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PDG/TTG Overview
Network Deployment(s) and Interfaces ▀
Cisco ASR 5000 Series Product Overview ▄
OL-22938-02
Network Deployment(s) and Interfaces
This section describes the PDG/TTG as it functions in a GPRS/UMTS data network.
The TTG in a GPRS/UMTS Data Network
The TTG is a GPRS/UMTS network element that enables the implementation of PDG functionality in existing GGSN
deployments. It achieves this by using a subset of the Gn reference point called the Gn' (Gn prime) reference point to
connect to currently-deployed GGSNs. This provides the means by which GPRS mobile operators can offer new
services to current subscribers by implementing PDG functionality using existing infrastructure.
The following figure shows a PDG implementation that consists of the TTG working together with a currently-deployed
GGSN. In this implementation, only a subset of the GGSN functionality is used.
Figure 127. The TTG and GGSN in a PDG Implementation
PDG
PDN/Internet
TTG
Wm
WLAN
UE
Wu
Gn’
GGSN
Subset of GGSN
functions
3GPP AAA
Gi
In the implementation above, the TTG terminates a secure IPSec tunnel for each WLAN UE subscriber session
established over the Wu reference point. The TTG also establishes a corresponding GTP (GPRS Tunneling Protocol)
tunnel over the Gn' reference point to the GGSN. The TTG and the subset of GGSN functions work together to provide
PDG functionality to the UEs in the WLAN.
The TTG functions as an SGSN in the GPRS/UMTS network to provide an SGTP (SGSN GPRS Tunneling Protocol)
service. The SGTP service enables the TTG to use GTP over the Gn' interface to carry packet data between itself and
the GGSN. The GGSN establishes a corresponding connection over the Gi reference point toward the PDN/Internet.