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![First “Internetting” – via Goonhilly 1977
» In the words ofVint Cerf: “The 1st demonstration of
the Internet (as we know it today)”:
» “Internetting” Packet Radio (PR) net, SATNET* & the
ARPAnet
› ‘grandfather’ of the Internet. [94,000 mile round-
trip]
» PR messages from a van in the Bay Area
» Across the US on ARPAnet to Etam*,WVirginia
» Over INTELSAT-IVA (AOR) toTanum* (Sweden)
» Land-line to NORSAR in Norway (seismic research)
» Subsea & land-line to University College London
» Land-line to Goonhilly* Downs,Cornwall
» Back over INTELSAT-IVA (AOR) to Etam (via
Goonhilly-02)
» Back across the US on ARPAnet to Information
Sciences Institute at University of SouthernCalifornia
24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
ARPAnet = Advanced Research Projects Agency network
*SATNET= Atlantic Packet Satellite Network (German &
Italian sites yet to be hooked in)](https://image.slidesharecdn.com/internetinspace-networkshop44-160324113105/85/Internet-in-space-Networkshop44-20-320.jpg)
Uploaded byJisc
Internet in space - Networkshop44
Goonhilly Earth Station played a key role in the development of the Internet. It was involved in the first demonstration of packet radio networking across the Atlantic in 1977. Goonhilly is now exploring ways to extend Internet connectivity to space, such as by developing disruption tolerant networking to enable an interplanetary Internet and supporting private lunar missions. Goonhilly also aims to diversify its business by offering commercial satellite services and partnering with universities on radio astronomy research.
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Internet in space - Networkshop44
- 1. Internet in Space MatthewCosby Chief Scientist
- 2. Contents 24/03/2016 Internet inSpace – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd »Overview of Goonhilly › Development of the teleport form the 1960s »The role that Goonhilly played in the development of Internet »Extending the Internet in space › Future role of Goonhilly in this development »Conclusions
- 3. Goonhilly Earth Station 24/03/2016Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd Goonhilly Earth Station Long : 6.0W
- 4. Goonhilly Earth Station 24/03/2016Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 5. Goonhilly Earth StationLtd 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 6. Goonhilly Earth StationLtd 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd »Private limited UK company »SME (Small/Medium Enterprise) »Owned by Directors »Private equity finance (Downing) »Acquired the entire Goonhilly site from BT Jan 2014
- 7. GES Ltd- BusinessModel 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd »Diversify revenue streams »Provide world-class commercial satellite services »Multiple uses for antennas, data services »Work closely with Universities, Research Institutions and UK Space Industry »Diversify activities on-site (with more “open access”) »Develop engaging and inspiring education outreach
- 8. Commercial Satellite Communications Tracking,Telemetry and Command(TT&C) Radio Astronomy and Deep Space Antenna Diversification Wide range of different antennas suited for different purposes 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 9. Low Earth OrbitTracking 24/03/2016Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd GHY-99 – a 5m LEO tracking antenna in radome built by GES Ltd for Planet Labs* This antenna is downloading hundreds of earth observation images per pass of Planet Labs ‘Dove’ satellites * Planet Labs is the San Francisco based satellite operator changing the paradigm for global satellite mapping. Their fleet of hundreds of satellites will eventually re-image the entire world several times per day.
- 10. SupportingTim Peake onthe ISS 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd Goonhilly is hosting the ARISS satellite link beamingTim Peake directly from the International Space Station into UK schools
- 11. Deep Space Communications 24/03/2016Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd With support from HMG and UK Space Agency we have plans to convertGHY-6 (32m) to become the world’s first privately owned Deep SpaceAntenna. This will allow UK to support NASA Orion missions to the Moon and drive new business to UK.
