IEEE Communications Magazine • March 2001
approach as well as for traffic management in a
satellite network. STP is based on the basic
operation of Service-Specific Connection-Orient-
ed Protocol (SSCOP). The sender periodically
requests the receiver to report successful recep-
tions, and retransmission is triggered by explicit
selective negative acknowledgment. It uses a
hybrid window and rate congestion control
mechanism. STP performs well in asymmetric
networks since the reverse traffic is significantly
reduced, but it does not distinguish between dif-
ferent sources of packet loss and also leaves the
fairness problem unsolved.
In this article we present an introduction to the
satellite-based Internet. Some possible architec-
tures based on bent-pipe and OBP satellites are
discussed. Several technical challenges, including
multiple access control, IP routing in LEO con-
stellations, unidirectional routing, and satellite
transport issues are investigated. In addition to
what we elaborate on in this article, some impor-
tant research issues are identified as follows:
• IP QoS support. There is no lack of
research regarding QoS support in satellite
systems. However, most of them are based
on ATM QoS classes [8, 15], and the map-
ping of ATM service classes to IP QoS
requirements is a nontrivial problem.
Moreover, the implementation of TCP/IP
over ATM brings much overhead, extra
processing time, and protocol complexity.
Direct support of the Internet integrated
or differentiated service model is desired.
In , multiprotocol label switching
(MPLS) is proposed to support Internet
QoS (integrated or differentiated service)
in a satellite-based network. The integra-
tion of space and terrestrial communica-
tion systems, internetworking different
satellite networks, and the advent of hybrid
satellite systems will bring more redundan-
cy and routing choices. QoS routing in
satellite systems will be a very important
• Traffic and congestion control. To ensure
that the satellite network achieves desired
performance and fulfills the IP QoS require-
ments, a set of mechanisms to control traffic
and avoid congestion is required. A well-
designed MAC protocol will not by itself
prevent congestion in the network. Traffic
management, traffic shaping, policing, and
scheduling are also required. Some preven-
tive congestion control schemes, such as
admission control, and efficient congestion
notification schemes are important to main-
tain the specified QoS guarantees.
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timedia Services on a TDMA-Based Satellite Network,”
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tion Networks,” Int’l. J. Satellite Commun., to appear.
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ATM Broadband Networks,” IEEE Commun. Mag., Mar.
1999, pp. 46–54.
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in Networks with Unidirectional Links,” Proc. 2nd Int’l.
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’97), Budapest, Hungary, Oct. 1997.
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sions for Space Communications,” ACM MobiComm
’96, Nov. 1996.
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mance over Satellite Links,” WOSBIS ’96), Nov. 1996.
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for Internet-Compatible Satellite Networks,” IEEE JSAC,
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Satellite ATM networks,” IEEE Commun. Mag., Mar.
1999, pp. 56–61.
YURONG HU (firstname.lastname@example.org) received her B.E. from
Tsinghua University, China, in 1999. She is currently an
M.Phil. student in the Department of Electrical and Elec-
tronic Engineering at the University of Hong Kong, China.
Her research interests are in the areas of satellite networks,
multimedia communications, and Internet QoS.
ICTOR O.K. LI [F] (email@example.com) received his S.B., S.M.,
E.E., and Sc.D. degrees in electrical engineering and com-
puter science from the Massachusetts Institute of Technol-
ogy in 1977, 1979, 1980, and 1981, respectively. He is
Chair Professor of Information Engineering at the Universi-
ty of Hong Kong, and Managing Director of Versitech Ltd.,
the technology transfer and commercial arm of the univer-
sity. Previously, he was professor of electrical engineering
at the University of Southern California (USC), Los Angeles,
and director of the USC Communication Sciences Institute.
He has published over 200 technical articles, and has lec-
tured and consulted extensively around the world. His
research interest is in information technologies, focusing
on the Internet and wireless networks.
One way to
effects of large
latency is to split
two or more
parts at the