### ptp_nj

```{eval-rst}
.. plantuml::

   @startuml
   title NTP -> PTP Grandmaster -> Slaves (vertical)
   
   top to bottom direction
   
   actor "External NTP\nServers" as NTP
   node "Grandmaster (Ubuntu)\nConnectX-6 NIC" as GM
   node "L2 Switch / Fabric\n(PTP Transparent/Boundary optional)" as SW
   node "Slave #1 (Ubuntu)\nConnectX-6 NIC" as S1
   node "Slave #N (Ubuntu)\nConnectX-6 NIC" as SN
   
   NTP -down-> GM : NTP (UDP/123)\nchrony disciplines CLOCK_REALTIME
   GM -down-> SW : PTP Announce/Sync\nptp4l (master, HW TS)
   SW -down-> S1 : PTP packets
   SW -down-> SN : PTP packets
   
   GM -[hidden]down-> S1
   
   note right of GM
     GM services:
     - chrony (NTP -> system clock)
     - ptp4l: master (-S, HW TS)
     - phc2sys: CLOCK_REALTIME -> /dev/ptp0
   end note
   
   note right of S1
     Slave services:
     - ptp4l (slave, HW TS)
     - phc2sys: /dev/ptp0 -> CLOCK_REALTIME
     - chrony disabled or no servers
   end note
   
   note right of SW
     If switch supports PTP
     Transparent/Boundary Clock,
     stability improves.
   end note
   @enduml