Simulation is the most widely used tool for evaluating network protocols in multihop wireless networks, yet this has so far been limited due to a lack of models for creating a wide range of scenarios of mobile nodes moving about. For example, for evaluating multihop routing protocols, the frequently used Random Waypoint model can only effectively be used in scenarios with relatively high node density, as sparser configurations (e.g., The same nodes in a larger area) result in frequently or always partitioned networks, with no possible multihop path between many different pairs of nodes. In this extended abstract, we summarize the design and evaluation of the Random Controlled Sparse (RCS) mobility model, a new dynamic mobility model that can be controlled for a wide range of scenarios with varying levels of node sparsity or density while avoiding network partitions. Our goal is to be able to create mobile scenarios that expose previously unexplored areas of wireless protocol performance, particularly for multihop routing protocols. We evaluate the performance of the model in generating scenarios and demonstrate the sometimes surprising performance results that different degrees of node density have on example multihop wireless routing protocols.

The use of asynchronous duty cycling at the MAC layer affords substantial energy savings in wireless networks. This technique is widely used in sensor networks and other types of wireless networks such as ad hoc networks. With asynchronous duty cycling, each node switches alternately between sleeping and active states; each node waking up asynchronously reduces network contention and wireless collisions caused by nodes waking up simultaneously, but also can have undesirable effects on higher layer protocols. In this paper, we study the problem of on-demand route discovery in asynchronous duty-cycling wireless networks and present four optimizations for such route discovery: Delayed Selection, Duty-Cycled Selection, Reply Updating, and Adaptive Backoff. Through detailed ns-2 simulations, we show that, without these optimizations, the routes discovered in asynchronous duty-cycling networks can be over 50% longer than the theoretical shortest routes and can have an ETX 90% larger than the ETX of the optimal routes. With only simple changes made at the MAC or network layers, our optimizations enabled nodes to substantially improve discovered routes, finding routes that were only 0.2% longer than the theoretical shortest routes or routes with an ETX only 9% larger than the ETX of the theoretical optimal-ETX routes, while also reducing route discovery latency and node energy consumption.

This paper presents PW-MAC (Predictive-Wakeup MAC), a new energy-efficient MAC protocol based on asynchronous duty cycling. In PW-MAC, nodes each wake up to receive at randomized, asynchronous times. PW-MAC minimizes sensor node energy consumption by enabling senders to predict receiver wakeup times; to enable accurate predictions, PW-MAC introduces an on-demand prediction error correction mechanism that effectively addresses timing challenges such as unpredictable hardware and operating system delays and clock drift. PW-MAC also introduces an efficient prediction-based retransmission mechanism to achieve high energy efficiency even when wireless collisions occur and packets must be retransmitted. We evaluate PW-MAC on a testbed of MICAz motes and compare it to X-MAC, WiseMAC, and RI-MAC, three previous energy-efficient MAC protocols, under multiple concurrent multihop traffic flows and under hidden-terminal scenarios and scenarios in which nodes have wakeup schedule conflicts. In all experiments, PW-MAC significantly outperformed these other protocols. For example, evaluated on scenarios with 15 concurrent transceivers in the network, the average sender duty cycle for X-MAC, WiseMAC, and RI-MAC were all over 66%, while PW-MAC's average sender duty cycle was only 11%; the delivery latency for PW-MAC in these scenarios was less than 5% that for WiseMAC and X-MAC. In all experiments, PW-MAC maintained a delivery ratio of 100%.

Medium access control (MAC) protocols for wireless sensor networks face many challenges, including energy-efficient operation and robust support for varying traffic loads, in spite of effects such as wireless interference or even possible wireless jamming attacks. This paper presents the design and evaluation of the EM-MAC (Efficient Multichannel MAC) protocol, which addresses these challenges through the introduction of novel mechanisms for adaptive receiver-initiated multichannel rendezvous and predictive wake-up scheduling. EM-MAC substantially enhances wireless channel utilization and transmission efficiency while resisting wireless interference and jamming by enabling every node to dynamically optimize the selection of wireless channels it utilizes based on the channel conditions it senses, without use of any reserved control channel. EM-MAC achieves high energy efficiency by enabling a sender to predict the receiver's wake-up channel and wake-up time Implemented in TinyOS on MICAz motes, EM-MAC substantially outperformed other MAC protocols studied. EM-MAC maintained the lowest sender and receiver duty cycles, the lowest packet delivery latency, and 100% packet delivery ratio across all experiments. Our evaluation includes single-hop and multihop flows, as well as experiments with heavy ZigBee interference, constant ZigBee jamming, and Wi-Fi interference.

