Satellite Network Technology

1. Satellite Network Technology Ha Yoon Song For ICT, TUWien

2. Satellite Internet Systems • Introduction • Satellite Communication Fundamentals • Satellite-Based Internet Architectures • Some Examples of Satellite Systems • Technical Challenges

3. Introduction • Source Material: • Y.Hu and V.Li. Satellite-based Internet: a Tutorial, IEEE Comm., March 2001. • J.Farserotu and R.Prasad. A Survey of Future Broadband Multimedia Satellite Systems, Issues and Trends, IEEE Comm., June 2000. • E.Lutz, M.Werner and A.Jahn. Satellite Systems for Personal and Broadband Communications, Springer, Berlin, 2000.

4. Introduction • Technical challenges to Internet development • Proliferation of applications • Expansion in the number of hosts • User impose • High-speed high-quality services needed to accommodate multimedia applications with diverse quality of service

5. Introduction • Satellite Network • Global coverage • Inherent broadband capability • Bandwidth-on-demand flexibility • Mobility support • Point-to-multipoint, multipoint-to-multipoint comm. • Satellite communication system is a excellent candidate to provide broadband integrated Internet services to globally scattered users

6. Satellite Communication Fundamentals • Construction of a satellite system • Space segment: satellites • Geostationary orbit (GSO) • Nongeostationary orbit (NGSO) • Medium earth orbit (MEO) • Low earth orbit (LEO) • Ground segment • Gateway stations (GSs) • Network control center (NCC) • Operation control centers (OCC)

7. Orbit Selection • GSO option: Larger Coverage (1/3 of Earth’s Surface) • Distance challenge: • Large delay (round-trip delay 250-280 ms) • Large propagation loss (requires higher transmitting powers and antenna gains) • NGSO option: Smaller Delay (LEO round-trip delay ~20ms) • Variable looking angle challenge: • Requires sophisticated tracking techniques or, most of the times, omni-directional antennas. • Requires support to handoff from one satellite to another.

8. Frequency Bands • C Band (4-8 GHz): very congested already. • Ku Band (10-18 GHz): Majority of DBS systems, as well as current Internet DTH systems (DirectPC and Starband). • Ka band (18-31 GHz): Offers higher bandwidth with smaller antennas, but suffers more environmental impairments and is less massively produced as of today (more expensive) when compared to C and Ka.

9. Satellite Payload • Bent pipe • Satellites act as repeaters. Signal is amplified and retransmitted but there is no improvement in the C/N ratio, since there is no demodulation, decoding or other type of processing. No possibility of ISL, longer delay due to multiple hops. • Onboard processing (OBP) • Satellite performs tasks like demodulation and decoding which allow signal recovery before retransmission (new coding and modulation). Since the signal is available at some point in baseband, other activities are also possible, such as routing, switching, etc. Allows ISL implementation.

10. Satellite-Based Internet Architectures • The satellite-based Internet with bent pipe architecture • Lack of direct communication path • Low spectrum efficiency and long latency • The satellite-based Internet with OBP and ISL architecture • Rich connectivity • Complex routing issues

11. The satellite-based Internet with bent pipe architecture

12. The satellite-based Internet with OBP and ISL architecture

13. Next Generation Satellite Systems

14. Case Study: Teledesic • Constellation consists of 288 satellites in 12 planes of 24 satellites. • Ka-band system. Uplink operates at 28.6–29.1 GHz, downlink at 18.8–19.3 GHz. It uses • Signals at 60 GHz for ISLs between adjacent satellites in each orbital plane. • Full OBP and OBS (on-board switching). • "Internet in the sky." • Offers high-quality voice, data, and multimedia information services. QoS performance designed for a BER < 10–10. • Multiple access is a combination of multifrequency TDMA (MF-TDMA) on the uplink and asynchronous TDMA (ATDMA) on the downlink.

15. Case Study: Teledesic • Network capacity planned to be 10 Gb/s. User connections of 2 Mb/s on the uplink and 64 Mb/s on the downlink possible. • Minimum elevation angle of 40.25 enables achievement of an availability of 99.9 percent. • Enormous complexity to the table in terms of untried technology, onboard switching and inter-satellite capabilities.

