Download April 15, 2008 - Access Methods for Satellite Networks

University of Kansas | School of Engineering
Access Methods for Satellite Networks providing
Internet Services
Anusha Reddy Bethi
Department of Electrical Engineering
and Computer Science
University of Kansas | School of Engineering
Outline
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Introduction
Motivation
Fundamentals of Satellite Systems
Characteristics of Satellite Communications
Satellite based Internet Architecture
Access Methods and Protocols
Routing Issues in Satellite Systems
Satellite Internet Services and Applications
Future of Satellite Communications
Summary
References
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Introduction
 Satellite communication system is an excellent candidate to provide
broadband integrated Internet services to globally scattered users.
 In a satellite-based Internet system, satellites are used to interconnect
heterogeneous network segments to provide ubiquitous direct Internet access
to homes and businesses.
 Various features:
• Global Coverage
• Broadcast capability
• Bandwidth-on-demand flexibility
• Support mobility
• Point-to-multipoint and multipoint-to-multipoint communications
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Motivation
 The most important reasons for the diffusion of satellite communications:
 Need for Broadband integrated Internet services to globally scattered users.
 Required in locations where terrestrial internet access is not available.
(Example: Rural or remote areas)
 In locations which move frequently or fast and flexible connections are
necessary.
(Example: maritime and aeronautical)
 High bandwidth
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Fundamentals of Satellite Communications
Elements of Satellite system:
Space segment
• Satellite or fleet of Satellites
Ground segment
• Gateway stations
• Network Coordination center(NCC)
• Network Operation center(NOC)
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F
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PSTN: Public Switched
Telephone Network
PLMN: Public Land
Mobile Network
PDN: Public Data
Network
TT&C: Telemetry,
Tracking and Command
NCS/NOC: Network
Coordination/operations
center
Elements of a Satellite System
From:Satellite communications systems move into the twenty-first century
Leonard S. Golding
Hughes Network Systems, Inc., Germantown, MD
20876, USA
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Space segment:
Composed of Satellites classified into the following according to the orbit altitude
above the earth’s surface.
Geostationary orbit satellite (GSO)
• Geostationary Earth Orbit (GEO)
Non-geostationary orbit satellite (NGSO)
• Medium Earth Orbit (MEO) satellite
• Low Earth Orbit (LEO) satellite
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Ground segment:
 Gateway stations
• Network interfaces between external networks and satellite network.
• Perform protocol, address and format conversions
 NCC and NOC handle the following:
• Network resource management
• Satellite operation
• Orbiting control.
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Satellite Payload
 The Payload is the communication subsystem, which carries out the communications
mission (receiving and transmitting information).
 It has one or more antennas, receivers, and transmitters, as well as hardware and
software that perform some information processing.
 It must be Simple and Robust.
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Characteristics of Satellite Communications
Frequency bands and services
Bandwidth efficiency
Latency and availability
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Frequency Bands and Services
Frequency Band
Frequency (GHz)
Type of Service
Example Systems
L-Band
1.5—1.6
Mobile voice and
data, distress
(downlink)
Inmarsat, Thurya
S-Band
2.4—2.6
Mobile voice and
data
ICO/Globalstar
C-Band
4—6
International
dialed and leased
circuits,
Broadcast TV
Intelsat, PanAmSat,
Dish
X-Band
7—8
Military services
Skynet 4 and 5, Nato
Ku-Band
11—14
TV broadcast, business
systems,
broadband Internet
to homes and
offices
SES-Astra, Eutelsat,
Intelsat
Ka-Band
20—30
Broadband to
homes and offices
Hughes,
Spaceway
V-Band
40—50
Non-real-time
fixed services
Hughes,
Galaxy
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From: The use of satellite for multimedia communications -M Fitch
BT Technology Journal • Vol 21 No 3 • July 2003
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Comparison of Bandwidth Efficiency for Satellite and Terrestrial
Systems
Service
Bandwidth efficiency
(bit/s/Hz)
Satellite mobile
0.7
Satellite DTH TV
1
GSM data
0.4
IS-95
1
Cable TV
2-6
Department of Electrical Engineering
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From: The use of satellite for multimedia communications -M Fitch
BT Technology Journal • Vol 21 No 3 • July 2003
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Latency and Availability
 Latency:
 Round-Trip delay of 250-280ms makes Latency noticeable in highly
interactive services like voice and games.
