Licklider Transmission Protocol Research Articles

Improving Bundle Routing in a Space DTN by Approximating the Transmission Time of the Reliable LTP

Because the operation of space networks is carefully planned, it is possible to predict future contact opportunities from link budget analysis using the anticipated positions of the nodes over time. In the standard approach to space delay-tolerant networking (DTN), such knowledge is used by contact graph routing (CGR) to decide the paths for data bundles. However, the computation assumes nearly ideal channel conditions, disregarding the impact of the convergence layer retransmissions (e.g., as implemented by the Licklider transmission protocol (LTP)). In this paper, the effect of the bundle forwarding time estimation (i.e., the link service time) to routing optimality is analyzed, and an accurate expression for lossy channels is discussed. The analysis is performed first from a general and protocol-agnostic perspective, assuming knowledge of the statistical properties and general features of the contact opportunities. Then, a practical case is studied using the standard space DTN protocol, evaluating the performance improvement of CGR under the proposed forwarding time estimation. The results of this study provide insight into the optimal routing problem for a space DTN and a suggested improvement to the current routing standard.

A Study of Licklider Transmission Protocol in Deep-Space Communications in Presence of Link Disruptions

Delay/disruption-tolerant networking (DTN) is widely recognized as a key internetworking technology for implementing a space system of systems (SoS). Aimed at being the main data transport protocol of DTN, Licklider transmission protocol (LTP) is expected to provide reliable data transmission service in a challenging space SoS networking environment regardless of random link disruptions. In this paper, a study of LTP in deep-space communication networks in presence of link disruptions is presented. An analytical framework is developed for the effect of multiple random link disruptions on LTP's reliable data delivery in deep-space networks. The study indicates that the models accurately predict the transmission performance of LTP over a deep-space communication channel in presence of multiple link disruptions. A threshold interval value, obtained from the analytical modeling results, is proposed as a means of determining the reducibility of two successive link disruptions to a single disruption; that threshold value is verified by the experiments.

Structural Considerations for Generating and Handling LTP Report Segments from an Interoperability Testing

Delay- and disruption-tolerant networking (DTN) technology is increasingly being considered for deep space exploration missions. In particular, DTN is being considered for trunk-line communications between ground and lunar elements of the Artemis program. Licklider transmission protocol (LTP) is a DTN protocol that supports reliable data transmission within a network and, as such, functions as a necessary “convergence-layer” protocol in the architecture. Korea Aerospace Research Institute (KARI) has recently developed an LTP reference implementation and performed an interoperability test with the National Aeronautics and Space Administration (NASA)’s Interplanetary Overlay Network (ION) DTN software. The test revealed that there can be significant variation in issuing report segments and data segment retransmission, which can lead to errors or malfunction during LTP transaction. This paper presents the results of the interoperability test between different implementations of LTP together with some implementation considerations suggested by the results to overcome the issues of the interoperability among different LTP implementations.

Performance improvement of licklider transmission protocol in complex deep space networks based on parameter optimization

A reasonable parameter configuration helps improve the data transmission performance of the Licklider Transmission Protocol (LTP). Previous research has focused mainly on parameter optimization for LTP in simplified scenarios with one to two hops or multihop scenarios with a custody mechanism of the Bundle Protocol (BP). However, the research results are not applicable to communications in Complex Deep Space Networks (CDSNs) without the custody mechanism of BP that are more suitable for deep space communications with LTP. In this paper, we propose a model of file delivery time for LTP in CDSNs. Based on the model, we propose a Parameter Optimization Design Algorithm for LTP (LTP-PODA) of configuring reasonable parameters for LTP. The results show that the accuracy of the proposed model is at least 6.47% higher than that of the previously established models based on simple scenarios, and the proposed model is more suitable for CDSNs. Moreover, the LTP parameters are optimized by the LTP-PODA algorithm to obtain an optimization plan. Configuring the optimization plan for LTP improves the protocol transmission performance by at least 18.77% compared with configuring the other parameter configuration plans.

