Feature Description:

IIN: number of the instances of the current microservice that are invoked in the current trace instance
Scope: Trace
Detail description:
    IIN is the number of the instances of the current microservice that are invoked in the current trace instance. For example, 
the trace instance is A1 -> B1 -> C1 -> D2 ("A" is microservice's name, "1" is the instance id), so the IIN of microservice A
is 1.