how to connect Grandstream to Cloud 3cx (self managed) without SBC

[DJ_AMIRSAM]

i want to connect my grandsteam to cloud 3cx without SBC because i am trying to also have a cellular backup connection incase the internet goes out

 

[JohnS_3CX]

Hi @DJ_AMIRSAM

I know you probably didn't realize this, but it would be disaster if you do what you are planning to do.

If you switch to cellular and don't have an SBC, your phone will probably not work at all and your backup will not really work as you want it. This is because cellular connections are almost guaranteed to be behind CG-NAT which breaks SIP.

So it's actually the other way round: You should install an SBC precisely because you will have a cellular connection.

 

[DJ_AMIRSAM]

Hi @DJ_AMIRSAM

I know you probably didn't realize this, but it would be disaster if you do what you are planning to do.

If you switch to cellular and don't have an SBC, your phone will probably not work at all and your backup will not really work as you want it. This is because cellular connections are almost guaranteed to be behind CG-NAT which breaks SIP.

So it's actually the other way round: You should install an SBC precisely because you will have a cellular connection.

I have wanted to get an SBC working but My issue is that I would need a massive UPS which is not in the budget
So assume I don’t have the cellular and I want to connect it to the cloud 3CX without SBC how would I do that

 

[JohnS_3CX]

I have wanted to get an SBC working but My issue is that I would need a massive UPS which is not in the budget

Originally you said you need a backup connection in case the internet goes out.
A UPS is a different consideration, in case the power goes out.
But anyway, a massive UPS is not needed if you install the SBC on a small Raspberry Pi 4.
It will consume about 3 to 5 watts which means it will probably run for many hours even on a small UPS.
So if this was your main consideration don't worry about it.

So assume I don’t have the cellular and I want to connect it to the cloud 3CX without SBC how would I do that

I can assume it if you want, but if you actually plan to use cellular failover you will have failures.
If you still want to do it anyway, you can use STUN mode provisioning on the phones, but you need to be aware of a number of things:

a) The cloud PBX must pass the firewall checker
b) you need to open SIP and RTP ports on your remote firewall (phones site)
c) you need to ensure there is no SIP ALG on your remote firewall (phones site)
d) you need to ensure there is no SIP ALG or SIP filtering on the ISP modem (phones site)
e) your connection will fail the moment you failover to cellular because all these forwards will become void (CG-NAT on cellular)
f) you might have to restart the phones and firewalls after going back to the main link following a failover event (stale routes)


If you can get a Raspberry Pi for SBC, all of this can be avoided and you will have a much more reliable service. The phones will continue to work after failover (probably less than a minute of downtime) without any actions needed from you.


Whatever path you choose to follow, make sure you test the failover by unplugging your main connection so you can simulate the failover event.

 

[DJ_AMIRSAM]

Originally you said you need a backup connection in case the internet goes out.
A UPS is a different consideration, in case the power goes out.
But anyway, a massive UPS is not needed if you install the SBC on a small Raspberry Pi 4.
It will consume about 3 to 5 watts which means it will probably run for many hours even on a small UPS.
So if this was your main consideration don't worry about it.




I can assume it if you want, but if you actually plan to use cellular failover you will have failures.
If you still want to do it anyway, you can use STUN mode provisioning on the phones, but you need to be aware of a number of things:

a) The cloud PBX must pass the firewall checker
b) you need to open SIP and RTP ports on your remote firewall (phones site)
c) you need to ensure there is no SIP ALG on your remote firewall (phones site)
d) you need to ensure there is no SIP ALG or SIP filtering on the ISP modem (phones site)
e) your connection will fail the moment you failover to cellular because all these forwards will become void (CG-NAT on cellular)
f) you might have to restart the phones and firewalls after going back to the main link following a failover event (stale routes)

If you can get a Raspberry Pi for SBC, all of this can be avoided and you will have a much more reliable service. The phones will continue to work after failover (probably less than a minute of downtime) without any actions needed from you.


Whatever path you choose to follow, make sure you test the failover by unplugging your main connection so you can simulate the failover event.

My cellular fall back device (inhand802) has a open vpn option would that solve my issues?