[Linphone-developers] How does ICE select the IP address?

[Florian Ulivi]

Hello all,

can someone help me to understand the behavior of SIP and ICE. My
problem is an iOS device not receiving any RTP data. The device sending
is a Linux system opening a WiFi network using hostapd and udhcpd
running a flexisip and linphone-sdk based SIP client.

Here are three INVITE packages from three connections, the first one is
working and the other two fail. This is  because in the first case, RTP
is sent to 10.12.17.100, which is correct, and in the other cases
to 192.168.2.245 and 127.0.0.1, which has to fail.

But why are 192.168.2.245 and 127.0.0.1 selected at all? How does the
candidate selection work with linphone?

Some explanations to the IPs:
 - 10.12.17. is the hostapd WiFi
 - 192.168.2. is a local network connected to the iOS device via
ethernet adapter
 - 10.18.119.11 is the mobile network data connection

INVITE sip:e519f6de-3470-4062-ad09-f0c3745e0742@10.12.17.1:50198;transp
ort=tcp SIP/2.0
Via: SIP/2.0/TCP
10.12.17.1;rport;branch=z9hG4bK.p97v1BgpcUev3810DSjZ7Djt7D
Via: SIP/2.0/TCP
10.12.17.100:49223;branch=z9hG4bK.72yXXed23;rport=49223
Record-Route: <sip:10.12.17.1:5060;transport=tcp;lr>
Max-Forwards: 69
From: <sip:ios-client@smartconnect-de519f.local>;tag=6g-6HgIkQ
To: <sip:e519f6de-3470-4062-ad09-f0c3745e0742@smartconnect-de519f.local
>
Call-ID: huNGe1nprF
CSeq: 20 INVITE
Contact: <sip:mobile@10.12.17.100:49223;transport=tcp>;+sip.instance="<
urn:uuid:df538ee0-5c3e-000f-af36-f8526b308c2a>"
User-Agent: smartwireless/ios/0.5.0
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE,
SUBSCRIBE, INFO, UPDATE
Supported: replaces, outbound, gruu
Content-Type: application/sdp
Content-Length: 1877
[1B blob data]
v=0
o=ios-client 1317 3000 IN IP4 192.168.2.245
s=Talk
c=IN IP4 192.168.2.245
b=AS:800
t=0 0
a=ice-pwd:05c4a6f75e61b6915195c658
a=ice-ufrag:c014008c
a=rtcp-xr:rcvr-rtt=all:10000 stat-summary=loss,dup,jitt,TTL voip-
metrics
m=audio 7078 RTP/AVP 96 97 98 0 8 101 99 100
c=IN IP4 10.12.17.100
a=rtpmap:96 opus/48000/2
a=fmtp:96 useinbandfec=1
a=rtpmap:97 speex/16000
a=fmtp:97 vbr=on
a=rtpmap:98 speex/8000
a=fmtp:98 vbr=on
a=rtpmap:101 telephone-event/48000
a=rtpmap:99 telephone-event/16000
a=rtpmap:100 telephone-event/8000
a=candidate:1 1 UDP 2130706303 10.18.119.11 7078 typ host
a=candidate:1 2 UDP 2130706302 10.18.119.11 7079 typ host
a=candidate:2 1 UDP 2130706303 10.12.17.100 7078 typ host
a=candidate:2 2 UDP 2130706302 10.12.17.100 7079 typ host
a=candidate:3 1 UDP 2130706303 192.168.2.245 7078 typ host
a=candidate:3 2 UDP 2130706302 192.168.2.245 7079 typ host
a=candidate:4 1 UDP 1694498687 10.12.17.100 7078 typ srflx raddr
10.18.119.11 rport 7078
a=candidate:4 2 UDP 1694498686 10.12.17.100 7079 typ srflx raddr
10.18.119.11 rport 7079
a=rtcp-fb:* trr-int 1000
a=rtcp-fb:* ccm tmmbr
m=video 9078 RTP/AVP 96
c=IN IP4 10.12.17.100
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42801F
a=recvonly
a=candidate:1 1 UDP 2130706303 10.18.119.11 9078 typ host
a=candidate:1 2 UDP 2130706302 10.18.119.11 9079 typ host
a=candidate:2 1 UDP 2130706303 10.12.17.100 9078 typ host
a=candidate:2 2 UDP 2130706302 10.12.17.100 9079 typ host
a=candidate:3 1 UDP 2130706303 192.168.2.245 9078 typ host
a=candidate:3 2 UDP 2130706302 192.168.2.245 9079 typ host
a=candidate:4 1 UDP 1694498687 10.12.17.100 9078 typ srflx raddr
10.18.119.11 rport 9078
a=candidate:4 2 UDP 1694498686 10.12.17.100 9079 typ srflx raddr
10.18.119.11 rport 9079
a=rtcp-fb:* trr-int 1000
a=rtcp-fb:* ccm tmmbr
a=rtcp-fb:96 nack pli
a=rtcp-fb:96 ccm fir