- 12. Goonhilly in Supportof Orion »Completing an ESA study on the feasibility of converting Goonhilly-6 into the European ORION ground station »Resulting antenna will be based on the new ESA DSA station configuration »Talking to several private companies in support of their lunar missions 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 13. »Completing an ESAstudy on the feasibility of converting Goonhilly-6 into the European ORION ground station »Resulting antenna will be based on the new ESA DSA station configuration »Talking to several private companies in support of their lunar missions 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 14. University Partnerships -CUGA We partner with 6 of the world’s leading radio astronomy research institutes; Leeds, Oxford, Manchester, Durham, Herts and Southampton Universities. Together they have formed a Consortium of Universities for Goonhilly Astronomy – CUGA. The consortium are in the process of adding receivers to two of our antennas to create highly capable radio telescopes. We have co-funded (along with JANET) a 10 Gbit/s direct JANET fibre optic connection to Jodrell Bank so that Goonhilly can become part of the eMERLIN telescope array. 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd Left: Cryostatic (super-cooled) radio astronomy receiver on the bench at Oxford University being assembled by our CASE student
- 15. eMERLIN –Very LongBaseline Interferometry 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd 405 km 198 km
- 16. Square Kilometre ArrayTelescope 24/03/2016Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 17. Goonhilly Enterprise Zone 24/03/2016Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd We are delighted to have been selected as one of the new Enterprise Zones as part of the Newquay Aerohub+ extension. Goonhilly is a key element in the Cornwall Economic Development Strategy touching all five of the named smart specialisations: • Space & Aerospace • eHealth • AgriTech • Maritime • Digital
- 18. Centre of Excellencein Satellite Applications 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd Goonhilly Earth Station has been selected to host the SatelliteApplicationsCatapult Regional Centre of Excellence for the SouthWest. TheCentre, led by Exeter University, will engage with academic and industry partners to promote and develop space application innovation and growth.
- 19. 24/03/2016 Internet inSpace – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd A Chronology of Internet in Space
- 20. First “Internetting” –via Goonhilly 1977 » In the words ofVint Cerf: “The 1st demonstration of the Internet (as we know it today)”: » “Internetting” Packet Radio (PR) net, SATNET* & the ARPAnet › ‘grandfather’ of the Internet. [94,000 mile round- trip] » PR messages from a van in the Bay Area » Across the US on ARPAnet to Etam*,WVirginia » Over INTELSAT-IVA (AOR) toTanum* (Sweden) » Land-line to NORSAR in Norway (seismic research) » Subsea & land-line to University College London » Land-line to Goonhilly* Downs,Cornwall » Back over INTELSAT-IVA (AOR) to Etam (via Goonhilly-02) » Back across the US on ARPAnet to Information Sciences Institute at University of SouthernCalifornia 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd ARPAnet = Advanced Research Projects Agency network *SATNET= Atlantic Packet Satellite Network (German & Italian sites yet to be hooked in)
- 21. Satellite Data Developments »Early Arpanet / SATNET experiments 56/64 kBit/s › Up to 800 channels available on Intelsat IV » TDMA (Time Division Multiple Access) › Initially developed at Goonhilly Labs › Combined incoming 2Mbit/s PCM multiplexes › 60MBit/s via Intelsat (GHY-3) › 120MBit/s via Eutelsat (GHY-4) › Operated for over 20 years 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 22. Satellite Data Developments »This form ofTDMA good for trunk communications between major teleports… » But… Growing business need for dedicated data connectivity 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 23. Satellite Data Developments »Advent of direct business to business connectivity via satellite » IBS Modem – point to point » Proprietary versions ofTDMA and DAMA (demand assigned multiple access) 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 24. SatelliteTV Signal 24/03/2016 Internetin Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd DATA CHROMENANCE LUMANENCE DVB-S Dongle ~$10
- 25. Fitting IP intoMPEG MPEG (DVB) Packet 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd IP Packet
- 26. DVB-RCS System »DVB –Forward Link »RCS (TDMA) – Return Link 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd Bandwidth
