Delay/disruption-tolerant networking (DTN) is a networking technology conceived to manage opportunistic connections with no consistent end-to-end link connectivity which is common in both terrestrial and space communication environments. DTN is recognized as a baseline technology for implementing deep-space networks. Considered as the primary transport protocol of DTN in space, Licklider transmission protocol (LTP) is expected to provide reliable data delivery service in a challenging networking environment regardless of presence of random link disruptions and/or extremely long propagation delays. The National Aeronautics and Space Administration (NASA) has implemented the use of DTN protocols on the International Space Station (ISS) for data delivery to the earth ground station. However, little work has been done in studying the performance of LTP for reliable data/file delivery in such a communication environment, especially in presence of link disruption. There is a lack of a solid performance evaluation of LTP for its use in the space station communications. In this paper, an analytical framework is presented to evaluate the performance of LTP for reliable file delivery between the space station and the ground stations with a focus on the effect of link disruption, which may occur either over the downlink or over the uplink. The effect of data loss due to channel error is also integrated. Realistic data block transmission experiments using a PC-based experimental infrastructure are conducted to validate the analytical models.

Pipeline monitoring is of the essence for nowadays oil and natural gas delivery. Wireless Sensor Network (WSN) is the best candidate due to its low cost, ad-hoc feature, and ease of maintenance. However, there are quite limited WSNs that are particularly designed for long pipeline monitoring. Meanwhile, directly applying existing protocols may cause insufficient use of these WSNs and downgraded performance, especially on the lifetime of the network, which is a crucial metric for pipeline monitoring. Some efforts for lifetime extension do not fully utilize the features of pipeline or has some impractical assumptions when applying to pipeline scenarios. In this paper, we fully consider the practical factors and unique features of pipeline and propose a joint design of deployment and routing for such typed networks. In our design, a novel sensor deployment and a corresponding load balancing routing protocol are derived in terms of the maximized lifetime. The design considers the node damage, redundant data generated from the same event, and energy holes caused by dead nodes. Extensive simulation results validate our optimization and demonstrate our design can significantly improve the lifetime of the network and enjoy less overhead than the existing work. The simulation platform we used the MATLAB platform.

Vehicular fog computing (VFC) is envisioned as a promising solution to process the explosive tasks in autonomous vehicular networks. In the VFC system, task offloading is the key technique to process the computation-intensive tasks efficiently. In the task offloading, the task is transmitted to the VFC system according to the 802.11p standard and processed by the computation resources in the VFC system. The delay of task offloading, consisting of the transmission delay and computing delay, is extremely critical especially for some delay-sensitive applications. Furthermore, the long-term reward of the system (i.e., jointly considers the transmission delay, computing delay, available resources, and diversity of vehicles and tasks) becomes a significantly important issue for providers. Thus, in this article, we propose an optimal task offloading scheme to maximize the long-term reward of the system where 802.11p is employed as the transmission protocol for the communications between vehicles. Specifically, a task offloading problem based on a semi-Markov decision process (SMDP) is formulated. To solve this problem, we utilize an iterative algorithm based on the Bellman equation to approach the desired solution. The performance of the proposed scheme has been demonstrated by extensive numerical results.

Space communications are characterized by link intermittent connectivity and long link propagation delay. The use of bundle protocol (BP) in space communications has been in debate. An analytical understanding of its performance for reliable data delivery in the presence of link intermittent connectivity, especially with a lengthy link disruption, is quickly needed. In this paper, analytical models are built to estimate the number of transmission rounds (or efforts) caused by the link disruption and the resulting delay in bundle delivery of BP for applications in space communication networks. The models are validated by conducting bundle delivery experiments using a testbed.

Delay/disruption tolerant networking (DTN) was proposed for reliable data transfer despite frequent link disruptions and long propagation delay that are typical of the deep-space communication environment. DTN communications rely heavily on its core bundle protocol (BP) for reliable data delivery. To date, little work has been seen in theoretical analysis of the performance of BP in deep-space communications. In particular, an analytical understanding of the performance of BP for reliable data delivery in a deep-space communication environment in the presence of link disruptions is quickly needed. In this paper, we present a study of the effect of link disruption on transmission performance of BP, in both analytical and experimental manners, in a deep-space communications system characterized by link disruptions accompanied by an extremely long propagation delay and lossy data links. For the first time, an analytical framework is built to estimate the effect of link disruption on the total bundle delivery time of BP depending on its starting time with respect to bundle delivery. The analytical models are validated by running experiments using a test bed.

