Interpretation of Jitsi SSRC groups and Chromium Unified Plan

Hi,

I’m trying to implement an application that use jicofo+jvb as a SFU server.
In case of 2 participatns (audio only) I get 2 SSRC groups in Jicofo responce:
one is “mixed” and another is “normal”

 <source xmlns="urn:xmpp:jingle:apps:rtp:ssma:0" ssrc="318325822">
    <parameter value="mixed" name="cname"/>
    <parameter value="mixedlabelaudio0" name="label"/>
    <parameter value="mixedmslabel mixedlabelaudio0" name="msid"/>
    <parameter value="mixedmslabel" name="mslabel"/>
    <ssrc-info xmlns="http://jitsi.org/jitmeet" owner="jvb"/>
  </source>

<source xmlns='urn:xmpp:jingle:apps:rtp:ssma:0' ssrc='4055006777'>
       <parameter xmlns='urn:xmpp:jingle:apps:rtp:ssma:0' value='krHG2mC9rD2L1W3W-2' name='cname'/>
       <parameter xmlns='urn:xmpp:jingle:apps:rtp:ssma:0' value='dfa22363-e1bf-4d9b-9fcc-23b749ce2ca2-2 ff66e4b2-3435-4b43-8956-07cca8d0d64f-2' name='msid'/>
       <ssrc-info xmlns='http://jitsi.org/jitmeet' owner='testroom@conference.192.168.0.250/3ca1c918'/>
</source>

How to interpret these SSRC groups?
Are there any specifications for this?
What are “mixed” SSRC?
How should I use “mixed” and “normal” values in my client application?

Another question is it how to convert these SSRC items to “Unified Plan” SDP?
I should write to SDP something like below:

a=ssrc:??? cname:???
a=msid:???  ???

Any help will be appreciated.

Thanks.

Can anyone clarify this?