- 27. TCP/IP Slow StartAlgorithm – and PEPs » TCP / IP Slow Start is the Network’s in-build self-defence against congestion » In satellite networksTCP / IP misinterprets the ‘round trip’ delay as congestion › Result: awful performance » Solution: Performance Enhancing Proxy …. Spoof the Ack 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 28. Consultative Committee forSpace Data Systems »CCSDS – An Agency-Led InternationalCommittee › Currently 11 Member agencies › Currently 29 Observer Agencies › Agencies represent 27 nations (and 3 European orgs) › Currently 118 CommercialAssociates »Also functions as an ISO Subcommittee › TC20/SC13 - Space Data & InfoTransfer Systems › Represents 20 nations 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 29. Consultative Committee forSpace Data Systems 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 30. Consultative Committee forSpace Data Systems Mission Ops & Info Mgt Services Space Internetworking Services Cross Support Services Space Link Services Spacecraft Onboard Interface Services One Organization’s Assets Another Organization’s Assets MISSION CONTROL CENTER MISSION CONTROL CENTER End Users End Users Applications/Archive s Systems Engineering Typical Mission Profile 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 31. ExoMars –Trace GasOrbiter 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 32. Planetary Communication 24/03/2016 Internetin Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 33. Interplanetary Internet (IPN) 24/03/2016Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 34. Why not useTerrestrialsystems on the IPN? »Short round trip times › short delays »Source and destination are always connected »Physical layer is error free › Low bit errors »Maximum frame length of 1500 bytes (Ethernet) »Symmetrical data rates Terrestrial systems assume the following: 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 35. DisruptionTolerant Networks (DTN) 24/03/2016Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 36. Interplanetary internet 24/03/2016 Internetin Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 37. Plans for DTN 24/03/2016Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd »DTN experiments are being conducted on the ISS ›ESA, NASA & JAXA experiments »Cubesat, nanosat and satellite constellations are proposed »Interplanetary cubesats / nanosats are proposed
- 38. Proposed Private LunarMission 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 39. Proposed Private LunarMission 24/03/2016 Internet in Space – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 40. Conclusions 24/03/2016 Internet inSpace – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd »The internet will be extended into deep space in 10 years time › Integrated into theTerrestrial Internet seamlessly for the end user »Terrestrial Internet will be deployed on the surface of solar system bodies to enable human exploration »The take up of these systems will be driven private enterprise
- 41. ThankYou 24/03/2016 Internet inSpace – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd
- 42. References 24/03/2016 Internet inSpace – MatthewCosby, Chief Scientist,Goonhilly Earth Station Ltd » http://xbbn.weebly.com/note-27.htm » http://blogs.esa.int/tim-peake/2016/03/15/space-to-ground-remote/ » www.ccsds.org » www.ewh.ieee.org/r6/lac/csspsvts/briefings/coe_20071025.pdf » Private correspondence with NASA DTN working group chair » Private correspondence with SSTL/GES LunarTeam
Editor's Notes
- #4 I should start by explaining that Goonhilly is a major space communications teleport in the far south-west of the UK – in Cornwall. It’s famous for being the world’s first commercial satellite ground station – and it received the first ever trans-Atlantic TV pictures from the TELSTAR satellite in 1962. It was the largest ground station in the INMARSAT network… It was a major TV uplink hub – beaming the 1969 Apollo moon landings to Europe (amongst many notable transmissions) ..and in 1977 Goonhilly was part of the first ever demonstration of a new technology called “the Internet” However, its fortunes waned, and in 2007, British Telecom announced plans to close (and demolish) the site.
- #5 I should start by explaining that Goonhilly is a major space communications teleport in the far south-west of the UK – in Cornwall. It’s famous for being the world’s first commercial satellite ground station – and it received the first ever trans-Atlantic TV pictures from the TELSTAR satellite in 1962. It was the largest ground station in the INMARSAT network… It was a major TV uplink hub – beaming the 1969 Apollo moon landings to Europe (amongst many notable transmissions) ..and in 1977 Goonhilly was part of the first ever demonstration of a new technology called “the Internet” However, its fortunes waned, and in 2007, British Telecom announced plans to close (and demolish) the site.
