@startuml
skinparam BackgroundColor F0F0F0

participant "Bluetooth Headset" as HS
participant "Pure Phone" as AG

    activate HS
    activate AG
    AG -> HS : Connection establishment
    AG -> HS : Ring
    ...
     -> HS : User initiated action
    HS -> AG : AT+CKPD=200
    AG -> HS : OK
    AG -> HS : SCO link establishment    
@enduml