No speech on calls between customer sites

[PBX_Programmer]

Hi all,

I have a customer with a slightly unusual setup. They have a 3CX hosted PBX (hosted by 3CX). They have a main office location and that is where their main phone is located, set up to act as an SBC/router phone (I will call this location A). They then have several remote offices (I will call these Location B and Location C) which are all connected to the main office via site-to-site VPN tunnels between their routers/firewalls and, as far as I'm aware, they are also connected to each other via VPN tunnels, kind of in a triangle topology I guess. At these remote locations they have some 3CX handsets which are set to use the SBC/router phone at the main office as their method of breaking out to 3CX in the cloud.

Basically everything is working as it should for most calls between most locations, however, there is a problem with calls between Location B and Location C. The calls connect, but there is no speech in either direction when answered.

We do not look after their network for them, or their routers/firewalls at any of the locations. They have a 3rd party IT company who takes care of that and I have been liaising with them about what needs to be open on the firewalls at each location, but we just can't seem to be able to get it working. They confirmed that SIP ALG was enabled at location C, I asked them to disable it which they say they have done, yet the issue remains.

I have this morning tried enabling the "PBX delivers audio" setting for the phone at Location C just to see if that makes a difference and I am awaiting their response. Whilst I'm waiting to hear from them, is there anything that I may have missed, maybe, something really simple? Anything common which we or their IT provider could check/try, please?

Thanks,

David

 

[Alphabetic]

Networking issue, get their IT to sort it.

or, stick an SBC phone at B and C.

i imagine that would create some lag running that over a VPN via an SBC surely?

 

[PBX_Programmer]

Networking issue, get their IT to sort it.

or, stick an SBC phone at B and C.

i imagine that would create some lag running that over a VPN via an SBC surely?

Thanks @Alphabetic , that confirms what we were thinking. I have asked the customer's IT to make sure that UDP ports 9000-10999 aren't being blocked by anything. Yes I think a separate SBC at each location would be a better option however I don't think that's immediately possible because the handsets they have at those remote locations are not models which are capable of that. It's definitely something we may look at though.

 

[NikosT_3CX]

@PBX_Programmer if you have a site to site VPN you can provision the phones as Local LAN.
Also if these sites communicate directly via private ip addresses, then the internal ports of the PBX are 7000 up to 8499.
So ensure that these are open as UDP as well.

 

[Alphabetic]

Thanks @Alphabetic , that confirms what we were thinking. I have asked the customer's IT to make sure that UDP ports 9000-10999 aren't being blocked by anything. Yes I think a separate SBC at each location would be a better option however I don't think that's immediately possible because the handsets they have at those remote locations are not models which are capable of that. It's definitely something we may look at though.

it may not just be firewall.. it could be a routing issue too.

you could spend the time running wireshark captures from the SBC / Phone to see if all traffic is reaching or you can just bang in an SBC.

@NikosT_3CX only the SBC phone is at Location A - the PBX is in the cloud

 

[NikosT_3CX]

@Alphabetic then yes I agree with this.
in this case from Location A they must whitelist outbound traffic with a policy from this site towards the
Public ip of the PBX and port 5090, TCP & UDP.
@PBX_Programmer have you done this ?