NTP for phones behind an SBC

[coreybrett81]

This is a minor complaint, but I have noticed that all my SIP phones are using pool.ntp.org as their NTP server. This seems like a inefficient config to me. Why not have the SBC as the NTP source for phones?

 

[cobaltit]

I mean I guess, but it's not like NTP traffic moves the needle on ANY internet circuit...

 

[Saqqara]

As above, why invent the wheel when their are many internet based ntp services

plus you can only have one ntp settings so it has to be global for all phones - sbc, stun and local

 

[coreybrett81]

Seems like it would be a pretty simple thing to do. Just add a little logic in the phone template code.

Something like “if SBC{NTP = SBCIP}else{NTP=PBXIP}.

That way, you’re PBX could be the “master” for your whole phone system, and SBCs would just be slaves to the PBX.
Phones using direct or stun connections, would use the PBX as their clock and phones using an SBC would use the SBC.

This would be better from an NTP standpoint and a firewall standpoint.

 

[complex1]

@coreybrett81

You mean something like this?

{IF network=SBC}
local_time.ntp_server1 = %%local_sbc_ip%%
local_time.ntp_server2 = %NULL%
{ELSE}
local_time.ntp_server1 = %%param::time_ntp_server%%
local_time.ntp_server2 = %NULL%
{ENDIF}

 

[coreybrett81]

@coreybrett81

You mean something like this?

{IF network=SBC}
local_time.ntp_server1 = %%local_sbc_ip%%
local_time.ntp_server2 = %NULL%
{ELSE}
local_time.ntp_server1 = %%param::time_ntp_server%%
local_time.ntp_server2 = %NULL%
{ENDIF}

Yep!

Or maybe

{IF network=SBC}
local_time.ntp_server1 = %%local_sbc_ip%%
local_time.ntp_server2 = %NULL%
{ELSE}
local_time.ntp_server1 = %%param::pbxpublicip%%
local_time.ntp_server2 = %NULL%
{ENDIF}

Then the 3CX folks would just need to install/enable NTP servers during the PBX and SBC install.

For smaller installs, it might not make much of a difference, but systems with a lot of deskphones, it could make a real difference. In my case, 1 system would be hitting the public NTP pool instead of 200+.

 

[cobaltit]

NTP traffic is outgoing so firewall maintenance is not really an issue unless you are the ultra paranoid type. And if you are that type, why would you want to put another server/service inside your network? And again, even with 200 devices hitting NTP the traffic is still neglible:

Currently most servers get about 5-15 NTP packets per second with spikes a couple of times a day of 60-120 packets per second. This is roughly equivalent to 10-15Kbit/sec with spikes of 50-120Kbit/sec. The project steadily acquires more timeservers, so the load should not increase dramatically for each server. In plain terms, you probably need at least 384-512Kbit bandwidth (in and out-going).

This is from the NTP Pool Project regarding bandwidth hitting a public server. Your traffic is going to be a lot less. Giving the multitude of PBX features that need development time I'd prefer zero time be spent on this. If it really bothers you, make a DNS entry ntp.yourdomain.com and use split DNS but it's really not worth the effort.

 

[TDJ211]

Your router should have an NTP server. Why not just poi t your phones at that??

 

[Saqqara]

Just one note - custom 3CX templates are not supported by 3CX. In the event of any issues you would have to revert back to 3cx standard templates.

Is it worth it, considering the very little of ntp is being generated