[IPFIX] Unit of flowActiveTimeout

Dear all,

I have one question about unit of flowActiveTimeout.

According to RFC 5102, unit of flowActiveTimeout is second.
Why IPFIX doesn't support a timer with a unit smaller than second, e.g.
millisecond or microsecond ? I want to know a history of discussion.

----
5.11.1.  flowActiveTimeout

   Description:
      The number of seconds after which an active Flow is timed out
      anyway, even if there is still a continuous flow of packets.
   Abstract Data Type: unsigned16
   ElementId: 36
   Status: current
   Units: seconds
---

On the other hand, IEs about flow timestamps and packet timestamps have
various units e.g. second, millisecond, microsecond and nanosecond.
---
flowStartSeconds
flowEndSeconds
flowStartMilliseconds
flowEndMilliseconds
flowStartMicroseconds
flowEndMicroseconds
flowStartNanoseconds
flowEndNanoseconds
flowStartDeltaMicroseconds
flowEndDeltaMicroseconds
systemInitTimeMilliseconds
flowStartSysUpTime
flowEndSysUpTime
observationTimeSeconds
observationTimeMilliseconds
observationTimeMicroseconds
observationTimeNanoseconds
---

Also PSAMP IEs about time-based sampling parameter support a unit of
microsecond. 
---
samplingTimeInterval
samplingTimeSpace
---

Best regards.

--

-- 
Shingo KASHIMA <kashima <at> nttv6.net>
NTT Information Sharing Platform Lab.

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