Aerospace and Electronic Systems - December 2018 - 40

Feature Article:

DOI. No. 10.1109/MAES.2018.180069

Queueing Analysis of DTN Protocols in Deep-Space
Communications
Guannan Yang, Nanjing University, Jiangsu, China and Nanjing University Jinling
College, Jiangsu, China
Ruhai Wang, Lamar University, Beaumont, TX, USA
Kanglian Zhao, Xinggan Zhang, Wenfeng Li, Nanjing University, Jiangsu, China
Xiongwen He, Beijing Institute of Spacecraft System Engineering, Beijing, China

INTRODUCTION
Delay/disruption tolerant networking (DTN) [1] is proposed as an
internetworking architecture for reliable data delivery despite a long
propagation delay and/or lengthy link disruptions. DTN targets challenging networking environments where traditional networking protocols such as the terrestrial Transmission Control Protocol/Internet
Protocol (TCP/IP) typically do not work effectively. The challenging
problem of mission control and data delivery in space communications is a typical application scenario of the DTN technology. Reliable
and highly efficient data delivery of DTN relies heavily on the bundle
protocol (BP) [2]. BP is intended to establish an overlay network that
is able to withstand intermittent data link connectivity in the delivery
of DTN data units, termed bundles. BP adopts a store-and-forward
mechanism and a custody transfer option for transmission reliability.
Various protocols can be operated immediately under the BP
layer at the convergence layer (CL) in a DTN protocol stack. These
protocols are termed "convergence layer protocols," and they send
and receive bundles on behalf of BP. The Licklider Transmission
Protocol (LTP) [3], [4] is one of the widely adopted CL protocols to
provide retransmission-based reliability over unreliable space communication channels that are typical of frequently interrupted link
and/or long delay. For file transmission using the BP/LTP architecture, a file is divided into fragments in bundles that are ultimately
encapsulated in protocol data units (PDUs) of LTP at the CL. The
PDU of LTP is known as segment. The LTP segments are encapsulated by the layers underneath the CL and then formed as packets
Authors' current addresses: G. Yang, K. Zhao, X. Zhang, W.
Li, School of Electronic Science and Engineering, Nanjing
University, Nanjing, Jiangsu Province 210093 P. R. China; corresponding author is K. Zhao (zhaokanglian@nju.edu.cn); R.
Wang, Phillip M. Drayer Department of Electrical Engineering,
Lamar University, 211 Red Bird Lane, Beaumont, Texas 77710;
X. He, Beijing Institute of Spacecraft System Engineering,
Beijing, 100076 P. R. China.
Manuscript received April 22, 2018, and ready for publication
June 12, 2018.
Review handled by M. De Sanctis.
0885/8985/18/$26.00 © 2018 IEEE
40

for transmission. LTP provides both reliable and unreliable transmission service according to the application requirements. Like the
traditional TCP, LTP performs automatic detection of data loss and
retransmission of the loss data. However, unlike TCP, it is not expected to exhibit severe performance degradation over extremely
long round-trip delays. For a comparison of protocol design and
operation between TCP and LTP, see [5].
Extensive work has been done in studying the performance of
BP/LTP for deep-space communications. We discuss this work in
the next section. However, there is a lack of an analysis of queueing process of BP/LTP for reliable file delivery. In this article, we
present an analytical method for predicting the transmission performance of the main DTN protocol stack-LTP operating underneath BP, i.e., BP/LTP. The analysis focuses on the average queue
delay and average file delivery delay in space communications
characterized by high data loss and intermittent link connectivity.
The file transmission experiments use a PC-based testbed that is
also conducted to validate our theoretical models. The analysis and
the result of the study presented in this article are expected to be
beneficial to practical deployment and optimization for the DTN.

RELATED WORK
A significant amount of effort has been done in developing networking protocols and architectures (including DTN) for satellite
and space communications, space networks, deep-space communications, and similar scenarios, leading to development of a variety
of protocol solutions [6]-[11]. Numerous literature surveys [12]-
[16] have also been conducted on these technologies.
Wang et al. have conducted a series of studies on protocol development and analysis of DTN, focusing on the TCP- and LTPbased convergence layers, in space communications [17]-[19]. In
[17], the team presented an experimental evaluation of the DTN architecture over a simulated cislunar communication channel with a
focus on the LTP convergence layer on top of User Datagram Protocol (UDP)/IP (i.e., BP/LTP/UDP/IP). A similar study done with
the TCP convergence layer under BP, using an implementation of
DTN-2, is presented in [18]. In [19], the team studied the effect of
data bundles aggregation at LTP layer in space communications

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DECEMBER 2018

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