Support for Radio Astronomy

1. Support for Radio Astronomy Michael Enrico DANTE

2. What is VLBI? Radio telescope Correlator Data flows (RT or non-RT)

3. Picture of (part of) MkIV Correlator...

4. Current arrangement uses tapes... • Tape technology nearing EOL • One supplier left • $1200 per tape • Drives no longer available • Expensive logistics • Effectively limits bit rates • Hence limits resolution • Slow turn around time • Real-time measurement not possible • Inflexible duty cycles

5. Information NRENs would like • BW requirements (what does 1Gbps really mean?) • confirm that service required is IP packet transport rather than SONET/SDH transport or other? IP • traffic profiles (continuous or bursty; if bursty then nature of burstiness) • does the traffic carry real-time or semi-real-time data flows (e.g. is it fed more or less directly from the radio telescope?) or is the traffic the result of some bulk FTP-like file transfers? • UDP or TCP? • if UDP, then is there some sort of higher layer congestion control? • sensitivity to transmission delays, packet loss, packet reordering, etc? • single UDP/TCP flows or multiple flows per radio telescope site? • packet sizes and rates • number and nature of traffic sources and sinks • IP addressing

6. What has been agreed so far? • NREN Policy Committee met on 28th Nov • Agreed in principle to support EVN PoC • PoC means: • Up to 5 radio telescope sites (not incl NL) • Duration: up to end of GÉANT contract (Nov 2004) • Support means: • Best effort IP service transiting NRENs and GÉANT • No significant upgrades to GÉANT (at least initially) • Support 512M and 1G real time modes of operation • Use existing NREN access ports • Limited resilience

7. Success Criteria (for PoC) • NREN/GÉANT point of view: • Connect at least three sites to JIVE • Observe significant usage (time and BW) • EVN point of view: • Perform good science in a more timely fashion than would have otherwise been possible • e.g. Real time network verification of burst phenomena

8. Who is supporting PoC? • Radio astronomy community (EVN) • JIVE • Radio telescope sites: • Westerbork (NL) • Effelsberg (DE) • Onsala Space Observatory (SE) • Medicina (IT) • Jodrell Bank (UK) • Torun (PL) • NRENs • GARR, UKERNA, DFN, NORDUnet (SUNET), PSNC • SURFnet (all roads lead to Dwingeloo!) • DANTE

9. EVN eVLBI Traffic Profile • 256Mbps, 512Mbps or 1Gbps modes of operation • per radio telescope site • Single unidirectional UDP flows towards JIVE • except “1Gbps” which is, in fact, two flows of ~512Mbps • where GE transport used then 2 x GE needed per “1G” flow • Current observation duty cycle: • 3 sessions per year each lasting ~25 days (continuous) • This is geared to tape usage logistics • Can be much more versatile with real-time network connectivity • Reasonably tolerant to: • Some packet loss and re-ordering • Differential transmission delays (up to ~100s of ms)

10. NORDUnet JANET SURFnet PSNC DFN GARR EVN Traffic Flows over GÉANT SE UK PL CZ BE NL DE2 DE1 FR CH AT 512M ?? 256M  1G  2.5G 10G IT

11. NORDUnet JANET SURFnet PSNC DFN GARR Potential Upgrades to GÉANT SE UK PL CZ BE NL DE2 DE1 FR CH AT 2.5G 10G IT

12. NORDUnet JANET SURFnet PSNC DFN GARR EVN Traffic over GÉANT SE UK PL CZ BE NL DE2 DE1 FR CH AT 256M  512M  1G  2.5G 10G IT

13. Things still to consider… (for PoC) • Better (pre-upgrade) support for 512M operation • Other failure scenarios (e.g. fail UK-NL and DE1-NL) • How to cope with them: • Use LBE (Less Than Best Effort)? • Static routing technique? • MPLS Traffic Engineering Techniques? • Quantify transmission delays for EVN traffic flows

14. LBE Solution • Mark eVLBI traffic as LBE • Multiple failures scenario will not then see BE being subjected to a DoS attack by the radio astronomers! • However, many (possibly all) telescope flows will experience huge amounts of packet loss • This may render all the eVLBI data useless

15. Static Routes • Useful for dumping complete flows under certain failure conditions • Leaves a reduced number of flows intact

16. MPLS Solution • JIVE prefix(es) (for eVLBI sinks) advertised by SURFnet tagged with community (e.g. “EVN”) • For these routes, on NL1, apply routing policy “next-hop-self” • Establish (unidirectional) LSPs (one per sending site) from ingress router to NL1 • For each LSP specify strict primary (and maybe secondary) path • However, will traffic simply reroute if LSPs are down? • Highly undesirable!

17. Overall Status of PoC • Early days! • NRENs mostly ready • SURFnet have already started on the necessary upgrades • Little progress on Local Loops: • NRENs/observatories working on this • First local loops should be in place by mid-2003 • More work to be done by EVN community: • Initial PC-PC tests (NREN/Uni POP to JIVE) to be done • Next generation of specialist VLBI equipment (so-called “Mk V”) has to be acquired and tested by observatories • Finally, real-time telescope to correlator observations at 256M, 512M and 1G flow rates

18. Beyond the PoC • Ultimately EVN would like to connect all 14 radio telescopes in Europe • includes one in Ukraine • And extend to other more distant observatories in: • Puerto Rico • South Africa • China • Probably needs bespoke (wavelength based?) solution • Beyond scope of current GÉANT contract • Need to consider this (and other GRID support projects) when designing “son of GÉANT”