16. Technical Challenges • Multiple Access Control • Routing Issues in Satellite Systems • Satellite Transport

17. Technical Challenges (MAC) • Multiple Access Control (MAC) • Performance • Schemes • Implementation

18. Technical Challenges (MAC) • Performance of MAC - Depends on shared communication media and traffic. - Long latency in Sat-channels excludes some MAC schemes that are used in terrestrial LAN - Limited power supply on board constrains computational capacity - Implementation of priorities required

19. Technical Challenges (MAC) • MAC Schemes • Fixed Assignment • Random Access • Demand Assignment

20. Technical Challenges (MAC) • Fixed Assignment • Techniques include FDMA,TDMA and CDMA • FDMA and TDMA uses dedicated channels • In CDMA, each user is assigned a unique code sequence • Data signal is spread over a wider brand width than the required to transmit the data.

21. Technical Challenges (MAC) • Random Access In RA schemes, each station transmits data regardless of the transmission status of others. Retransmission after collision creates - Packet delay - Frequent collisions

22. Technical Challenges (MAC) • Demand Assignment - DAMA protocols dynamically allocate systembandwidth in response to user accounts - Resource Reservation can be made - PODA and FIFO combine requests

23. Technical Challenges (Routing Issues) • Routing Issues in LEO Constellation • IP Routing • ATM Switching at the satellites • External Routing Issues

24. Technical Challenges (Routing Issues) • Routing Issues in LEO Constellation • Dynamic Topology - Handles Topological variations - ISL Maintenance • DT-DVTR - Works offline - Sets time intervals and remains constant until next time interval - No of consecutive routing tables are stored and then retrieved when topology changes • VN -Hiding of topology changes from routing protocols

25. Technical Challenges (Routing Issues) IP Routing at Satellites • Seems to be straightforward • Dealing with variable-length packets • Scalability problems • Computational and processing capacity • Research yet to be made on this scheme

26. Technical Challenges (Routing Issues) ATM Switching at the satellites • Many proposed systems use ATM as the network protocol • An ATM version of DT-DVTR is investigated • Modified S-ATM packet

27. Technical Challenges (Routing Issues) External Routing Issues • Internal routing done by Autonomous systems • Internal routing is handled by AS’s own internal routing protocol

28. Technical Challenges (Routing Issues)

29. Technical Challenges (Satellite Transport) TCP/IP UDP/IP These 2 protocols will continue for now as they have tremendous legacy • Performance will be any way affected by long latency and error prone characteristics of satellite links • Researchers are still working in NASA on TCP/IP • TCP performance will definitely improve

30. Technical Challenges (Satellite Transport) • TCP performance over satellite - Positive feedback mechanism - Achieve rate control and reliable delivery • Performance enhancement - TCP selective acknowledgement - TCP for transaction - Persistent TCP connection - Path Maximum Transfer Unit

31. Technical Challenges • Satellite Transport • Performance Enhancements • TCP spoofing • The divided connections are isolated by the GSs • which prematurely send spoofing acknowledgments upon receiving packets • The GSs at split points are also responsible for retransmitting any missing data • TCP splitting • Instead of spoofing, the connection is fully split • A proprietary transport protocol can be used in a satellite network without interference to standard TCP in terrestrial networks • more flexible • some kind of protocol converter should be implemented at the splitting points • Web caching • the TCP connection is split by a Web cache in the satellite network • need not set up TCP connections all the way to servers outside if the required contents are available from the cache • reduces connection latency and bandwidth consumption

32. Conclusion • Possible architectures • Bent-pipe • OBP satellites • Technical Challenges • MAC • IP routing in LEO • Unidirectional routing • Satellite transport issues • QOS • Congestion Control

33. Satellite ATM Networks: A survey

34. Introduction ATM technology offers users integration and the flexibility of accessing bandwidth on demand Increasing recognition of the benefits and advantages of using satellite transmission systems

35. Satellite ATM Network- ATM Architecture - Key Component • ASIU • real-time bandwidth allocation • network access control • system timing and synchronization control • call monitoring • error control • traffic control

