[sr-dev] about rtpengine trust-address flag and "received from" key

[Juha Heinanen]

i would like to return to rtpengine trust-address flag.  README says:

  trust-address - flags that IP address in SDP should be trusted. Without
  this flag, the RTP proxy ignores address in the SDP and uses source
  address of the SIP message as media address which is passed to the RTP
  proxy.

the first part makes sense, i.e., if the flag is present, then ip
address in the sdp is trusted.

the second part does not make sense to me and neither does "received
from" key of request passed to rtpengine.

rtpengine doc tells about "received from":

  Contains a list of exactly two elements. The first element denotes the
  address family and the second element is the SIP message's source
  address itself. The address family can be one of IP4 or IP6. Used if
  neither the trust address flag nor the media address key is present. 

there is at least two reasons why it does not make sense to pass source
ip address of sip request to rtpengine:

1) the proxy that is calling rtpengine_offer() may not be the first hop
proxy of the sip ua.

2) even when sip proxy is the first hop, sip ua may not use the same ip
address for sip signaling and rtp media

so what is the reason for the existence of "received from" key?  is
there anything lost if the key is removed?  if not, then lets get rid of
it in order to simplify things and to avoid confusion.

-- juha