Performance modeling of Licklider transmission protocol (LTP) via proactive transmission of signaling segments in deep‐space network

SummaryDelay‐tolerant networking (DTN) bundle protocol is considered one of the best transmission protocols to be used in space communications by NASA. There are studies that evaluated the performance, measuring the total transfer time of a complete file from sender to receiver, of the DTN protocol via simulation or emulated experiments beyond the real space‐based experiences. In addition, there is a very few additional research works available for the modeling of the Licklider transmission protocol (LTP). However, these past studies on LTP modeling are implemented as a Logarithmic approach that is based on the calculation of loss segments in file delivery. In this work, the approach is investigated in a different manner. Specifically, the performance model was created based on the probability of the segment's successful delivery on the LTP. Moreover, the original model is enhanced via introducing a burst of transfer and equal interval distribution of signaling segments, specifically check point (CP), along with the retransmission time out (RTO). The results from the developed model for the original DTN protocol and enhanced versions align with the results obtained by PC‐based testbeds.

An Analytical Framework for Disruption of Licklider Transmission Protocol in Mars Communications

As one of the main data transport protocols of delay/disruption-tolerant networking (DTN), Licklider transmission protocol (LTP) is designed to provide reliable data delivery in an interplanetary Internet environment characterized by frequent and lengthy link disruptions and extremely long signal propagation delays. Some studies have been done on the performance of LTP in cislunar and Mars communications. However, to date the effect of link disruption on LTP for Mars communications has received little attention. In this paper, an analytical framework is presented for the effect of link disruption on reliable data delivery and performance of LTP in Mars communications. The analysis focuses on how various link disruptions affect the number of transmission attempts, the consequent round-trip time (RTT) of data exchange, and the resulting goodput performance of LTP for reliable data block delivery in Mars communications. The analytical framework is validated by means of realistic data block transmission experiments using a PC-based experimental infrastructure, and it can be used to predict the performance of LTP over a deep-space vehicle communication channel in presence of link disruption.

Review on Free-Space Optical Communications for Delay and Disruption Tolerant Networks

The increase of data-rates that are provided by free-space optical (FSO) communications is essential in our data-driven society. When used in satellite and interplanetary networks, these optical links can ensure fast connections, yet they are susceptible to atmospheric disruptions and long orbital delays. The Delay and Disruption Tolerant Networking (DTN) architecture ensures a reliable connection between two end nodes, without the need for a direct connection. This can be an asset when used with FSO links, providing protocols that can handle the intermittent nature of the connection. This paper provides a review on the theoretical and state-of-the-art studies on FSO and DTN. The aim of this review is to provide motivation for the research of an optical wireless satellite network, with focus on the use of the Licklider Transmission Protocol. The assessment presented establishes the viability of these networks, providing many examples to rely on, and summarizing the most recent stage of the development of the technologies addressed.

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.

Transmission Efficiency of Licklider Transmission Protocol (LTP) and Bundle Protocol (BP) in DTN Architecture

From Near-Earth orbit (NEO) to Earth-Sun Lagrangian points will continue to be a majority of Near Earth missions ranging from Near-Earth orbit (NEO) to Earth-Sun Lagrangian points will continue to be a majority of future space missions. A few works have been done with delay/disruption tolerant networking (DTN) technology for Near-Earth orbit (NEO)-space center and deep space communications and provided feasibility for its adoption in NEO-space and deep space missions. [1] However, no much work has been done to fully evaluate the transmission efficiency of DTN in such an environment, especially in the presence of long link disruption, data corruption and lost rate, and link asymmetry. In this paper, we present an experimental performance evaluation of DTN architecture and protocol stack, with Licklider transmission protocol (LTP) serving as a convergence layer adapter (CLA) underneath bundle protocol (BP), in typical NEO-satellite system and deep space communication infrastructures accompanied by a very long link delay, various packet corruption and lost rates, and channel rate symmetry and asymmetry. In addition, we present an experimental research of the transmission efficiency of DTN custody transfer with long link delay. The experiment was conducted by performing realistic file transfers over a virtual server-based test-bed.

