Cost-effectivenesss of highly-accurate clocks for NTP

Lamar Owen lowen at pari.edu
Mon May 16 16:16:13 UTC 2016


On 05/15/2016 03:16 PM, Måns Nilsson wrote:
> ...If you think the IP implementations in IoT devices are naîve, wait 
> until you've seen what passes for broadcast quality network 
> engineering. Shoving digital audio samples in raw Ethernet frames is 
> at least 20 years old, but the last perhaps 5 years has seen some 
> progress in actually using IP to carry audio streams. (this is 
> close-to-realtime audio, not file transfers, btw.) 

Close to realtime is a true statement.  Using an IP STL 
(studio-transmitter link) has enough latency that the announcer can no 
longer use the air signal as a monitor.

And the security side of things is a pretty serious issue; just ask a 
major IP STL appliance vendor about the recent hijacking of some of 
their customers' IP STL devices.... yeah, a random intruder on the 
internet hijacked several radio stations' IP STL's and began 
broadcasting their content over the radio.  Not pretty.  I advise any of 
my remaining broadcast clients that if they are going to an IP STL that 
they put in a dedicated point to point IP link without publicly routable 
IP addresses.

Digital audio for broadcast STL's is old tech; we were doing G.722/G.723 
over switched-56 in the early 90's.  But using a public-facing internet 
connection with no firewalling for an IP STL appliance like the Barix 
boxes and the Tieline boxes and similar? That borders on networking 
malpractice.

> ... But, to try to return to "relevant for NANOG", there are actual 
> products requiring microsecond precision being sold. And used. And 
> we've found that those products don't have a very good holdover. ... 
Television broadcast is another excellent example of timing needs; thanks.

Valdis mentioned the scariest thing.... the scariest thing I've seen 
recently?  Windows NT 3.5 being used for a transmitter control system, 
within the past five years.  I will agree with Valdis on the scary 
aspects of the public safety communications Mel mentioned. Thanks, Mel, 
for the educational post.



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