[Serusers] rtpproxy logs

[SER Users]

hello,

how can I access/enable/find logs from rtpproxy ?
I see in rtpproxy sources that logs are being generated with 
"rtpp_log_write", but where are there or how can I "enable" them.
I am interested to see when a session is "active", when a packet from 
both caller/callee are received in order to track down a problem I have 
with 2 UAs.

something else: when everything is OK how many ports should be opened 
for s single proxy session ? 2 (1 RTP+1 RTCP) or 4 (2RTP + 2RTCP) ?

when two UAs can not come to an agreement regarding a codec, is there 
any RTP traffic between the two, or media negotiation is based solely on 
SDP messages contained within INVITE/OK SIP messages ?

thanks,
razvan radu