Network evaluation and protocol deployment for complex deep-space networks based on DTN

Previous research on deep-space networks based on delay-tolerant networking (DTN) has mainly focused on the performance of DTN protocols in simple networks; hence, research on complex networks is lacking. In this paper, we focus on network evaluation and protocol deployment for complex DTN-based deep-space networks and apply the results to a novel complex deep-space network based on the Universal Interplanetary Communication Network (UNICON-CDSN) proposed by the National Space Science Center (NSSC) for simulation and verification. A network evaluation method based on network capacity and memory analysis is proposed. Based on a performance comparison between the Licklider Transmission Protocol (LTP) and the Transmission Control Protocol (TCP) with the Bundle Protocol (BP) in various communication scenarios, a transport protocol configuration proposal is developed and used to construct an LTP deployment scheme for UNICON-CDSN. For the LTP deployment scheme, a theoretical model of file delivery time over complex deep-space networks is built. A network evaluation with the method proposed in this paper proves that UNICON-CDSN satisfies the requirements for the 2020 Mars exploration mission Curiosity. Moreover, simulation results from a universal space communication network testbed (USCNT) designed by us show that the LTP deployment scheme is suitable for UNICON-CDSN.

Transmission Performance of Licklider Transmission Protocol (LTP) and Bundle Protocol (BP) in DTN Architecture

From Near-Earth orbit (NEO) to Earth-Sun Lagrangian points will continue to be a majority of future space exploration quests. A few works have been done with long distance delay/disruption tolerant networking (DTN) technology for Near-Earth orbit (NEO) transmission and provided feasibility for its adoption in NEO and long distance exploration quests. [1] However, no much work has been done to fully evaluate the performance of DTN architecture in such an environment, especially in the presence of long link disruption, data corruption and loss, and link asymmetry. [2] In this research, we present an experimental performance evaluation of DTN architecture and protocol stack, with Licklider transmission protocol (LTP) serving as a convergence layer adapter (CLA) underneath bundle protocol (BP), in typical NEO and long distance transmission infrastructures accompanied by a very long link outage, various packet corruption and loss rates, and channel rate symmetry and asymmetry. [3] In addition, we present an experimental investigation of the performance of DTN custody transfer with long link break. The experiment was conducted by performing realistic file transfers over a virtual server test-bed.

Study on Checkpoint Timer Optimal Setup of Licklider Transmission Protocol

As the main data transport protocol of delay/disruption-tolerant networking, Licklider transmission protocol (LTP) is developed to provide reliable and highly efficient data delivery over unreliable deep-space and interplanetary communication channels. For reliable data delivery, a checkpoint (CP) segment of LTP is sent, with a timer set (or, simply, CP timer) to check the arrival status of the entire data block at the receiver, and it is retransmitted upon the expiration of the CP timer prior to reception of an acknowledgment. Little work has been seen in analysis of the CP timer length for optimal performance of LTP in energy-efficient, reliable data delivery. In this article, a packet-level analysis of the CP timer length setting is presented for the reliable data delivery of LTP over unreliable deep-space communication channels based on realistic file transfer experiments conducted using a PC-based testbed. It is our intent to find an optimal CP timer setting so that the reliable file delivery in deep space is ensured with a minimum number of retransmission attempts. By this, the energy-efficient, reliable data delivery of LTP can be achieved in deep-space communications.

