Incoming call Audio issue

Discussion in '3CX Phone System - General' started by techdummy, Oct 19, 2017.

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  1. techdummy

    techdummy New Member

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    Hi,

    This happened yesterday.
    On incoming calls, we are not able to understand what the caller is saying. It is heavily distorted audio. This happens only for a few mins, and at other times we are able to hear them clearly.
    And they are not facing any issues with audio on their side, they can hear us clearly.
    Any ideas on what could be the issue here?

    Thanks.
     
  2. lneblett

    lneblett Well-Known Member

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    You failed to mention what type of telephone service - analog, SIP, PRI, etc..
    I will assume SIP as this is where the issue you describe is most often seen. This issue is oftentimes related to bandwidth congestion. Simply put, the demands exceed the supply and as a result the voice data packets are competing with data packet delivery and are unable to maintain a constant and steady stream and this results in a choppy or clipped sounding speech and if the condition worsens, then data packets start to drop and the conversation develops the chop sound as well as gaps and/or gibberish. Ultimately, if the packet drop gets worse, the call connection may drop.

    You need to insure that your Internet speeds/bandwidth is suitable for the highest demand expected. You should also try and settle in on a common codec that is universal from phone to pbx to provider. Most providers only support one or two codecs; yet the PBX and phones have a broader capability as they need to be able to support whatever codec is the standard in their installed locale and/or for special uses. If nothing else, put the common ones at the top. This simply makes the negotiation a little less complicated between the devices.

    You may need to have your connection checked. It is somewhat unusual for the downstream voice to undergo this issue as usually the downstream side has the greater bandwidth in an asymmetrical connection or an equal to the upstream bandwidth in a symmetrical connection. This is not to say that it can't and doesn't occur, but unless folks are eating up the downstream with videos, file downloads and the like, it should be less likely.

    There are a couple of VoIP testing websites that may help. Do a Google search and then run the tests using the max simultaneous calls that the PBX supports or what the site will allow, which is greater. You may need to run it every so often to get a feel for the quality of the connection as you did indicate that it only happens on the download side and not all the time.

    There are other possible causes, but the above should get you started.
     
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  3. giwm

    giwm New Member

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    If your downstream connection is being overloaded (as mentioned above) you may need to enable QoS for your voice traffic. Best practice would be to have it enabled regardless of bandwidth just to play it safe.
     
  4. techdummy

    techdummy New Member

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    @lneblett Thank you for the reply.

    Yes, it is SIP. I'm not sure if it can be related to the overuse, unless someone has been downloading something at the same time. We have 20 simultaneous calls supported, and I don't recall the calls being higher than 12.
    I will however have to check whether the broadband speed is varying from time to time.
    As far as codecs are concerned, we have set G.729 as the preferred codec. It is the same for all the devices.
    I'm checking out a few testing websites now, thank you for all your suggestion. Appreciate it!
     
  5. techdummy

    techdummy New Member

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    Thank you for the suggestion @giwm .
    We haven't enabled QOS because Voip is on a different Lan altogether. Also, our 3cx is outside the firewall.
     
  6. lneblett

    lneblett Well-Known Member

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    When reporting that 3CX is outside the firewall, I take this to mean that the system is exposed directly to the Internet? Is there a reason for this?

    To me, you are exposing the system to the world and to all who would like to be unknown and yet be your new best telephone buddies. These folks can be relentless in their efforts to find a way to connect to or otherwise infiltrate the system in the hopes of finding the magic that allows them to take over the system or least find a way to get a connection. While 3CX has a pretty decent anti-hacking scheme, this still requires the system to spend CPU cycles and resources trying to defend itself while at the same time handling valid requests.

    I have had other systems (not 3CX) be attacked to the extent that the CPU utilization was pegged at 100%, when normally it should have been almost idle. This indeed impacted call quality. Once I found out what caused it and then used the router's firewall rules to allow only the desired IPs and then drop the rest, all returned to normal and I have never looked back and have subsequently been using this mechanism ever since. It just makes sense to let the firewalls do what they do best so the PBX can also handle its primary function....calls.
     
  7. giwm

    giwm New Member

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    I'm not certain what you mean by "it's on another LAN". You mean the phone system is wired/switched/served on an isolated physical network? Or do you mean it's on its own VLAN? Do your phones all reside outside of the firewall, too? Because if not, the traffic from the phone to the 3CX box is subject to QOS issues at every switch.

    And... yes... your 3CX box not being behind a firewall is begging for problems. Even residential cable modems have BASIC firewall capabilities that should be leveraged.
     
  8. OCWI

    OCWI New Member

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    giwm, from your border controller (if your not using a border controller stop now and reconfigure it using a raspberry pi) ping www.google.com If its higher than 30 ms call up your isp and tell them to come and fix it.

    We see this all the time. Its more often times than not the isp. even when a speed test shows a good latency, download, and upload speed.
     
  9. Soho3cx

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    Sorry to "hijack" this thread, but should we configure QoS for LAN to WAN and vice versa?
     
  10. John Ranger

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    Hi Techdummy,

    QoS should be "End-to-End". That means:

    From your telephones->all LAN Switches where a phone is connected--> If you have: large Core Switches ->Server where the 3CX central is installed->your Firewalls-->the WAN-Router-->the link over to your ISP-->Internet uplink from your ISP to the Internet --> Your VoiP Provider's Internet link and their internal LAN infrastructure.

    On the last two you don't really have any influence but maybe you can ask your ISP if they have/can enable QoS for SIP/RTP on their Internet uplink.

    The most important one you should take care of is your WAN router because the Settings there directly influence the most "narrow" part of all of the Connections: The WAN-Link from your Office to the internet.

    What Kind of WAN link do you have?

    1. ADSL/vDSL?
    2. Cable (via TV cable)?
    3. 3G/4G?
    What Kind of LAN cabeling do you have?

    1. Standard Ethernet Cabeling (100 MBit/s)?
    2. Standard Ethernet cabeling (1GBit/s)?
    3. Some Connections where phones are affected via Powerline or WiFi?
    With Kind regards,

    John
     
  11. lneblett

    lneblett Well-Known Member

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    I am going to back up for a minute as I may have missed a relevant point...that being "This happened yesterday".

    Reading this I assume that the system had been fine prior to this point? Is it still occurring or was it just a temporary thing? While all of the points made previously still have validity, constitute good practice and should still be investigated, it may have been nothing more than a bad hair day for the ISP if the quality has returned to normal.
     
  12. techdummy

    techdummy New Member

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    Hi @lneblett , thank you for the response.
    The only think between our 3cx and Internet is the Router. There isn't any reason, it was the way this was setup way before I joined the organization and they don't want to change it.
    We also block any attempt to reach the 3cx, at the Router itself. Also, I have changed the 3cx from Blacklisting to white-listing. Security wise, I think it should be enough.
     
  13. techdummy

    techdummy New Member

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    I mean, the 3cx and all the IP phones are on a different network. VOIP is completely isolated from all the other network traffic.
     
  14. techdummy

    techdummy New Member

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    Yes, system was working fine prior to this. Only on that particular day did we face this issue, and that too for 15 mins or so. After that, it was all back to normal. So we too believe that it could have been some small issue from ISP side, also our VOIP provider did inform us that there is an upgrade that will happen later that day which might affect the calls. Anyway, the issue hasn't happened again, but just wanted know if this had happened to anyone else and if possible get some info about it.
    Thanks
     
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