Traditional contention-based random-access wireless MAC protocols such as IEEE 802.11 DCF are designed for single-hop wireless networks and do not perform well in multi-hop scenarios due to inefficiency in their medium reservation mechanisms. In this paper, we introduce a new MAC protocol, called EMAC, which improves the efficiency of wireless medium reservation for general asynchronous multi-hop wireless networks. By exploiting limited routing information at the MAC layer, EMAC enables multiple asynchronous stations along a delivery path to cooperate in their random medium access. In particular, a control frame can travel across a multi-hop path composed of asynchronous nodes, and make synchronized medium reservations for an upcoming data frame transmission. This distributed cooperation at the MAC layer can greatly improve the medium reservation efficiency by reducing intra-flow contentions. Simulation results show that EMAC can improve end-to-end throughput compared to IEEE 802.11 DCF in chain scenarios by up to 85% and can avoid throughput starvation in cross scenarios.

The use of asynchronous duty-cycling in wireless sensor network MAC protocols is common, since it can greatly reduce energy consumption and requires no clock synchronization. However, existing systems using asynchronous duty-cycling do not efficiently support broadcast-based communication that may be used, for example, in route discovery or in network-wide queries or information dissemination. In this paper, we present the design and evaluation of ADB (Asynchronous Duty-cycle Broadcasting), a new protocol for efficient multihop broadcast in wireless sensor networks using asynchronous duty-cycling. ADB differs from traditional multihop broadcast protocols that operate above the MAC layer, in that it is integrated with the MAC layer to exploit information only available at this layer. Rather than treating the data transmission from a node to all of its neighbors as the basic unit of progress for the multihop broadcast, ADB dynamically optimizes the broadcast at the level of transmission to each individual neighbor of a node, as the neighbors asynchronously wakeup. We evaluate ADB both through ns-2 simulations and through measurements in a testbed of MICAz motes using TinyOS, and compare its performance to multihop broadcast based on X-MAC and on RI-MAC. In both evaluations, ADB substantially reduced energy consumption, network load, and delivery latency compared to other protocols, while achieving over 99% delivery ratio.

Duty cycling is a widely used mechanism in wireless sensor networks (WSNs) to reduce energy consumption due to idle listening, but this mechanism also introduces additional latency in packet delivery. Several schemes have been proposed to mitigate this latency, but they are mainly optimized for light traffic loads. A WSN, however, could often experience bursty and high traffic loads, such as due to broadcast or convergecast traffic. In this paper, we present a new MAC protocol, called Demand Wakeup MAC (DW-MAC), that introduces a new low-overhead scheduling algorithm that allows nodes to wake up on demand during the Sleep period of an operational cycle and ensures that data transmissions do not collide at their intended receivers. This demand wakeup adaptively increases effective channel capacity during an operational cycle as traffic load increases, allowing DW-MAC to achieve low delivery latency under a wide range of traffic loads including both unicast and broadcast traffic. We compare DW-MAC with S-MAC (with and without adaptive listening) and with RMAC using ns-2 and show that DW-MAC outperforms these protocols, with increasing benefits as traffic load increases. For example, under high unicast traffic load, DW-MAC reduces delivery latency by 70% compared to S-MAC and RMAC, and uses only 50% of the energy consumed with S-MAC with adaptive listening. Under broadcast traffic, DW-MAC reduces latency by more than 50% on average while maintaining higher energy efficiency.

