Asymmetric Channel Rates Research Articles

Acknowledgment Mechanisms for Reliable File Transfer Over Highly Asymmetric Deep-Space Channels

Deep-space network channels are characterized “in part” by asymmetric channel rates. The effect of the asymmetric channel rates is that the slow acknowledgement (ACK) channel cannot effectively support transmission of the ACK segments generated at the data receiver. Increment of data block size and extension of the retransmission timeout (RTO) timer are widely used transmission mechanisms for eliminating the effect of highly channel-rate asymmetry. The aggregate custody signal (ACS) is recently proposed to resolve the effect of asymmetric channel rates in deep-space networks. In this article, these three acknowledgment mechanisms are studied, with a focus on a comparison of their effectiveness evaluation over highly asymmetric deep-space network channels accompanied by data loss. The study is conducted through realistic file delivery via an experimental testbed infrastructure. It is found that the ACS mechanism shows significant performance advantages over other two mechanisms for both the “normalized” goodput and total data amount in successful file delivery. In particular, the ACS mechanism makes it a better choice to operate with small data bundles without increasing the RTO timer length.

A Study of Cross-Layer BP/LTP Data Block Size in Space Vehicle Communications Over Lossy and Highly Asymmetric Channels

The bundle protocol (BP) and Licklider transmission protocol (LTP) were developed to provide reliable and highly efficient data delivery over unreliable space vehicle communication channels. Some preliminary studies on cross-layer BP/LTP data block size in space vehicle communications have been done. However, the effect of data losses on the block has been ignored. Data loss caused by lossy space channels is one of the key features that characterize space vehicle communications, and therefore its effect cannot be left out. In this article, the cross-layer BP/LTP block size in space vehicle communications is studied with focus on its characterization and performance over lossy space channels. An analytical model is presented for calculating the minimum number of bundles that should be aggregated within an LTP block for transmission over a lossy channel so that the report segment (RS) delay imposed by highly asymmetric channel rates can be resolved. The model is validated by realistic file transfer experiments over an experimental testbed infrastructure and packet-level analysis of the results. The transmission performance of LTP with respect to variations of the aggregated block size, channel date rate and channel loss rate are discussed.

Reliable Deep-Space File Transfers: How Data Transfer Can Be Ensured Within a Single Round-Trip Interval

The challenging problem of mission control and data delivery in deep-space explorations is a typical application scenario of delay-/disruption-tolerant networking (DTN) technology. The development of protocols and efficient data transmission mechanisms for space-vehicle networks and deepspace-vehicle communications is presently underway. In this article, we show how to ensure successful file transfers in deep-space-vehicle communications within a single round-trip interval using a bundle protocol (BP), the main protocol of DTN, despite the high rate of data loss, long signal propagation delay, and highly asymmetric channel rates that characterize deepspace channels. The key concept is anticipatory retransmission: bundles are proactively retransmitted, long before the round-trip interval elapses, based on expected transmission failure rather than detected transmission failure.

Bundle Protocol Over Highly Asymmetric Deep-Space Channels

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.

Optimal RTO Timer for Best Transmission Efficiency of DTN Protocol in Deep-Space Vehicle Communications

The delay/disruption-tolerant network (DTN) was proposed as an end-to-end networking architecture for file delivery service in a stressed communication environment. A typical application of DTN technology is for reliable data delivery in deep-space vehicle communications. The main protocol of DTN, i.e., bundle protocol (BP), utilizes a store-and-forward mechanism and a custody transfer option for transmission reliability. However, little work has been done on the performance evaluation of DTN's BP in deep-space communications. In this paper, we present a study of the retransmission timeout (RTO) timer setting for the use of BP for reliable file (or data) transmission over a relay-based deep-space vehicle communication infrastructure characterized by extremely long latency, lossy data links, and highly asymmetric channel rates. Unlike most studies proposed for terrestrial Internet for which the RTO timer is set equal to or longer than the round-trip time (RTT), we propose to set the RTO timer shorter than the RTT and expect that it will increase delivery efficiency per unit of time. We intend to find an RTO timer setting for maximum data delivery performance of BP, which is considered to be an optimal RTO timer, for deep-space missions. For the first time, analytical models are built for delivery performance involving the RTO timer. Using the built models, we tune the RTO timer toward the highest data delivery performance. The models are validated by running text file transfer experiments using a PC-based testbed and tuning the RTO timer toward the best performance of BP. A performance comparison between the optimal RTO timer proposed in this study and the existing commonly used RTO timers is also presented.