Bundle protocol (BP) is the main protocol of delay/disruption-tolerant networking which is developed to provide reliable data delivery services in a stressed communications environment. A typical application of BP is for data delivery in a challenging deep-space communication environment. However, little work has been done in analyzing the performance of BP in deep-space communications, especially in presence of highly channel-rate asymmetry. In this paper, we present analytical modeling of the transmission performance of BP over deep-space communication channels characterized by highly asymmetric channel rates. The model is built to estimate the expected file delivery time (and goodput) of the protocol for reliable data delivery in a deep-space transmission scenario. The model is validated by conducting data transfer experiments using a PC-based experimental test bed.

Delay/disruption tolerant networking (DTN) was proposed as an end-to-end networking architecture providing file delivery service in and/or through stressed communication environments. Bundle protocol (BP) of DTN utilizes the well-known store-and-forward mechanism together with custody transfer option for which a node agrees to hold a file in memory (disk storage in this paper) until its successful reception is acknowledged by the next node. The variation in memory occupancy constrains the volume of memory that is available for other DTN functions. Characterizing the memory dynamics of BP during file transfer is crucial. In this paper, we present a study of memory variation dynamics and transmission performance in the operation of BP for file transmissions over a typical relay-based deep-space communication system characterized by multiple data source nodes, an extremely long signal propagation delay, and lossy data links with both symmetric and asymmetric channel rates. Analytical models are built to estimate the memory variation dynamics and the total file delivery time (and goodput) characterizing BP transmission in deep space. The models are validated by running file transfer experiments using a testbed.

Delay/Disruption Tolerant Networking (DTN) architecture is expected to play a promising role in future deep space missions. Scientific data interactions over space DTN involve several hops inevitable, since simultaneous and direct connectivity among all intermediate nodes are becoming more difficult in space scenarios. Therefore, the characteristics and capabilities of the node storage are vital factors for the quality of data delivery over space DTN. This paper proposes an analytical framework based on multi-dimension Markov chain to evaluate the dynamic on storage of intermediate nodes in space DTN. According to the proposed framework, we develop a delay model and consequently a success probability model for bundles delivery over space DTN, both of which are dependent closely on the sojourn time in node storages. The numerical results show that: a) dividing source-file data into bigger bundles can bring longer high-storage-occupancy time on intermediary nodes; b) the shorter storage occupation time of node is more susceptible to the bundle sizes than to LTP segment sizes. c) the delivery success probability of the bundles is more dependent on smaller DTN bundles than on LTP segment sizes given the constrains on Time-to-live of bundles in space missions.

Some work has been done with the DTN convergence layer adapters (CLAs) such as TCP-based CLA (i.e., TCPCL), Licklider transmission protocol CLA (i.e., LTPCL) and user datagram protocol (UDP)-based CLA (i.e., UDPCL) in space communication, running as an individual protocol. Because each DTN CLA is designed for a different type of communication link, using any single CLA under BP is generally inefficient over a heterogeneous end-to-end interplanetary infrastructure. In this paper, we propose to use a hybrid of DTN CLAs for efficient file transmission in interplanetary environment, i.e. using one CLA for one hop of the end-to-end path and a different CLA for another hop of the path. Based on experimental investigation of DTN protocols over a typical relay-type of interplanetary infrastructure, we found that a hybrid of TCPCL and LTPCL has significant goodput advantage over single-CL-protocol configurations at long link delays, especially with a high BER, and a transmission with LTPCL utilized over a long-delay hop is more tolerant of long channel delay and high channel error.

