White Rabbit Switch Hardware 4.0


This page summarizes the GSI requirements in context with the development of a new version of the White Rabbit Switch.

A workshop on this topic took place on 26 June 2020. The slides are available here.

We (GSI/FAIR) have purchased ~350 pcs of the WRS hardware version 3. However, we will need more switches in the future
  • for extension of the facility
  • as replacement of broken WRS
Hence, we will need to buy more WRS in the future.

Regarding WRS v3, we expect
  • it will be difficult to build new WRS v3 in a few years due to electric components no longer available on the market
  • at some moment, support will come to an end because
    • FPGA resources on WRS v3 are exhausted
    • WRS developer will focus on WRS v4

To conclude, the option of purchasing and using WRS v4 is important.


A main reason to obtain WRS v4 is as drop-in replacement for WRS v3. The most important criterea are
  • the WRS v4 must be 1U. It must physically fit in the the same place as WRS v3, but it may be longer (towards the back of the rack)
  • the WRS v4 must support at least 18 ports @1GBit/s Ethernet
    • we have thousands of nodes that support WR @1GBit/s only
    • if the switch has more ports, the additional ports may support WR @ 10GBit/s
    • all ports must be capable of Ethernet switching. Our main use-case is broadcast traffic with upper bound latency

My (db) five cent: I don't care about stuff like redundant power supplies that make the switch more expensive. Just assume the following we need to replace 30 half-broken WRS we have only 100kEuros: If I had the choice between a basic switch for 3k/piece and a fancy switch for 5k/piece, it makes more sense to replace all 30 half broken switches by new basic ones. It does not help if I can only buy 20 fancy switches, but there remain 10 dying old switches jeopardizing the network.


These are the main requirements.
  • locator light on the back (usefull when you have 20 WRS in the rack and you like to replace one in operatoin, it is important to find the right mains-cable)
  • most important: continued supply of WRS as drop-in replacement for WRS v3. Use case: Broken WRS3 switch in a rack. The new switch must have at least 18 ports with 1GB. Height 1U, it must physically fit into the same space as WRS3.
  • full backward compatibility to 1GBit for at least 18 ports
  • 20 ports or 24 ports are fine too. In case there are a few additional (to the 18) ports, they may support 10 GBit/s
  • Ethernet switching between all ports with focus on low latency for broadcast traffic; of course: all 'soft' features (management via ssh, dot-config, SNMP, VLANs....) of hardware version 3 shall be supported on version 4.
  • some solution that prevents dust sucked (by internal fans) into connectors on the front side
  • price
    • comparable to WRS v3
    • better skip fancy stuff like super redundant hot swappable fans and power supplies?
    • but use fans with a large MTBF
  • 4 IOs for clocks; PPS and 10MHz in, PPS and 10MHz out
  • form factor 1U; must fit in the same space as WRS v3; but it may be a bit longer (towards the back of the rack), if this makes cooling or building easier
  • front panel connectors may be located differently on the front panel (in case this helps for the cooling concept)
  • no need for a display; it just makes cooling and mechanics more difficult and has a limited life-time
  • full open hardware design
  • of course: CE and so on...

-- DietrichBeck - 6 Aug 2020
Topic revision: r3 - 06 Aug 2020, DietrichBeck
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