Blf keys and voice delay

hi to all,
after a lot of researches I found that enabling a lot of blf in my network introduces a voice delay during external calls ringing. deativating blf on 2/3 of my ip phones fixed the issue. I have around 40 total fanvil X4g and 30 that rings all simultaneously with 30blf keys in every phone so around 120blf keys. network is GB and firmware version the latest. This is a production call center and external calls rings continuously so this delay is not acceptable. any idea to fix this?

What do you mean a voice delay?


  • ext 101 is in a flawless conversation with ext102.
  • external call comes and all the extensions with 30 blf keys starts ringing.
  • ext 101 is starting to listening the ext102’s voice clear but with 1,5 seconds of delay
  • if phones stops ringing, slowly the delay disappears, but this never happens cause in this office the phones are ringing continuosly.

this doesn’t happen’s if blf keys are disabled on 60% of the phones.

Hint status propagation can become quite resource intensive on that much hints, not only on the server but on the phones themselves too. If you are using pjsip for your extensions and your endpoints support resource lists, you might want to try those. Also monitor your CPU status when this situation happens, maybe the CPU is being maxxed out when this happens.

This sounds like phone issue to me. Not PBX as asterisk just will drop BLF updates if it is to busy.

all my extensions and trunks are already pjsip and chan_sip is disabled, cpu on the server is always behind 40% (8 core 8GB RAM running on fast ssd), I think in ip phone issue too, but I can confirm that if I disable blf in most of ip phones the delay completely disappears… this is really annoying cause for this kind of call center is very usefull to monitor the colleagues states. Maybe this can be related to the fact that pbx is KVM virtualized? but except of this blf issue everything is really flawless

Then try to move BLF to a resource list.

thank you I will learn your documentation cause I don’t know about this kind of solution

There is no FreePBX support for Resource Lists yet, but there is an open feature request:

Even though there is no FreePBX support yet, this can easily be done manually by editing the right configuration file.


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