Delay/disruption tolerant networking (DTN) offers a new solution to highly stressed communications in space environments. It is considered one of the most suitable technologies to be employed in space internetworking. To date, little work has been done in investigating how to achieve the best performance of DTN transmission over lossy, long-delay space channels. In this paper, we present an experimental investigation of how the throughput performance of Licklider transmission protocol (LTP)-based DTN is affected by the LTP flow control “window” size, established by the Number of Sessions (NOS) and Number of Bytes per Session (NBS) characterizing the LTP channel. The intent of the work is, in particular, to find a relationship between the window size and throughput performance of DTN in a typical lossy and long delay cislunar communications infrastructure. One major conclusion is that a bigger NOS generally results in higher throughput than a low NOS, and NBS does not affect the throughput significantly.

Delay/disruption tolerant networking (DTN) is considered one of the most suitable technologies to handle challenging space communications. Aggregation of multiple DTN bundles within a data transport block for space communications has been in controversy for years. In this paper, we present an experimental investigation, using a PC-based testbed, of whether aggregation of multiple DTN bundles within a single Licklider transmission protocol (LTP) block has performance advantage over the default approach of “one bundle per block” for channelrate asymmetric cislunar communications.

Interplanetary Overlay Network (ION) is an implementation of delay/disruption tolerant networking (DTN) developed as infrastructure for space communications in interplanetary flight mission systems. To date, no work has been done in evaluating the effectiveness of ION when it is applied to an interplanetary Internet involving very long link delay and highly asymmetric channel rates. In this paper, we present an experimental evaluation of ION over a typical three-node interplanetary infrastructure in the presence of a long link delay, highly asymmetric channel rates and varying data loss rate. One major conclusion is that the hybrid of TCP and Licklider transmission protocol (LTP) convergence layer protocols has significant goodput advantage over other protocol options as the ratio of data channel rate to ACK channel rate increases.

Cognitive radio has potential to improve spectrum efficiency in future wireless multimedia communications. There exist various performance problems in the dynamic spectrum resource management, frequency sense and utilization for cognitive radio. In this paper, a novel frequency sense solution based on the double-station cooperation and multi-hop tracing localization is proposed to resolve the hidden and exposed problems in spectrum resource management. In specific, the solution is proposed to improve reliability and efficiency of frequency sense and increase the utilization of spectrum. With this solution, a secondary user can obtain more accurate primary user's location by an improved centroid localization algorithm cooperated with a known position user. The tracing localization accuracy is also analyzed. Simulation results show that the proposed solution significantly improves the performance while location accuracy is still within controllable range after multiple tracing hops.

Delay/disruption-tolerant networking (DTN) technology offers a new solution to highly stressed communications in space environments, especially those with long link delay and frequent link disruptions in deep-space missions. To date, little work has been done in evaluating the performance of the available “convergence layer” protocols of DTN, especially the Licklider Transmission Protocol (LTP), when they are applied to an interplanetary Internet (IPN). In this paper, we present an experimental evaluation of the Bundle Protocol (BP) running over various “convergence layer” protocols in a simulated cislunar communications environment characterized by varying degrees of signal propagation delay and data loss. We focus on the LTP convergence layer (LTPCL) adapter running on top of UDP/IP (i.e., BP/LTPCL/UDP/IP). The performance of BP/LTPCL/UDP/IP in realistic file transfers over a PC-based network test bed is compared to that of two other DTN protocol stack options, BP/TCPCL/TCP/IP and BP/UDPCL/UDP/IP. A statistical method of$t$-test is also used for analysis of the experimental results. The experiment results show that LTPCL has a significant performance advantage over Transmission Control Protocol convergence layer (TCPCL) for link delays longer than 4000 ms regardless of the bit error rate (BER). For a very lossy channel with a BER of around 10$^{-5}$, LTPCL has a significant goodput advantage over TCPCL at all the link delay levels studied, with an advantage of around 3000 B/s for delays longer than 1500 ms. LTPCL has a consistently significant goodput advantage over UDPCL, around 2500–3000 B/s, at all levels of link delays and BERs.

