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 Earths rotation.
• Altitude 35,786 km above equator
• Coverage approx. 1/3 of Earths 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
  satellites 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
  satellites 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

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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
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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.