recently received attention in large scale, mobile systems as it does not require end- to-end path establishment and pre-computed packet forwarding routing structure at nodes. These properties make Geo-routing robust to highly dynamic route changes. For best performance, however, several parameters must be carefully tuned. In this paper we study the joint optimization of TCP and Geo-routing parame- ters to handle high speeds. We first introduce two highly mobile ad hoc scenarios that require reliable delivery, namely the vehicle urban grid and the airborne swarms. Then, we study the impact of critical system parameters (e.g., hello message ex- change rate, delay timer in TCP for out-of-order delivery, etc) on the performance of both UDP and TCP. We improve hello message effciency in Geo-routing by using an adaptive hello exchange scheme. Then, we fix the out-of-order problem in TCP by using a receiver-side out-of-order detection and delayed ack strategy. We show that these parameter adjustments are critical for effcient TCP over Geo-routing in highly mobile applications. With these enhancements our TCP with Geo-routing solution easily outperforms TCP over traditional ad hoc routing schemes, such as AODV.1st IFIP International Conference on Ad-Hoc NetWorkingRed de Universidades con Carreras en Informática (RedUNCI

Heterologous expression of cytotoxic sesquiterpenoids from the medicinal mushroom Lignosus rhinocerotis in yeast

Background: Genome mining facilitated by heterologous systems is an emerging approach to access the chemical diversity encoded in basidiomycete genomes. In this study, three sesquiterpene synthase genes, GME3634, GME3638, and GME9210, which were highly expressed in the sclerotium of the medicinal mushroom Lignosus rhinocerotis, were cloned and heterologously expressed in a yeast system. Results: Metabolite profile analysis of the yeast culture extracts by GC-MS showed the production of several sesquiterpene alcohols (C 15 H 26 O), including cadinols and germacrene D-4-ol as major products. Other detected sesquiterpenes include selina-6-en-4-ol, ß-elemene, ß-cubebene, and cedrene. Two purified major compounds namely (+)-torreyol and a-cadinol synthesised by GME3638 and GME3634 respectively, are stereoisomers and their chemical structures were confirmed by 1 H and 13 C NMR. Phylogenetic analysis revealed that GME3638 and GME3634 are a pair of orthologues, and are grouped together with terpene synthases that synthesise cadinenes and related sesquiterpenes. (+)-Torreyol and a-cadinol were tested against a panel of human cancer cell lines and the latter was found to exhibit selective potent cytotoxicity in breast adenocarcinoma cells (MCF7) with IC 50 value of 3.5 ± 0.58 µg/ml while a-cadinol is less active (IC 50 = 18.0 ± 3.27 µg/ml). Conclusions: This demonstrates that yeast-based genome mining, guided by transcriptomics, is a promising approach for uncovering bioactive compounds from medicinal mushrooms

Distributed Multicast Group Security Architecture for Mobile Ad-hoc Networks

Multicast communication is an efficient means to support key network applications such as real-time teleconferencing and data dissemination. In this paper we devise a security architecture for multicast communications in mobile ad hoc networks (MANETs). Our design is both suitable in MANET environment and compliant to the IETF standard Multicast Group Security Architecture (MGSA) [1]. Because centralized servers are vulnerable to network dynamics and security attacks in a distributed MANET, we distribute the function of MGSA's Group Control Key Server (GCKS) to a dedicated subset of mobile backbone nodes in MANET. Unlike distributed GCKS nodes in stationary infrastructure networks, our GCKS backbone nodes are mobile, fully distributed and adaptive to network dynamics, in particular the constant and instant changes in network topology, node density and node mobility. We study the characteristics of our GCKS backbone design and its impacts on ad-hoc multicast security research. Our simulation study and Linux implementation confirm the effectiveness of the new MANET MGSA design. I

TCP with delayed ack for wireless networks

Abstract — This paper studies the TCP performance with delayed ack in wireless networks (including ad hoc and WLANs) which use IEEE 802.11 MAC protocol as the underlying medium access control. Our analysis and simulations show that TCP throughput does not always benefit from an unrestricted delay policy. In fact, for a given topology and flow pattern, there exists an optimal delay window size at the receiver that produces best TCP throughput. If the window is set too small, the receiver generates too many acks and causes channel contention; on the other hand, if set the window too high, the bursty transmission at the sender triggered by large cumulative acks will induce interference and packet losses, thus degrading the throughout. In wireless networks, packet losses are also related to the length of TCP path; when traveling through a longer path, a packet is more likely to suffer interference. Therefore, path length is an important factor to consider when choosing appropriate delay window sizes. In this paper, we first propose an adaptive delayed ack mechanism which is suitable for ad hoc networks, then we propose a more general adaptive delayed ack scheme for ad hoc and hybrid networks. The simulated results show that our schemes can effectively improve TCP throughput by up to 30% in static networks, and provide more significant gain in mobile networks. The proposed schemes are simple and easy to deploy. I

