Support for Radio Astronomy

Michael Enrico

DANTE

What is VLBI?

Radio telescope

Correlator

Data flows(RT or non-RT)

Picture of (part of) MkIV Correlator...

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

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

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

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

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

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)

EVN Traffic Flows over GÉANT

UK

SE

FR

NLBE

DE1

DE2

CZ

PL

CH

IT

AT

SURFnet

JANET

GARR

PSNC

DFN

NORDUnet

2.5G10G

256M

1G 512M ??

Potential Upgrades to GÉANT

UK

SE

FR

NLBE

DE1

DE2

CZ

PL

CH

IT

AT

SURFnet

JANET

GARR

PSNC

DFN

NORDUnet

2.5G10G

256M 512M 1G

EVN Traffic over GÉANT

UK

SE

FR

NLBE

DE1

DE2

CZ

PL

CH

IT

AT

SURFnet

JANET

GARR

PSNC

DFN

NORDUnet

2.5G10G

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

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

Static Routes

• Useful for dumping complete flows under certain failure conditions

• Leaves a reduced number of flows intact

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!

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

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”