HSLTP—An LTP Variant for High-Speed Links and Memory Constrained Nodes

Delay/disruption-tolerant networking architecture relies on the use of Licklider Transmission Protocol (LTP) on interplanetary links. LTP loss recovery is based on automatic repeat request retransmissions, which, when the propagation delay is very long, are costly. Alternatively, losses could be recovered by using Packet Layer Forward Error Correcting codes, as done by the authors in ECLSA (error Coding Link Service Adapter), recently presented in a companion paper, where LTP segment retransmissions are limited to the unlikely case of decoding failures. However, on high bandwidth-delay-product links, the very possibility of segment retransmission requires that a huge number of Rx buffers be available. To resolve this problem, high-speed LTP, presented here, has a more disruptive approach than ECLSA: it enforces almost one-to-one correspondence between LTP blocks and FEC codewords, and never requires LTP segment retransmissions. In the unlikely case of a FEC failure, the partially received block is discarded and its bundles are resent directly by the bundle protocol. The advantages and disadvantages of this approach are explored in the article. On nodes limited in memory, the results are significantly improved.

Packet Layer Erasure Coding in Interplanetary Links: The LTP Erasure Coding Link Service Adapter

Interplanetary networks are affected by long propagation delays, intermittent connectivity, possible packet losses due to residual errors, and other impairments. To cope with these challenges, the delay-/disruption-tolerant networking (DTN) architecture utilizes the Licklider transmission protocol (LTP) as convergence layer on space links. The LTP reliable service (red) relies on Automatic Repeat reQuest, but very long propagation delays make packet layer forward error correcting (PL-FEC) codes very appealing to protect LTP segments from losses. The key advantage of FEC is that LTP retransmissions would be limited to the unlikely case of decoding failures. To this end, a new FEC-based protocol, to be inserted immediately below LTP, the erasure coding link service adapter (ECLSA), is presented here. ECLSA is completely transparent to LTP, relies on two alternative external libraries for coding/decoding, LibecDLR and OpenFEC, both using low density parity check codes and it is fully integrated with the ION DTN software package of NASA-JPL. This paper aims to provide a solid description of ECLSA, including features functional in a real deployment (such as the dynamic selection of codes). Performance is evaluated at the end of the paper, with nearly ideal results. ECLSA is released as free software and is already included in the “contrib” section of ION.

Analysis of Licklider Transmission Protocol for Reliable File Delivery in Space Vehicle Communications With Random Link Interruptions

Delay/disruption tolerant networking (DTN) was proposed as a networking architecture for reliable data delivery in space vehicle communications despite long propagation delays and/or lengthy link disruptions. As one of the main data transport protocols of DTN, Licklider transmission protocol (LTP) was proposed by the NASA for reliable data delivery in challenging space environments in which the existing transport protocols of DTN, TCP, and UDP do not perform effectively. Pair-wise comparisons among LTP, TCP, and UDP running in the DTN stack have previously been done using statistical methods; evaluation results and performance analysis are available in the existing LTP research literature. However, there is as yet no solid analytical model of LTP performance in the presence of link disruptions. In this paper, we present an analytical method to predict transmission performance of LTP for reliable file delivery in space vehicle communications with focus on the expected file delivery delay (or latency) over space channels characterized by random link disruptions. Realistic file-transmission experiments using a PC-based infrastructure are presented to validate the analytical models. The analysis and study results presented in this paper are expected to be useful in understanding the impact of transmission conditions and configurations, on the efficiency of LTP when deployed for reliable data delivery in space missions using communication links that are subject to frequent and random interruptions.

A Congestion Control Approach for Licklider Transmission Protocol

Delay Tolerant Networks (DTN) are designed to deal with the long delay of space network and frequent link interruption, in 2002. Licklider Transmission Protocol (LTP) was designed to replace the Internetworking Protocol (IP) and Transmission Control Protocol (TCP) in the DTN protocol stack. However, LTP has no congestion control mechanism. If a packet is dropped, the performance of the network will be worse. To deal with this problem, this paper proposes the Ecn-based TFRC Licker Transmission Protocol (ET-LTP) which extends the LTP data packet to record the network condition. The ET-LTP refers to congestion control approach applied on streaming media transmission on this question. A detailed control strategy is proposed in this paper as well. Finally, the simulations are built to test the performance of the ET-LTP. The results prove that the ET-LTP is more robust than LTP when facing the congestion.

