GGSN:

The GGSN or Gateway GPRS Support Node is one of the new network elements that need to be introduced for GPRS. The GGSN is part of the GPRS core network and interconnects the PLMN towards external packet data networks via the Gi-interface.
  • Like the SGSN, the GGSN is a packet switch with some extra functionality which is required for its additional functions in a mobile network.
  • From the perspective of an external network like the internet the PLMN looks like a normal IP-subnetwork and the GGSN appears to be an IP-router.
  • Note that GPRS supports IP, PPP and IHOSS as packet data protocols (PDP). However, which PDP's are supported depends on the capabilities of the different GGSN(s). Again, not every GGSN supports all PDP's. When activating a PDP-context, a mobile station needs to access the correct GGSN that may serve that request. Another option is that the SGSN selects the correct GGSN based on subscription details or APN.
  • Please note that different GGSN's within a PLMN may support different packet data protocols or they may have different capabilities. For instance:
    => GGSN A in the figure below represents the operator's ISP-GGSN while
    => GGSN B interconnects the PLMN towards the internet and
    => GGSN C is a specialized GGSN that interconnects only to the IP-based intranet of one specific volume customer (e.g. large corporation).

Figure 1: Different GGSN's with Different Access Capabilities

  • The Mobile Network Operator as ISP:
    In figure 1 the GGSN A comes with all features and functions that are required for an ISP:
    => The network operator of GGSN A needs his own IPv4-number range for dynamic address allocation.
    => He has his own DHCP and DNS servers or access to those functions provided by another operator
    => He has access (leased line) towards the internet.
    In other words: With GPRS, the mobile network operators can enter into a completely new business area, which is mobile internet. The GGSN's need to be equipped accordingly.

    IP plus dynamic IP-address allocation

    PPP

    PPP-Tunneling

    Figure 2: Typical Protocol Stacks of a GGSN (PPP and IP with DHCP)

Functions of the GGSN:

Interface Function:
It is the GGSN which interconnects a PLMN to the external world. The external world, that's the packet data networks that the mobile users shall be connected to, namely the internet. However, other packet data protocols can be supported via PPP (e.g. Appletalk, Banyan Vines, NOVELL IPX).

Anchor Function:
Obviously, a mobile network such as GSM/GPRS provides for roaming. However, roaming is a capability that fixed packet data protocols like IP, PPP or IHOSS do not support. Therefore, the GGSN remains the anchor point for a packet data transaction throughout its duration, even when the SGSN needs to give control to another SGSN. This procedure is illustrated below.


Figure 2: The GGSN remains the anchor point throughout the lifetime of a PDP-context

Activation and Deactivation of PDP-Contexts / Session Management:
The GGSN is heavily involved in the activation and deactivation of PDP-contexts and decides about the QoS-Profile that is granted to a subscriber.

Charging:
The GGSN will, in addition to the SGSN, collect call data records and forward them to the charging gateway (CG). Please note that opposed to the SGSN, the GGSN will collect call data records based on the usage of external network resources. In other words, charges that arise from other packet data or mobile network operators are collected by the GGSN.

Parameter Description Type (Mandatory / Optional - Fixed (Unchangeable) / Variable
IMSI Subscriber Identity M/F
NSAPI Network Service Access Point Identifier M/F
MSISDN Telephone Number M/F (more than one number is possible)
PDP Type IP or PPP M/V
PDP Address The fixed PDP-address of the mobile station (empty if dynamic IP-addressing is used)
The mnemonic address of the serving GGSN (e.g. www.abcd.d2.gprs) applying to the DNS-rules.
M/V
Dynamic Address Dynamic or static PDP Address M/V
APN in Use Indicates the APN Network Identifier M/V
TEID Tunnel Endpoint Identifier M/V
TFT Traffic Flow Template O/V
QoS Profile Negotiated The Quality of Service profile negotiated M/V
SGSN Address IP-Address (either IPv4 or IPv6) of the currently serving SGSN O/V
MNRG Mobile station reachable for PS or not M/V
Recovery SGSN is performing database recovery or not M/V
GTP-SND Contains the GTP-U sequence number of the next N-PDU sent in Downlink to the SGSN O/V
GTP-SNU Contains the GTP-U sequence number of the next N-PDU sent in Uplink from the SGSN O/V
Charging Id The Charging Identifier identifies the recorded charges from the SGSN and the GGSN M/V
Charging Characteristics Contains the charging characteristics for this PDP context M/V
Trace Reference Identifies a record or a collection of records for a particular trace O/V
Trace Type Contains the Type of trace O/V
Trigger Id Contains the Identity of the entity that initiated the call O/V

OMC Identity

Contains Identity of the OMC that shall receive the recorded trace

O/V

Table 1: Information Storage within the GGSN

[2GTS 02.60 / 3GTS 23.060 / 3GTS 29.060]