[Serusers] ser behind firewall?

My home lan: cable modem-->routre(192.168.0.1): one linux (192.168.0.123) and one windows(192.168.0.124)

I have installe ser in linux machine and I can use xten lite(UA) register with ser, but my friend can't register his xten to my ser using my public ip from cable company. I have configure my route with ser vitual server. and serctl ps shows 192.168.0.123:5060 is listening.. why my friend can't register to my ser. please help! by the way, I am new to ser, if some one want to share ser experience, please call me anytime use my FreeWorldDealup 395104. Peter

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