[ntp:questions] Better QoS support

Philip Prindeville philipp_subx at redfish-solutions.com
Tue Dec 26 19:24:35 UTC 2006


Danny Mayer wrote:

>Philip Prindeville wrote:
>  
>
>>Hi.
>>
>>I added better support for setting IPTOS_PREC_* in ntpd/ntp_io.c
>>and ntpd/ntp_config.c.
>>
>>so the code seems to be mostly working...  except that "qos"
>>seems to be called (and processed, as seen from the debug lines
>>ntokens/flag/tos) after the sockets have been created.  Not sure
>>why.  Does the "qos" need to appear earlier in the config file?
>>
>>I'll dig through the code some more and see the order of
>>processing...
>>
>>I've attached the patches for the FC5 .spec file, the
>>SOURCES/ntp.conf file, and of course the changes to the BUILD/
>>tree itself.
>>
>>-Philip
>>
>>    
>>
>
>Please do not try to use attachments for the email list, it's not
>allowed by the mailing-list. If you want to add an enhancement use
>Bugzilla: http://bugs.ntp.isc.org/ and add the attachment there. It will
>need to be reviewed and we need to figure out how to keep it optional.
>Why do you need to have QOS for NTP?
>
>Danny
>  
>

Well, you already use QoS for NTP, but you set it to Low-Delay.  This is
using the original IP ToS-bit definitions, which are largely obsolete.

For subscribers on links that are using traffic shaping and QoS queueing
where a large portion of the bandwidth is reserved (such as for anyone
using multiple VoIP trunks), you can experience severe jitter if the traffic
isn't properly categorized.  Jitter, of course, is the hobgoblin of accurate
synchronization.  Especially for multicast clients.

By using current QoS tagging, the traffic can be better accommodated
by heavily subscribed QoS networks.

-Philip



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