| HSS | Home Subscriber Server
| CSCF
| Call State Control Function
| P-CSCF
| Proxy-CSCF
| S-CSCF
| Serving-CSCF
| I-CSCF
| Interrogating-CSCF
| MGW
| Media Gateway
| MGCF
| Media Gateway Control Function
| SGW
| Signaling Gateway
| T-SGW
| Transport Signaling Gateway Function
| R-SGW
| Roaming Signaling Gateway Function
| MRF
| Multimedia Resource Function
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