The SIP client at N97 always uses the same RTP port (the first one) from a Media Port range. It never uses other ports from the range.

Now I have: Start media port = 49152 (default), End media port = 65534 (default)

It always uses only the 49152 port even though there is a range of ports available - the End media port is 65534.
I have also tried other Media Port range definitions, but without any effect. All calls have the same SDP media description parameter set to:
m=audio 49152 RTP/AVP 8 98

Is it possible to configure the N97 SIP client to use dynamically other ports from the Media Port range?

SIP VoIP Settings Application: "S60 5.x SIP VoIP 3.1 Settings" (file SIP_VoIP_3_1_Settings_S60_5_x_v1_0_en.sis)
N97 Firmware: 20.0.019

The problem arises when using some (probably buggy) NAT routers - for example ZyWALL 2 - and when RTP streams are transfered via an external RTP Proxy. The first call is always OK, but the second call and other subsequent calls have no incoming audio (incoming in relation to N97). Outgoing audio (in the direction of RTP Proxy) is OK. The cause is partially in the NAT router - not updated router path and port translation for subsequent calls. The second portion of the problem is at N97, which does not cycle RTP ports within the defined range and uses only the first port.

Please, do you have any idea?

With my best regards