The problem of idle listening is one of the most significant sources of energy consumption in wireless sensor nodes, and many techniques have been proposed based on duty cycling to reduce this cost. In this paper, we present a new asynchronous duty cycle MAC protocol, called Receiver-Initiated MAC (RI-MAC), that uses receiver-initiated data transmission in order to efficiently and effectively operate over a wide range of traffic loads. RI-MAC attempts to minimize the time a sender and its intended receiver occupy the wireless medium to find a rendezvous time for exchanging data, while still decoupling the sender and receiver's duty cycle schedules. We show the performance of RI-MAC through detailed ns-2 simulation and through measurements of an implementation in TinyOS in a testbed of MICAz motes. Compared to the prior asynchronous duty cycling approach of X-MAC, RI-MAC achieves higher throughput, packet delivery ratio, and power efficiency under a wide range of traffic loads. Especially when there are contending flows, such as bursty traffic or transmissions from hidden nodes, RI-MAC significantly improves throughput and packet delivery ratio. Even under light traffic load for which X-MAC is optimized, RI-MAC achieves the same high performance in terms of packet delivery ratio and latency while maintaining comparable power efficiency.

Duty-cycle MAC protocols have been proposed to meet the demanding energy requirements of wireless sensor networks. Although existing duty-cycle MAC protocols such as S-MAC are power efficient, they introduce significant end-to-end delivery latency and provide poor traffic contention handling. In this paper, we present a new duty-cycle MAC protocol, called RMAC (the routing enhanced MAC protocol), that exploits cross-layer routing information in order to avoid these problems without sacrificing energy efficiency. In RMAC, a setup control frame can travel across multiple hops and schedule the upcoming data packet delivery along that route. Each intermediate relaying node for the data packet along these hops sleeps and intelligently wakes up at a scheduled time, so that its upstream node can send the data packet to it and it can immediately forward the data packet to its downstream node. When wireless medium contention occurs, RMAC moves contention traffic away from the busy area by delivering data packets over multiple hops in a single cycle, helping to reduce the contention in the area quickly. Our simulation results in ns-2 show that RMAC achieves significant improvement in end-to-end delivery latency over S-MAC and can handle traffic contention much more efficiently than S-MAC, without sacrificing energy efficiency or network throughput.

Simulation and physical implementation are both valuable tools in evaluating ad hoc network routing protocols, but neither alone is sufficient. In this paper, we present the design and performance of PRAN, a new system for the physical implementation of ad hoc network routing protocols that unifies these two types of evaluation methodologies. PRAN (physical realization of ad hoc networks) allows existing simulation models of ad hoc network routing protocols to be used - without modification - to create a physical implementation of the same protocol. We have evaluated the simplicity and portability of our approach across multiple protocols and multiple operating systems through example implementations in PRAN of the DSR and AODV routing protocols in FreeBSD and Linux using the standard existing, unmodified ns-2 simulation model of each. We illustrate the ability of the resulting protocol implementations to handle real, demanding applications by describing a demonstration with this DSR implementation transmitting real-time video streams over a multihop mobile ad hoc network; the demonstration features mobile robots being remotely operated based on the real-time video stream transmitted from the robot over the network. We also present a detailed performance evaluation of PRAN to show the feasibility of our architecture

Distributed wavelet processing within sensor networks holds promise for reducing communication energy and wireless bandwidth usage at sensor nodes. Local collaboration among nodes de-correlates measurements, yielding a sparser data set with significant values at far fewer nodes. Sparsity can then be leveraged for subsequent processing such as measurement compression, de-noising, and query routing. A number of factors complicate realizing such a transform in real-world deployments, including irregular spatial placement of nodes and a potentially prohibitive energy cost associated with calculating the transform in-network. In this paper, we address these concerns head-on; our contributions are fourfold. First, we propose a simple interpolatory wavelet transform for irregular sampling grids. Second, using ns-2 simulations of network traffic generated by the transform, we establish for a variety of network configurations break-even points in network size beyond which multiscale data processing provides energy savings. Distributed lossy compression of network measurements provides a representative application for this study. Third, we develop a new protocol for extracting approximations given only a vague notion of source statistics and analyze its energy savings over a more intuitive but naïve approach. Finally, we extend the 2-dimensional (2-D) spatial irregular grid transform to a 3-D spatio-temporal transform, demonstrating the substantial gain of distributed 3-D compression over repeated 2-D compression.

