[Serusers] isco 2600 as sip gw, no ringing tone on call frowarding

Hello I use a cisco 2600 as sip gw, and i have an error when i make call forwarding, the caller do not receive the ringing tonne. example: the GW receive a call from the pstn (caller1), and he forward this call to the proxy. on the proxy a call forwarding is activated to a mobile phone, so the proxy rewrite the sip uri, and the call is forwarded to the same GW. the problem is that caller1 never receive the ringing tone. I see that the GW correctly send and receive the 183 Session Progress message but he never send this on the pstn. I have also tried to used 2 different GW but I have the same problem. Laurent 8.313239 1x.x.x.x70 -> 1x.x.x.x13 SIP/SDP Request: INVITE sip:4202371@spadatel.org:5060, with session description 8.315617 1x.x.x.x13 -> 1x.x.x.x70 SIP Status: 100 trying -- your call is important to us 8.316326 1x.x.x.x13 -> 1x.x.x.x14 SIP/SDP Request: INVITE sip:0244203036@sip.spadatel.org:5060, with session description 8.318357 1x.x.x.x14 -> 1x.x.x.x13 SIP Status: 100 trying -- your call is important to us 8.318876 1x.x.x.x14 -> 1x.x.x.x70 SIP/SDP Request: INVITE sip:0244203036@1x.x.x.x70:5060, with session description 8.386719 1x.x.x.x70 -> 1x.x.x.x14 SIP Status: 100 Trying 15.636038 1x.x.x.x70 -> 1x.x.x.x14 SIP/SDP Status: 183 Session Progress, with session description 15.636451 1x.x.x.x14 -> 1x.x.x.x13 SIP/SDP Status: 183 Session Progress, with session description 15.637680 1x.x.x.x13 -> 1x.x.x.x70 SIP/SDP Status: 183 Session Progress, with session description 15.662967 1x.x.x.x70 -> 1x.x.x.x13 SIP Request: PRACK sip:1x.x.x.x13:5060;ftag=A5A7C-2313;lr=on 15.663123 1x.x.x.x13 -> 1x.x.x.x70 SIP Request: PRACK sip:0244203036@1x.x.x.x70:5060