Ruhai Wang

MAC security and security overhead analysis in the IEEE 802.15.4 wireless sensor networks

Sensor networks have many applications. However, with limited resources such as computation capability and memory, they are vulnerable to many kinds of attacks. The IEEE 802.15.4 specification defines medium access control (MAC) layer and physical layer for wireless sensor networks. In this paper, we propose a security overhead analysis for the MAC layer in the IEEE 802.15.4 wireless sensor networks. Furthermore, we survey security mechanisms defined in the specification including security objectives, security suites, security modes, encryption, authentication, and so forth. Then, security vulnerabilities and attacks are identified. Some security enhancements are proposed to improve security and to prevent these attacks such as same-nonce attack, denial-of-service attack, reply-protection attack, ACK attack, and so forth. Our results show that, for example, with 128-bit key length and 100 MIPS, encryption overhead is 10.28 s per block, and with 100 MIPS and 1500-byte payload, the encryption overhead is as high as 5782.5s.

Design of a space channel simulator using virtual instrumentation software

The ability to simulate satellite channels gives protocol designers the ability to test design options prior to their use in space communications. Here, we describe a software-based space channel simulator with variable channel error-rate, channel delay, and user bit error rate. This simulator is used to model the communications channel for testing various Internet-type protocol options for space communications.

Licklider transmission protocol (LTP)-based DTN for cislunar communications

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.

Protocols for reliable data transport in space internet

A variety of protocols have been proposed for reliable data transport in space Internet and similar network environments. It is necessary to conduct a survey on these protocols to investigate and compare among them. In this article, we present a survey on the protocols proposed for reliable data transport in space Internet, with a focus on the latest developments. The survey includes the following contents: (1) classification of these protocols into different approaches; (2) discussions and comments on the design and operation methods of the protocols; and (3) comparisons and comments on the main techniques and performance of the protocols.

Which transmission mechanism is best for space Internet: window-based, rate-based, or a hybrid of the two?

There is an urgent need to find the best congestion-control mechanism for space Internet. This article presents an experimental study of rate-based congestion control, window-based congestion control, and a hybrid of the two in a simulated small-satellite environment using the space-to-ground link simulation (SGLS) testbed. The study is done by examining the throughput performance and transmission behavior of pure rate-control and a variant of each of the window-based transmission control protocol (TCP) selective acknowledgment (TCP-SACK) and TCP-Vegas congestion-control mechanisms, with and without the channel-rate control being hybridized. The study reveals that the traffic-shaping mechanism of a rate-based transmission mechanism is more effective than the bursty flow of window-based mechanisms in error-prone space environments with a long link delay. Pure rate-control is preferable to other mechanisms in space in which channel resource reservation is available. The performance differences arise from their different behaviors in controlling data transmission.

LTP Aggregation of DTN Bundles in Space Communications

Delay-/disruption-tolerant networking (DTN) offers a solution to highly stressed communications in space environments. Very little work has been done in investigating how to accommodate highly asymmetric space communication channels for high performance of DTN transmission in space. We study the effect of aggregation of data bundles in space communications characterized by asymmetric and low channel rates and intend to find the number of bundles which should be aggregated within a block for the best performance over highly asymmetric cislunar channel rates. A channel ratio (CR) threshold is derived considering the lengths of an aggregated data block and an acknowledgment (ACK) packet and channel rates, and it must be maintained to avoid delay of ACK transmission of DTN Licklider transmission protocol (LTP) due to space channel asymmetry.

Unreliable CCSDS File Delivery Protocol (CFDP) over 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 deep space missions. There has been theoretical and experimental evaluation on the performance of CFDP operation in low Earth orbit (LEO) and geo-stationary Earth orbit (GEO) space environments. However, very few works have evaluated the performance of CFDP in cislunar space, even though 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, operating with reliable transmission control protocol (TCP), over a simulated cislunar communication link under various channel conditions. Our intention is to evaluate the transmission effectiveness of the core file-delivery operation in unreliable CFDP running on top of a reliable TCP/IP stack over a long-delayed cislunar link, especially when accompanied by link disruptions and a high bit error rate (BER). The performance of unreliable-CFDP/TCP is also compared with other protocol options of CFDP, such as reliable-CFDP/TCP and reliable-CFDP/UDP. The experiment was carried out through realistic file transfers by running the CFDP protocol stack over a communication test-bed incorporating the qualities that define cislunar communication channel characteristics. The research results and discussions presented in this paper should work equally well in any space mission with a round-trip time (RTT) that is comparable to that of the cislunar space.

Window-based and rate-based transmission control mechanisms over space-Internet links

Space communications urgently need an effective transmission control mechanism. This paper presents an experimental, comparative analysis of window-based transmission control, rate-based transmission control, and a hybrid of the two over error-prone, congestion-free, high-latency, point-to-point space communication links simulated using the space-to-ground link simulation (SGLS) test-bed. The results revealed that the traffic shaping mechanism of rate-based transmission protocol is more effective than the bursting flow of window-based protocol over simulated space communication links with a high error rate and a long link delay. The window-based transmission mechanisms show performance degradation due to traffic bursts and frequent packet retransmissions caused by their acknowledgment (ACK)-clocked transmission control algorithms. Pure rate-control is always preferable to other mechanisms in the simulated congestion-free, error-prone, point-to-point, geostationary-Earth orbit (GEO)-space communication channels, and its advantages become more pronounced when the channel rates are asymmetric. The performance differences come from their different behavior in controlling data transmission.

Impact of Van Jacobson header compression on TCP/IP throughput performance over lossy space channels

The impact of Van Jacobson header compression (VJHC) on the throughput performance of Transmission Control Protocol/Internet Protocol (TCP/IP) over lossy space channels is studied in an experimental manner using a test-bed. The experimental results show that VJHC benefits the transmission at bit error rates (BERs) around 10/sup -6/ or less, but also results in performance degradation in an environment with higher BER.

Performance of DTN protocols in space communications

Delay/disruption tolerant networking (DTN) was developed to enable automated network communications despite the long link delay and frequent link disruptions that generally characterize space communications. The performance of DTN convergence layer adapter (CLA) protocols over asymmetric space communication channels has not yet been comprehensively characterized. In this paper, we present an experimental performance evaluation of DTN CLA protocols for reliable data transport over a space communication infrastructure involving asymmetric channel rates, with particular attention to the recently developed Licklider transmission protocol (LTP) CLA (i.e., LTPCL). The performance of LTPCL is evaluated in comparison with other two reliable CLAs, TCP CLA and a hybrid of TCP CLA and LTPCL, for long-delay cislunar communications in the presence of highly asymmetric channel rates. LTPCL is also evaluated and analyzed in a deep-space communication scenario characterized by a very long link delay and lengthy link disruptions.