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Core network aspects 1

IV.4 Service composition during call establishment

When an MUE creates several service components through multiple network interfaces, the service
components can be composed into one to serve application and the remote UE. The procedure in the figure
below takes place during call establishment. This procedure supports several of the use cases described in
[b-ITU-T Y-Sup.9].

MUE_A MUE_A
IF (1) IF (2) SCF (1) SCF (2) MAS-F UE_B
1. SC-1 initial Req
2. SC-2 initial Req
3. Forward SC-1 initial Req
4. Forward SC-2 initial Req

5. Initial SC-3 with
composed SC related
info of SC-1 and SC-2
6. SC-3 initial Req
7. Forward SC-3 initial Req
8. SC-3 initial response

9. Forward SC-3 initial Resp
10. Decompose SC
related info and
construct 2 responses
11. SC-1 initial Resp
12. SC-2 initial Resp
13. Forward SC-1 initial Resp
14. Forward SC-2 initial Resp

Service component from MUE_A IF (1) Service component
to UE_B
Service component from MUE_A IF (2)

Y.2027(12)_FIV.5

Figure IV.5 – Service composition during call establishment

1)-4) MUE_A initiates two service components (SC-1 and SC-2) from two interfaces, i.e., MUE_A IF(1) and
MUE_A IF(2). The initial requests are sent to the corresponding SCEs through different networks,
and are forwarded to MAS-F respectively.
5) MAS-F identifies that the requests belong to a same call and can be composed. Hence, it composes
the information of SC-1 and SC-2, and initiates a new service component (SC-3) to UE_B, which can
be a multi-connection UE or even an ordinary UE.
6)-7) The initial request of SC-3 is routed to a SCF, which is SCF (2) in the figure but could be any
appropriate one, and is forwarded to UE_B. UE_B can be a multi-connection UE or an ordinary UE.
8)-9) UE_B negotiates media parameters to establish SC-3. Then, UE_B constructs a response for SC-3,
and returns it along the transmission path. The response is then forwarded to MAS-F.

10) MAS-F decomposes service components related information from the response, and constructs two
responses for SC-1 and SC-2.

11)-14) MAS-F constructs two responses for SC-1 and SC-2. The responses are routed to MUE_A along the
original paths.

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