Delay/disruption tolerant networking (DTN) technology offers a new solution to highly stressed communications in space environments, especially those with long link delay and frequent link disruptions in deep space missions. To date, little work has been done in evaluating the effectiveness of the available DTN protocols when they are applied to an interplanetary Internet. In this paper, we present an experimental evaluation of the Bundle Protocol (BP) running over various "convergence layer" protocols in a simulated cislunar communications environment characterized by varying degrees of signal propagation delay and data loss. We focus on the Licklider Transmission Protocol (LTP) convergence layer adapter running on top of UDP/IP (i.e., BP/LTPCL/UDP/IP). The performance of BP/LTPCL/UDP/IP in realistic file transfers over a PC-based testbed is compared with that of two other DTN protocol stacks, BP/TCPCL/TCP/IP and BP/UDPCL/UDP/IP. The experiment results show that LTPCL has a significant performance advantage over TCPCL for link delays longer than 4 sec when bit error rate (BER) is 10E-6 or lower. For a lossy channel with a BER of around 10E-5, LTPCL has a significant goodput advantage over TCPCL at all the link delay levels studied, with an advantage of around 3000 bytes/s for delays longer than 1.5 sec.

With demands increasing in lunar and Mars explorations, the need for a new space communication standard protocol is becoming more and more critical. The DTN Research Group (DTNRG) is developing a series of communication protocols with new architecture, generally called DTN protocols, to tolerate highly stressed communication environments with long propagation delays and frequent link disruptions. In this paper, we present an experimental investigation of the bundle protocol (BP), over Licklider transmission protocol (LTP sometimes called the long-haul transmission protocol), operating with unreliable User Datagram Protocol (UDP), over an emulated cislunar networking under various channel conditions. Our intention is to investigate the transmission performance of the BP/LTP protocol, running on top of an unreliable UDP stack, over a cislunar link with long propagation delays, frequent disconnects, and a high bit error rate (BER). A comparison between BP/LTP/UDP and another DTN protocol suite is also presented.

TCP experiences severe performance degradation in cislunar communications because of some assumptions built into its design. Delay/disruption tolerant networking (DTN) is a class of network techniques that is developed to work over Internet protocols to accommodate long link delay and frequent link disruptions in space communication environment. Most of the work concerning DTN protocols and techniques focused on its application in terrestrial wireless network and sensor-based networks. In this paper, we present an experimental evaluation of the DTN protocols with BP/TCPCL running on top of TCP/IP over a long-delay cislunar communication channel with and without link disruption. We hope the experiment results and analysis in this paper will apply equally well in any deep space mission with a round-trip time (RTT) that is comparable to that of the Earth-Moon system.

Owing to the diverse geographical distributions of users, multi-layered satellite networks tend to exhibit high variances causing traffic concentrations at particular satellites to increase drastically. This results in high packet drop rates and severe degradation of Quality of Service (QoS). The Explicit Load Balancing (ELB) scheme was developed to address these issues in Low Earth Orbit (LEO) satellite networks by having the satellites, which experience heavy traffic, redirect a portion of the traffic via alternative paths. To cope with network congestion (over a single layer) and for better traffic distribution, multi layer satellites were proposed. In this paper, we propose an efficient traffic distribution scheme for multi-layered satellite networks based on ELB in which we extend the range for exchanging the traffic-load information for achieving further reductions in packet drop rates. We also present an enhanced technique for efficiently computing the detouring ratio. The effectiveness of the envisioned approach is validated via simulations.

While the window-based mechanism is not favorable in a space communication environment which is characterized by a large BDP, the potential of the rate-based Internet-type protocols to have low loss by maintaining a smooth data flow has made them attractive in space. However, very few studies have been done on the development and evaluation of rate-based transmission control for space environments. This paper presents an experimental, comparative analysis of channel delay impact on the rate-based and the window-based transmission mechanisms over space-Internet links. This work focuses on the effectiveness of rate-based and window-based transmission control mechanisms in coping with space-channel delay from low earth orbit (LEO) satellite links, geo-stationary earth orbit (GEO) satellite links, and cislunar communication links.

