2. The PTS SE recognizes the checkstop pending condition, and calls the PTS SE STP code. 

3. The PTS SE sends an ECAR request thorough HMC to the Backup Time Server (BTS) SE. 

4. The BTS SE communicates with the BTS to start the takeover. 

ECAR support is faster than the original CAR support because the console path changes from a 2-way path to a 1-way path. Also, almost no lag time is incurred between the system checkstop and the start of CAR processing. Because the request is generated from the PTS before system logging, it avoids the potential of recovery being held up. 

## Requirements 

ECAR is available on z14 M0x, z14 ZR1, and z13/z13s systems on Driver 27 and later only. In a mixed environment with previous generation machines, you should define a z14 M0x, z13, or z13s system as the PTS and CTS. 

Attention: z14 ZR1 does not support InfiniBand connectivity; therefore, it cannot be connected by using coupling/timing links to a zEC12 or zBC12 CPC. As such, in a CTN with zEC12 or zBC12, the z14 ZR1 cannot be assigned a role (PTS, CTS or Arbiter; its failure affects the time synchronization functionality of other servers in the CTN). 

## 11.5.8 CTN Split and Merge 

For more information about planning and setup, 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 

With HMC 2.14.1, STP management was enhanced with two new actions: CTN split and CTN merge. 

## CTN Split 

The HMC menus for Server Time Protocol (STP) were enhanced to provide support when one or more systems must be split in to a separate CTN without interruption in the clock source. 

The task is available under the Advanced Actions menu in the Manage System Time task. Several checks are performed to avoid potential disruptive actions. If targeted CTN only has members with the roles, task launch fails with error message. If targeted CTN has at least one system without any roles, task launches. An informational warning is presented to the user to acknowledge that sysplex workloads are divided appropriately. 

## Merging two CTNs 

When two separate CTNs must be merged in to the single CTN without interruption in the clock source, the system administrator must perform the Join existing CTN action, which is available in the Advanced Actions menu. 

Note:  After joining the selected CTN, all systems within the current CTN are synchronized with the Current Time Server of the selected CTN. A coupling link must be in place that connects the CTS of the selected CTN and the CTS of the current CTN. 