36. Satellite ATM Network- ATM Architecture - Protocol stack for the satellite ATM network

37. Satellite ATM Network- ATM Architecture - • Interface between the ASIU and other modules • SONET – Synchronous Optical Network • SDH – Synchronous Digital Hierarchy • PDH – Plesiochronous Digital Hierarchy • PLCP – Physical Layer Convergence Protocol

38. Satellite ATM Network- ATM Architecture - Internal Architecture of ASIU

39. The Cell Transport Method • PDH • some inefficiencies • too many ADD operate • stuffing bit • rerouting(e.g. network fail) – extremely difficult

40. The Cell Transport Method • SDH • Advantage • without multiplexing stage • directly identifies the position of the payload • very accurate clock rate • easier and lower cost multiplexing • Disadvantage • overhead; pointer byte • incorrect pointer -> incorrect payload

41. The Cell Transport Method • PLCP • IEEE P802.6 • DS3(44.736Mbps); 125us – 53byte

42. The Cell Transport Method • PLCP • POI (Path Overhead Indicator) • POH (Path OverHead)

43. Link Layer-Satellite Link Access Methods- • FDMA, TDMA, CDMA • MF-TDMA (Multi-Frequency TDMA) • inefficiency – the destination of the bursts • reduce satellite antenna sizes and transmission power • increase satellite network bandwidth • DAMA • Dynamic allocation – satellite power and bandwidth • Random Access & QoSguarantee • DAMA with MF-TDMA or SCPC • achieve a greater efficiency in satellite ATM networks ※ SCPC(single channel per carrier) – userside ATM UNI interface channel

44. Link Layer-Error Control- • The Impact of Burst Error Characteristics • HIGHER BER than Terrestrial Network • HIGHER RTT (Round Trip Time) – time for error detection? • Burst error; satellite • ATM HEC(Head Error Check); burst error cannot be correct • CRC can detect burst error • ALL1 and ALL3/4 • the length of burst error is beyond 10 the error may not be detected • ALL5 • 32-bit CRC; powerful • overhead / not optimal solution

45. Link Layer-Error Control- The SAR-PDU format of ALL1 The SAR-PDU format of ALL3/4 • ATM cell • Cell header and Payload • Interleaving Mechanism; (similarly ATM cell) • efficient way to solve the burst error problem • may still contain errors

46. Link Layer-Error Control- • Error Recovery Algorithm • ARQ: stop-and-wait, Go-Back-N, selective-repeat • Coding Scheme for Improving Error Performance • FEC (Forward error correction) code • RS (Reed Solomon) code • cost-effective solution

47. Traffic Management-Performance Aspects- • Necessary to maintain the QoS of ATM connections over satellite • QoS parameters • CLR (Cell Loss Ratio) • most stringent criteria for satellite ATM network • CTD (Cell Transfer Delay) • marks the difference between ATM and satellite links • CDV (Cell Delay Variation) • synchronization between different connections • CER (Cell error ratio) • the sum of successfully cells / errored cells • SECBR (Severely Errored Cell Block Ratio) • CMR (Cell Miss-insertion Ratio) • caused by an undetected cell header error

48. Traffic Management -The Impact of Transmission Delay Characteristics • ATM technology – most of capability • Satellite ATM network – the long delay • Video and Voice Serv. • Real-time – very sensitive to the delay • the satellite can provide a connection of high quality • Text or Data Serv. • not very sensitive to delay • Video Telephony • ITU-T Recommendation H.261 is greater than the satellite delay • But, future video telephony will demand less delay • CSCW App. • acceptable from the app’s point of view • But, maybe the poor performance

49. Traffic Management-Traffic Control- • Traffic Control (for ATM -> for terrestrial ATM networks) • Traffic shaping • changes the traffic char. of a cell stream to achieve a desired modification of those traffic char. • CAC (Connection Admission Control) • the set of actions taken by a network to establish • whether an ATM connection can be accepted or rejected in order to avoid congestion

50. Traffic Management-Congestion Control- • Selective Cell Discard • CLP = 0 or 1 ; priority • EFCI (Explicit Forward Congestion Indication) • convey congestion notification to source • FECN (Forward Explicit Congestion Notification • inappropriate in satellite ATM • a one-way propagation delay • BECN (Backward ECN) • send a notification in the reverse direction of the congested path • faster than FECN • Buffering • VC(Virtual Channel)