The Consultative Committee for Space Data Systems (CCSDS) file delivery protocol, also known as CFDP, is a new standard protocol designed to meet a comprehensive set of file transfer requirements in space communications, especially for deep space missions. However, the performance of CFDP in cislunar space has not yet been evaluated, although the protocol has been particularly developed for deep space communications. In this work, we discuss an experimental investigation of the core file-delivery operation of unreliable CFDP in cislunar space communications. Presented is an experimental performance evaluation of unreliable CFDP operating with reliable transmission control protocol (TCP) and reliable CDFP operating with UDP over the simulated cislunar communication link with intermittent link connectivity.

TCP is a reliable transport protocol tuned to perform well over traditional wired networks. Although it performs well for wired networks, TCP's implicit assumption that any packet loss is due to congestion is not valid any longer in mobile ad hoc networks. It is observed that TCP induces the over-action of routing protocol and reduces the performance of the connection. Fraction window increment (FeW) scheme for TCP improves the connection performance by limiting TCP's aggressiveness. But to some extent, this limitation is too strict in that it eliminates the possibility to deliver more bytes under the same congestion window. To solve this problem, we propose an adaptive packet size (APS) scheme to work on top of FeW for TCP. The proposed scheme utilizes the advantages of both legacy TCP and FeW to achieve high performance over multihop 802.11 networks. Extensive simulation results demonstrate that APS over FeW outperforms FeW alone by 10 -25 % according to different scenarios, e.g., chain-topology, grid-topology, and random-topology with mobility.

In traditional call admission control (CAC) schemes, mobile users are always the passive roles during the admission procedures and the base station determines whether to admit or reject the call requests without the involvement of mobile users. In this paper, we propose a novel stochastic CAC framework that allows the mobile user to be an active entity during the CAC process. The objective of each mobile user is to maximize its utility function based on its own decision (i.e., to join the queue or not to join the queue). The optimal stochastic decision is in the sense that the probability for a mobile user to join the queue will maximize the expectation of the utility function. In other words, in the long run, the mobile user will benefit from the optimal joining probability p*. We further show that the optimal join probability for a mobile user could be quite different depending on the number of mobile users waiting in the queue. Finally, we illustrate the structure of the optimal join probability p* under various utility functions, which indicates that the optimal user's policy depends on the utility functions. Moreover, we find that even if the theoretical structure of service time in the system are quite different for various queue scheduling schemes, the optimal pi* are identical in most of circumstance.

Some work has been done in evaluating the performance of the rate-based SCPS-pure rate control and the store-and-forward CFDP protocol. In this paper, we present an experimental performance comparison between SCPS-pure rate control and the CFDP in the deferred mode over a simulated error-pone, long-delayed, point-to-point cislunar communication link. The focus of this work is to see which protocol is more effective in coping with a long cislunar-link delay, especially when hybridized with a high bit-error-rate (BER), and which one has throughput performance advantage over another. The comparison results show that SCPS-pure rate control has a better performance than CFDP-TCP and Linux-TCP over both symmetric and asymmetric cislunar communication channels with all BERs, and its throughput advantage is higher than 3000 bytes/s over both symmetric and asymmetric channels at all levels of BER The advantage is more significant over asymmetric cislunar channel with a high BER around 10-5. The rate-based SCPS-pure rate control is more effective in coping with a long cislunar link delay, especially when hybridized with a high BER. CFDP-TCP and Linux-TCP do not have significant performance difference in any cases.

The performance evaluation of delay-tolerant CFDP is seen in the literatures. In this work, we focus on experimental performance investigation of the delay-tolerant CFDP in the deferred NAK mode over a simulated low earth orbit (LEO)-satellite communication link. A rate-based transmission protocol is taken as a reference. This work is to see how the delay-tolerant CFDP protocol performs over a LEO- satellite link delay, especially when compounded with a high bit- error-rate (BER). The investigation results show that the rate- based protocol shows superior throughput performance over both symmetric and asymmetric channels, especially at higher BERs. Quantitatively, the throughput advantage of the rate- based protocol over CFDP-TCP in symmetric channel at BER=10"5 is approximately 2200 bytes/sec, and in asymmetric channel is approximately 8500 bytes/sec.