"Direction" forwarding for highly mobile, large scale ad hoc networks

Abstract-- １ In this paper, we present a novel packet forwarding scheme for wireless ad hoc networks ---"Direction" Forwarding (DFR). Popular routing protocols such as DSDV and AODV use "predecessor" based forwarding, namely, the packet is forwarded to the predecessor on the shortest path from destination, as advertised during the last update. Predecessor forwarding may fail in large scale networks where the routing update rate must be reduced by the need to maintain link O/H below reasonable levels. If nodes are mobile, the routing table entries may become "stale" very rapidly. In other words, the "predecessor" listed in the routing table may have moved away and predecessor based packet forwarding fails! DFR is designed to overcome the "stale" routing table entry problem. Suppose our ad hoc network is equipped with a geo coordinate system, either global (e.g., GPS) or local (e.g., virtual coordinates locally computed via trilateration). When the routing update arrives, the node remembers not only the predecessor delivering the update, but also the update "direction" of arrival. When a packet must be forwarded to destination, it is first forwarded to the node ID found in the routing table. If the node has moved and ID forwarding fails, the packet is "direction" forwarded to the "most promising" node in the indicated direction. If the network is sufficiently dense, direction forwarding will recover from most "predecessor" ID forwarding failures. At first glance, DFR seems to combine the features of table based routing and geo-routing. However, direction forwarding differs from geo-routing in that the direction is learned from the routing updates, instead of being computed from the destination coordinates. Thus, DFR does not require destination coordinates, global coordinate system, or Geo Location Server. In the paper we show the application of DFR to a scalable routing scheme, LANMAR. Through simulation experiments we show that DFR substantially enhances LANMAR performance in large, mobile network scenarios

Bluetooth: Carrying voice over ACL links

connect a wide range of electronic devices such as laptops, headsets, cellular phones etc. Bluetooth devices can connect to form a piconet, which consists of a master and upto 7 slaves. The master controls the medium access in the piconet using a polling scheme. Two types of connections can be established in a piconet: the Synchronous Connection-Oriented (SCO) link, and the Asynchronous Connectionless (ACL) link. SCO links provide a circuit-oriented service with constant bandwidth based on a fixed and periodic allocation of slots. They require a pair of slots once every two, four or six slots, depending upon the SCO packet used. ACL connections, on the other hand, provide a packet-oriented service and span over 1, 3 or 5 slots. The master of the piconet uses a polling mechanism to divide the piconet bandwidth among the ACL links. Since SCO links require a periodic allocation of a pair of slots, they leave very little of the piconet bandwidth available to ACL links. Moreover, the controlled access of Bluetooth ensures that no ACL link gets starved. Under such an access mechanism, ACL links may be sufficient to carry high-quality voice and SCO links may not be needed. Our simulation and hardware experiments show that though the voice quality is affected slightly by using ACL instead of SCO links for voice, TCP connections perform much better if SCO links are not used. This paper, thus, makes a case for using ACL in place of SCO links for carrying voice. This renders SCO links redundant. 1

On Demand Multicast Routing with Unidirectional Links *

Abstract — In wireless ad-hoc networks, unidirectional links occur for several reasons: non uniform transmit power, non uniform background noise, and external interference. Several researchers have addressed unidirectional links and the associated unidirectional routing problem. The main focus has been so far on “unicast ” routing; the consensus is that unidirectional links should be detected and avoided. In this paper, we consider the multicast case and derive a different conclusion: namely, it pays to exploit unidirectional links rather then avoid them. To prove the point, we select a popular ad hoc multicast protocol, On-Demand Multicast Routing Protocol (ODMRP) and introduce a slightly modified version, ODMRP-ASYM, that can handle unidirectional links. Specifically, ODMRP-ASYM reroutes the Join Reply packet when a unidirectional link is detected on the Join Query path. The option is invoked only when a unidirectional link is detected. The main advantages are: control overhead comparable with ODMRP even in highly asymmetric topologies; virtually no performance degradation in presence of unidirectional links (while ODMRP typically suffers up to 15 % drop in delivery performance), and; 2-connectivity maintenance even if no bidirectional path exists between sender and receiver (in this case, unidirectional link avoidance strategies fail). Extensive simulation experiments demonstrate ODMRP-ASYM robustness to unidirectional links and superiority over conventional ODMRP