As mobile ad hoc network applications are deployed, security emerges as a central requirement. In this paper, we introduce the wormhole attack, a severe attack in ad hoc networks that is particularly challenging to defend against. The wormhole attack is possible even if the attacker has not compromised any hosts, and even if all communication provides authenticity and confidentiality. In the wormhole attack, an attacker records packets (or bits) at one location in the network, tunnels them (possibly selectively) to another location, and retransmits them there into the network. The wormhole attack can form a serious threat in wireless networks, especially against many ad hoc network routing protocols and location-based wireless security systems. For example, most existing ad hoc network routing protocols, without some mechanism to defend against the wormhole attack, would be unable to find routes longer than one or two hops, severely disrupting communication. We present a general mechanism, called packet leashes, for detecting and, thus defending against wormhole attacks, and we present a specific protocol, called TIK, that implements leashes. We also discuss topology-based wormhole detection, and show that it is impossible for these approaches to detect some wormhole topologies.

In this paper, we present the initial design and evaluation of two techniques for routing improvement using directional antennas in mobile ad hoc networks. First, we use directional antennas to bridge permanent network partitions by adaptively transmitting selected packets over a longer distance, still transmitting most packets a shorter distance. Second, in a network without permanent partitions, we use directional antennas to repair routes in use, when an intermediate node moves out of wireless transmission range along the route; by using the capability of a directional antenna to transmit packets over a longer distance, we bridge the route breakage caused by the intermediate node's movement, thus reducing packet delivery latency. Through simulations, we demonstrate the effectiveness of our design in the context of the dynamic source routing protocol (DSR).

With most routing protocols for ad hoc networks, shorter paths are generally considered more desirable, making some areas of network more prone to congestion and decreasing overall network throughput. We examine the use of congestion information to avoid these network hotspots. By locally monitoring the network interface transmission queue length and MAC layer behavior at each node, a node can establish an approximation of the degree to which the wireless medium around it is busy; this measurement reflects not only the behavior of the node itself, but also the behavior of other nearby nodes sharing the wireless medium. We suggest a number of uses of such congestion information in an ad hoc network, in the network, transport, and higher layers, and we evaluate a set of such uses through simulation. Our results based on modifications to the dynamic source routing protocol (DSR) and TCP demonstrate substantial performance improvement in terms of scalability, packet delivery, overhead, and fairness resulting from this use of congestion information.

Summary form only given. Recent advances in technology have made low-cost, low-power wireless sensors a reality. A network of such nodes can coordinate among themselves for distributed sensing and processing of certain phenomena. We propose an architecture to provide a stateless solution in sensor networks for efficient addressing and routing. We name our architecture TreeCast. We propose a unique method of address allocation, building up multiple disjoint trees which are geographically inter-twined and rooted at the data sink. Using these trees, routing messages to and from the sink node without maintaining any routing state in the sensor nodes is possible. Next, we use this address allocation method for scoped addressing, through which sensor nodes of a particular type or in a particular region can be targeted. Evaluation of our protocol using ns-2 simulations shows how well our addressing and routing schemes perform.

Recent advances in technology have made low cost, low power wireless sensors a reality. Clock synchronization is an important service in any distributed system, including sensor network systems. Applications of clock synchronization in sensor networks include data integration in sensors, sensor reading fusion, TDMA medium access scheduling, and power mode energy saving. However, for a number of reasons, standard clock synchronization protocols are unsuitable for direct application in sensor networks. In this paper, we introduce the concept of adaptive clock synchronization based on the need of the application and the resource constraint in the sensor networks. We describe a probabilistic method for clock synchronization that uses the higher precision of receiver-to-receiver synchronization, as described in Reference Broadcast Synchronization (RBS) protocol. This deterministic protocol is extended to provide a probabilistic bound on the accuracy of the clock synchronization, allowing for a tradeo between accuracy and resource requirement. Expressions to convert service specifications (maximum clock synchronization error and confidence probability) to actual protocol parameters (minimum number of messages and synchronization overhead) are derived. Further, we extend this protocol for maintaining clock synchronization in a multihop network.