 This will result in an overall reduction in throughput and reliability.
 Availability:
 Though, availability is dominated by weather conditions such as rain and
clouds several Power control and other fade mitigation techniques can be used to
overcome weather effects.
 Satellite Internet services are typically dimensioned to provide 99.9% availability.
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Satellite based Internet Architecture
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The satellite-based Internet has several architectural options due to the diverse designs
of satellite systems, in orbit types (GSO, MEO, LEO), payload choice (OBP or bent
pipe), and ISL designs.
Three types of Satellite-Based Internet Architectures:
Bent pipe Architecture
OBP and ISL Architecture
Internet access via DBS
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Satellite Based Internet with Bent-Pipe Architecture
 The satellites adopted can be
GEO, MEO or LEO. They serve as
Bent-Pipes. They act as Repeaters
between two communication points
on the ground. There is no Onboard
Processing.
 It provides Internet access as well
as data trunking service.
 The satellite network interfaces
with the ground Internet
infrastructure via GSs on the Earth.
It may be the only access method for
some users (e.g., user A) when no
other communication method is
available, or a backup connection in
addition to an existing terrestrial
access network (e.g., user B).
 Though this architecture is simple
and easy to implement it lacks direct
communication paths in space and
results in low spectrum efficiency
and long latency.
Department of Electrical Engineering
and Computer Science
From: Satellite Based Internet Technology and Services:A Tutorial
Yurong Hu and Victor O. K. Li, The University of Hong Kong
IEEE Communications Magazine • March 2001
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Satellite Based Internet with OBP and ISL Architecture
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OBP and ISLs may be used to
help construct a network in the sky.
 This architecture is a combination
of access and backbone network.
 Teledesic is one such system
using a constellation of 288 LEO
satellites with ISLs.
 The rich connectivity in space will
provide more flexibility but also
bring complex routing issues.
From: Satellite Based Internet Technology and Services:A Tutorial
Yurong Hu and Victor O. K. Li, The University of Hong Kong
IEEE Communications Magazine • March 2001
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Internet Access via DBS
 Due to Internet traffic asymmetry where
considerably more data is transmitted from the
server to the end user than in the reverse direction
(e.g., Web browsing), there is a trend to offer
Internet access via Direct Broadcast Satellites
(DBSs) used for television broadcasting.
 Each home has a receive-only satellite dish to
collect data delivered in the high-speed satellite
broadcast channel. The reverse path to the server
is provided by a terrestrial link.
 Hughes’s DirecPC system is an example.
 In order to make full use of the wide bandwidth
of satellite broadcast links, DBS is also extended
by using the receive-only terminals as gateways to
interconnect remote networks.
Department of Electrical Engineering
and Computer Science
From: Satellite Based Internet Technology and Services:A Tutorial
Yurong Hu and Victor O. K. Li, The University of Hong Kong
IEEE Communications Magazine • March 2001
17
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Examples of some worldwide broadband satellite systems that provide high-speed
Internet service
From: Satellite Based Internet Technology and Services:A Tutorial
Yurong Hu and Victor O. K. Li, The University of Hong Kong
IEEE Communications Magazine • March 2001
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Access Methods and Protocols
Satellite Protocol Reference Model
SI-SAP: Satellite-IndependentService Access Point
IPV4/IPV6: Internet Protocol version4/
Internet Protocol version6
UDP: User Datagram Protocol
TCP: Transport control Protocol
Figure 1. Satellite protocol stack architecture by ETSI TC-SES/BSM.
From: Cross-Layer Protocol Optimization for Satellite Communications networks: A Survey
Giovanni Giambene and Sastri Kota
INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING
Int. J. Satell. Commun. Network. 2006; 24:323–341 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/sat.853
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MAC Protocols for satellite links
 MAC schemes based on the bandwidth allocated can be categorized into
following groups:
Fixed Assignment
• FDMA
• TDMA
• CDMA
Random Access (used by VSAT and USAT)
• ALOHA
Demand Assignment
• Demand Assignment Multiple Access(DAMA)
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Demand Assignment Multiple Access(DAMA)
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In situations where the traffic of each earth station is bursty, fixed allocation of satellite bandwidth
to earth stations is inefficient. It is desirable to dynamically allocate the transponder bandwidth in
response to earth station requests, using a Demand Assignment Multiple Access (DAMA) protocol.
