5 Traffic Flow in the LTE Network
5.2 Traffic flow in downlink direction
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Traffic flow from Internet to UE
  1. A P-GW receives IP packets destined for a UE over the Internet.
  2. The P-GW encapsulates the user IP packets with the S5 GTP tunnel header and forwards the resulting outer IP packets to the S-GW. Here, the P-GW selected a “TEID” value (i.e. DL S5-TEID), “Destination IP Address” (i.e. S-GW IP address), and “Source IP Address” (i.e. P-GW IP address) to make the S5 GTP tunnel header.
  3. After receiving the outer IP packets, the S-GW strips off the S5 GTP tunnel header, encapsulates the user IP packets (the inner IP packets) with the S1 GTP tunnel header and forwards the resulting outer IP packets to the eNB. Here, the S-GW selected a “TEID” value (i.e. DL S1-TEID), “Destination IP Address” (i.e. eNB IP address), and “Source IP Address” (i.e. S-GW IP address) to make the S1 GTP tunnel header.
  4. After receiving the outer IP packets, the eNB gets the user IP packets by stripping off the S1 GTP tunnel header and transfers them to the UE through the Data Radio Bearer (DRB) over the radio link.