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原文：https://freeswitch.org/confluence/display/FREESWITCH/Variables
verbose_sdp
Enable this variable to fix a bug in certain VoIP phones.
The a=rtpmap lines are optional (RFC 3264) for static payload types according to the SDP standard, but not all phones implement this correctly and fail if these lines are missing.
By default FreeSWITCH will omit these lines so that the SDP is smaller (which lowers bandwidth use and avoids packet fragmentation). If this variable is set to true, FS will instead send these a=rtpmap for all codecs.
For example, Polycom phone requires you to list all codecs in the RTP map even though the SDP is valid, but they seem not to look at any codecs that are not in the map.
Usage: in vars.xml
verbose_sdp=true