- #6 In 2008, a chance meeting of two former colleagues set the course for the re-birth of Goonhilly. Goonhilly retiree, Des Prouse, met with Satellite Engineer, Ian Jones, and told him of the imminent demise of the earth station. BT had set their minds on achieving their carbon-footprint targets by demolishing the antennas and building a wind farm. The demolition contracts were in place – and some had been carried out. Whilst this was a perfectly valid business action for BT, many were hugely upset at the prospect of losing such an iconic and ground-breaking facility. A new business model was needed – which could utilise the unique assets at Goonhilly – and that required a new company to be formed to acquire the site from BT.
- #7 It took almost three years to for the embryonic “Goonhilly Earth Station Ltd” to negotiate a deal with BT to buy the site. But as the new company had no track record or any business, the deal consisted of a short-term, 3 year lease, with an option to purchase the site at a pre-agreed price. If the site hadn’t been bought by the end of the three years, then the whole deal was off. This deal gave GES Ltd a low-cost start – with time to build the business and find the necessary finance to complete the purchase. In January 2011, GES Ltd, now just three people, signed the deal with BT... And the clock was ticking. During three very tough years, during the world’s largest recession, GES Ltd restored several antennas, won commercial contracts and found a financial backer! With literally days to spare, GES Ltd handed over the cash to BT and in January 2014 the acquisition was complete.
- #8 So what made GES Ltd think they could succeed to grow Goonhilly when BT clearly didn’t think it was viable? Firstly, GES started life as a tiny company – but with lots of friends, good will and experience. .. And of course, the assets at Goonhilly, although old, were extremely well built. The large, relatively high-maintenance antennas at Goonhilly were not necessary for a modern commercial satellite station, so we devised a business model with a wide-ranging, diverse set of applications – and this paid off, allowing us to provide premium services – such a ‘flying’ satellites – and drifting them to new orbital locations! From the outset, it was clear that the large antennas were useful to the scientific community – especially for Radio Astronomy. So from day one, we worked closely with a group of leading universities: Manchester, Oxford, Leeds and Herts to establish a unique collaboration. We recognise that Goonhilly can act at the boundary of academic research and early commercialisation and we are very keen to encourage that. We also understood that Goonhilly could play its part in the emerging UK Space growth plan – and we have worked hard to ensure that Goonhilly is seen as an open location for collaboration. The Goonhilly site – being THE UK’s former international communications gateway, is well equipped for expansion and collaboration… and we are now seeking new partners to help to continue this growth. We are growing commercial satellite communication AND data centre services. Last, but certainly not least, we are extremely keen to promote STEM – in fact STE(A)M - and we recognise the part Goonhilly has to play in helping to inspire the next generation of students. Relative to our turn-over, we aim to be the biggest contributor to education outreach in the UK of any company. In combination, the small scale, diverse model with low overheads delivers a sustainable, growing business with huge potential to transform the local economy.
- #9 The image here illustrates the wide range in size of the different antennas at Goonhilly. In 1975, when Goonhilly 3 here was built, it was necessary to have a 30m dish to communicate with the relatively weak satellites However, modern communication satellites can happily operate with one of these much smaller 4.5 or 6.1m antennas these days. Our ‘medium sized’ antennas – like GHY-61 here are really useful for tracking and telemetry services. Actually they are over-powered for normal use, but if an emergency occurs, and the satellite starts to tumble in space, they have sufficient gain to send a very powerful command signal to restore the link and re-gain control. And that leaves our giant antennas free for some interesting work – such as deep space communication and radio astronomy…. Or possibly other future research activities such as space debris tracking or geodesic VLBI.
- #10 Tracking LEO (or low earth orbiting) satellites brings its own challenges. LEO satellites (including the International Space Station) travel at 28,000 km/h. Tracking antennas generally have special articulation in their mounts to allow direct overhead passes. Goonhilly has already won two contracts for tracking LEO satellites…. One with the California Earth-Mapping company Planet Labs……
- #11 …and the other with the Satellite Applications Catapult. Here you can see Goonhilly-99 waiting to track Astronaut Tim Peake on the International Space Station. This project is a fantastic collaboration between the Sat Apps Catapult, UK Space Agency, and the Amateur Radio community – especially AmSat UK and ARISS delivering video contacts from Tim Peake directly into UK schools. The video signal is generated on board the Space Station by a DVB encoder and transmitter built by amateur radio enthusiasts. It is received at Goonhilly and sent via our JANET internet connection onto the public internet where the schools are able to log in and download the signal.
