PBX Delievers Audio, and QoS

Discussion in '3CX Phone System - General' started by rocketnick, Jul 25, 2012.

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  1. rocketnick

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    Okay. So long story short I was having latency issues on my calls placed or received over a sip trunk (VoIP.ms), so, I upgraded the server, (it is better then my desktop now) and read up on 3cx latency. Apparently the PBX delivers audio option introduces latency, so if you don't need to use it, you can un-check it to speed up round trip time. Well I have done that, and I did notice improved latency.

    I don't fully understand this option, but what I gather / infer, is that it establishes a direct connection from the voip phone (spa504) to the voip.ms server and skips the pbx box after a call is established.

    Here is my question. At the moment my QoS is setup only to prioritize packet leaving my 3cx box for the internet. Do I need to add the IP's of all phones (or use DSCP or some other qos tagging tech) to my QoS config now that the PBX is not brokering all calls?

    I have noticed some increased call popping and garbling, but much less latency with the PBX Delivers Audio option off.

    Thanks!
    Nick
     
  2. lneblett

    lneblett Well-Known Member

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    Your understanding of delivering audio is pretty much on. You can certainly implement qos at the phone level, it won't hurt, but you never really gave an indication about how much latency you experienced. If your network is not heavily burdened, then you likely will not notice any difference. Keep in mind that qos does not come into play once tha packets leave your environment and enter the Internet realm.

    There are web based test sites like http://www.pingtest.net and the like that might give you some insight. Unless you have a really slow system(CPU), most of the time it is the carrier between you and your provider. It can be related to how they route, number of hops and distance.
     
  3. rocketnick

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    Well the latency was bad enough that my users would certainly complain about it, saying they had 2 second pauses and the like. Obviously users exaggerate but I noticed high latency in call as well. The latency made calls unnatural.

    That's the other thing, I ran speed tests to two of the closest voip.ms serves to my location and one was very very good, usually 20ms or so with no jitter to speak of, and the other was 70ms or so with minimal jitter.

    That's why I was surprised with how high the in call latency seemed. The BPX hardware is a brand new dell workstation with an i5, tons of ram.

    PS we have a fiber connection at 7 down and 7 up Mbps
     
  4. lneblett

    lneblett Well-Known Member

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    Wow. Sounds like you have it pretty well covered. You may have to try and pin it down to being outside of your realm. You might try getting the client's permission to record some of the calls. It could be that they are doing some call forwarding out to cell (cumulative latency due to the added switching and cell network), that only certain calls to certain numbers are affected (PBX on the other end.), etc. You may also need to enlist the aid of your provider. I am fighting a similar battle, but using PSTN and I was able to get in front of the PBX at the analog level and prove that the latency was not with the Gateway or 3CX, but with the carrier and not on all lines and not always present.
    Good luck and maybe others have some suggestions.
     
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