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calls between external phones

Discussion in '3CX Phone System - General' started by vosmartijn, Nov 19, 2011.

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  1. vosmartijn

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    Hi All,

    I've a working setup with two external phones (cisco 504G) in a same network, but not in the same as the 3cx server. I've done all the work with the firewall and almost all options are working:

    - register phones to 3CS
    - calling between and external phones to internal or external numbers (both signaling and audio is working)
    - setup two calls (with both phones) to internal or external numbers (both signaling and audio is working)
    - calls to voicemail.
    - calling to ring group

    the only thing which isn't working is to call between the external phones by the internal numbers. The signaling is right, but I don't have any audio. I tried to call from one phone to the other by dialing an external number which is routed to the other phone. That is working, but this can be explained because 3CX handles those calls as an outbound and inbound call.

    the only thing is why I don't have any audio between the phones.

    logging doesn't show any errors.

    is someone familiar with this problem ?

    regards,

    Martijn Vos
     
  2. eagle2

    eagle2 Well-Known Member

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    Depends on your router(s) / NAT.
    Have you tried 'PBX delivers audio' option in extension settings ?

    Regards
     
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  3. 3cx

    3cx

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    Can you check in your extension settings ->Phone Provisioning that both these two extensions have the same codecs listed in the same order. If this still doesnt work then we eliminate that its not a codec issue and we can focus on other possibilities
     
  4. leejor

    leejor Well-Known Member

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    Since signalling seems to be OK, I assume that you've given each set a unique port number.
     
  5. vosmartijn

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    All,

    thank you for your support. I've checked all you mentioned and I've found the solution.

    I only needed to enable the checkbox 'PBX deliveres audio'. Still a bit confused why this helps, because without this option, I was able to setup a phonecall from an external phone to an internal one.

    but.... nevertheless... live could be simple by enabling one checkbox.

    thanx a lot.

    Martijn
     
  6. leejor

    leejor Well-Known Member

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    In simple terms....I suspect that the issue arises because when external sets, behind a router, register, they do so using the pubic IP and their local port number. If you set it so that once a call is made and 3CX "drops out", then it says "Ok you two, talk between yourselves", so public IP + 5060 you "talk" to public IP + 5061, BUT, the two devices have to work out which ports are to used for the voice packets and that probably causes problems with your router.
     
  7. eagle2

    eagle2 Well-Known Member

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    This behavior vastly depends on your router(s). By idea signaling (SIP messaging) always pass through the PBX (3CX server), while voice (RTP media) is intended to pass directly from peer to peer (which significantly decreases the load on PBX processor). If traffic is internal (same LAN with PBX) there are no problems with RTP. Also there are usually no problems with internal to external traffic or vice-verse (except some NAT issues), as the traffic again passes through the PBX (or at least the router in front); normally this means also one external location to another. In case there are 2 or more remote phones in one location usually low end class routers are not handling correctly the RTP packets, i.e. packet originating from remote LAN with destination the same LAN is lost due to the router, as it contains the same public address as source and destination, hopefully with different ports. Many routers are not doing this correctly even for signaling, in such case you need different SIP ports for each device. The countermeasure is to check the box 'PBX delivers audio', this will force all RTP packets (voice) to pass through the PBX itself for corresponding extensions and in most cases will solve the problem (still depending on routers). Different codecs also will force RTP packets to be manipulated by the PBX, but this will increase the load significantly and will limit the number of simultaneous calls the system can handle, so this should be avoided in design of your system.

    Hope this helps.
    Regards
     
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