UserAgent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36

Steps to reproduce the problem:
1. Make an audio call from PeerA to PeerB by passing 'sdpSemantics':'unified-plan' in the RTCPeerConnection config 
2. During Offer/Answer, originator side observed the below error message - 

Uncaught (in promise) DOMException: Failed to set remote answer sdp: The order of m-lines in answer doesn't match order in offer. Rejecting answer.

What is the expected behavior?
Offer/Answer should be successful with Unified-Plan SDP as the same scenario works fine when plan-B SDP is used.

What went wrong?
-------------------------------------------

Offer SDP

"v=0
o=- 1074097161605665046 2 IN IP4 182.74.59.186
s=-
t=0 0
a=group:BUNDLE 0
a=msid-semantic: WMS 3f739cd8-e61e-4e58-9ad6-eeeca6a4e104
m=audio 59597 UDP/TLS/RTP/SAVPF 111 103 104 9 0 8 106 105 13 110 112 113 126
c=IN IP4 182.74.59.186
a=rtcp:9 IN IP4 182.74.59.186
a=ice-ufrag:w0vt
a=ice-pwd:Pmj5Z3c+uNTqrXNNAWXW8Ba6
a=ice-lite
a=fingerprint:sha-256 AB:4D:F3:8A:48:12:08:03:DD:A3:B5:CB:55:24:E8:3B:B1:7C:13:32:FB:2F:AF:85:F0:6B:26:2B:62:A5:23:C4
a=setup:actpass
a=mid:0
a=extmap:1 urn:ietf:params:rtp-hdrext:ssrc-audio-level
a=extmap:9 urn:ietf:params:rtp-hdrext:sdes:mid
a=sendrecv
a=msid:3f739cd8-e61e-4e58-9ad6-eeeca6a4e104 f23e8d87-70af-44d0-b79d-c9278b367f93
a=rtcp-mux
a=rtpmap:111 opus/48000/2
a=rtcp-fb:111 transport-cc
a=fmtp:111 minptime=10;useinbandfec=1;cbr=0;maxaveragebitrate=77824
a=rtpmap:103 ISAC/16000
a=rtpmap:104 ISAC/32000
a=rtpmap:9 G722/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:106 CN/32000
a=rtpmap:105 CN/16000
a=rtpmap:13 CN/8000
a=rtpmap:110 telephone-event/48000
a=rtpmap:112 telephone-event/32000
a=rtpmap:113 telephone-event/16000
a=rtpmap:126 telephone-event/8000
a=ssrc:1449574788 cname:1aJQot/fACg5DhTL
a=ssrc:1449574788 msid:3f739cd8-e61e-4e58-9ad6-eeeca6a4e104 f23e8d87-70af-44d0-b79d-c9278b367f93
a=ssrc:1449574788 mslabel:3f739cd8-e61e-4e58-9ad6-eeeca6a4e104
a=ssrc:1449574788 label:f23e8d87-70af-44d0-b79d-c9278b367f93
a=candidate:1145357613 1 udp 2122129151 10.10.64.79 59597 typ host generation 0 ufrag w0vt network-id 1
a=candidate:3977988856 1 udp 1685921535 182.74.59.186 59597 typ srflx raddr 10.10.64.79 rport 59597 generation 0 ufrag w0vt network-id 1
"

------------------------------------------

Answer SDP

----------------------------------------

"v=0
o=- 2685524817880610585 2 IN IP4 182.74.59.186
s=-
t=0 0
a=msid-semantic: WMS f2eb0a0f-faf5-45f4-b558-a101aab03519
m=audio 49628 RTP/SAVPF 111
c=IN IP4 182.74.59.186
a=rtcp:9 IN IP4 182.74.59.186
a=ice-ufrag:Z7a4
a=ice-pwd:YXt/80a2rCeoUDv5iZHsP8yM
a=ice-lite
a=fingerprint:sha-256 1E:F9:EB:70:D8:4A:C2:42:A0:1B:30:5F:07:02:5B:A5:21:30:0E:67:1E:3F:2C:C4:72:2D:55:62:EA:CA:BD:AC
a=setup:active
a=mid:audio
a=extmap:1 urn:ietf:params:rtp-hdrext:ssrc-audio-level
a=extmap:9 urn:ietf:params:rtp-hdrext:sdes:mid
a=sendrecv
a=msid:f2eb0a0f-faf5-45f4-b558-a101aab03519 e6a92767-719f-4389-9c7a-19deb6e6927c
a=rtcp-mux
a=rtpmap:111 opus/48000/2
a=rtcp-fb:111 transport-cc
a=fmtp:111 minptime=10;useinbandfec=1;cbr=0;maxaveragebitrate=77824
a=ssrc:666547743 cname:pp34Ol/SF0bcCsRW
a=candidate:696130316 1 udp 2122260223 10.10.64.166 49628 typ host generation 0 ufrag Z7a4 network-id 1
a=candidate:3748553432 1 udp 1686052607 182.74.59.186 49628 typ srflx raddr 10.10.64.166 rport 49628 generation 0 ufrag Z7a4 network-id 1
"

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Does this work in other browsers? N/A

Chrome version: 69.0.3497.100  Channel: stable
OS Version: 6.1 (Windows 7, Windows Server 2008 R2)
Flash Version:
 

Deleted: SDP_Failure.png 86.9 KB

	SDP_Failure.png 86.9 KB View Download