SGSN Pool Networking

SGSN Pool Networking

The prerequisite of the SGSN pool networking is that the connections in the network use the Gb over IP or Iu over IP bearer mode. All SGSNs and base station controllers/radio network controllers (BSCs/RNCs) must be logically connected. If the connections use the time division multiplexing (TDM) or asynchronous transfer mode (ATM) bearer mode, the whole interconnection may be not implemented because of limited transmission resources, particularly in the case when the SGSNs are directly connected to the radio access network (RAN). Therefore, the SGSN pool networking scheme only takes the IP bearer into account.

The basic requirements of the networking are as follows:

• Each RNC rather than the BSC/packet control unit (PCU) possesses independent signaling point coding.
• Each SGSN possesses independent signaling point coding.
• The MTP3 User Adaptation Layer (M3UA) link data must be configured between the RNCs and the SGSNs.
• The SGSNs and the RNCs/BSCs are all connected at the IP layer.

The Iu/Gb interface between an RNC/BSC and an SGSN uses the IP bearer mode.

Typical networking of the SGSN pool:

This Pic shows the typical all-IP networking. The RNCs/BSCs in an equipment room are connected to the SGSNs through a local area network (LAN). The RNCs/BSCs in different equipment rooms are connected to the SGSNs through an IP backbone network.

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GPRS/UMTS CN-PS Solution

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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Network Structure of the GPRS/UMTS

Network Structure of the GPRS/UMTS






MS: mobile station
RAN: radio access network
CN-CS: core network-circuit switching
CN-PS: core network-packet switching
BSS: GSM base station subsystem
UTRAN: UMTS terrestrial radio access network
BTS: base transceiver station
BSC: base station controller
NodeB: UMTS base station
RNC: radio network controller
SGSN: serving GPRS support node
GGSN/FA: gateway GPRS support node/foreign agent
CG: charging gateway
HA: home agent
BG: border gateway
DNS: domain name server
AAA: authentication, authorization and accounting
UAP: UMTS access point

 A GPRS/UMTS network consists of the following parts:

• Mobile station (MS): user equipment capable of originating and receiving calls over the air interface. To handle data services, the MS establishes a logical link with the packet switched (PS) domain.
• Radio access network (RAN): handles all radio related functions.
• Core network-circuit switching (CN-CS): provides circuit services and connects to external circuit switched networks, such as a public switched telephone network (PSTN).
• CN-PS: provides packet data services and connects to external public data networks (PDNs), such as the Internet.

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Solution of Huawei R5

In the Huawei 3GPP R5 solution, the IMS for long is networked with the CS CN of 3GPP R4 as a service control network built on top of the PS domain. The two networks can supplement each other. It also converges mobile networks with fixed networks.

Due to continuous improvement in real-time IP service QoS mechanism of the PS air interface, increasing enhancement to the IP processing capability of wireless terminals, and mature end-to-end session-based QoS mechanism of the IMS bearer network, the IMS will gradually replace the CS R4 in the 3G access domain. The MSOFTX3000 can be expanded smoothly into the equipment with the MGCF, and the UMG8900 can be upgraded to the IM MGW. This ensures investment protection.

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3GPP R4 networking

3GPP R4 networking

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3GPP R99 networking

3GPP R99 networking

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Difference between 3GPP R4 and 3GPP R99

Difference between 3GPP R4 and 3GPP R99

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3GPP Networking Evolution of Packet Switch

3GPP Networking Evolution

The 3^rd Generation Partnership Project (3GPP) is a set of telecommunications standards used for cooperation. Currently, mobile communications comply with 3GPP standards.

With the evolution of 3GPP standards, the networking for mobile communications and available services are changing.

• Mobile communications network
  The mobile network has developed from the 2G global system for mobile communications (GSM) and the 2.5G general packet radio service (GPRS) to the 3G universal mobile telecommunications system (UMTS). Currently, mobile communications cover wide areas, boast high-speed wireless data transmission, and allow access to the Internet.
• Available services
  Services such as voice, data, and video services are available, which meets users' requirements for communicating with others anywhere anytime.

In the 3GPP protocol, no major modification is made to the packet switched (PS) domain, but the architecture of the bearer independent control network is introduced for the circuit switched (CS) domain in the 3GPP R4 version and the mobile switching center (MSC) in the 3GPP R99 version is planned as two network elements (NEs): MSC server and media gateway (MGW). In this case, bearer and control are separated.

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