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University of Kansas | School of Engineering

Department of Electrical Engineering and Computer Science

Access Methods for Satellite Networks providing Internet Services

Anusha Reddy Bethi



Outline 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 CommunicationsElements of Satellite system:Space segment

• Satellite or fleet of SatellitesGround segment

• Gateway stations• Network Coordination center(NCC)• Network Operation center(NOC)

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Elements of a Satellite System

F

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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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



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 servicesBandwidth efficiencyLatency and availability

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Frequency Bands and ServicesFrequency Band Frequency (GHz) Type of Service Example Systems

L-Band 1.5—1.6 Mobile voice anddata, distress(downlink)

Inmarsat, Thurya

S-Band 2.4—2.6 Mobile voice anddata

ICO/Globalstar

C-Band 4—6 Internationaldialed and leasedcircuits,Broadcast TV

Intelsat, PanAmSat,Dish

X-Band 7—8 Military services Skynet 4 and 5, Nato

Ku-Band 11—14 TV broadcast, businesssystems,broadband Internetto homes andoffices

SES-Astra, Eutelsat,Intelsat

Ka-Band 20—30 Broadband tohomes and offices

Hughes,Spaceway

V-Band 40—50 Non-real-timefixed services

Hughes,Galaxy

11From: The use of satellite for multimedia communications -M Fitch BT Technology Journal • Vol 21 No 3 • July 2003



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

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 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

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

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.

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Satellite Based Internet with OBP and ISL Architecture



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.

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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.

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Examples of some worldwide broadband satellite systems that provide high-speed Internet service



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Access Methods and ProtocolsSatellite Protocol Reference Model

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 NETWORKINGInt. 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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SI-SAP: Satellite-Independent- Service Access Point IPV4/IPV6: Internet Protocol version4/ Internet Protocol version6UDP: User Datagram ProtocolTCP: Transport control Protocol



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) 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 on-

demand 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) 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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Figure: Uplink TDMA frame structure.

Uplink TDMA frame structure

From: A predictive demand assignment multiple access protocol for Internet access over broadband satellite networksZhifeng Jiangy and Victor C. M. Leung

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKINGInt. 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. LeungINTERNATIONAL 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 networksZhifeng Jiangy and Victor C. M. Leung

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKINGInt. J. Satell. Commun. Network. 2003; 21:451–467 (DOI: 10.1002/sat.759)

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Performance comparisons with other DAMA protocols

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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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.

Transport Control Protocol(TCP)

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Performance Enhancing Proxies 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 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)

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 TechnologiesHughesNet 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 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 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 Remote control and login Information dissemination and broadcast Videoconferencing Information retrieval (WWW, FTP) Interactive gaming

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Future of Satellite Communications 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 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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References1. 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 20033. 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=04. 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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http://ieeexplore.ieee.org/iel5/35/19642/00910603.pdf?tp=&isnumber=&arnumber=910603



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. 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 University10. An Operational concept for a Demand Assignment Multiple Access System for the Space Network Stephen Horan-Center for Space Telemetering and Telecommunications Systems11. http://en.wikipedia.org/wiki/Satellite_Internet_access12. http://en.wikipedia.org/wiki/HughesNet 13. 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.HTM14. http://cigno.isti.cnr.it/~alberto/Alberto/Papers.html 15. 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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