As mobile ad hoc network applications are deployed, security emerges as a central requirement. In this paper, we introduce the wormhole attack, a severe attack in ad hoc networks that is particularly challenging to defend against. The wormhole attack is possible even if the attacker has not compromised any hosts, and even if all communication provides authenticity and confidentiality. In the wormhole attack, an attacker records packets (or bits) at one location in the network, tunnels them (possibly selectively) to another location, and retransmits them there into the network. The wormhole attack can form a serious threat in wireless networks, especially against many ad hoc network routing protocols and location-based wireless security systems. For example, most existing ad hoc network routing protocols, without some mechanism to defend against the wormhole attack, would be unable to find routes longer than one or two hops, severely disrupting communication. We present a new, general mechanism, called packet leashes, for detecting and thus defending against wormhole attacks, and we present a specific protocol, called TIK, that implements leashes.

An ad hoc network is a group of mobile wireless nodes that cooperatively form a network among themselves without any fixed infrastructure. Increasingly, power consumption within ad hoc networks is becoming a core issue for these low-power mobile devices. This paper focuses on a novel approach for energy conservation within the routing protocol of the ad hoc network. A wireless network interface in sleep mode expends an order of magnitude less power than in idle mode, but no packets can be sent or received while in sleep mode. We propose two probabilistic algorithms for scheduling transition from idle mode to sleep mode. Performance evaluation of these strategies show a substantial reduction in power usage, with only a slight decrease in performance.

a secure on-demand routing protocol for ad hoc networks.

In an ad hoc network, the use of source routing has many advanctages, including simplicity, correctness, and flexibility. For example, all routing decisions for a packet are made by the sender of the packet, avoiding the need for up-to-date routing information at intermediate nodes and allowing the routes used to be trivially guaranteed loop-free. It is also possible for the sender to use different routes for different packets, without requiring coordination or explicit support by the imtermediate nodes. In addition, on-demand source routing has performed very strongly when compared against other proposed protocol designs. However, source routing has the disadvantage of increased per-packet overhead due to the source route header that must be present in every packet orginated or forwarded. In this paper, we propose and analyze the use in ad hoc networks of implicit source routing while avoiding the associated per-packet overhead in most cases. We evaluated this technique through detailed simulations of ad hoc networks based on the Dynamic Source Routing protocol (DSR), an on-demand ad hoc network routing protocol based on source routing. Although routing packet overhead increased slightly with implicit source routing, by about 12.3%, the total number of bytes of overhead decreased substantially, by between 44 and 86%. On all other metrics evaluated, the performance or DSR either did not change significantly or actually improved somewhat, due to indirect effects of of the reduced routing overhead

The use of on-demand techniques in routing protocols for multi-hop wireless ad hoc networks has been shown to have significant advantages in terms of reducing the routing protocol's overhead and improving its ability to react quickly to topology changes in the network. A number of on-demand multicast routing protocols have been proposed, but each also relies on significant periodic (non-on-demand) behavior within portions of the protocol. This paper presents the design and initial evluation of the Adaptive Demand-Driven Multicast Routing protocol (ADMR), a new on-demand ad hoc network multicast routing protocol that attemps to reduce as much as possible any non-on-demand components within the protocol. Multicast routing state is dynamically established and maintained only for active groups and only in nodes located between multicast senders and receivers. Each multicast data packet is forwarded along the shortest-delay path with multicast forwarding state, from the sender to the receivers, and receivers dynamically adapt to the sending pattern of senders in order to efficiently balance overhead and maintenance of the multicast routing state as nodes in the network move or as wireless transmission conditions in the network change. We describe the operation of the ADMR protocol and present an initial evaluation of its performance based on detailed simulation in ad hoc networks of 50 mobile nodes. We show that ADMR achieves packet delivery ratios within 1% of a flooding-based protocol, while incurring half to a quarter of the overhead.

