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SRX IP Phone problem with mobilphone calls

  • 1.  SRX IP Phone problem with mobilphone calls

    Posted 05-07-2021 07:45

    Hello all,

    I have a problem and I am really desperate at the moment. I have a SRX220H2 with the software version 12.1X46-D20.5. Yes I know there is the Next-Gen Firewall and also there are newer software versions. Unfortunately, there are newer software versions for the SRX220 no longer for sale, so I have to cope with what I have for now.


    About my network setup:

    I have a router from an ISP that connects to the Internet. At the same time, the router is the telephone system. Behind the router is the Juniper firewall. Between firewall and router was defenced as Untrust. Router has Ip and firewall on port GE0/0/0 has


    Behind the firewall there are two networks ( and In both networks there are various network devices such as computers, printers, cameras... but also IP phones.

    Let's take the one IP phone as an example. It has the address



    About my problem:

    The IP telephony is limited. I cannot make calls to the mobile network.


    Phone => mobile network = does not work

    Phone => phone = works

    Phone via TAPI (Phone Suite CTI) => mobile network = works


    All incoming calls work regardless of fixed or mobile network

    Internal calls work


    What I mean under the point "does not go": mobile rings, you pick up. On cellular the talk time is running but can't talk or hear anything. The phone keeps ringing as if there was no conversation. If you hang up on the mobile device, the phone continues to ring as if it is still trying to establish a conversation.


    Firewall configuration:

    Nat active for =>

    Nat active for =>


    ALG enabled:




     For the IP phone an extra incoming and outgoing rule was created which allows everything.


    Since I know no more advice and solution, I am grateful for any help!

    Timo Hesseler