Re: [CCAMP] Magnus Westerlund's Discuss on draft-ietf-ccamp-rsvp-te-bandwidth-availability-14: (with DISCUSS)

["Yemin (Amy)" <[e-mail]>]

Hi Magnus, 

Thanks for the comments, please see reply inline below. 

BR,
Amy
________________________________________
发件人: Magnus Westerlund via Datatracker [[e-mail]]
发送时间: 2019年4月8日 18:13
收件人: The IESG
抄送: [e-mail]; Daniele Ceccarelli; [e-mail]; [e-mail]; [e-mail]
主题: Magnus Westerlund's Discuss on draft-ietf-ccamp-rsvp-te-bandwidth-availability-14: (with DISCUSS)

Magnus Westerlund has entered the following ballot position for
draft-ietf-ccamp-rsvp-te-bandwidth-availability-14: Discuss

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https://datatracker.ietf.org/doc/draft-ietf-ccamp-rsvp-te-bandwidth-availability/



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DISCUSS:
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Section 3.1:

      Availability (4 octets): a 32-bit floating point number describes
      the decimal value of availability requirement for this bandwidth
      request. The value MUST be less than 1and is usually expressed in
      the value of 0.99/0.999/0.9999/0.99999.

It appears that this format has some very clear limitations when it comes to
store availability numbers. Assuming that this 32-bit float is an IEEE-754
representation which should be explicitly stated.

In that case representing availabilities higher than 0.999999 starts to
introduce significant errors in relation to intended precision. Intended value
Error                                             Actual value 0.999999
 -1.3278961181640625E-8              0.999998986721038818359375 0.9999999
 -1.920928955078125E-8                0.99999988079071044921875 0.99999999
1E-8                                                   1 (Which is not allowed)

So at a minimal the limitations for what is practical to express needs to be
provided. Secondly, are this range sufficient in all cases?
[Amy] The floating point number may not be the perfect unit. But since the OSPF extension RFC8330 use the floating-point number, we would like to continue using it. 
Regarding the range, normally five 9s 0.99999 is highest value in telecom network, that's 5 minutes outage in a year.
So floating point is capable to represent this range.