Solved 3CX over poor internet connection

[Alphabetic]

Hi Guys,

I have a potential customer.

However, they're moving to a place which gives them ADSL with up to 5Mbps up and 0.5Mpbs down.

BT have offered them two internet connections to run phones and computers seperate.

They will have 4 handsets.

Can you tell me if it's possible to have 4 handsets over SBC on those speeds?

Any tips to minimise bandwidth for the phones?

Thanks!

 

[YiannisH_3CX]

Hello @kieferschild

Assuming that there is a dedicated line for phones and nothing else is using the line then you should be ok. To minimise traffic make sure that you are not using a lot of BLF keys on the phones that require sip traffic to update. To further minimise the overhead you can also use a low bandwidth codec like G729.
You can find more details in the following link. One thing to note as the guide is a bit outdated is that G729 now uses only 1 Sim. Call. https://www.3cx.com/blog/docs/bandwidth-utilised-for-voip/

 

[Alphabetic]

Hi @yiannishH_3CX thanks for the reply.

would you consider 6 BLFs per phone too much?

 

[YiannisH_3CX]

That depends on the codecs you are using and the usage of the BLFs. You should still be OK but if using G711 is cutting it a bit close (If all phones are on the phone at the same time).
Please note that the connection of the SBC to the PBX needs some bandwidth also.

 

[Alphabetic]

So, I'm best off not using PBX Delivers audio. Setting the EXT and SIP Provider to use G729 and GSM only. Should I change the priority of codec order from the parameter settings to put G729 and GSM first or will that not matter with me not using PBX delivers audio?

 

[YiannisH_3CX]

PBX will always deliver audio for external calls. You will save some bandwidth however with calls between the extensions. First make sure that your provider supports these low bandwidth codecs before applying them. The change the priority under the trunk and extension settings.

 

[Alphabetic]

Hi @YiannisH_3CX

Im playing on my test system and i've set SIP Provider to G729 and i can see in the captures that the INVITE is G729. However, When I make an outbound call, my extension is offering more codecs that i've specified under extension preferences. (Only have G729 and G722 here).

I've reset the phone and reprovisioned and it's doing the same thing. Is it the PBX doing it? My handset is a Fanvil X3G

**Update
I modified the codec priority under the 3CX SIP Trunk "Options" Tab.

the SDP now shows G729, PCMu and PCMA only. However, should G729 show at the top of the list as defined in EXT and SIP Trunk properties?

**Update2

I restarted the media server service and G729 now shows at the first one in the SDP.

Are PCMU and PCMA codecs put in by the PBX?

thanks

 

[YiannisH_3CX]

The order of codecs for an outbound call to a provider as you found out is defined by the codecs under the trunk settings.
PCMU and PCMA are G711a and G711u codecs.

 

[Alphabetic]

So, i've got the following:

EXT Pref
G729
G722

SIP Trunk Pref
G729
G.711U
G.711A

If i dial in and out it uses G711 first. The only way I get it to use G729 first is If I enable only G729 from my SIP provider control panel. Am i going to run in to problems specifying this codec only?

Ideally I wanted it to use G729 first and then others if not available. How does one acheive this?

thanks.

**Update

I can see the handset is offering G729 but the session in process is using PCMU, PCMA then G729. Do I need to be in contact with my SIP Provider to get them to prioritise?

 

[Alphabetic]

Ok conclusion.
I've had to disable all other codecs from SIP Provider control panel which makes both in and out G729.

you can close this ticket, thanks for your help.

 

[YiannisH_3CX]

Glad i could assist. To answer your question, the codec that is used depends on the priority the provider and the phone system uses. If you leave only G729 in the phone system however then the provider has no other choice than to use that.