STP over coupling links provides time synchronization to all systems. Selection of the  appropriate CF link technology Coupling Express Long Reach (CE LR) or Integrate Coupling  Adaptor Short Reach (ICA SR and SR1.1) depends on the system configuration and how  distant they are physically. For more information about link technologies, see “Coupling links”  on page 196. Parallel Sysplex is an enabling technology that allows highly reliable, redundant, and robust  IBM Z technology to achieve near-continuous availability. A Parallel Sysplex consists of one or  more (z/OS) operating system images that are coupled through one or more Coupling  Facilities.  A correctly configured Parallel Sysplex cluster maximizes availability in the following ways: Note:  Parallel sysplex coupling and timing links connectivity for z15 (M/T 8561) is  supported to N-2 generation CPCs (z15, z14, z13/z13s).  Through state-of-the-art cluster technology, the power of multiple images can be harnessed  to work in concert on common workloads. The IBM Z Parallel Sysplex cluster takes the  commercial strengths of the platform to improved levels of system management, competitive  price performance, scalable growth, and continuous availability. The LPAR that is running the CFCC can be on z15, z14/z14 ZR1, z13, and z13s systems. For  more information about CFCC requirements for supported systems, see “Coupling facility and  CFCC considerations” on page 288. Consideration:  z15, z14, z14 ZR1, z13, and z13s servers cannot coexist in the same  sysplex with System zEC12 or earlier generation systems. 3.9.1 CF Control Code GLYPH<SM590000> Continuous availability: Changes can be introduced, such as software upgrades, one  image at a time, while the remaining images continue to process work. For more  information, see  Parallel Sysplex Application Considerations , SG24-6523. GLYPH<SM590000> High capacity: 1- 32 z/OS images in a Parallel Sysplex operating as a single system. GLYPH<SM590000> Dynamic workload balancing: Because it is viewed as a single logical resource, work can  be directed to any operating system image in a Parallel Sysplex cluster that has available  capacity.  GLYPH<SM590000> Systems management: The architecture defines the infrastructure to satisfy client  requirements for continuous availability. It also provides techniques for achieving simplified  systems management consistent with this requirement. GLYPH<SM590000> Resource sharing: Several base z/OS components use CF shared storage. This  configuration enables sharing of physical resources with significant improvements in cost,  performance, and simplified systems management. GLYPH<SM590000> Single logical system: The collection of system images in the Parallel Sysplex is displayed  as a single entity to the operator, user, and database administrator. A single system view  means reduced complexity from operational and definition perspectives. GLYPH<SM590000> N-2 support: Multiple hardware generations (normally three) are supported in the same  Parallel Sysplex. This configuration provides for a gradual evolution of the systems in the  Parallel Sysplex without changing all of them simultaneously. Software support for multiple  releases or versions is also supported. Chapter 3. Central processor complex design  145