4.3　CS Domain Network Organization

4.3.1　In the CS network of WCDMA，the A/Iu interface between MSC Server，MGW and BSC/RNC，Nc interface between（G）MSC Server and（G）MSC Server（BICC signal），Nb interface between（G）MGW and（G）MGW shall preferably use the IP bearer when it is available，or TDM when it is not available.

4.3.2　In the CS core network of WCDMA，the Mc interface between（G）MSC Server and（G）MGW shall adopt the IP bearer.

4.3.3　When CN uses the IP bearer，the network organization shall abide by the following principles:

1　The Nc interfaces should be networked by planes or hybrid-layer method，in which provincial NEs should be in planes，inter-provincial NEs should be in layers and BICC signaling message may be redirected through CMN；

2　The Nb interface should be networked by planes，while provincial and inter-provincial NEs shall be connected directly through the IP bearer network；

3　A dedicated bearer shall be selected as the IP bearer network，and the dedicated VPN shall be established for signaling messages；

4　（G）MSC Server，MGW，CMN，TMSC Server and TMG should be connected to the dedicated IP bearer network though CE equipment.

4.3.4　When TDM is used as the bearer in the CN，the network organization should comply with the requirements stipulated in Design Specification for 900/1800MHz TDMA Digital Cellular Mobile Communication System Engineering YD/T 5104.

4.3.5　When MSC POOL is employed in networking，the following requirements shall be satisfied:

1　The Nb，Nc and Mc interfaces shall be IP-based as a prerequisite for networks with MSC Pool deployment；

2　The number of nodes should not be less than three for MSC Servers with MSC Pool employment；

3　MSC Pool should be constructed within the scope of the local network；

4　The redundancy configuration set up during MSC Pool networking shall satisfy the traffic load bearing after the switchover from the retiring MSC Server with the maximum capacity to other MSC Servers within the MSC Pool；

5　MSC Pool networking should be overlapped；

6　During planning MSC Pool，continuous distribution within the coverage area of the pool should be maintained；

7　The networking structure should be determined with the incorporation of the actual situation of supporting equipment and the network scale.The NNSF functions may be realized at MGW side or in the RNC of the radio network acess side NE.Within the same MSC Pool，simultaneous use of MGW for NNSF and BSC/RNC for NNSF should be avoided.