+-------+  Diameter  +-------+
                                       |  HSS  |------------|  SPR  |
                                       +-------+            +-------+
                                           |                    |
        +------+   +------+      S4        |                +-------+
        |  3G  |---| SGSN |----------------|------+  +------| PCRF  |
     ^  |NodeB |   |      |---------+  +---+      |  |      +-------+
+-+  |  +------+   +------+   S3    |  |  S6a     |  |Gxc       |
| |  |                          +-------+         |  |          |Gx
+-+  |       +------------------|  MME  |------+  |  |          |
MT   v       |       S1MME      +-------+  S11 |  |  |          |
       +----+-+                              +-------+     +-------+
       |4G/LTE|------------------------------|  SGW  |-----|  PGW  |
       |eNodeB|            S1U               +-------+  +--|       |
       +------+                                         |  +-------+
                                  +---------------------+    |  |
 S1U GTP Tunnel traffic           |          +-------+       |  |
 S2a GRE Tunnel traffic           |S2A       | ePDG  |-------+  |
 S2b GRE Tunnel traffic           |          +-------+  S2B     |SGi
 SGi IP traffic                   |              |              |
                             +---------+   +---------+       +-----+
                             | Trusted |   |Untrusted|       | CDN |
                             |non-3GPP |   |non-3GPP |       +-----+
                             +---------+   +---------+
                                  |             |
                                 +-+           +-+
                                 | |           | |
                                 +-+           +-+
                                 MT            MT