Thus it is supposed that the as old acting SGSN receives {HEAD ~ a GTP U packet} from {TAIL ~ a GGSN} 
Thus it is supposed that the as old acting SGSN receives { HEAD ~ a GTP U packet } from { TAIL ~ a GGSN }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL