Satellite Networking

1. Satellite Networking Cheryl-Annette Kincaid

2. Why satellites? • Global coverage • Remote locations • High-velocity mobile users

3. Frequency Bands • C band: 4-8 GHz • Ku band: 10-18 GHz • Ka band: 18-31 GHz

4. Space Segment Orbits • GSO – Geostationary Orbit • Revolution: synchronized with Earth’s rotation. • Altitude: 35,786 km above equator • Coverage: approx. 1/3 of Earth’s surface • Propagation Delay: 250-280 ms • Real estate: limited

5. Space Segment Orbits • NGSO – Nongeostationary Orbit • MEO – Medium Earth Orbit • Altitude: 3000 km – GEO altitude • Propagation Delay: Typically 110-130 ms • LEO – Low Earth Orbit • Altitude: 200 – 3000 km • Propagation Delay: Typically 20-25 ms

6. Ground Segment • GS - Gateway stations • NCC - Network control center • OCC - Operation control center

7. Architectural options Bent-pipe architecture

8. Architectural options OBP and ISL architecture

9. Architectural options DBS – Direct broadcast satellite

10. Challenge – Traffic Management Many user terminals are located within a single satellite’s footprint. These terminals must contend with each other for the uplink channel.

11. Challenge – Traffic Management Objectives: • Fairness • Efficient Resource Utilization • Bounded Queuing Delay • Stability • Fast Transient Response • Scalability

12. Challenge – Traffic Management Medium Access Control schemes: • Fixed Assignment • FDMA • TDMA • CDMA • Random Access • ALOHA and variants • Demand Assignment • DAMA

13. Challenge – Traffic Management Medium Access Control schemes: • Fixed Assignment • FDMA & TDMA • Contention free channels • Some QoS guarantees • Inefficient resource utilization • Best suited for small-scale networks with stable traffic patterns • CDMA • Efficient resource utilization • Flexible for system expansion

14. Challenge – Traffic Management Medium Access Control schemes: • Random Access ALOHA and variants • Accommodates bursty traffic • Low throughput when congested

15. Challenge – Traffic Management Medium Access Control schemes: • Demand Assignment • DAMA – Demand Assignment Multiple Access • Dynamically allocates bandwidth in response to user requests • Explicit or implicit requests

16. Challenge – Traffic Management Medium Access Control schemes: • Demand Assignment DAMA Variants: • Reservation ALOHA • PODA – Priority-Oriented Demand Assignment • FODA – FIFO Ordered Demand Assignment • CFDAMA – Combind Free/Demand Assignment Multiple Access • CRRMA – Combined Random Access and TDMA-reservation Multiple Access • RRR – Round-Robin Reservation

17. Challenge – Routing Dynamic Topology LEO satellites have a very short visible period to motionless users. Efficient methods of handling intersatillite handover are needed. Frequent interbeam handover also occurs within a satellite’s visible period.

18. Challenge – Routing Dynamic Topology DT-DVTR – Discrete-time Dynamic Virtual Topology Routing • Takes advantage of periodic nature of orbits • Works completely offline • Divides system period into intervals • Changes in topology only occur at the beginning of an interval • Stores each interval as a static routing table

19. Challenge – Routing Dynamic Topology VN – Virtual Node • Hides topology changes from routing protocols • Sets up a virtual topology that does not change with satellite movement • Stores routing tables and user information as state information in the virtual nodes • Transfers the assignment of VNs to new satellites as needed

20. Challenge – Routing External Routing Issues • Details of heterogeneous internal routing schemes should remain hidden from the terrestrial Internet. • Isolation is achieved by means of autonomous systems.

21. Challenge – Routing External Routing Issues

22. Challenge – Routing Unidirectional Routing With unidirectional routing, such as is used in DBS, direct reverse links do not exist. Three solutions to this problem are: • Routing Protocol Modification • Tunneling • Static routing

23. Challenge – Routing Unidirectional Routing Routing Protocol Modification • Feeder • Receiver • As the receiver obtains routing updates, it identifies potential feeders and stores useful information about the topology. Periodically, the receiver sends a routing update via the terrestrial reverse channel.

24. Challenge – Routing Unidirectional Routing Tunneling • Link layer approach to hide network asymmetry from routing process • Packets from the user are encapsulated and sent along a virtual link by means of the reverse channel • Packets are decapsulated at the satellite and forwarded to the routing protocol • Path appears to be bidirectional to protocol

25. Challenge – Quality of Service Issues • Latency • Scintillation • Fade • Geomagnetic Storms • Throughput • Security

26. Challenge – Quality of Service Layered view

27. Other Challenges • TCP Performance • Cross Layer Protocol Design • Interworking • Standards

28. Future - HAP High Altitude Platforms

29. Future – Global heterogeneous

30. Conclusion • Satellite networking provides global coverage and enables remote regions to connect with the rest of the global network. • Satellite technologies are beginning to offer more real-time, high bandwidth services to more users. • Satellites have several unique attributes that lead to many challenges. These must be overcome before satellite networking can become a reliable backbone in the next generation of global communication.

31. Sources • J.P. Conti, “Hot spots on rails”, Communications Engineer, vol. 3, no. 5, Oct.-Nov. 2005, pp. 18-21. • Y. Hu, and V.O.K. Li, “Satellite-Based Internet: A Tutorial”, IEEE Communications Magazine, Mar. 2001, pp. 154-162. • S. Karapantazi, and F. Pavlidou, “The Role of High Altitude Platforms in Beyond 3G Networks”, IEEE Wireless Communications, Dec. 2005, pp. 33-41. • S.L. Kota, “Broadband Satellite Networks: Trends and Challenges”, IEEE Communications Society / WCNC 2005, vol. 3, 13-17 Mar. 2005, pp. 1472-1478.