Increases system throughput.
A resource request must be granted before actual data transmission. After a successful reservation,
bandwidth is allocated on an overall FDMA or TDMA architecture, and data transmission is
guaranteed to be collision-free.
The reservation process can be implicit or explicit.
The reservation may be made under centralized control or distributed control.
For Internet data applications, there exist several DAMA protocols that operate in this efficient ondemand reservation mode.
Pure DAMA (P_DAMA) assigns bandwidth based on the traffic load of earth stations without
considering how to utilize the unassigned free bandwidth.
Combined Free DAMA (CFDAMA) removes this shortcoming by allocating the free bandwidth
according to some schemes (such as round robin R_CFDAMA.)
Weighted CFDAMA (W_CFDAMA) allocates free bandwidth in proportion to the traffic load of
different stations one RTT before.
But better among these protocols is the Predictive DAMA(PRDAMA).
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Predictive Demand Assignment Multiple Access(PRDAMA)
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Enhancement of W_CFDAMA
PRDAMA allocates free bandwidth resources by estimating the positive varying trend of the
Internet traffic to facilitate prediction of the bandwidth requirements of the earth stations.
It can work with both explicit and implicit reservations.
Simulation results demonstrate that PRDAMA achieves a lower average delay and delay jitter
compared with other DAMA protocols under highly bursty traffic due to its accurate traffic trend
prediction.
 PRDAMA Protocol:
 The PRDAMA protocol can be applied to both bent-pipe and on-board processing (OBP)
satellite systems.
 It can be used in both centralized control or distributed control.
 Here we adopt a distributed mode so that it can be used with bent-pipe satellite systems and save
one RTT time and can also be used with OBP satellite systems with centralized processing.
 The physical TDMA or MF-TDMA channel (frame) is used and divided into fixed control and
data sub-frames. The data sub-frame is divided into time slots each holding one packet.
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Uplink TDMA frame structure
Figure: Uplink TDMA frame structure.
From: A predictive demand assignment multiple access protocol for Internet access over broadband satellite networks
Zhifeng Jiangy and Victor C. M. Leung
INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING
Int. J. Satell. Commun. Network. 2003; 21:451–467 (DOI: 10.1002/sat.759)
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Implementation of PRDAMA
Figure. PRDAMA states in earth station
From: A predictive demand assignment multiple access protocol for Internet access over broadband satellite
networks
Zhifeng Jiangy and Victor C. M. Leung
INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING
Int. J. Satell. Commun. Network. 2003; 21:451–467 (DOI: 10.1002/sat.759)
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System model
Model of a GEO Satellite System
From: A predictive demand assignment multiple access protocol for Internet access over broadband satellite networks
Zhifeng Jiangy and Victor C. M. Leung
INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING
Int. J. Satell. Commun. Network. 2003; 21:451–467 (DOI: 10.1002/sat.759)
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Performance comparisons with other DAMA protocols
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PRDAMA improves the performance of satellite system by taking in account of application layer
traffic characteristics in the MAC protocol operation.
The performance of PRDAMA is superior in comparison with the other DAMA protocols
Lower average delay
Lower average delay jitter
This can be attributed to the accuracy and effectiveness of the proposed predictive assignment
method, which results in more packets being sent sooner using free bandwidth assignments
without having to wait for the bandwidth reservations to be processed.
Improves satellite communication system throughput or bandwidth utilization.
The effectiveness of the method is based upon accurate prediction of the trends of each earth
station’s traffic source, thus enabling free assignments to be directed to those earth stations that
have a predicted need and avoiding needless free assignments to other earth stations that are not
in need.
This predictive assignment method is also a good candidate for MAC protocols in other types of
radio networks.
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Transport Control Protocol(TCP)
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Support application protocols like FTP(File transfer Protocol), HTTP and BGP( Border
Gateway Protocol) External routing Protocol.
 TCP Performance over satellite networks
 TCP uses a positive feedback mechanism to achieve rate control and reliable delivery.
 The long latency of satellite links (especially GSO links) increases the TCP end-to-end
delay
 The slow feedback weakens the functionality of rate control and congestion avoidance and
thus affect the throughput.
 Large variations in RTT caused by dynamic topology in LEO constellation Networks result
in false timeouts and retransmissions.
