http://images.google.com.pk/imgres?imgurl=http://www.packetizer.com/ipmc/sip/papers/understanding_sip_voip/sip_call_flow.png&imgrefurl=http://www.packetizer.com/ipmc/sip/papers/understanding_sip_voip/&usg=__OpElrBAYBYEwLrXe8BrJVEefN8k=&h=425&w=541&sz=12&hl=en&start=18&tbnid=R3YeNbzkjcdpYM:&tbnh=104&tbnw=132&prev=/images%3Fq%3DCall%2Bflow%2Bin%2BSIP%26gbv%3D2%26hl%3Den%26sa%3DGPosted by Hash007 Posted by snjysanjay05 Posted by sagitraz