- #12 We are planning to convert our largest antenna, Goonhilly-6, into the world’s first privately owned Deep Space Antenna. We have just completed the first, study phase of the work… the next step is a full refurbishment of the radio frequency equipment and the tracking systems We’re hopeful that a collaboration between UK Space Agency, ESA and NASA will mean that Goonhilly – and the UK – will be the chosen tracking station for NASA’s Orion missions – taking humans back to the Moon. Providing Internet services into Deep Space has its own challenges – and I’ll talk about that in a few minutes.
- #15 Our Radio Astronomy Partnership has grown and now also includes Southampton and Durham, with other universities keen to join as well.. We are planning projects on two of our largest antennas… GHY-1 and GHY-3 Here you can see the super-cooled receiver that’s being designed and built at Oxford University that will be fitted to GHY-3
- #16 …and GHY-1 will become part of the Jodrell Bank eMERLIN interferometer network. In interferometry, pairs of antennas are pointed to the same object in the sky. These pairs form a “baseline”. The signal from a distant object passes through space and arrives at the antennas at almost (but not quite exactly) the same time. The difference in time of arrival is critical because if the signals can be accurately phased up, they can be combined to form a stronger signal. Furthermore, any noise, or interference – which is a random process - tends to cancel out. (There are several other advantages I won’t go into.) GES Ltd is working closely with JANET, Manchester University and the other university partners, and Manchester Uni spin-off company Adaptive Array Systems to develop a new system for sending this highly accurately timed, ultra high bandwidth signal between Goonhilly and Jodrell Bank. JANET has installed a 10 Gbit/s IP link between the two locations and Adaptive Array Systems is developing a data encapsulation processor capable of masking out TCP/IP jitter. This will preserve the timing accuracy of an atomic clock – that’s the equivalent of 1 second in a million years!
- #17 Taking interferometry to the extreme, the Square Kilometre Array Telescope will have hundreds (maybe thousands) of baselines and ultimately will occupy more bandwidth than the global Internet! UK and European Universities are leading the research and development of this telescope – and Internet developments such as the Goonhilly / Jodrell Bank link will be important technology demonstrators or test facilities. It’s possible that the sub-sea cable that connects Africa directly to Goonhilly could be used to bring SKA data onto the JANET network.
- #18 In a few days time, on 1 April, Goonhilly will become an Enterprise Zone. This will further encourage collaboration projects and inward investment. Cornwall has a devolved budget including European Regional Development Funds and has selected five highly relevant “smart specialisations” for its regional economic development strategy: Space & aerospace, eHealth, AgriTech, Maritime and Digital… And the Cornwall & Isles of Scilly LEP are very keen to promote inward investment. In the recent budget it was announced that the South West will become the first region to roll out “Hyperfast” broadband. Goonhilly and JANET are already ahead of the game with the announcement last week of a new commercial JANET connection into Goonhilly. The current 10 Gbit/s link will have a redundant 100GBit/s link added. GES Ltd will be investing further in data centre technology for storage and ultra fast processing. The nature of the Goonhilly JANET contract allows for commercialisation of services and this makes for very interesting scenarios for collaboration with academic commercialisation projects and spin offs.
- #19 We have also recently become the host of the “Satellite Applications Catapult Regional Centre of Excellence” working alongside Exeter, Plymouth and Falmouth Universities, the Met Office PML and Rothamsted Research. The Centre will have a remit to seek new Academic/Industry links where satellite data can be developed or used for new commercial applications.