 Satellite links are subject to various impairments (i.e., interference, fading, shadowing, and
rain attenuation). Therefore, a high bit error rate (BER) is expected.
 Satellite Network asymmetry can also impair TCP performance
 Occurs in two situations.
 In Asymmetric DBS Internet access architecture.
 Bandwidth asymmetry in interactive satellite terminals.
 Fairness issue between different TCP connections with various RTTs.
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Performance Enhancing Proxies
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TCP Selective Acknowledgement (SACK)
TCP for transaction (T/TCP)
Persistent TCP connection
Path maximum transfer unit (MTU) discovery mechanism
FEC is employed in link layer protocols
Splitting TCP connections over satellite links:
• TCP spoofing
• TCP splitting
• Web caching
 Satellite Transport Protocol (STP)
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Routing Issues in Satellite Systems
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Dynamic Routing issue in LEO constellation
(Due to satellite movements)
 Mechanisms to handle the issue
• DT-DVTR (Discrete-Time Dynamic Virtual Topology Routing)
• VN (Virtual Node)
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IP Routing at the Satellites
 ATM Switching at the Satellites
 External Routing Issues
 Used for inter-AS routing
 Unidirectional routing in internet Access via DBS
 Mechanisms to handle the issue
• Static routing
• Routing Protocol Modification
• Tunneling
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Satellite Internet Services and Applications
Basic three types of Satellite Internet Services are:
 One-way Multicast Internet Service
 Used for Internet Protocol (IP) multicast-based data, audio and video distribution.
 Internet content such as web pages are distributed over a one-way system by "pushing"
them out to local storage at end user sites, though full interactivity is not possible.
 This is much like TV or radio content which offers little user interface.
 One-way with Terrestrial Return Internet Service
 This service is used with traditional dial-up access to the Internet, with outbound data
traveling through a telephone modem, but downloads sent via satellite at a speed near that
of broadband Internet access.
 Another type of 1-way satellite internet system involves the use of General Packet Radio
Service (GPRS) for the back-channel.
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 Two-way Satellite Internet Service
 This service sends data from remote sites via satellite to a hub, which then sends the
data to the Internet.
 The satellite dish at each location must be precisely positioned to avoid interference
with other satellites.
 Also, each location must use power management to adjust the amount of transmit
power to compensate for conditions such as rain fade.
 There are several types of two way satellite Internet services, including time
division multiple access (TDMA) and single channel per carrier (SCPC).
 Two-way systems can be simple VSAT terminals with a 60-100cm dish and output
power of only a few watts intended for consumers and small business or larger
systems which provide more bandwidth.
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Various Satellite Broadband Internet Technologies
HughesNet
 It is the brand name of the one-way and two-way satellite broadband Internet technology and service
in U.S. and Europe owned by Hughes Network Systems.
 The service was originally called DirecPC and was only available as a one-way satellite Internet
option, as uploading was accomplished with a dial-up modem connection.
 It uses Internet Access via Direct Broadcast Satellites(DBS).
 HughesNet satellite Internet system uses a VSAT platform for two-way Internet service via satellite.
 It uses FSS(Fixed Service Satellite)-type Ku band(from 11.45 to 11.7 and 12.5 to 12.75 GHz in
Europe, and 11.7 to 12.2 GHz in the United States) satellites for transmission of data from the
HughesNet network operations center's Internet connection to its customers' personal computers.
WidBlue
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The company offers satellite broadband Internet services to both home and business customers.
WildBlue uses the Ka-band instead of Ku band exclusively for both the receiving end and the return
path on two satellites( Anik-F2 and WildBlue-1) using VSAT technology.
For improved performance, it uses many "spot beams" instead of a single, broad beam covering the
entire market.
It has adopted DOCSIS technology to reduce costs while maintaining quality of service.
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It offers 1.5 megabits per second download and 256 kilobits per second upload.
Real-time interactive applications sometimes perform poorly because of the actual distance of
23,000 miles resulting in a .12 second latency between satellite and ground stations which results in
actual end-to-end latency of at least 650 ms and more typically 900ms to 1200ms.While web
browsing can work fine with this level of latency, many online games and interactive network
applications do not.
 Starband
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StarBand is a two-way satellite broadband Internet service available in the U.S.