An on-demand routing protocol for wireless and hoc networks is one that searches for and attempts to discover a route to some destination node only when a sending node originates a data packet addressed to that node. In order to avoid the need for such a route discovery to be performed before each data packet is sent, such routing protocols must cache routes previously discovered. This paper presents an analysis of the effects of different design choices for this caching in on-demand routing protocols in wireless ad hoc networks, dividing the problem into choices of cache structure, cache capacity, and cache timeout. Our analysis is based on the Dynamic Source Routing protocol (DSR), which operates entirely on-demand. Using detailed simulations of wireless ad hoc networks of 50 mobile nodes, we studied a large number of different caching algorithms that utilize a range of design choices, and simulated each cache primarily over a set of 50 different movement scenarios drawn from 5 different types of mobility models. We also define a set of new mobility metrics that allow accurate characterization of the relative difficulty that a given movement scenario presents to an ad hoc network routing protocol, and we analyze each mobility metric's ability to predict the actual difficulty in terms of routing overhead experienced by the routing protocol across the scenarios in our study.

This paper presents preliminary quantitative results from data collected during runs of our multi-hop wireless ad hoc network testbed. The network successfully carried a composite workload including voice, bulk data, and real-time data. Careful analysis of recorded runs highlights radio propagation issues that network protocols will need to address in the future.

A number of different routing protocols proposed for use in multihop wireless ad hoc networks are based in whole or in part on what can be described as on-demand behavior. By on-demand behavior, we mean approaches based only on reaction to the offered traffic being handled by the routing protocol. In this paper, we analyze the use of on-demand behavior in such protocols, focusing on its effect on the routing protocol's forwarding latency, overhead cost, and route caching correctness, drawing examples from detailed simulation of the dynamic source routing (DSR) protocol. We study the protocol's behavior and the changes introduced by variations on some of the mechanisms that make up the protocol, examining which mechanisms have the greatest impact and exploring the tradeoffs that exist between them.

An ad hoc networkis a collwtion of wirelessmobile nodes dynamically forminga temporarynetworkwithouttheuse of anyexistingnetworkirrfrastructureor centralizedadministration.Dueto the limitedtransmissionrange of ~vlreless nenvorkinterfaces,multiplenetwork"hops"maybe neededfor onenodeto exchangedata ivithanotheracrox the network.In recentyears, a ttiery of nelvroutingprotocols~geted specificallyat this environment have been developed.butlittle pcrfomrartwinformationon mch protocol and no ralistic performancecomparisonbehvwrrthem ISavailable.~Is paper presentsthe results of a derailedpacket-levelsimulationcomparing fourmulti-hopwirelessad hoc networkroutingprotocolsthatcovera range of design choices: DSDV,TORA, DSR and AODV.\Vehave extended the /~r-2networksimulatorto accuratelymodelthe MACand physical-layer behaviorof the IEEE 802.1I wirelessLAN standard,includinga realistic wtrelesstransmissionchannelmodel, and present the resultsof simulations of net(vorksof 50 mobilenodes.This work was supported in

No abstract available.

IP version 6 (1Pv6) is being designed within the IETF as a replacement for the current version of the IP protocol used in the Internet (1Pv4).We have designed protocol enhancements for 1Pv6, known as Mobile 1Pv6, that allow transparent routing ofiPv6 packets to mobile nodes, taking advantage of the opportunities made possible by the design of a new version of IP.In Mobile IPv6, each mobile node is always identified by its home address, regardless of its current point of attachment to the Internet.While away from its home IP subnet, a mobile node is also associated with a care-of address, which indicates the mobile node's current location.Mobile 1Pv6 enables any 1Pv6 node to learn and cache the care-of address associated with a mobile node's home address, and then to send packets destined for the mobile node directly to it at this care-of address using an 1Pv6 Routing header.

