5.3　Packet-switch Network Organization

5.3.1　The Iu_PS interface between RNC and SGSN may be connected through the leased line or IP bearer network.

5.3.2　Interconnectivity between CN inner nodes shall abide by the following principles:

1　If PS domain equipment is used on the IP network，the private IP network or public network may be used as the PS bearer according to telecommunications operators actual situation.

2　SGSN，GGSN，DNS and BG shall be interconnected via corresponding equipment according to the organization principles of the IP bearer network.When the above equipment involved is deployed on the same bureau location，interconnectivity may be achieved through the LAN.

3　SGSN，GGSN and independently deployed CG may be interconnected through an IP network or leased line.

5.3.3　PS domain SGSN and GGSN should be connected with associated signaling points through quasi-associated signaling.

5.3.4　Different ways of network organization shall be used to realize its interconnectivity according to external applications.The possible organization methods include dedicated direct connection and public network tunnel.

5.3.5　Routing shall abide by the following principles:

1　Three routing methods are provided to subscribers using PS data service in the home PLMN:

1）Service initiated by a subscriber in home province shall be sent from the home SGSN through the home GGSN to the external data network；

2）When subscribers roam to the visited province and use regional APN service，the traffic shall be sent from the visited SGSN through the visited province or from the home GGSN to the external data network；

3）When subscribers roam to the visited province and use regional APN service，the traffic shall be sent from the visited SGSN through the home GGSN to the external data network.

2　Two routing methods are provided to subscribers using PS data service in a visited PLMN:

1）Traffic shall be sent from the SGSN and GGSN of the visited PLMN to the external data network；

2）Traffic shall be returned from the SGSN of the visited PLMN through BGs of both sides to the GGSN of the province or the backbone GGSN the home PLMN belongs to the external data network.

5.3.6　When SGSN POOL is introduced into PS domain，the following principles shall be abided by:

1　SGSN POOL should be employed by province through the Gb/IuPS interface of an IP bearer.SGSN POOL should be used in the following regions:

1）In data service areas with significant tidal effect，areas with uneven distribution of peak-time voice traffic，and areas with large traffic capacity fluctuation during holidays and normal business days；

2）In high handover and high signaling load areas，areas with discontinuous wireless coverage and frequent 2G/3G inter-operations；

3）Areas with high demand for real-time disaster recovery，such as areas with on-going conventions，and areas with high capacity single-site.

2　POOL integration shall be implemented in 2G and 3G networks.The number of nodes in a single SGSN POOL should not be less than three.

3　NNSF（NAS Node Selection Function）nodes should be deployed on BSC/RNC.

5.3.7　Inter-connection between PS domains shall abide by the following principles:

1　PS domain connects through BG to the PS domain of other telecom operators.

2　BGs of both sides may be connected through the leased line or a VPN over an IP network.