L2TP Access Concentrator
▀ Supported LAC Service Configurations for the GGSN and P-GW
▄ Cisco ASR 5x00 Packet Data Network Gateway Administration Guide
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sessions. If no outbound information is configured, the subscriber’s International Mobile Subscriber Identity (IMSI) is
used as the username at the peer LNS.
1.
The GGSN returns an affirmative Create PDP Context Response to the SGSN over the Gn interface.
2.
The GGSN passes data received from the MS to a LAC service.
3.
The LAC service encapsulates the IP packets and forwards it to the appropriate Gi interface for delivery to the
LNS.
4.
The LNS un-encapsulates the packets and processes them as needed. The processing includes IP address
allocation.
Non-transparent IP PDP Context Processing with L2TP Support
The following figure and the text that follows describe how non-transparent IP PDP contexts are processed when L2TP
tunneling is enabled.
Figure 42.
Non-transparent IP PDP Context Call Processing with L2TP Tunneling
1.
A Create PDP Context Request message for a subscriber session is sent from the SGSN to the GGSN service
over the Gn interface. The message contains information such as the PDP Type, APN, and charging
characteristics.
2.
The GGSN determines whether or not it is configured with an APN identical to the one specified in the message.
If so, it determines how to process the session based on the configuration of the APN.