The StarBand satellite Internet system is a VSAT platform that uses Ku band satellites for
transmission of data from users' PCs to the StarBand network operations center.
Two-way bandwidth for residential users is up to 1.5 Mbps download speed and 256 kbit/s upload
speed, with unlimited usage and online hours.
A .75 meter satellite dish is needed.
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Common Satellite Internet Applications
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Remote control and login
Information dissemination and broadcast
Videoconferencing
Information retrieval (WWW, FTP)
Interactive gaming
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Future of Satellite Communications
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Satellite will continue to have a major role in the implementation of the so-called global
information infrastructure in the future. This is because of the particular feature of the satellite
that can provide wide coverage independent of the actual land distance between any pair of
communicating entities.
The new generation of broadband satellite systems, which can provide high-speed data
transmission and connectivity to terrestrial data networks, will create profound changes in all
aspects of the emerging data communications applications such as Internet and electronic
commerce.
Satellites offer a promising alternative for mobile access to the Internet by both pedestrians, and
more importantly, from vehicles. As such, satellites provide an essential complement to the
cellular radio (UMTS-Universal Mobile Telecommunications System) infrastructure in sparsely
populated areas where high bandwidth UMTS cells cannot be economically deployed.
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Summary
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We have seen various reasons for the diffusion of satellite systems for providing Internet Services.
Discussed various satellite based Internet Architectures. Various characteristics involved with it.
Discussed the various MAC Protocols involved.
Discussed various internet services and applications.
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References
1. Satellite Based Internet Technology and Services: A Tutorial
Yurong Hu and Victor O. K. Li, The University of Hong Kong
IEEE Communications Magazine • March 2001
http://ieeexplore.ieee.org/iel5/35/19642/00910603.pdf?tp=&isnumber=&arnumber=910603
2. The use of satellite for multimedia communications-M.F itch
BT Technology Journal • Vol 21 No 3 • July 2003
3. Satellite communications systems move into the twenty-first century
Leonard S. Golding, Hughes Network Systems, Inc., Germantown, MD 20876, USA
International Journal of Satellite Communications and Networking
Volume 22, Issue 6 ,Published Online: 20 Oct 2004 -Copyright © 2004 John Wiley & Sons, Ltd.
http://www3.interscience.wiley.com/cgi-bin/abstract/109717506/ABSTRACT?CRETRY=1&SRETRY=0
4. http://www.aero.org/publications/crosslink/winter2002/01_sidebar3.html
5. http://www.cs.wustl.edu/~jain/cis788-97/ftp/satellite_data/index.htm#TOP
6. Cross-layer protocols for satellite communication networks: Part I
INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING
Int. J. Satell. Commun. Network. 2006; 24:319–322 Published online in Wiley InterScience
(www.interscience.wiley.com).
7. Cross-layer protocol optimization for satellite communications networks: A survey -Giovanni Giambene and Sastri
Kota- INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING
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8. A predictive demand assignment multiple access protocol for internet access over broadband satellite networks
Zhifeng Jiangy and Victor C. M. Leung
INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING
9.
10.
11.
12.
13.
14.
15.
Medium Access Control Protocols for Space and Satellite Communications: A Survey and Assessment
H. Peyravi Computer Science Program Department of Mathematics and Computer Science Kent State University
An Operational concept for a Demand Assignment Multiple Access System for the Space Network
Stephen Horan-Center for Space Telemetering and Telecommunications Systems
http://en.wikipedia.org/wiki/Satellite_Internet_access
http://en.wikipedia.org/wiki/HughesNet
Satellite Communications in the Global Internet: Issues, Pitfalls, and Potential
Yongguang Zhang< [email protected],> Dante De Lucia [email protected] .Bo Ryu [email protected]
Son K. Dao [email protected] ,Hughes Research Laboratories USA
http://www.isoc.org/inet97/proceedings/F5/F5_1.HTM
http://cigno.isti.cnr.it/~alberto/Alberto/Papers.html
Quality of service for satellite IP networks: a survey- Sastri Kota and Mario Marchese
INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING
Int. J. Satell. Commun. Network. 2003; 21:303–349 (DOI: 10.1002/sat.765)
16. Role of Satellites in global IT: Trends and Implications
Abbas Jamalipour and Tracy Tung, The University of Sydney
IEEE Personal Communications • June 2001
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