Daily Image
13-06-2025
LOFAR Multicast roll-out
| Submitter: | For the CEP Project: Wilco Baan Hofman, Jan David Mol & Steyn Hulshof |
| Description: | One of the major improvements envisioned for LOFAR2.0 is the network connection, the central nervous system of the telescope. In addition to an order of magnitude increase in data transfer rates, LOFAR2.0 will use Multicast. Multicast is a network technology that allows the same data to be sent once to groups of devices, replicating inside the network. A sender only needs to transmit the data once, and interested parties can subscribe to the Multicast group. The same technology is used for TV broadcasts and within Internet Service Provider networks for IPTV. Multicast allows us to duplicate antenna data streams in the network. This has three important implications. First, it makes LOFAR more flexible, as it enables streaming data to multiple users and science cases. In addition, we can run A/B and development tests with two software versions on the same data, which directly benefits the Cobalt3 software development. And finally, it allows us to remove the first transpose action in the Cobalt software, and transition to a new Cobalt architecture without Infiniband. Network changes impact all LOFAR sub-systems. This makes changing it a potentially tedious task. For LOFAR2.0 the Multicast roll-out was planned for 20 May, during a busy day dedicated to this effort. A core team of experts spent the full day to update the system and fixing resulting problems. All three LOFAR2.0 Production Test System stations were transferred to the LOFAR2.0 network, which includes better security through segmentation and filtering. This reduces the risk of failures, as problematic devices can now only cause trouble within a station and will not affect the entire network. The Uniboard configuration was updated to use unique MAC addresses, and to transmit to a Multicast group. The first change removed tens of thousands MAC moves per second in the LOFAR switches, which were not within Ethernet specifications. The second change ensures that the Uniboards never send data to unknown addresses, which can flood the entire network. These two changes make the LOFAR network fully Ethernet compliant and more robust. The next step was to enable Multicast in the network itself. The transfer to Multicast encountered many small and some large hurdles and required some additional bug fixing and updating on the next day. The system was operational again by Thursday 22 May. This change has achieved many milestones needed for the LOFAR2.0 network, and allows the new LOFAR2.0 stations to connect directly to the new network. The image shows how data streams from the router receiving the station data into the Cobalt correlator nodes (green and blue lines in the image). Center top is the router, which talks to the top-rack switch ACX-B3-0. From the switch the Cobalt2 nodes are receiving multiple data streams with different data rates. Node CBT206 is subscribed to 6 and 9 Gbps, at the same time Cobalt node CBT201 subscribes to 3 and 6 Gbps. Receiving these two simultaneous streams is the trademark of a Multicast system. |
| Copyright: | CEP Project team |
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