Subject: Re: [Capwap] AC Timestamp Format for CAPWAP

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Wed, 10 Sep 2008 14:14:17 -0700

This was addressed through the IETF Last Call, and the resulting text
(now in -12) is:
 
4.6.6.  AC Timestamp
 
   The AC Timestamp message element is sent by the AC to synchronize the
   WTP clock.
 
      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Timestamp                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
   Type:   6 for AC Timestamp
 
   Length:   4
 
   Timestamp:   The AC's current time, allowing all of the WTPs to be
      time synchronized in the format defined by Network Time Protocol
      (NTP) in RFC 1305 [RFC1305].  Only the most significant 32 bits of
      the NTP time is included in this field.
 
PatC

________________________________

From: Glenn Chagnot [mailto:[email-masked]] 
Sent: Wednesday, September 10, 2008 12:42 PM
To: Pat Calhoun (pacalhou); [email-masked]
Subject: AC Timestamp Format for CAPWAP

Hi,

The AC timestamp format in section 4.6.6 isn't particularly clear about
the units of the timestamp.  I have included the text from this section
for reference:

   Type:   6 for AC Timestamp

   Length:   4

   Timestamp:   The AC's current time, allowing all of the WTPs to be
time synchronized in the format defined by Network Time Protocol (NTP)
in RFC 1305 [RFC1305].

The way I read the text, I think that the timestamps format should
follow the NTP format defined in RFC-1305.  The text from RFC-1305
states the following with respect to timestamp formats:

"NTP timestamps are represented as a 64-bit unsigned fixed-point number,
in seconds relative to 0h on 1 January 1900. The integer part is in the
first 32 bits and the fraction part in the last 32 bits."

The timestamp field defined in section 4.6.6 is only 4 octets long so
cannot include the above format.  If I am erroneously trying to apply
the RFC-1305 format then please advise as to the units that should be
used in the AC timestamp field.

Thanks,

Glenn

Glenn Chagnot

Chief Architect

VeriWave, Inc.

817-898-0369

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From: "Glenn Chagnot" <[email-masked]>
Date: Wed, 10 Sep 2008 14:41:35 -0500

Hi,

The AC timestamp format in section 4.6.6 isn't particularly clear about the
units of the timestamp.  I have included the text from this section for
reference:

   Type:   6 for AC Timestamp

   Length:   4

   Timestamp:   The AC's current time, allowing all of the WTPs to be time
synchronized in the format defined by Network Time Protocol (NTP) in RFC
1305 [RFC1305].

The way I read the text, I think that the timestamps format should follow
the NTP format defined in RFC-1305.  The text from RFC-1305 states the
following with respect to timestamp formats:

"NTP timestamps are represented as a 64-bit unsigned fixed-point number, in
seconds relative to 0h on 1 January 1900. The integer part is in the first
32 bits and the fraction part in the last 32 bits."

The timestamp field defined in section 4.6.6 is only 4 octets long so cannot
include the above format.  If I am erroneously trying to apply the RFC-1305
format then please advise as to the units that should be used in the AC
timestamp field.

Thanks,

Glenn

Glenn Chagnot

Chief Architect

VeriWave, Inc.

817-898-0369