External Time Source

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An STP CTN can be configured to use a Network Time Protocol (NTP) or Precision Time Protocol (PTP) server with pulse per second (PPS) output as its external time source. These external time devices are available worldwide from several vendors that provide network timing solutions. The NTP and PTP timing networks connect directly to the oscillator card(s) in the CPC drawer(s) because the NTP or PTP client runs in a firmware partition within the CPC drawer.

Precision Time Protocol (PTP) considerations: To exploit Precision Time Protocol (PTP) for STP, a PTP TimeTransmitter (PTP time source) must be present on the existing, Ethernet based management network. In addition, it is recommended that all network devices connected between the PTP time source and the CPC drawer(s) have PTP support enabled.

External Time Source (ETS) IP network considerations: When planning the Ethernet based External Time Source network, it is recommended that one or two subnets corresponding to ETS1 and ETS2 are routable to the desired NTP/PTP time source(s).

Important:
  • Ethernet switch ports must support auto-negotiation at 10/100/1000 Mbps when connected to the ETS1/ETS2 ports. During system initialization (IML/POR), ETS ports undergo brief link state transitions as part of normal timing synchronization causing Ethernet switch ports fixed at ≥1 Gbps (without auto-negotiation) to misinterpret this as link flapping, triggering protection mechanisms and resulting in STP link loss.
  • One NTP or PTP time server can be configured to each PPS port.
  • Connecting the pulse per second coaxial cable to the NTP or PTP time server may be done by either customer or service personnel.
  • ETS1/ETS2 ports support 1000BASE-T Ethernet connections with auto-negotiation up to 1 GbE full duplex.
  • When installing ETS Ethernet cables, consider the minimum recommended bend radius. Generally, it is recommended that the bend radius of solid core Ethernet to be no less than 8 times the size of the outer jacket; consult your Ethernet vendor for exact specifications.
  • Installation with top exit (FC 5819) or (FC 5823) feature:
    • ETS cables should enter the frame through the D hole at the top, front of the A frame.
  • Installation with bottom exit (FC 5820) feature:
    • ETS cables should be pre-installed and terminated with excess of 5.5 meters from the bottom cable exit point in the back of the A frame. This includes the (up to two) Ethernet cables required for ETS1/ETS2 connections and the (up to two) coaxial cables for PPS0/PPS1 (if configured).
    • During installation, these cables should be routed through the hole on the upper portion of the A frame and back down to CPC drawer A10/A15.
  • For more information, see 9176 Single Frame External Cabling Best Practices Guide (https://www.ibm.com/support/pages/node/7276709).

The Ethernet output of the NTP or PTP time server is connected to the input Ethernet connector provided on the oscillator card on the 9176.

  • If the 9176 has 1 CPC drawer, the PPS and ETS ports correspond to the oscillator cards as follows:
    • PPS0 to port J02 of OSC0 (H101) in CPC0 (ACP0)
    • PPS1 to port J02 of OSC1 (H102) in CPC0 (ACP0)
    • ETS1 to port J03 of OSC0 (H101) in CPC0 (ACP0)
    • ETS2 to port J03 of OSC1 (H102) in CPC0 (ACP0)
    Figure 1. Single CPC drawer configuration - front view
    This graphic shows the PPS ports for single CPC drawer configuration.

  • If the 9176 has 2 CPC drawers, the PPS and ETS ports correspond to the oscillator cards as follows:
    • PPS0 to port J02 of OSC0 (H101) in CPC0 (ACP0)
    • PPS1 to port J02 of OSC0 (H101) in CPC1 (ACP1)
    • ETS1 to port J03 of OSC0 (H101) in CPC0 (ACP0)
    • ETS2 to port J03 of OSC1 (H102) in CPC1 (ACP1)
    Figure 2. Multiple CPC drawer configuration - front view
    This graphic shows the PPS ports for single CPC drawer configuration.

The pulse per second (PPS) port on the oscillator cards requires a signal with the characteristics listed in Table 1. Your network timing solution vendor can assist with the necessary cabling and signal distribution hardware required to meet these characteristics for your specific machine installation.

With a low signal loss PPS distribution, timing solutions can be achieved to exceed 150 feet (45 meters) between the last distribution point and the oscillator card PPS port.

For the input signal received at the oscillator card PPS port, the rise time/fall time of the PPS signal must be shorter or equal to 50 microseconds.

Table 1. PPS signal characteristics
  Unit of measure Minimum Typical Maximum
Voltage Level LOW volt 0   0,15
Voltage Level HIGH volt 3,2   5,2
Rise time microsecond     50
Fall time microsecond     50
Pulse width millisecond 50 125 450