INVITE sip:e519f6de-3470-4062-ad09-f0c3745e0742@10.12.17.1:50198;transp
ort=tcp SIP/2.0
Via: SIP/2.0/TCP
10.12.17.1;rport;branch=z9hG4bK.1g4caS63j4pF584eX1gm1yDcrD
Via: SIP/2.0/TCP
10.12.17.100:49233;branch=z9hG4bK.ohUVjb4R3;rport=49233
Record-Route: <sip:10.12.17.1:5060;transport=tcp;lr>
Max-Forwards: 69
From: <sip:ios-client@smartconnect-de519f.local>;tag=TZMol9M0J
To: <sip:e519f6de-3470-4062-ad09-f0c3745e0742@smartconnect-de519f.local
>
Call-ID: CHVRC7TH0A
CSeq: 20 INVITE
Contact: <sip:mobile@10.12.17.100:49233;transport=tcp>;+sip.instance="<
urn:uuid:1f1a9953-3125-004b-bfb5-3dc11b16a005>"
User-Agent: smartwireless/ios/0.5.0
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE,
SUBSCRIBE, INFO, UPDATE
Supported: replaces, outbound, gruu
Content-Type: application/sdp
Content-Length: 1234
[1B blob data]
v=0
o=ios-client 169 2864 IN IP4 192.168.2.245
s=Talk
c=IN IP4 192.168.2.245
b=AS:800
t=0 0
a=ice-pwd:a2cc84f31cc9f2f7210bd6c2
a=ice-ufrag:392d2d68
a=rtcp-xr:rcvr-rtt=all:10000 stat-summary=loss,dup,jitt,TTL voip-
metrics
m=audio 7078 RTP/AVP 96 97 98 0 8 101 99 100
a=rtpmap:96 opus/48000/2
a=fmtp:96 useinbandfec=1
a=rtpmap:97 speex/16000
a=fmtp:97 vbr=on
a=rtpmap:98 speex/8000
a=fmtp:98 vbr=on
a=rtpmap:101 telephone-event/48000
a=rtpmap:99 telephone-event/16000
a=rtpmap:100 telephone-event/8000
a=candidate:1 1 UDP 2130706303 10.12.17.100 7078 typ host
a=candidate:1 2 UDP 2130706302 10.12.17.100 7079 typ host
a=candidate:2 1 UDP 2130706303 192.168.2.245 7078 typ host
a=candidate:2 2 UDP 2130706302 192.168.2.245 7079 typ host
a=rtcp-fb:* trr-int 1000
a=rtcp-fb:* ccm tmmbr
m=video 9078 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42801F
a=recvonly
a=candidate:1 1 UDP 2130706303 10.12.17.100 9078 typ host
a=candidate:1 2 UDP 2130706302 10.12.17.100 9079 typ host
a=candidate:2 1 UDP 2130706303 192.168.2.245 9078 typ host
a=candidate:2 2 UDP 2130706302 192.168.2.245 9079 typ host
a=rtcp-fb:* trr-int 1000
a=rtcp-fb:* ccm tmmbr
a=rtcp-fb:96 nack pli
a=rtcp-fb:96 ccm fir


INVITE sip:e519f6de-3470-4062-ad09-f0c3745e0742@10.12.17.1:50198;transp
ort=tcp SIP/2.0
Via: SIP/2.0/TCP
10.12.17.1;rport;branch=z9hG4bK.HD2U0jHXcHc82S4ppmXSjyDS5g
Via: SIP/2.0/TCP
10.12.17.100:49239;branch=z9hG4bK.3esMuOCKF;rport=49239
Record-Route: <sip:10.12.17.1:5060;transport=tcp;lr>
Max-Forwards: 69
From: <sip:ios-client@smartconnect-de519f.local>;tag=dhqyjOOUN
To: <sip:e519f6de-3470-4062-ad09-f0c3745e0742@smartconnect-de519f.local
>
Call-ID: 14tsocTIoN
CSeq: 20 INVITE
Contact: <sip:mobile@10.12.17.100:49239;transport=tcp>;+sip.instance="<
urn:uuid:42cf79c1-db3b-0078-b8f9-63c890f7b46e>"
User-Agent: smartwireless/ios/0.5.0
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE,
SUBSCRIBE, INFO, UPDATE
Supported: replaces, outbound, gruu
Content-Type: application/sdp
Content-Length: 987
[1B blob data]
v=0
o=ios-client 1323 2781 IN IP4 127.0.0.1
s=Talk
c=IN IP4 127.0.0.1
b=AS:800
t=0 0
a=ice-pwd:706fc507110904ccab015b02
a=ice-ufrag:3dfc252b
a=rtcp-xr:rcvr-rtt=all:10000 stat-summary=loss,dup,jitt,TTL voip-
metrics
m=audio 7078 RTP/AVP 96 97 98 0 8 101 99 100
a=rtpmap:96 opus/48000/2
a=fmtp:96 useinbandfec=1
a=rtpmap:97 speex/16000
a=fmtp:97 vbr=on
a=rtpmap:98 speex/8000
a=fmtp:98 vbr=on
a=rtpmap:101 telephone-event/48000
a=rtpmap:99 telephone-event/16000
a=rtpmap:100 telephone-event/8000
a=candidate:1 1 UDP 2130706303 10.12.17.100 7078 typ host
a=candidate:1 2 UDP 2130706302 10.12.17.100 7079 typ host
a=rtcp-fb:* trr-int 1000
a=rtcp-fb:* ccm tmmbr
m=video 9078 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42801F
a=recvonly
a=candidate:1 1 UDP 2130706303 10.12.17.100 9078 typ host
a=candidate:1 2 UDP 2130706302 10.12.17.100 9079 typ host
a=rtcp-fb:* trr-int 1000
a=rtcp-fb:* ccm tmmbr
a=rtcp-fb:96 nack pli
a=rtcp-fb:96 ccm fir


Regards
Florian