Tuesday, June 5, 2012

GPRS/UMTS CN-PS Solution

  • Tuesday, June 5, 2012
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    • GPRS/UMTS CN-PS Solution


    The GPRS/UMTS CN-PS consists of the following main network entities:
    • Serving GPRS support node (SGSN)
      The SGSN is a functional entity that provides packet data services. It forwards incoming and outgoing internet protocol (IP) packets to the mobile stations (MSs) within its service area.
      The SGSN provides the following functions:
      • Routing and forwarding of data packets
      • Encryption and authentication
      • Session management
      • Mobility management
      • Logical link management
      • Generation and output of call detail records (CDRs)
      Apart from performing the functions of itself, the SGSN9810 is integrated with the UMTS access gateway (UAG) function, which implements the access and management of UMTS access points (UAPs) and forwarding of CS data and signaling between a UAP/MS and the MGW/MSC server, and the access of PS services through the UAP.
    • Gateway GPRS support node (GGSN) and foreign agent (FA)
      The GGSN is also a functional entity that provides packet data services. It routes and encapsulates packet data between the GPRS/UMTS network and an external PDN.
      The GGSN provides the following functions:
      • Interface to an external PDN
        The GGSN serves as a gateway for an MS to access the external PDN. For the external network, the GGSN serves as a router for all equipment in the GPRS/UMTS network.
      • GPRS/UMTS session management
        The GGSN sets up a connection between an MS and the external PDN.
      • Data routing and forwarding
        The GGSN receives data from the MS and then forwards the data to the external PDN. It also receives data from the external PDN and selects a transport channel in the GPRS/UMTS network based on the destination address to forward the data to the SGSN.
      • FA functions
        To support Mobile Internet Protocol (MIP) services, the GGSN is embedded with FA functions. In this case, the GGSN/FA serves as a gateway of the GPRS/UMTS network and an FA of the network visited by the MS.
      • Charging for postpaid services
        The GGSN generates and outputs CDRs based on the usage of the external network by the subscribers.
      • Call control and service switching functions for prepaid services
        For prepaid services, the GGSN serves as a service switching point (SSP) that connects a mobile network and an intelligent network.
    • Home agent (HA)
      The HA is an entity that is used to support mobile IP access. It is an enhanced router that also maintains the current location information of the MSs.
      The HA has the following function:
      • Sending broadcast messages to the MSs so that the MSs know if they are on the home network.
      • Handling and replying the registration requests from an MS. Generating mobility binding records (MBRs) between the MS home address and care-of address.
      • Agency and forwarding: The HA reports the availability of network prefixes for the MS home address so that the packets to the MS home address can be routed to the home network. After encapsulating the packets, the HA tunnels them to the GGSN/FA, and then the GGSN/FA finally forwards the packets to the MS.
    • Charging gateway (CG)
      The CG collects, consolidates, and preprocesses CDRs generated by the SGSN or the GGSN. It provides an interface to the billing center.
      The CDRs are generated by several network entities when a GPRS or UMTS subscriber visits the Internet. Each entity may generate several CDRs.
      The CG is used to reduce the work load of the billing center by consolidating and preprocessing the CDRs before sending them to the billing center. With the CG in the network, the SGSN or the GGSN need not provide the charging interface to the billing center.
    • Authentication, authorization, accounting (AAA) server
      The AAA server carries out authentication, authorization and accounting according to the Remote Authentication Dial-In User Service (RADIUS) protocol.
      The AAA server is not specific to the GPRS/UMTS system.
    • Domain name system (DNS) server
      There are two types of DNS server in a GPRS/UMTS network.
      The first is the DNS between the GGSN and the external PDN. As an ordinary DNS on the Internet, this DNS resolves the domain name of the external PDN.
      The second is the DNS on the GPRS/UMTS CN. The main functions of the DNS server include the following:
      • Resolving the GGSN IP address according to the access point name (APN) to set up a connection between the GGSN and the MS when the MS accesses the external PDN.
      • Resolving the SGSN IP address according to the old routing area code during the inter-SGSN routing area update.
      • Resolving the SGSN IP address according to the new radio network controller (RNC) identity (ID) during RNC relocation.
      The DNS server is not specific to the GPRS/UMTS system.
    • Border gateway (BG)
      The BG is a router. In addition to security functions, it provides a routing function between the SGSN and the GGSN in different PLMNs.
      The BG is not specific to the GPRS/UMTS system.

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