I´m wondering if it´s possible to setup the UC520 to use RTP ports from 30000 to 30030 only, this is due to a SIP trunk provider who has put the QoS on these ports on the DSL line. We´ve tested this solution on the SPA9000 and it works great.
There is no way to control the RTP ports on the SIP Trunk of the UC520. The RTP port range is from 16384 to 32767 (even numbered ports only in this range).
You probably need to talk to the SP to ensure QoS on the above port range or rely on other classification criteria such as DSCP