5 Architecture model and reference points

23.1673GPPIP Multimedia Subsystem (IMS) emergency sessionsRelease 17TS

5.1 Reference architecture

This specification introduces an additional CSCF role to those defined in the IMS architecture TS 23.002 [12], called Emergency CSCF (E‑CSCF), see figure 5.1.

Legend:

Dashed lines: optional interfaces

Figure 5.1: E‑CSCF in reference architecture

NOTE 1: P‑CSCF, MSC Server enhanced for ICS, EATF and E-CSCF are always located in the same (serving) network; this is the visited network when the UE is roaming. For emergency session initiation, the S-CSCF and AS are only applicable for non-roaming cases.

NOTE 2: For simplicity, not all functional components, e.g. IBCF, MGCF and BGCF, are shown in this figure.

NOTE 3: Based on operator policy, the E‑CSCF can route the emergency IMS session to the PSAP via an ECS. See the details in Annex D.

5.2 Reference points

The E‑CSCF uses Mw, Mg, Mi, Ml, Mm, Mx and I4 reference points to connect to other IMS entities and other IP Networks.

I4 is a reference point between an E-CSCF and an EATF. See TS 23.237 [32].

I5 is a reference point between an I‑CSCF and an EATF. See TS 23.237 [32].

I6 is a reference point between an MSC Server enhanced for ICS and E-CSCF. See TS 23.292 [46].

Sh is a reference point between LRF and HSS. See TS 29.328 [43].