Visited MSC Server (VMSC Server)
As VMSC Server, it provides switching and signaling functions for mobile subscribers in local MSC area, supporting RNC and BSC access at the same time. For subscribers in MSC Server area, it processes circuit-switched incoming/outgoing calls.
VLR is embedded in VMSC Server. VLR stores all data necessary for MSC Server to create and release calls and provides roaming and supplementary services. It also tracks the dynamic location changes of mobile subscribers that enters local VMSC Server area and stores all information about them (such as IMSI, MSISDN, MSRN, TMSI and SGSN ID). Here, mobility management, security management and call control functions are carried out
Gateway MSC Server (GMSC Server)
As GMSC Server, it is a gateway function node between WCDMA core network circuit domain and external network. It can be connected with PSTN, ISDN or other PLMN, enabling communication service between fixed subscribers and mobile subscribers.
GMSC Server can query the location of a mobile subscriber based on the MSISDN number. After getting the MSRN, it connects the call to VMSC Server of the called.
When GMSC Server acts as the inter-network mobile gateway, it performs important functions such as route analysis, inter-network access and inter-network settlement.
Service switching point (SSP)
SSP implements SSF, CCF and built-in SRF functions in CAMEL DFP. It is service control, call control and resource management functional entities.
With MSC Server as the platform, SSP performs call flow control based on operation code, resource code and detection point (DP) in SCP message. It also performs resource scheduling and returns the execution result and detected status to the SCP to determine the subsequent service orientation.
ZXUN iCX can be deployed as a MGCF to interwork IMS and CS/PSTN services, acting as a gateway between IMS network and CS/PSTN network.
In addition, MGCF also implements signaling conversion between SIP and BICC/ISUP.
CS Fallback is a technology that allows UEs in an EPC network to fall back to CS domain and obtain voice continuity with CS network infrastructure.
ZXUN iCX supports the CSFB function, which enables LTE users to register in the CS network when voice services are needed, and to return to the LTE network when voice services are not needed, so that the users can enjoy both the stability of voice services in CS network and the high-speed data services in LTE network.
SRVCC is a single-frequency voice continuity technology that is used to handover the voice calls of IMS user from the LTE network to the CS network, in order to ensure the continuity of voice services.
ZXUN iCX can be deployed as visited MSCS to support SRVCC and directly connect to the BSC/RNC. When the SRVCC handover occurs, it switches to the 2/3G network under the control of ZXUN iCX.
ZXUN iCX can also be deployed as SRVCC Proxy MSCS and connects with other visited MSCS. When the SRVCC handover occurs, MSCS acts as a proxy node and performs the handover of call to the 2/3G access which is under the control of visited MSCS.
ICS refers to the centralized control of services in the IMS. The CS domain only serves as an access channel for the IMS and provides a mechanism for using the CS media bearer for IMS sessions.
ZXUN iCX supports the ICS function based on I2 interface. Through the ICS function, all services of mobile users can be provided by IMS. When a user accesses through CS mode, the session initiated by the user is also controlled by IMS.