The Consultative Committee For Space Data Systems (CCSDS) file delivery protocol (CFDP) offers selectable quality of service, according to mission requirements and transmission capability, ranging from an unacknowledged option to a fully acknowledged option providing error recovery through retransmission. The performance of CFDP in the deferred NAK mode has been evaluated in a theoretical manner. In this paper, we present an experimental performance evaluation of CFDP in the deferred NAK mode over the direct, point-to-point geostationary earth orbit (GEO)-satellite links simulated using a test-bed. We compare CFDP running over TCP with the CCSDS space communication protocol standards (SCPS) protocol stack to see which one is more effective over a GEO-satellite link. The experimental results show that CFDP does not have performance advantage over other protocols over a less lossy channel with a BER less than or equal to 10-6. However, along with the increase of BER, CFDP shows significant performance advantage. Quantitatively, for a symmetric channel with BER=10-5, CFDP-TCP protocol has the highest throughput which is 2000 bytes/sec higher than SCPS-VJ and almost 3500 bytes/sec higher than SCPS-Vegas. The throughput advantage of CFDP with BER=10-5is 1500 bytes/sec over SCPS-VJ and 2800 bytes/sec over SCPS- Vegas, over asymmetric channel with BER=10-5.

A substantially long round trip time (RTT) in space channel hurts TCP interactions between the sending and receiving ends. The consultative committee for space data systems (CCSDS) file delivery protocol (CFDP) is a new international standard developed to meet a comprehensive set of deep space file transfer requirements. There is a need in NASA to have controlled, experimental evaluation of CFDP performance in space, especially on its effectiveness in coping with long channel delay. This paper presents an experimental evaluation of channel delay impact on throughput performance of CFDP over LEO-satellite link, GEO-satellite link, and cislunar communication link in comparison with the widely deployed TCP and a space transport protocol, SCPS-TP. The experimental results show that CFDP/TCP in the deferred NAK mode is much more effective than other two stacks in the simulated point-to- point space communication links, especially when operated with a long link delay, a high BER and channel-rate asymmetry. We have found that CFDP/TCP is less sensitive, and FTP/TCP and SCPS-FP/SCPS-TP are highly sensitive, to the increase of link delay.

Space communication protocol standards-transport protocol (SCPS-TP) is a set of TCP extensions aimed at reliable transfer of information between space mission end systems. Some works have been done on throughput performance evaluation of SCPS-TP over LEO- and GEO-satellite channels. In this paper, we present an experimental performance evaluation of SCPS-TP over a simulated cislunar communication link. We intend to see how effective both the window-based and the rate-based transmission control mechanisms of the SCPS-TP cope with a long cislunar link delay, especially when hybridized with a high bit-error-rate (BER), and which option has throughput advantage over the other. The experimental results reveal that the protocols have statistically significant performance difference over an error-prone link with a BER around 10-5at which pure rate control shows superior performance over other three protocols. SCPS-Vegas performs poorly over a long-delayed, error-prone cislunar channel. Quantitatively, the throughput advantage of SCPS-pure rate control is around 3000 bytes/sec over all other three protocols over both symmetrical and asymmetrical channels at BER=10-5. We conclude that pure rate control is very suitable for a long-delayed, error-prone cislunar communication links.

Some work has been done in evaluating the performance of CFDP and the rate-based SCPS-pure rate control over space communication channels. In this paper, we present an experimental performance comparison between SCPS-pure rate control and the CFDP in the deferred mode over a simulated geostationary earth orbit (GEO) communication link. We intend to see which protocol is more effective in coping with a long GEO-satellite link delay, especially when hybridized with a high bit-error-rate (BER), and which one has throughput performance advantage over another. Based on the analysis of the experimental results, we found that the rate-based SCPS-pure rate control outperforms CFDP and standard TCP with a much higher throughput, and the throughput advantage becomes more pronounced when the channel rates are asymmetric. Quantitatively, SCPS-pure rate control has a performance advantage around 6600 bytes/sec over symmetric channel and around 8500 bytes/sec over asymmetric channel in comparison to CFDP-TCP and Linux-TCP.

