[Megaco] stop ringing signal on the terminating side.

When i am doing some interop betweem RGW and third party Softswitch product,I found that the callee in RGW side doesn't stop ringing when Softswitch send Subtract + Modify to it. I know the callee will work well if Softswitch send command with Signal Descriptor SG{}.But currently,the Softswitch only send Subtract + Modify commands with embedded new signal descriptor to RGW (see belowing message trace) Should RGW stop the current ringing signal on the termination according to protocol?

Pls clear my mind on this topic.

Message trace:

09:17:20.368446 eth0 > coco1.11122 > 138.203.243.36.27000: udp 134 (DF)

!/1 [138.203.242.94] T=15593{C=8{MF=rgw_7501/2{E=589829{al/of{strict=exact},al/on{strict=exact},g/sc},SG{al/ri}},MF=rtp/8{SG{cg/rt}}}}

09:17:20.466317 eth0 < 138.203.243.36.27000 > coco1.11122: udp 58

       !/1 [138.203.243.36]
       P=15593{C=8{MF=rgw_7501/2,MF=rtp/8}}

**** Callee is ringing ****

09:17:37.570306 eth0 < 138.203.243.36.27000 > coco1.2944: udp 81

!/1 [138.203.243.36]
T=27{C=7{N=rgw_7501/1{OE=393217{19700102T18482090:al/on}}}}..

09:17:37.590616 eth0 > coco1.11122 > 138.203.243.36.27000: udp 178 (DF)

!/1 [138.203.242.94] T=15595{C=8{S=*},C=-{MF=rgw_7501/2{E=589829{al/of{strict=exact,EM{SG{cg/dt},E=393217{dd/ce{ DM=dialplan1},al/on{strict=exact},g/sc}}},al/on{strict=exact}}}}}