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Recent eVLBI developments at JIVE

Explore the latest developments in eVLBI at the Joint Institute for VLBI in Europe (JIVE), covering protocols, tuning issues, tests, and results. Discover the move to disk-based operations, enhanced reliability, and the potential of real-time eVLBI using fiber optics. This overview delves into network monitoring, centralised control, and future advancements in VLBI technology.

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Recent eVLBI developments at JIVE

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  1. Recent eVLBI developments at JIVE Arpad Szomoru Joint Institute for VLBI in Europe

  2. Outline • Introduction • Protocols, tuning issues • Tests and results • ftp-based • Dual buffered • Single buffered • Real-time • Jumbo frames • Network monitoring • Centralised control

  3. Introduction Disk based recording • Move to disk-based operations nearly complete • More reliable, data quality • Cheaper to maintain • Ease of use • Direct access compared • Unattended operations • eVLBI: the future? • No consumables • High bandwidth • Fast turn-around eVLBI using fiber

  4. POC targets: • for the EVN and JIVE • Feasibility of eVLBI:- Costs, timescales, logistics. • Standards:- Protocols, parameter tuning, procedures at telescope and correlator. • New Capabilities:- Higher data rates, improved reliability, quicker response. • for GÉANT and the NRENs • To see significant network usage with multiple Gbit streams converging on JIVE. • Minimum is three telescopes (not including Westerbork) • Must be seen to enable new science and not just solve an existing data-transport problem • Real-time operation is seen as the ultimate aim, buffered operation accepted as a development stage.

  5. Current status: • JIVE: 6 lambdas via Netherlight, each capable of 1 Gbps • 1 Gbps connections to Westerbork, Torun, Onsala, (Metsahovi?), 2.5 to Jodrell • 155 Mbps to Arecibo • Connection of Medicina at 1 Gbps planned later this year GE lines to correlator LX Optics converters Cisco ONS 15252 Optical Splitters Fibre pair from Amsterdam Correlator Interface

  6. Protocols • Use of existing protocols, available hardware • TCP: maximal reliability, very sensitive to congestion • UDP: connectionless, fast(er) but not reliable (enough?) • Different protocols will be tested in the near future (tsunami?)

  7. Tuning issues • Dramatic improvement of TCP performance possible by adjusting default settings: • congestion window: product of roundtrip time and bandwidth • size of queues between kernel and NIC • SACK (Selective Acknowledgment) implementation • MTU size (jumbo frames) • Interrupt moderation: cpu may be bottleneck http://sravot.home.cern.ch/sravot

  8. Tuning issues • Dramatic improvement of TCP performance possible by adjusting default settings: • congestion window: product of roundtrip time and bandwidth • size of queues between kernel and NIC • SACK (Selective Acknowledgment) implementation • MTU size (jumbo frames) • Interrupt moderation: cpu may be bottleneck

  9. Mem-mem transfer via patch

  10. Disk2net2disk via patch, jumbo

  11. Disk2net-net2disk Dwingeloo-Bologna

  12. Network stress test (iperf)

  13. Iperf (TCP) 30s intervals

  14. Mark 5 Motherboard Upgrade • Intel(R) SE7501BR2 • Intel(R) 7501 chip set • Dual Intel(R) Xeon (single, 2.8G, 512K L2 cash installed) • Dual channel DDR266 registered SDRAM (512MB) • Dual peer PCIX 64/100, 2+2 slots32/33 PCI, 2 slots • On-board TX1000 and T10/100 NICs • On-board Ultra320 SCSI • On-board PATA

  15. Test results

  16. Test results

  17. Huygens descent tracking • Data recorded at Mopra and Parkes, flown to Sydney, transported via dedicated 1Gbps lightpath to Jive • Peak transfer rate ~400Mbps • Use of modified tsunami protocol • “slow start” algorithm • Transfer freezes occasionally • Quite buggy (but not everybody thinks so..)

  18. eVLBI Transfer modes • ftp-based: bandwidth not critical, has greatly improved response to technical problems at telescopes • Dual buffered: recorded on Mk5 diskpack, transferred through disk2net and net2disk, played back at correlator • Single buffered: streamed directly from formatters to diskpacks at JIVE • Real-time: directly from formatters to correlator without disk buffering

  19. First real-time eVLBI Image eVLBI Transfer modes • ftp-based: bandwidth not critical, has greatly improved response to technical problems at telescopes • Dual buffered: recorded on Mk5 diskpack, transferred through disk2net and net2disk, played back at correlator • Single buffered: streamed directly from formatters to diskpacks at JIVE • Real-time: directly from formatters to correlator without disk buffering

  20. IRC+10420 eVLBI, September 2004 MERLIN, March 2002

  21. Jumbo frames • Tested with: • Onsala @4470 • Torun @8192 • Westerbork @9000 • Results inconclusive, but… • Transfer between Mk5’s (bench) • UDP: <500 Mbps • TCP: >500 Mbps, ONLY with jumbo frames • Other hardware platform needed?

  22. Network monitoring • BWCTL installed at most stations • More measuring points along the way needed • Script-based tools for inspection and visualisation of state of network

  23. Centralised control • New operating model for EVN; correlator as integral part of network

  24. Centralised control • New operating model for EVN; correlator as integral part of network • Monitoring tools at stations • Reliability of correlator, stability of Mark5 units • Choice of platform?

  25. Conclusions • Mark5 not very well suited for eVLBI • Hardware limitations (interrupt conflicts, outdated motherboards, proprietary hardware) • Software limitation (stuck to kernel 2.4 because of Jungo drivers, proprietary software) • Next platform? • support for 4Gbps, PCI Xpres? • as much off-the-shelf as possible • as simple as possible (no disks!) • Dedicated lightpaths…

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