remote extensions / branch office

[cfive]

Hi,

Given the following scenario:

Head office:
3CX V10
Fixed public IP
PSTN gateway

Branch Office 1:
6 extensions
Fixed or dynamic IP

Branch Office 2:
2 extensions
Fixed or dynamic IP

Would/could we use remote extension 'tunnel' for the branch office extensions, or is it too much to expect - and site<>site VPN's should be used?

Thanks - Les.

 

[garyjduk]

I'd just use the 3cx Sip Proxy Manager, you will get less problems with it and it just works. Even people using VPN's seem to have problems - just search the forum and you'll see. Install it on a computer that is always on like a server and it will install as a service and you won't even know it's running and then point the external extensions at it.

It should work fine even with 6 extensions, the only thing to check is upload bandwidth depending on which codec you are using.

 

[cfive]

Thanks Gary, I'll give that a go.

 

[eagle2]

I would recommend using some smart inexpensive routers (like Mikrotik RB-750G) capable of establishing EoIP tunnel (LAN bridge or pseudo-wire), GRE or even IP-sec tunnel. This will allow also running applications like MyPhone, etc. plus you can benefit from increased security.

Regards

 

[cfive]

So far, I have 3 remote sites on DSL connections, each using 3cx proxy to connect to the 3cx server site. At the 3cx server site, I have a patton 4114 with PSTN connected.

Everything works at a basic infrastructure level, but there are some voice quality issues. For the most part, extension to extension calls between the remote sites and from remote site to the 3cx server site are fine.

The problem seems to be when PSTN is involved. If a remote site 3cx extension places an external call, the 3cx extension end can hear the external party perfectly, but the external party cannot hear the 3cx extension end very well. The audio is very choppy. When an external caller places a call to a 3cx remote extension, same problem. Calls from the main 3cx site placed to external numbers don't seem to be a problem.

This is telling somebody something, but I don't know what ;-).

The topology is a bit more complicated thatn it should be - I could see what can be done to simplify it if that might make a difference:

Remote Extension > 3xc proxy > ISP provided SL device (router, DHCP, switch) > (internet) > fixed IP on cable modem > main site router (fortigate) > switch > WS2k8 R2 host > 3cx v10 running on WS2k8 R2 Hyper-v child. The Patton 4114 is connected at the switch, along side the 3cx server.

The extensions are Grandstream GXP285 and 1200, as well as 3cx Phone v6.

If anyone has some ideas to put me on track to troubleshoot the voice quality issues, I am grateful. I'm not really sure where to start.

Thanks, Les.

 

[eagle2]

Obviously there are some issues with your Internet connection speed -- bad voice quality in one direction means usually the speed of download / upload is not sufficient (test it with http://speedtest.net or similar tool). Negotiate with the provider(s) better speed.

Recommendations for improving voice quality in similar situation are:
1. implementing QoS on all routers involved
2. reorganizing the voice path - you are saying in some cases it's working - so try using 'PBX delivers audio' or vice-versa for that extension
3. changing the codecs extension uses to ones requiring narrow bandwidth, e.g. G.729a, etc.

Regards

 

[cfive]

Hi Eagle, thanks for the response.

I noticed that the bad voice quality is like this: all of the 'bits' are there, but with gaps.

I leave a voice mail, and while replaying it (from an emailed wav file) it is choppy, intermittently some parts are fine. All of the words are there, but sometimes interrupted with short periods of silence. A long word like supercalafragalisticexpialidocious might be broken into sup ercalafra ga listicexpialidocious, with the spaces representing a short silence ;-).

Regarding codecs, which order do you suggest for testing purposes? By default the Grandstream shows this order:

PCMU
PCMA
G.723.1
G729A/B
G726-32
iLBC
G.722
GSM

The ISP reports (advertises) 3 down and 2 up SL at the remote location I'm focusing on, while the 3cx server location has 3 down 1 up. I'll do some testing on both for starters.

 

[eagle2]

It looks like you are loosing packets between the offices. Try establishing VPN tunnel, or at least implement QoS to prioritize the voice traffic.

Regarding codecs:

(1) PCMU / PCMA or G.711u / G.711a is 64 kbit/s, with overhead - about 88 kbit/s (normally with 20ms frames)
The 'u' version is standard in USA, while 'a' is stadnard in Europe. The same apply to ISDN lines.
This codec provides the best quality, only G.722 is better (same bandwidth).

