Solved Android App not working outside of local network

[ZoloN]

I have still problems with the Android App - last version I've tried is the latest beta (3CXPhone for Android 16.4.0.111) - I cannot make calls - in the call log are the calls logged as " type: 11, dn: DirectSIP ".
I've realized, that the Android App connects to the tunnel service regardless of the current location. OK for me. but the INVITE message format is not corresponding with this approach.
I've assumed, that tunnel connection is something like VPN - so I don't understand, why the INVITE from outside of LAN targets public FQDN instead of local 3CX IP.

is this an intention, "feature" or a bug??? because then the 3CX forwards the INVITE really to public FQDN (public IP of the WAN port), which causes troubles.


here are captured messages:

via LTE - connected to tunnel via public FQDN / INVITE message looks like:

INVITE sip:22@****.my3cx.at:5061;tag3cx=****** SIP/2.0
Via: SIP/2.0/TCP 127.0.0.1:50195;rport;branch=******;alias
Max-Forwards: 70
From: "ZoloN" <sip:12@[local 3CX IP]:5061>;tag=******
To: <sip:22@****.my3cx.at:5061;tag3cx=******>
Contact: "ZoloN" <sip:[email protected]:5060;rinstance=******>
Call-ID: ******
CSeq: 10053 INVITE
Allow: PRACK, INVITE, ACK, BYE, CANCEL, UPDATE, INFO, SUBSCRIBE, NOTIFY, REFER, MESSAGE, OPTIONS
Supported: replaces, 100rel, timer, norefersub
Session-Expires: 1800
Min-SE: 90
User-Agent: 3CXPhone for Android 16.4.0.111


via local LAN - connected to tunnel via internal IP / INVITE message looks like:

INVITE sip:22@[local 3CX IP]:5061;tag3cx=****** SIP/2.0
Via: SIP/2.0/TCP 127.0.0.1:50195;rport;branch=******;alias
Max-Forwards: 70
From: "ZoloN" <sip:12@[local 3CX IP]:5061>;tag=******
To: <sip:22@[local 3CX IP]:5061;tag3cx=******>
Contact: "Zoltan Nemeth" <sip:[email protected]:5060;rinstance=******>
Call-ID: ******
CSeq: 12089 INVITE
Allow: PRACK, INVITE, ACK, BYE, CANCEL, UPDATE, INFO, SUBSCRIBE, NOTIFY, REFER, MESSAGE, OPTIONS
Supported: replaces, 100rel, timer, norefersub
Session-Expires: 1800
Min-SE: 90
User-Agent: 3CXPhone for Android 16.4.0.111


/BR
ZoloN

 

[ZoloN]

hi Vali,

I see, thank you for explanation.

on the other hand, from network point of view, the tunnel acts as VPN tunnel encapsulating the SIP and voice packets to single TCP connection and routing them directly to the 3CX PBX host traversing thru lot of routers, NAT setups, etc... (for example, while on LTE my mobile gets a private 10.x.x.x IP which is then NATed to some shared public IP) - and the PBX should only know, where to route the responses (to tunnel instead of LAN). honestly, I don't see any reason behind to use public FQDN in the SIP INVITE packets. it's little bit confusing while analyzing the captured network traffic.
changing this to unified INVITE format (using internal FQDN/IP) could prevent some unintentional noob misconfigs...
and another reason for unifying could be: as the App connects to the PBX via tunnel even on local network, to simplify the App code - no need for location discovery and double handling of SIP protocol, which can contribute to more clean code of App and avoid possible errors in future versions

/BR
ZoloN

 

[Vali_3CX]

I'm not an expert in networking, but in my opinion the best configuration for the PBX is to have an unique FQDN for both internal/external (I think this is split DNS)

 

[ZoloN]

conclusion: after setting up the FQDNs with split DNS based on advice from Vali all is working fine.

case closed!