Policies in the Timing Network

  • The timing network is managed by TOS and TOS defines the policies.
  • The timing network is a "field-bus" synchronizing the actions of the accelerator.
  • The operation of the accelerator has the top-most priority.
  • Exceptions from the rules described here require approval by TOS.

General Policies

  • It is the task of TOS to guarantee operation of the timing network and to provide White Rabbit links as well as machine relevant information to connected equipment.
  • The person responsible for connected equipment must support, maintain and operate the equipment and make sure the equipment does not disturb the operation of the timing network.
  • In case connected equipment is suspicious of not following the policies, it is the task of the person responsible for the equipment to prove the equipment is operating correctly or to solve the problem. TOS may disconnect such equipment from the timing network at any time.


  • Support
    • Only equipment provided by TOS is supported by TOS.
    • Don't expect support, if you bring your own equipment.
  • Connection
    • Equipment must not be connected to the network, unless it is successfully registered at TOS.
    • Until further notice, equipment other than the one provided by ACO must not be connected to the network. Equipment must be flashed with "known good" gateware / firmware.
  • All switches in the timing network are provided and managed by TOS.
  • Equipment must not send any traffic to the timing network except WR-PTP. BOOTP tbd.
  • Features like firewalls and VLAN are not guaranteed and connected equipment should not rely on such features.

Priorities and Bandwidth

  • Sending messages across the network in hard real-time is a feature reserved for the data master.
  • Several priorities exist for non real-time networking.
  • Downstream bandwidth.
    • All time critical traffic shares a common budget of bandwidth. The bandwidth is limited to a rate of 100 MBit/s and must be respected even in "bursts".
    • Bandwidth for low priority traffic is limited to a rate of 10 MBit/s.
  • Upstream bandwidth. Not specified - nodes other than the data master must not send any messages at all (except WR-PTP, BOOTP tbd).
  • Interframe gap (Ethernet). The value is defined by TOS. The present (10/2017) value equals the default value.

Examples for Policy Violation

  • Access to and manipulation of switches.
  • Connecting equipment to a switch ports other than the port it was agreed on by TOS.
  • Connecting equipment that is not registered.
  • Changing the MAC address of registered equipment.
  • MAC address spoofing.
  • Sending network packets other than WR-PTP (BOOTP tbd) to the timing network.

Examples for Policy Conformity

  • Connecting equipment provided by ACO (SCUs, PEXARIAs,...) - if it is registered.

Examples for Exceptions

  • Access to BIOS console of SCUs. This has been decided to save costs for a dedicated management network for SCUs. This is considered as low priority traffic not requiring hard real-time.
  • Using the famous "return channel" or peer-to-peer connections - this must be approved by TOS for each case separately!


The timing network is vital for the real-time control of the accelerator. Don't expect that policies are less strict than for normal networks.

At present (11/2019), some features of the timing network can only be achieved by conventions. On-going development might help to provide better means for managing and controlling the resources of the network. However, an increase of the performance is almost excluded. Moore's law does not apply here!

At present (11/2019) messages via the return channel or peer-to-peer connections are not available.

-- DietrichBeck - 17 Nov 2019
Topic revision: r21 - 17 Nov 2019, DietrichBeck
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