(2) G.729a is the next choice and widely used (16 kbit/s, requires 31 kbit/s bandwidth). The drawback is that is licensed (paid), loads heavily the CPU. Not available with free 3CX and 3CX softphone. Normally I increase the gain with 3dB to compensate the lower voice volume when using G.729a codec.

(3) GSM is supported by 3CX and is even more economical, but voice quality may be is not satisfactory already. Test it.

This should be default order. Other codecs may be ignored in most cases. In case you are experiencing bandwidth problems, try to rearrange them in reverse order at remote extension to test the effect. So:
(1) GSM
(2) G.729a/b
(3) G.711u / G.711a

Regards

 

[cfive]

Thank you, Orlin.

One thing I may have forgotten to mention - calls between extensions, regardless of their location, have excellent voice quality. So I think this might be isolated to calls that originate or are destined for PSTN. That would narrow it down to the network segments connecting the 3CX server to the Patton Gateway, the gateway, or the PSTN lines themselves.?

Funny thing is, calls from 3CX extensions on the same lan as the gateway, to/from PSTN, are fine. I'm not sure what that's telling us ;-). But am thinking about it.

Thanks again, Les.

 

[eagle2]

If you are familiar with Wireshark try to capture and analyze the traffic - there should be an obvious reason - probably the voice path is problematic between the remote extension and the gateway.

Have you tried 'PBX delivers audio' for remote extensions (I don't remember)?

What is the codec for PSTN lines in the gateway?

 

[nibb]

Im new to 3cx and what benefits you consider using the proxy over a VPN?

Security procedures tells you NOT to run a PBX with external lines over the Net, the correct way is to connect the extensiones only trough a VPN.

So im a little impressed to read this, specially how many companies where hacked (mostly running asterix) because they had their PBX running on a public network just to allow their external connections to connect.

What problems do you mention exactly when running with a VPN? Running the software in a server with fixed IP, none ports blocked, you can connect just fine, even without proxy or VPN, security is another story...

 

[cfive]

If you are familiar with Wireshark try to capture and analyze the traffic - there should be an obvious reason - probably the voice path is problematic between the remote extension and the gateway.

Have you tried 'PBX delivers audio' for remote extensions (I don't remember)?

What is the codec for PSTN lines in the gateway?

Something discovered yesterday - the extensions behind the 3cx proxy tunnel experience 1-way audio when calling each other. So I switched to "pbx delivers audio" - that appears to have resolved both the voice quality and 1-way audio issue. I wonder however if there isn't something else going on.

I don't know what the codec is for PSTN lines in the gateway - does 3cx do something "default" when it generates the Patton config file?

 

[eagle2]

3CX proxy server is establishing a tunnel like the 3cx softphone, so this is generally secure.
The other option is to establish a tunnel with routers, which could be expensive, despite can be more secured (IP-SEC).

3CX version 10 is blocking by default extensions outside of LAN, if you are using tunnel these extensions are 'internal'.
More over there is a built-in mechanism analyzing attacks to the PBX, which blocks the suspicious addresses for some time (adjustable), so 3CX version 10 is much more secure than Asterisk system, requires strong passwords, etc. In Asterisk generally you can block some addresses / networks and allow another. By default Asterisk is exposed to attacks.

Of course you should pay attention to security issues.

It is OK to use 'PBX delivers audio' for remote extensions.

 

[cfive]

Hi Orlin,

I've installed a dedicated internet connection at the 3CX PBX side for the remote extensions, connectivity between remotes (via 3CX proxy installed at each location) is good. G729 is the top priority codec for the remote extensions, all GXP 1200.

Setting the remote extensions in 3CX console to 'pbx delivers audio' helped with remote extension to local extension voice quality, but voice between remote extensions and outside parties (PSTN via patton 4114) were still horrible. When I selected 'pbx delivers audio' on the Patton, the voice quality is actually quite good. (None of this is needed for good voice quality for local extensions.)

I'm not sure what that's telling me, and I'm a bit concerned that if I leave it this way and the system goes into full production with th 16 call license and 8 PSTN trunks there could be issues.

What do you make of this?

thanks, Les.

 

[eagle2]

Having 16 call licenses, you will have only 8 G.729 channels available (this is the way 3CX is licensed).
I don't have experience with Patton gateways, but generally you should avoid codec changing (this would require more CPU power), so I suggest all phones and gateway to use either G.729 or G.711 (PCM) codec as first priority.

You should not experience problems with production version.

Regards