A Service Control Signalling Path is used to transport service control signalling between the ICS UE and the SCC AS, for enabling IMS services when using CS or PS access. The Service Control Signalling Path is used when needed, e.g. on session establishment and/or service control of IMS sessions using CS voice bearers. For ICS UE sessions, the SCC AS combines the service control signalling received over the Service Control Signalling Path with the description of the bearer established via the CS network to present an IMS session on behalf of the UE. The service control signalling elements from Gm / I1 such as A party address shall be used together with the bearer description signalling received via CS bearer control signalling path to construct the signalling for the remote leg. The Service Control Signalling Path is established via the PS or CS network. Figure 7.1.1-1 illustrates how signalling and bearer paths established by the ICS UE are combined at the SCC AS when the Service Control Signalling Path is established via the PS network using the Gm reference point.

Upon session initiation, the ICS UE or the SCC AS establishes the Service Control Signalling Path for communication of service control signalling via the PS network using the Gm reference point. The ICS UE also sets up the CS Bearer Control Signalling Path using standard CS network procedures to establish the circuit media. The SCC AS combines the service control signalling received over the Service Control Signalling Path with the description of the bearer established using the CS Bearer Control Signalling Path by acting as a B2BUA as below:

• Access Leg: The Access Leg is formed with a combination of the Service Control Signalling Path and the CS Bearer Control Signalling Path.
• Remote Leg: The Remote Leg is presented by the SCC AS to the CSCF as an IMS session using IMS SIP signalling on behalf of the UE.

The TAS and other Application Servers are executed on the Remote Leg as part of standard service execution logic at the CSCF. The SIP UA at the UE maintains the SIP/SDP state machine with the SCC AS also maintaining a copy of the state data. Figure 7.1.1-2 illustrates how signalling and bearer paths established by the UE are combined at the SCC AS when the Service Control Signalling Path is established via the CS network using the I1 reference point.

Upon session initiation, the ICS UE or the SCC AS establishes the Service Control Signalling Path for communication of service control signalling via the CS network using the I1 reference point. In parallel, the ICS UE or the SCC AS sets up the CS Bearer Control Signalling Path using standard CS network procedures to establish the circuit media. The SCC AS combines the Service Control Signalling Path with the bearer established using the CS Bearer Control Signalling Path by acting as a B2BUA as described above for the case of Service Control Signalling Path established via the PS network.

Figure 7.1.2-1 illustrates signalling and bearer paths for sessions which are established using standard CS call control procedures and MSC Server .

Upon session initiation, the UE or the remote end sets up a call and the call is directed to IMS using standard CS procedures; IN (e.g. CAMEL) triggers are used to redirect CS originated calls to IMS. The SCC AS acts a B2BUA for presentation of the UA behaviour on behalf of the UE to IMS. The TAS and other Application Servers are executed on the Remote Leg as part of standard service execution logic at the CSCF.