[ntp:questions] SNTP server + ntpd 4.2.4 client

Bill Unruh unruh at physics.ubc.ca
Tue Mar 18 22:05:02 UTC 2008

andy.helten at dot21rts.com (Andy Helten) writes:

>I use PoE every day -- it powers the outdoor antennae that connects to
>my wireless ISP (distance of about 5 miles).  I have gotten up to
>3000kb/s over this link (which is slightly higher than what I'm paying
>for).  So, whatever you are debating here, PoE is almost certainly *not*
>the problem.

OK, learn something new every day! I do agree that it is weird that they
would have put SNTP on that thing rather than NTP. 

How much did it cost?

>David Woolley wrote:
>> Unruh wrote:
>>> Just looked it up. A bit bizarre-- power over the ethernet? The ethernet
>>> has no power supply capability. Do you mean that you have to supply the
>>> device with 60V running on one of the unused ethernet cable lines? Sounds
>>> noisy to me. 
>> I believe it is a relatively new, but very real, standard.  The power is 
>> transmitted as a phantom between two pairs.  In one variation, they are 
>> the pairs used for normal, 10baseT.  I gather one reason is that there 
>> are exemptions in electrical codes for ELV power feeds as part of 
>> datacommunication systems, whereas a normal feed would require a 
>> formally qualified (not just competent) electrician.
>> The feed is 48V DC.  I'm not 100% sure that counts as ELV, but it is the 
>> same as most analogue telephone systems.
>> The apparent source specification is IEE 802.3-2005, although I haven't 
>> gone to source.
>> As the power is common mode with respect to the signals, the noise 
>> should not be excessive.

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