Performance of bundle protocol for deep-space communications

Delay/disruption tolerant networking (DTN) was developed to enable automated network communications despite frequent and lengthy link disruptions and long link delay. DTN communications rely heavily on a bundle protocol (BP) that uses the well-known approach of store and forward with optional custody transfer for which a node agrees to hold BP data units, bundles, in memory (or storage) until its successful reception is acknowledged by the next node. However, in the presence of long link disruptions, little work has been done regarding performance modeling of BP for reliable data transfer in deep-space communications. In this paper, we present a study of BP over a relay-based deep-space communications system, characterized by lengthy link disruptions accompanied by an extremely long propagation delay, lossy data links, and asymmetric channel rates. An analytical model is built to estimate the total delivery time of a file (message) that is transmitted as the contents of one or more BP bundles over a deep-space channel. A model is also built to characterize the dynamics of memory occupancy and release when BP is used for reliable data delivery in the presence of link disruptions. The constructed models are validated by running experiments using a test bed.

Bundle protocol for data delivery over highly asymmetric deep-space channels

Bundle Protocol is the main protocol of delay-/disruption-tolerant networking. Its store-and-forward mechanism and custody transfer option enable it to provide reliable file delivery services in a stressed communications environment. A typical application of Bundle Protocol is for data delivery in a deep-space communication environment, which is characterized by an extremely long signal propagation delay. However, little work has been seen in performance of Bundle Protocol transmission in deep-space communications. In this article, we present an overview of file transfer operation and performance of Bundle Protocol over a relay-based deepspace communication infrastructure characterized by highly asymmetric channel rates based on file transfer experiments. An optimal Bundle Protocol bundle size for the best transmission performance is also under investigation in this article.

Modeling RTT for DTN Protocol Over Asymmetric Cislunar Space Channels

Extensive work has been done in the performance evaluation of delay-/disruption-tolerant networking (DTN) technologies in cislunar and deep-space communications using simulation or emulation file transfer experiments. However, little work has been seen for studying in an analytical manner the performance of DTN protocols for space communications characterized by asymmetric channel rates. Accurate estimate of file delivery latency [i.e., round trip time (RTT)] is essential for efficient transmission control, reliable delivery, and bandwidth usage optimization of a protocol. In this paper, we present a performance analysis of the main DTN convergence layer adapter (CLA), i.e., Licklider transmission protocol (LTP) CLA (LTPCL adapter), over cislunar space channels, focusing on RTT estimates, in the presence of asymmetric channel rates. Analytical models are built for the RTT estimate of LTPCL transmissions with the effect of delay caused by space channel-rate asymmetry, channel impairment, and link disruption taken into consideration. The models are validated by file transfer experiments using a PC-based test bed. It is found that a smaller LTP data block size results in a longer delay in acknowledgement (ACK) transmission and thus a longer RTT. With a block size equal to or larger than a calculated threshold size, the ACK delay is avoided; thus, their RTT is consistently very low, leading to significantly shorter file delivery time and goodput advantage.

RTO timer for best transmission efficiency of bundle protocol in deep-space communications

Delay/disruption tolerant networking (DTN) was proposed as an overlay-network technology for reliable data delivery in a stressed communication environment. A typical application of DTN is for reliable data delivery in deep-space communications, which is characterized by an extremely long signal propagation delay, random and lengthy link disruptions, lossy data links, and asymmetric channel rates. At present, the National Aeronautics and Space Administration (NASA) and several other space agencies consider DTN to be the most effective technology to handle the lengthy link delays and link disconnection inherent in deep-space communications. Bundle protocol (BP), developed as the main protocol of DTN, is used to build an overlay network and to provide custody-based, store-and-forward message transmission.

Memory Dynamics and Transmission Performance of Bundle Protocol (BP) in Deep-Space Communications

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.

Analytical characterization of licklider transmission protocol (LTP) in cislunar communications

The performance of delay/disruption tolerant networking (DTN) protocols in cislunar and deep-space communication systems has previously been studied by simulation. However, little work has been seen in characterizing in an analytical manner the performance of DTN protocols for space with respect to asymmetric channel rates. We present a performance characterization of the recently developed DTN Licklider transmission protocol (LTP) convergence layer adapter (CLA) (or simply LTPCL) over cislunar space channels with data-rate asymmetry. Analytical models are built to characterize LTPCL with respect to the minimum number of bundle protocol (BP) bundles that should be aggregated to avoid delay in acknowledgment (ACK) transmission and the optimal number of bundles to be aggregated for the best transmission efficiency of BP/LTPCL, with the effect of full overhead at all layers taken into consideration. The models are validated by file transfer experiments running BP/LTPCL protocols using a PC-based testbed.

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.

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.

Which DTN CLP is best for long-delay cislunar communications with channel-rate asymmetry?

Delay-/disruption-tolerant networking is considered one of the most suitable technologies to handle the delays and disconnection inherent in space internetworking. To date, little work has been done in evaluating its effectiveness in cislunar communications involving long link delay and highly asymmetric channel rates. In this article, we present an experimental study of DTN convergence layer protocols over a typical cislunar communication infrastructure accompanied by a very long link delay, various asymmetric channel rates, and varying data loss rate. The intent of the work was to find answers to two questions: which CLP is the best for long-delay cislunar communications in the presence of highly asymmetric channel rates, and whether aggregation of bundle protocol bundles is helpful for improving goodput of DTN in the presence of IPN channel asymmetry.