New ACU Configuration

Network Interfaces

The ACU requires two (minimum) interfaces:
  • one for site network
  • (10MBit) interface for the CCU and SCU.

Currently the second interface uses a PCI Ethernet card with a 10 Base 2 (coaxial) interface, and media converters. A 10base2 to fiber converter drives the SCU, and the other end terminates at the CCU. One plan was to try to reduce the parts count by using a PCI card which drives the SCU fiber directly (like a AL-2700?) and to change use a thin-net to AUI on the CCU chassis. This would break the CCU-SCU sharing of the low-bandwidth link (a good thing).

With the revised configuration shown below, the ACU now has three network interfaces: one thinnet for the site (100/1000MB); one thinnet (10MB) directly to the CCU; and one fiber (10MB) to the SCU.

The new machines purchased to upgrade the ACU have two 1000/100/10 thinnet interfaces built-in. Additional components needed:
  • AUI-to thinnet for CCU chassis
  • 10Mbit fiber PCI card, (possibly new fiber connectors on SCU fiber?)
  • a serial card for the 1-PPS timing signal (one is available on motherboard, needs connector)


Network Interfaces

The configuration should follow the ACU host configuration noted here. Obviously the network portions will differ. I'd use separate subnets on the CCU and SCU networks. (The existing CCU/SCU network interface is; I'd keep that for CCU and add for the SCU interface.)

Time Synchronization

The ACU uses a 1PPS signal (with converter box) into the DCD pin of a serial port. A helper program (ntp_shmem) examines the apparent clock offset and disciplines ntp via its shared memory clock interface.


  • Verify number of PCI slots in gbtspare machines [2 PCI and 2 PCIe slots, enough to add the fiber card] DONE
  • Order two fiber network cards (Chris suggested the AT-2451FTX Allied Telesis) for SCU [1+spare] DONE
  • Install connector/cable for serial port
  • Install gbtspare1 at telescope as 'prima'
  • Install gbtspare2 in equipment room as 'donna'
  • Locate a thinnet to AUI adapter for the CCU VME chassis (have one in hand) DONE
  • Replace 10Base2 (coax) ethernet cabling from CCU to ACU with thinnet link
  • Using a crossover cable and thinnet to AUI, connect the thinnet link to the CCU (Need to locate crossover cable PICK)
  • Replace optical jumper cable (if necessary) to connect the SCU fiber to the AT-2451FX card
  • Connect 1-PPS signal into serial port DCD pin and reconfigure shmem_clock to use correct tty port
  • Verify everything works

-- JoeBrandt - 27 May 2009
Topic revision: r7 - 2009-06-01, JoeBrandt
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