Analysis of the Block Delivery Time of the Licklider Transmission Protocol.

The Licklider transmission protocol is a point-to-point communication protocol designed for space links, which commonly involve extreme delays, disruptions, and lossy transmissions. The protocol sends application data in blocks, which in turn are sent in segments. It achieves reliable block delivery through multiple transmission rounds, each one re-sending the segments lost during the previous round. This retransmission process drives protocol performance. We derive exact and approximate methods to find the average number of rounds per block. Then, we estimate the block delivery time and other metrics using this value. We found that the common practice of matching segment lengths to the maximum transfer unit of the link layer may lead to suboptimal performance. The models provide accurate protocol performance prediction, which can help to optimize protocol parameters for specified operating conditions.

Design and performance evaluation of LTP enhancements for lossy space channels

SummaryThis paper deals with the performance of Licklider Transmission Protocol (LTP) in space environment, focusing on the impact of segment losses and the design of possible improvements. The in‐depth analysis of retransmission mechanisms carried out in the paper shows that, while LTP already achieves delivery time performance very close to the theoretical optimum in ideal conditions (no losses) and when losses affect data segments, a substantial improvement is still possible concerning signaling segments, whose loss can result in a significant increase of the LTP block delivery time. To this end, 2 simple enhancements, the Closing State and the proactive retransmission of signaling segments, are proposed and evaluated in the paper. Both enhancements have been added as optional features to the original Interplanetary Overlay Network LTP implementation (ION 3.5.0), in order to evaluate their effectiveness on a GNU/Linux testbed running the full protocol stack. Results presented in the paper confirm the validity of the proposed enhancements, as they significantly reduce the average delivery time in the presence of high losses and provide the additional advantage, even when losses are relatively low, of largely reducing the difference between average and worst cases.

Licklider Transmission Protocol for GEO-Relayed Space Internetworking

As one of the most important convergence layer (CL) protocol for delay/disruption-tolerant networking (DTN), Licklider transmission protocol (LTP) is designed for deep space communications, but it has rarely been considered for near earth applications. In this paper, LTP is proposed instead of TCP as CL with Bundle protocol (BP) for future application in GEO-relayed space networks (GRSN). Analytical models are built to estimate the file delivery time of LTP in GRSN. Experiments are also conducted on our computer based testbed in emulation of the basic scenarios during data transmission from LEO satellite to a ground station in GRSN. The results show that in transmission efficiency BP with LTPCL outperforms other protocols, such as BP with TCPCL, direct terrestrial TCP (TCP Cubic) and TCP variants (TCP Hybla) for space segments in most scenarios. It could be envisioned that DTN with LTPCL for space segment is currently the best choice for future GEO-relayed space internetworking. Moreover, performance of two different networking schemes,i.e. the on-board DTN routers and the bent-pipe relays are compared. It is observed that bent-pipe relays outperform the on-board DTN routers scheme when the channel condition is good, while the on-board DTN routers scheme performs better with high data loss ratio.

Performance Modeling of LTP-HARQ Schemes Over OSTBC-MIMO Channels for Hybrid Satellite Terrestrial Networks

Recently, with the development of Ka-band high throughput satellites and hybrid satellite-terrestrial networks, distributed/virtual multiple-input multiple-output (MIMO) technology over satellites have attracted considerable research interest. In this paper, a novel performance analysis framework is proposed for MIMO with orthogonal space-time block coding under Licklider transmission protocol (LTP) for emerging hybrid satellite terrestrial networks, where we derive the closed-form expressions of the mean number of transmission rounds by using Laplace transform for reliable data delivery in automatic repeat request (ARQ) and hybrid-ARQ schemes. Furthermore, we obtain the throughput expressions and unit information energy for lossless- and truncated-(H)ARQ schemes, and the maximum throughput and minimum unit information energy value on information rate. We also investigate the LTP file delivery time over Rayleigh and Rician fading channels. Simulations results are provided to demonstrate the validity of our theoretical results and show the effect of antenna number on the system performance.