Interoperability Between Machine-to-Machine Communication System and IP Multimedia Subsystem - Interoperability and Open-Source Solutions for the Internet of Things - page 110

Fig. 5. M2M service - video service
4 UAA accepts data.
5 UAA (UE-A - user equipment A) initiates registration and sends a SIP
REGISTER towards the user's home network domain (Request URI pre-
configured in the UE). The REGISTER includes the user's public address
to be registered as well as their private address and the IP address of
the UE. The REGISTER is routed to a P-CSCF using a proxy address
that is pre-configured in the UE.
6 The P-CSCF stores the UE-A contact (IP) address, before it adds a Path
header to the REGISTER and proxies it to an I-CSCF by inserting a
Route header. The Route-header is composed using the received Request
URI of the REGISTER and a locally configured prefix. The Path header
contains a P-CSCF-URI to inform the S-CSCF where to route future
terminating requests for the user.
7 The I-CSCF sends a Cx USER AUTHORISATION REQUEST (Diame-
ter) containing the user's private and public address to the HSS (address
determined using locally configured data).
8 The HSS returns the required S-CSCF capabilities to the I-CSCF.
9 Based on the received information (and locally configured data), the
I-CSCF selects the S-CSCF and forwards the REGISTER to the selected
S-CSCF by inserting the S-CSCF URI in a Route-header. The S-CSCF
stores the contents of the REGISTER Path header (the P CSCF address;
to be used for routing terminated requests towards this public address)
and the UE-A IP address (received in REGISTER Contact header).