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SNAP

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1. Satellite Network Access Point (SNAP) Associate Professor Adrian Barbulescu (adrian.barbulescu@unisa.edu.au) Institute for Telecommunications Research University of…
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  • 1. Satellite Network Access Point (SNAP) Associate Professor Adrian Barbulescu (adrian.barbulescu@unisa.edu.au) Institute for Telecommunications Research University of South Australia SNAP 25/04/2009 1
  • 2. “School of Athens” Raphael, Vatican “Necessity, who is the mother of invention.” Plato, 427-347 BCE SNAP 25/04/2009 2
  • 3. What is necessity? The best technical solution depends on how the answer to this question is formulated. Example: I want to be able to watch the latest movie release. SNAP 25/04/2009 3
  • 4. Historical perspective: ‘80s: one satellite transponder (36 MHz) was used for a single analogue TV channel. (36 MHz per SDTV) ‘90s: one satellite transponder (36 MHz) was used for six digital MPEG2 channels transmitted using DVB-S. (6 MHz per SDTV) ‘00s: one satellite transponder (36 MHz) was used for twenty digital MPEG4 channels transmitted using DVB-S2. (1.8 MHz per SDTV) SNAP 25/04/2009 4
  • 5. Assumptions: • US$3,000/month/MHz for satellite bandwidth • MPEG4 and DVB-S2 • an average of 2 MHz bandwidth per video channel. Necessity #1: “I need access to as many movies I want, at any time I want.” satellite time used = 24 hours/day US$6,000/month SNAP 25/04/2009 5
  • 6. Necessity #2: “I need to watch a movie a day, any time I want.” satellite time used = 2 hours/day assuming that one can make a request and receive the movie say, in the next half hour, any time of the day US$500/month SNAP 25/04/2009 6
  • 7. Necessity #3: “I need to watch a movie a day, any time I want, but I am prepared to order it well in advance.” satellite time used = 2 hours/day but, chances are that another 50 people want to watch the same new release as you. The movie will be downloaded over satellite once and then distributed for free to all 50 users over a WiFi or WiMax network US$10/month SNAP 25/04/2009 7
  • 8. Have you considered that your individual needs combined with your community needs may define the optimum satellite based technical solution ? Education Internet Education Internet Think aggregation Local Local Telehealth Telehealth of Business Business services ! Local Local Government Government SNAP 25/04/2009 8
  • 9. Are you an informed user when trying to find out the truth about satellite communications solutions? Most important questions for the optimum solution : Q#1: What is the latest available satellite modem technology ? Q#2: Is the service optimised for my type of traffic? Q#3: How can the amount of satellite traffic be reduced ? Q#4: How can the cost of satellite time be reduced ? Q#5: How does an individual-based solution compare with a community-based solution ? SNAP 25/04/2009 9
  • 10. Q#1: What is the latest available satellite modem technology ? SNAP 25/04/2009 10
  • 11. Non-equiprobable constellations for non-linear satellite channels SNAP 25/04/2009 11
  • 12. Bit Error Rate of 10-10 at Eb/N0 = 1.5 dB Cost of satellite time depends on bandwidth and power ! Eb/No required for BER < 1E-10 6 Premier 5 (S-Tec) 5 CDM600 (TPC) Eb/No [dB] 4 M5 (TPC) 3 P300 (TPC) 2 DMD20 (TPC) 1 0 QPSK Rate 1/2 QPSK Rate 3/4 SNAP 25/04/2009 12
  • 13. Q#2: Is the service optimised for my type of traffic? Internet traffic is an ON-OFF process, Self-Similar traffic. It has a Pareto distribution, not a Poisson distribution. SNAP 25/04/2009 13
  • 14. Video transmission over a VSAT link at an average of 256 kbit/s and maximum bandwidth limitation of 512 kbit/s. SNAP 25/04/2009 14
  • 15. Video transmission over a SNAP link at an average of 256 kbit/s with bursts of up to 2,048 kbit/s for the same cost. SNAP 25/04/2009 15
  • 16. Q#3: How can the amount of satellite traffic be reduced ? Compression techniques: ratios vary (1.5 to 3.5), more efficient techniques require longer compression and decompression times (1 to 13 seconds) Example of savings assuming US$2,000,000/year for a 45 Mbit/s transponder using a US$3,000 compression device at each end with an average compression ratio of 2:1. Ex: http://www.expand.com/solutions/Satellite.html http://www.juniper.net/products/appaccel/ SNAP 25/04/2009 16
  • 17. Compression Advantages Bandwidth: 8-2 Mbit/s 64-64 kbit/s Connection: forward/return symmetric Total bandwidth: 10Mbit/s 128 kbit/s Cost of BW: $444,444/y $5688/y Nr. compression devices 2 2 Cost of compression devices:$6,000 $6,000 Bandwidth savings: $222,222/y $2,844/y Payback 10 days 2.1 years SNAP 25/04/2009 17
