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.
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] |