I had an issue where I would get call drops only when you were using mobile data on iPhone and Android to place a call. This would also happen when using the OS X soft phone app tethered to a mobile phone.
in examining the logs of the IOS app in Xcode, I could see that the call via and Contact fields were showing 127.0.0.1. this caused the other side to not be able to respond properly. I was getting audio, but I think It was trying to connect back and it couldn’t
Via: SIP/2.0/TLS 192.168.188.138:61897;rport=47521;received=555.666.777.888;branch=z9hG4bK.n2lpdNQhT
Call-ID: A5nSH~U9LX
From: "300" <sip:[email protected]>;tag=GCNMUU5ub
To: "102" <sip:[email protected]>;tag=688c2751-3198-4d12-abb6-bec08774d8ce
CSeq: 21 INVITE
Server: FPBX-15.0.17.55(16.20.0)
Allow: OPTIONS, REGISTER, SUBSCRIBE, NOTIFY, PUBLISH, INVITE, ACK, BYE, CANCEL, UPDATE, PRACK, MESSAGE, REFER
Contact: <sip:127.0.0.1:5061;transport=TLS>
Supported: 100rel, timer, replaces, norefersub
P-Asserted-Identity: "2nd DeskPhone" <sip:[email protected]>
Content-Type: application/sdp
Content-Length: 337
v=0
o=- 274 1409 IN IP4 111.222.333.444
s=Asterisk
c=IN IP4 111.222.333.444
t=0 0
m=audio 19692 RTP/SAVP 0 8 101
a=crypto:1 AES_CM_128_HMAC_SHA1_80 inline:8m4kfXUYKqOncS6k/Dvxp2PRAGiIbBWjzzJCEevf
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=ptime:20
a=maxptime:150
a=sendrecv
2021-11-16 08:29:15:103 [linphone/belle-sip] MESSAGE channel [0x7fbc1f6df000] [658] bytes parsed
2021-11-16 08:29:15:103 [linphone/belle-sip] MESSAGE channel [0x7fbc1f6df000] read [337] bytes of body from [MYHOST.EXAMPLE.NET:5061]
2021-11-16 08:29:15:103 [linphone/belle-sip] MESSAGE Found transaction matching response.
2021-11-16 08:29:15:104 [linphone/belle-sip] MESSAGE Dialog [0x600001d614a0]: now updated by transaction [0x600001934000].
2021-11-16 08:29:15:104 [linphone/belle-sip] MESSAGE Dialog retransmitting last ack automatically
2021-11-16 08:29:15:104 [linphone/belle-sip] MESSAGE belle_sip_channel_init(); peer_cname=127.0.0.1
2021-11-16 08:29:15:105 [linphone/bctbx] MESSAGE Background task belle-sip send channel started. Unknown remaining time since application is not fully in background.
2021-11-16 08:29:15:105 [linphone/belle-sip] MESSAGE channel [0x7fbc2011a000]: starting send background task with id=[35].
2021-11-16 08:29:15:105 [linphone/belle-sip] MESSAGE channel [0x7fbc2011a000]: starting resolution of 127.0.0.1
2021-11-16 08:29:15:106 [linphone/belle-sip] MESSAGE channel[0x7fbc2011a000]: entering state RES_IN_PROGRESS
2021-11-16 08:29:15:106 [linphone/belle-sip] MESSAGE channel[0x7fbc2011a000]: entering state RES_DONE
2021-11-16 08:29:15:106 [linphone/belle-sip] MESSAGE channel[0x7fbc2011a000]: entering state CONNECTING
2021-11-16 08:29:15:106 [linphone/belle-sip] MESSAGE Trying to connect to [TLS://::ffff:127.0.0.1:5061]
2021-11-16 08:29:15:155 [linphone/belle-sip] MESSAGE Response [0x60000092b5d0] absorbed by dialog [0x600001d614a0], skipped from transaction layer.
2021-11-16 08:29:15:155 [linphone/belle-sip] MESSAGE channel [0x7fbc1f6df000]: ending recv background task with id=[34].
2021-11-16 08:29:15:156 [linphone/belle-sip] MESSAGE Garbage collecting unowned object of type belle_sip_hop_t
2021-11-16 08:29:15:174 [linphone/belle-sip] ERROR Connection failed for fd [26]: cause [Connection refused]
2021-11-16 08:29:15:175 [linphone/belle-sip] ERROR Cannot connect to [TLS://127.0.0.1:5061]
Since this was originating from the PBX, I checked the servers ability to lookup its own hostname and it returned 127.0.0.1 (ping HOSTNAME)… the host file did not have the proper IP/Hostname in it… once I added the entry all works fine…