- #20 I’d like to run through a very brief history of the part that space has played in the development of the Internet – and also where it’s going in the future…
- #21 Back in 1977, embryonic packet switched networks, such as ARPAnet and SATNET were coming into existence allowing data to be routed to different end-points based on information contained within the ‘header’ of a ‘datagram’ – or packet. It was decided to set up a demonstration to show how these different networks could be interconnected to transmit data around the world using “Inter-network Gateways”, land and subsea cables…. And satellites. And so this experiment was set up – which Vint Cerf (the father of the Internet) described as “The first demonstration of the Internet as we know it today” Messages were relayed from a Packet Radio van in California onto the Packet Radio Net…. Across onto ARPANET…. Transmitted across country to Etam earth station… relayed via Intelsat Iva to Tanum in Sweden on the SATNET network, via land and sub-sea cable to NORSTAR in Norway… by subsea cable to UCL in London… across country to Goonhilly… back over Intelsat IVa to ETAM and finally via ARPANet again to the Information Sciences Institute of Southern California. Perhaps not me most efficient internet message ever sent! ….. But then again…. Possibly not the slowest either!
- #22 From early trial to commercial service….. Up to 120 Mbit/S TDMA But only really for telecom carriers (not for individual businesses)
- #23 How TDMA works….. Each station transmits in an allocated time slot Trick – to fill them all up without timing clashes
- #24 Businesses demanded satellite services for data transfer…. Only available solution was direct modem to modem service Later supplemented by proprietary multiple access solutions These could transfer IP packets but were not really capable of routing We needed a solution for IP routing via satellite….
- #25 In the Satellite TV world Analogue TV – in the form of D-MAC was being replaced by DVB DVB chip sets manufactured in huge quantities became extremely cheap…..
- #26 The structure of IP datagrams is very similar to that of an MPEG (DVB) packet ….. And therefore it was relatively easy to encapsulate IP within DVB
- #27 The DVB-RCS system uses DVB – Digital Video Broadcast - system to transmit a large forward carrier. It is capable of carrying multiple IP streams and is broadcast to the entire satellite footprint. Receiving terminals will pick up all of the data, but much like TCP/IP will simply discard packets that are not addressed directly to it. Because the DVB signal is transmitted from a large satellite earth station, the signal can be powerful – and have sufficient bandwidth to carry all the data necessary. The RCS – Return Channel System – is quite different. Typically a network might consist of a set of hundreds of users. The antennas are small with limited transmit power – and more importantly they all want to access the single hub station. The answer is to use Time Division Multiple Access (TDMA) where each terminal is allocated a time slot in which to transmit. In the DVB-RCS system, congestion usually occurs when all of the time slots are fully allocated. When that happens it is possible for the transmitter to be commanded to jump to an additional adjacent frequency and start a new TDMA channel.
- #28 The “elders of the internet” devised a clever mechanism to avoid network congestion. Built into every TCP/IP stack is a “Slow Start” algorithm which throttles back the speed of outgoing packets until the round-trip delay has been measured. Since round trip delay is a good indication congestion, the speed will not build up until several packet acknowledgements have been received. Thereafter, the packet speed will rapidly ramp up until the first packet loss is detected at which point the speed will again be throttled – but this time to 50%. Unfortunately for satellite internet, the round trip time due to the limitation of the speed of light time to the satellite and back is around 600mS (and to make matters worse, the “ACK” must also suffer this 600mS delay)…. and this is interpreted by the TCP / IP stack as congestion and the data packets are reduced in speed to a whimper….. Which is unfortunate when the customer has paid good money for the satellite capacity! There is a solution. In the hub station, a performance enhancing proxy reads each TCP/IP header and as well as forwarding the packet over the satellite… instead of waiting for the reply, immediately sends its own “ACK” to the sender rather than waiting for the return via the satellite link This works very well – except for IPSEC VPN networks – where the header is encrypted so the proxy can’t read the “source address”
- #33 Exomars (TGO) joining MRO, ODY MEX, Maven as a CCSDS spacecraft Still mandroulic managed point to point links
- #34 Current - point to point links
- #35 The idea of IPN – why not use terrestrial protocols
- #36 Source and destination are always connected - this is a key one. Spacecraft are not visiable to ground station all the time. Even the ISS.
- #38 Interplanetary internet – Vint Cerf.
- #39 This is to aim human exploration of surface of distant plant – eg mars