The consultative committee for space data systems (CCSDS) file delivery protocol (CFDP) operates in a store-and-forward model to ensure the efficient transfer of information in a wide variety of mission configurations, from relatively low earth-orbiting spacecrafts to complex arrangements of inter-planetary space links. The performance of CFDP in the deferred NAK mode has been evaluated in a theoretical manner. In this paper, we present an experimental performance evaluation of CFDP in the deferred NAK mode over direct point to point low earth orbit (LEO)-satellite links simulated using a test-bed. We compare CFDP/TCP with the commonly used TCP and space communication protocol standards (SCPS) protocol stacks to see which one is more effective over a LEO-satellite link. The evaluation results show that CFDP outperform other two protocols over lossy and asymmetric channels. We found that CFDP is more tolerant of heavy noise and asymmetric channel rate. The superior performance of CFDP over lossy links is attributed to that data are stored pending transmission opportunity and portions of file can be made available to the user as soon as they arrive and its ability to minimize link traffic because of aggregated selective negative acknowledgements.

Location information is an important feature of users' mobility profile in cellular mobile networks. In this paper, continuing our existing work on constructing a mobility-based anomaly detection scheme, we further address a challenging problem - how to adaptively adjust the detection threshold of Intrusion Detection Systems (IDSs) in the context of cellular mobile networks. This is especially critical when we consider the different mobility patterns demonstrated by the mobile users. Utilizing a high order Markov model, we apply a weighted blending scheme to compute the entropy of our Exponentially Weighted Moving Average (EWMA) based mobility trie. This reflection of the uncertainness of the users' normal profile could help us adaptively adjust the detection threshold of our anomaly detection algorithm. Simulation results show that our proposed adaptive mechanisms can further reduce the false positive rate without decreasing the detection rate. Detailed analysis of the simulation results is also provided.

Significant security concerns have come to the attention of both service providers and end users in cellular mobile systems. In these systems, misuse-based intrusion detection approaches are not effective since a potential wide variety of mobile users' behaviors are not taken into consideration. In this paper, by exploiting the location history traversed by mobile users, we propose an anomaly detection scheme to identify a group of especially harmful insider attackers - masqueraders. A realistic network model integrating geographic road-level granularities is proposed to effectively utilize users' location information. Based on this model, an Instance-Based Learning (IBL) technique is presented to construct mobile users' movement patterns. Simulation results demonstrate the effectiveness of the proposed scheme in terms of false positive rate and detection rate.

In this paper, we present a detection technique based on Bayes decision rule to identify a group of especially harmful insider attackers - masqueraders. In this technique, we exploit the calling patterns demonstrated by mobile users in mobile cellular networks. Specifically, we formulate the intrusion detection problem as a multi-feature two-class pattern classification problem. Call duration time, call inactivity period and call destination are extracted to form a feature vector to reflect users' calling activities. A nonparametric technique, Parzen window approach with a Gaussian kernel, is used to estimate the smooth class-conditional probability density function. A Bayes decision rule is applied in order to achieve the minimum error rate. Using users' calling activities to demonstrate different behaviors, we carried out simulations to evaluate the proposed scheme in terms of false positive rate and detection rate.

Space Communication Protocol Standards (SCPS) has been developed for the reliable transfer of information in the space Internet. There is a need to have an evaluation of the SCPS protocol in a realistic space environment with a large bandwidth- delay product (BDP). An experimental evaluation of SCPS-TP was done by transferring user files using the SCPS protocol over the NASA's Advanced Communications Technology Satellite (ACTS) links. However, the user files were so small that the steady performance of the protocol could not be accurately evaluated. This paper describes an experimental evaluation of SCPS-TP over high-speed, asymmetric space links by transferring a large user file over asymmetric ACTS link, leading to its steady performance.

