2.7.6 Setting up Server Time Protocol STP provides the means by which the time of day (TOD) clocks in various systems can be  synchronized by using messages that are transported over coupling links. STP operates  along with the TOD-clock steering facility, which provides a new timing mode, timing states,  external interrupts, and machine check conditions. STP connectivity for z14 ZR1 and CTN roles:  The z14 ZR1 server does not support  coupling connectivity by using the InfiniBand feature. As such, the z14 ZR1 CPC only can  connect for transmitting coupling or timing (STP) data to a z13/z13s or to another z14  M0x/z14 ZR1 CPC. In a CTN that also contains zEC12/zBC12 servers, z14 ZR1 cannot  play a role in the CTN (PTS/BTS/Arbiter) for availability reasons. The HMC provides the user interface to manage an STP-only Coordinated Timing Network  (CTN). Consider the following points when setting up an HMC for STP: GLYPH<SM590000> A CTN ID must be unique for all IBM Z servers that will be part of the CTN. GLYPH<SM590000> To synchronize IBM Z servers to an External Time Source (ETS), network Time Protocol  (NTP) server information (and network connectivity that uses NTP/NTPS protocol with  optional pulse per second [PPS]) must be provided. GLYPH<SM590000> Customer must have the time zone offset, Daylight Saving Time offset, and leap second  offset. GLYPH<SM590000> Optional, the HMC can be configured as an NTP server. GLYPH<SM590000> For the IBM Z servers that are part of a CTN, STP roles must be planned (Preferred,  Backup, and Current Time Servers and Arbiter).  GLYPH<SM590000> As part of a migration, changing the Current Time Server must be done before migration to  the new platform (z14 ZR1). Note:  The z14 ZR1 supports STP stratum level 4. This feature avoids the added  complexity and expense of system reconfiguration. This change must be installed all  systems that might become exposed to this situation. Stratum level 4 should be used only  during a migration, and for a short period. For more information, see Chapter 8, “Preparing for Sysplex and configuring Server Time  Protocol” on page 159 . For more information about planning, implementing, and managing an STP environment, see  the following publications: GLYPH<SM590000> Server Time Protocol Planning Guide , SG24-7280 GLYPH<SM590000> Server Time Protocol Planning Guide , SG24-7280 GLYPH<SM590000> Server Time Protocol Recovery Guide , SG24-7380 2.8 Activities centered on the IODF This section describes the information (I/O configuration) in the IODF. Chapter 2. Planning considerations for CPC in PR/SM mode  17