title: JsSIP Firefox - InvalidSessionDescriptionError: Answer tried to set recv when offer did not set send
body: <p>I was recently working with JsSIP. We tried to connect conference with one way (incoming) audio stream, but for Firefox was not working. </p>
  
  <p>Firefox error message: </p>
  
  <blockquote>
    <p>InvalidSessionDescriptionError: Answer tried to set recv when offer did not set send</p>
  </blockquote>
  
  <p>So our JsSIP configuration is: </p>
  
  <pre><code>mediaConstraints: {'audio': false, 'video': false},
  rtcOfferConstraints: {
      offerToReceiveAudio: true,
      offerToReceiveVideo: false
  },
  sessionTimersExpires: 120,
  pcConfig: {
      iceServers: [{'url': 'stun:stun.services.mozilla.com'}, {'url': 'stun:stun.l.google.com:19302'}]
  }
  </code></pre>
  
  <p>Here is the  offer body</p>
  
  <pre><code>v=0
  o=mozilla...THIS_IS_SDPARTA-39.0 1234582256825317267 0 IN IP4 0.0.0.0
  s=-
  t=0 0
  a=sendrecv
  a=fingerprint:sha-256 78:FF:54:2C:9A:B0:DC:2B:FC:31:83:89:17:AA:33:AF:FC:EC:C5:9E:0C:8B:E4:AA:23:47:15:09:71:DD:4D:A0
  a=group:BUNDLE sdparta_0
  a=ice-options:trickle
  a=msid-semantic:WMS *
  m=audio 44686 RTP/SAVPF 109 9 0 8
  c=IN IP4 x.x.x.x
  a=candidate:0 1 UDP 2122252543 x.x.x.x 44686 typ host
  a=candidate:0 2 UDP 2122252542 x.x.x.x 52130 typ host
  a=candidate:2 1 UDP 1686110207 x.x.x.x 44686 typ srflx raddr x.x.x.x rport 44686
  a=candidate:2 2 UDP 1686110206 x.x.x.x 52130 typ srflx raddr x.x.x.x rport 52130
  a=recvonly
  a=end-of-candidates
  a=extmap:1 urn:ietf:params:rtp-hdrext:ssrc-audio-level
  a=ice-pwd:06bf8e8ece7e22f262546b874e13010e
  a=ice-ufrag:d0d3aae0
  a=mid:sdparta_0
  a=rtcp-mux
  a=rtpmap:109 opus/48000/2
  a=rtpmap:9 G722/8000/1
  a=rtpmap:0 PCMU/8000
  a=rtpmap:8 PCMA/8000
  a=setup:actpass
  </code></pre>
  
  <p>Here is answer body:</p>
  
  <pre><code>v=0
  o=matrix 1454436711 1454436712 IN IP4 x.x.x.x
  s=matrix
  c=IN IP4 x.x.x.x
  t=0 0
  a=msid-semantic: WMS PrZnRR78adkqAdzI3cJ4tKDYF1CojinZ
  m=audio 22178 RTP/SAVPF 0
  a=rtpmap:0 PCMU/8000
  a=ptime:20
  a=fingerprint:sha-256 56:34:DC:1D:D5:94:2B:F5:F0:BA:13:45:FD:A7:54:78:A0:BF:D0:BB:45:DD:FC:E9:D0:33:0B:88:12:DC:84:30
  a=rtcp-mux
  a=rtcp:22178 IN IP4 x.x.x.x
  a=ssrc:4206958201 cname:zddhVagVdrcDuBco
  a=ssrc:4206958201 msid:PrZnRR78adkqAdzI3cJ4tKDYF1CojinZ a0
  a=ssrc:4206958201 mslabel:PrZnRR78adkqAdzI3cJ4tKDYF1CojinZ
  a=ssrc:4206958201 label:PrZnRR78adkqAdzI3cJ4tKDYF1CojinZa0
  a=ice-ufrag:DMiXmMLSDe7NmkDM
  a=ice-pwd:nGT8GZUKgWdBogPSSXG5AiO4
  a=candidate:9067675717 1 udp 659136 x.x.x.x 22178 typ host generation 0
  </code></pre>
  
  <p>P.S. on Chrome, this configuration works well</p>