Space communication protocol standards-transport protocol (SCPS-TP) is a set of extensions to transmission control protocol (TCP) aimed at improving TCP performance over space links. Some work has been done on performance evaluation of SCPS-TP based on its methodology, or by testing it as an isolated entity or over satellite that deploys performance enhancing proxies (PEPs). It is needed to have an experimental evaluation of SCPS-TP in coping with heavy noise using the complete SCPS protocol stack, especially by comparing it with state-of-the-art terrestrial TCP. This paper describes an experimental evaluation of SCPS-TP over congestion free, error-prone, high-latency, point-to-point space links, through file transfer experiment by running the actual SCPS protocol stacks via a testbed. The results reveal that SCPS-TP is more tolerant of heavy noise and has significant throughput advantages over TCP. The performance advantage of SCPS-TP in a lossy link is attributed to its novel SNACK scheme and the advantage in asymmetric channel is from the contributions of the channel rate control and acknowledgment reduction mechanisms.

The default acknowledgment (ACK) strategy of TCP easily overruns the constrained ACK channel capacity of the asymmetric network links. There is no effective ACK mechanism to address the asymmetric channel problem for space-Internet. A configurable ACK delay (CAD) mechanism has been developed to delay the ACKs for a configurable period of time to improve the TCP throughput performance over asymmetric space-Internet links. This paper introduces the CAD mechanism and presents a performance evaluation of it in an experimental manner. The experimental results show that the CAD mechanism has significant performance advantages in asymmetric space links with a channel ratio higher than 50/1. The higher the asymmetric channel ratio is, the more advantageous the CAD is over the default ACK strategy.

Advanced encryption standard has been proposed and implemented for several years as a new cipher to replace data encryption standard. There are many researches and applications using this new cipher. However, there is a need to provide its performance analysis in scenarios of network applications. In this paper, we provide an overhead analysis of advanced encryption standard and its performance in wireless networks.

Space communication protocol standards-transport protocol (SCPS-TP) is a set of extensions to transmission control protocol (TCP) aimed at improving TCP performance in space communications. It is expected to have an experimental evaluation of the throughput performance of SCPS-TP over lossy communication links in a small satellite environment, especially by comparing it with standard TCP. This paper describes a performance evaluation of TCP and SCPS-TP over lossy links in a simulated small satellite environment using a test-bed. The results show that SCPS-TP is more tolerant of heavy noise and asymmetric channel and shows a much better performance, which make it more favorable over standard TCP in similar communication environments.

A substantially long round trip time (RTT) in space channel hurts TCP interactions between the sending and receiving sides, and limits the usefulness and effectiveness of TCP feedback from the remote endpoint for space communications. Space communication protocol standards-transport protocol (SCPS-TP) is a set of extensions to transmission control protocol (TCP) aimed at improving TCP performance in space communications. Some work has been done on performance comparison between SCPS-TP and the widely used TCP. It is expected to have an evaluation of SCPS-TP in coping with long channel delay which is one of the primary features in space communications. This paper describes an experimental evaluation of channel delay impact on throughput performance of SCPS-TP over LEO/GEO-stationary space links using a test-bed, by comparing it with the widely used TCP.

There are hardly any experimental results seen in support of the discussions on the impact of TCP-IP Van Jacobson header compression (VJHC) in harsh environments. This paper studies the impact of VJHC over geohop satellite channels based on realistic experiments using a test-bed. The results show that enabling VJHC would result in performance degradation in a high-BER environment and suggests that it is better to disable it when the transmission condition becomes harsh. In addition, TCP-IP with VJHC disabled is less sensitive to the increase of BER but is more sensitive to the decrease of acknowledgment channel-rate compared to TCP-IP with VJHC enabled. Considering many similarities between satellite and wireless environments when observed from the perspective of network protocols, the results are also expected to be useful in wireless community.

TCP Vegas is a "proactive" congestion control mechanism which predicts when congestion is about to happen and then reduces the sending rate just before discarding of packets gets started. The techniques of Vegas are expected to be very supportive to space communication which is dominated by frequent packet losses as a result of heavy noise. This is because Vegas is specially designed to minimize packet losses to achieve high throughput. However, very few studies have been done on its usage in space communication. This paper studies the behavior of Vegas over space channel by comparing it over the widely used VJ congestion control using the SGIS test-bed. It is concluded that Vegas achieves much higher throughput than VJ in error prone links such as satellite and wireless channels, which makes it more favorable over VJ in similar environments. It is suggested to use Vegas congestion control mechanism in space and wireless links with similar adverse conditions.