## STP enhancements on z14 ZR1 

Important:  For more information about configuring an STP CTN with three or more servers, see the Important Considerations for STP server role assignments  white paper that is available at the IBM Techdocs Library website. 

If the guidelines are not followed, it might result in all the servers in the CTN becoming unsynchronized. This condition results in a sysplex-wide outage. 

STP on z14 ZR1 features the following enhancements: 

GLYPH<SM590000> Additional stratum level 

The limit was STP Stratum 3 before z14. The extra stratum allows CPCs to operate as part of CTN at STP stratum level 4, which can avoid the extra complexity and expense of system reconfiguration. 

Warning:  This extra stratum level should be used only as a temporary state during reconfiguration. Customer should not run with machines at stratum level 4 for extended periods because of the lower quality of the time synchronization. 

GLYPH<SM590000> Graphical display of a Coordinated Timing Network (CTN) 

This graphical display improved the user interface to STP controls. This type of visual display of the CTN status, which provided a clearer view of CTNs, can avoid outages, such as a user intentionally took down the CTS, but did not realize the BTS was down. 

For more information about STP configuration, see the following publications: 

GLYPH<SM590000> Server Time Protocol Planning Guide , SG24-7280 

GLYPH<SM590000> Server Time Protocol Implementation Guide , SG24-7281 

GLYPH<SM590000> Server Time Protocol Recovery Guide,  SG24-7380 

## Pulse per second input 

A pulse per second (PPS) signal can be received from an external time source (ETS) device. One PPS port is available on each of the two oscillator cards. These cards are installed into slots LG11 and LG12 of the CPC drawer rear of the frame of z14 ZR1 servers (see Figure 2-20 on page 49). 

Connections to the CPC drawer provide redundancy for continued operation and concurrent maintenance when a single oscillator card fails. Each oscillator card includes a Bayonet Neill-Concelman (BNC) connector for PPS connection support, which attaches to two different ETSs. Two PPS connections from two different ETSs are preferable for redundancy. 

The time accuracy of an STP-only CTN is improved by adding an ETS device with the PPS output signal. STP tracks the highly stable accurate PPS signal from ETSs. It maintains accuracy of 10 µs as measuredat the PPS input of the z14 ZR1 server. If STP uses an NTP server without PPS, a time accuracy of 100 meters (328 feet) to the ETS is maintained. ETSs with PPS output are available from various vendors that offer network timing solutions. 