Basing rollback recovery on optimistic message logging and replay avoids the need for synchronization between processes during failure-free execution. Some previous research has also attempted to reduce the need for synchronization during recovery, but these protocols have suffered from three problems: not eliminating all synchronization during recovery, not minimizing rollback, or providing these properties but requiring large timestamps. This paper makes two contributions: we present a new rollback recovery protocol, based on our previous work, that provides these properties (asynchronous recovery, minimal rollback) while reducing the timestamp size; and we prove that no protocol can provide these properties and have asymptotically smaller timestamps.

Host mobility is becoming an important issue due to the recent proliferation of notebook and palmtop computers, the development of wireless network interfaces, and the growth in global internetworking. This paper describes the design and implementation of a mobile host protocol, called the Internet mobile host protocol (IMHP), that is compatible with the TCP/IP protocol suite, and allows a mobile host to move around the Internet without changing its identity, In particular, IMHP provides host mobility over both the local and wide area, while remaining transparent to the user and to other hosts communicating with the mobile host. IMHP features route optimization and integrated authentication of all management packets. Route optimization allows a node to cache the location of a mobile host and to send future packets directly to that mobile host. By authenticating all management packets, IMHP guards against possible attacks on packet routing to mobile hosts, including the interception or redirection of arbitrary packets within the network. A simple new authentication mechanism is introduced that preserves the level of security found in the Internet today, while accommodating the transition to stronger authentication based on public key cryptography or shared keys that may either be manually administered or provided by a future Internet key management protocol.>

This paper describes a new protocol for transparently routing packets to mobile hosts operating in a large internetwork. The protocol, called the Mobile Host Routing Protocol (MHRP), allows any host to become mobile at any time, yet there is no penalty for a host being "mobile capable", since the protocol automatically uses only the standard internetwork routing mechanisms and adds no overhead when a mobile host is currently connected to its home network. The paper concentrates on the design of MHRP as it applies to the Internet using IP. Mobile hosts use only their "home" IP addresses, regardless of their current location in the Internet. No changes are required in stationary hosts that communicate with mobile hosts, and no changes are required in mobile hosts above the IP level. MHRP introduces several new features to provide better robustness for routing to mobile hosts, and provides better scalability to very large numbers of mobile hosts than previous mobile host protocols.>

A transparent rollback-recovery method that adds very little overhead to distributed application programs and efficiently supports the quick commit of all output to the outside world is introduced. Each process can independently choose at any time either to use checkpointing alone (as in consistent checkpointing) or to use optimistic message logging. The system is based on a new commit algorithm that requires communication with and information about the minimum number of other processes in the system, and supports the recovery of both deterministic and nondeterministic processes.>

Abstract The Peregrine RPC system provides performance very close to the optimum allowed by the hardware limits, while still supporting the complete RPC model. Implemented on an Ethernet network of Sun‐3/60 workstations, a null RPC between two user‐level threads executing on separate machines requires 573μs. This time compares well with the fastest network RPC times reported in the literature, ranging from about 1100 to 2600 μs, and is only 309 μs above the measured hardware latency for transmitting the call and result packets in our environment. For large multi‐packet RPC calls, the Peregrine user‐level data transfer rate reaches 8.9 Mbit/s, approaching the Ethernet's 10 Mbit/s network transmission rate. Between two user‐level threads on the same machine, a null RPC requires 149 μs. This paper identifies some of the key performance optimizations used in Peregrine, and quantitatively assesses their benefits.

Consistent checkpointing provides transparent fault tolerance for long-running distributed applications. Performance measurements of an implementation of consistent checkpointing are described. The measurements show that consistent checkpointing performs remarkably well. Eight computation-intensive distributed applications were executed on a network of 16 diskless Sun-3/60 workstations, and the performance without checkpointing was compared to the performance with consistent checkpoints taken at two-minute intervals. For six of the eight applications, the running time increased by less than 1% as a result of the checkpointing. The highest overhead measured was 5.8%. Incremental checkpointing and copy-on write checkpointing were the most effective techniques in lowering the running time overhead. It is argued that these measurements show that consistent checkpointing is an efficient way to provide fault tolerance for long-running distributed applications.>