  • 18. Compression Ratios (www.cisco.com/en/US/products/ps6587) SNAP 25/04/2009 18
  • 19. Caching (www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/) SNAP 25/04/2009 19
  • 20. Caching/Pre-fetching Caching (browser caching and shared caching: Squid, CISCO) is widely used in all terrestrial networks. As a rule of thumb: 50% hit ratio and 33% bandwidth savings. Pre-fetching (downloading the embedded objects on a HTML page and send them => reduces downloading time) Multiple TCP connections, in aggregate, are able to use more of the available bandwidth. Applications designed for satellite links could open multiple simultaneous TCP connections, send part of a file over each connection and reassemble it at the receiver end. SNAP 25/04/2009 20
  • 21. Statistical Multiplexing Gain (SMG) The system requirements depend on the peak rates needed: • video:average rate = 75 kb/s, but peak rate of 384 kb/s Scenario 1: 10 individual VSAT channels need: average rate = 750 kb/s, but peak rate of 3840 kb/s Scenario 2: 1 aggregated channel for 10 users needs: average rate = 750 kb/s, but peak rate of 1150 kb/s due to statistical multiplexing As peaks occur at different moments in time (statistical multiplexing), there is a need of only a small increase of the average rate, say 400 kb/s, to allow enough margin for any user to reach peak rates, the system therefore needs only 750+400 =1150 kb/s instead of 3840 kb/s. SNAP 25/04/2009 21
  • 22. Statistical Multiplexing Gain (SMG) SMG = peak bit rate / beam capacity Traffic scenario for a satellite link of 8,192 kb/s [1]: • data: non-real-time 64 kb/s with activity factor 1%, • video: peak rate of 384 kb/s and peak-to-average ratio 5, • voice: 64 kb/s, activity factor 40%. [1] T.Le-Ngoc, “Switching for IP-Based Multimedia Satellite Communications”, IEEE Journal on Selected Areas in Communications, VOL.22, NO. 3, pp.462-471, April 2004. SNAP 25/04/2009 22
  • 23. Q#4: How can the cost of satellite time be reduced ? Aggregation of applications and services using the latest satellite technologies provides the optimum mechanism to service the communication needs of a community rather than individual users. Turbo Coding Satellite modems Education Internet Local Telehealth Business Local Government Bandwidth Wireless LAN Management SNAP 25/04/2009 23
  • 24. Satellite Network Access Point - antenna SNAP 25/04/2009 24
  • 25. Satellite Network Access Point – indoors unit SNAP 25/04/2009 25
  • 26. Satellite Network Access Point – traffic shaping SNAP 25/04/2009 26
  • 27. Wireless LAN Courtesy of www.proxim.com SNAP 25/04/2009 27
  • 28. The 100BASE-TX Ethernet connection between ITR and the world was replaced by a 2 Mbit/s Satellite connection. Equivalent to an SMG of 50 !!! SNAP 25/04/2009 28
  • 29. Q#5: How does an individual-based solution compare with a community-based solution ? Parameters VSAT SNAP Satellite BW reduction factor 1 ½ to ¼ (1 / coding rate / modulation) (4/3/2=0.67) (8/7/8 = 0.14) Compression, caching NO YES Traffic Burstiness Capability NO YES Optimised Satellite Protocol NO (TCP) YES (XTP) Traffic Management (statistical NO YES multiplexing, congestion control) Operating point (Eb/No) for bit 3 to 5 dB 1.5 dB error rates less than 1E-10 Scalability NO 1 to 20 Mbit/s End users Individuals Community SNAP 25/04/2009 29
  • 30. Satellite communication is EXPENSIVE! Cost of a GEO satellite: USD500 million Capacity: 100 Gbps Cost per Gbps: USD5,000,000 Cost of a fiber optic cable: USD300 million (US- Japan, 10,000 km long) Capacity: 8 Tbps Cost per Gbps: USD37,500 SNAP 25/04/2009 30
  • 31. O3B Networks (Sep. 2008) http://www.o3bnetworks.com/ O3b Networks, funded by Google Inc., Liberty Global, Inc. and HSBC Principal Investments, will deploy the world’s first ultra-low-latency, Medium Earth Orbit (MEO), Ka-band, fiber-speed satellite network designed to improve Internet access for millions of consumers and businesses in emerging markets like Africa. Service activation and ground equipment is scheduled for late 2010. The new Gilat MEO VSAT equipment will enable automatic tracking of the satellites and seamless handoff between satellites. Specific terminals target 3G Cellular/WiMAX backhaul, IP trunking, and broadband connectivity for SMEs and ISP backhaul. SNAP 25/04/2009 31
  • 32. “We are questioning beings… who must search out the reason of things, and not accept them from custom and authority” Socrates 469-399 BCE SNAP 25/04/2009 32
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