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GGSN Support in GPRS/UMTS Wireless Data Services

How GGSN Works ▀

Cisco ASR 5000 Series Product Overview ▄

OL-22938-02

DHCP-proxy

: The system acts as a proxy for client (MS) and initiates the DHCP Discovery Request

on behalf of client (MS). Once it receives an allocated IP address from DHCP server in response to
DHCP Discovery Request, it assigns the received IP address to the MS. This allocated address must
be matched with the an address configured in an IP address pool on the system. This complete
procedure is not visible to MS.

DHCP-relay

: The system acts as a relay for client (MS) and forwards the DHCP Discovery Request

received from client (MS). Once it receives an allocated IP address from DHCP server in response to
DHCP Discovery Request, it assigns the received IP address to the MS.

In addition to the above methods, IP addresses for subscriber Mobile IP sessions are also dynamically assigned by the
subscriber‘s home network upon registration. The GGSN/FA, in turn, provide the assigned address to the mobile station.

Subscriber Session Call Flows

This section provides information on how GPRS/UMTS subscriber data sessions are processed by the system GGSN.
The following data session scenarios are provided:

Transparent IP:

The subscriber is provided basic access to a PDN without the GGSN authenticating the

subscriber. Either a static or dynamic IP address can be assigned to the MS in this scenario.

Non-transparent IP

: The GGSN provides subscriber authentication services for the data session. Either a static

or dynamic IP address can be assigned to the MS in this scenario.

Network-initiated

: An IP Packet Data Unit (PDU) is received by the GGSN from the PDN for a specific

subscriber. If configured to support network-initiated sessions, the GGSN, will initiate the process of paging
the MS and establishing a PDP context.

PPP Direct Access

: The GGSN terminates the subscriber‘s PPP session and provides subscriber authentication

services for the data session. Either a static or dynamic IP address can be assigned to the MS in this scenario.

Virtual Dialup Access

: The GGSN functions as an LAC, encapsulates subscriber packets using L2TP, and

tunnels them directly to an LNS for processing.

Corporate IP VPN Connectivity

: Similar to the Virtual Dialup Access model, however, the GGSN is

configured to tunnel subscriber packets to a corporate server using IP-in-IP.

Mobile IP

: Subscriber traffic is routed to their home network via a tunnel between the GGSN/FA and an HA.

The subscriber‘s IP PDP context is assigned an IP address from the HA.

Proxy Mobile IP

: Provides a mobility solution for subscribers whose Mobile Nodes (MNs) do not support the

Mobile IP protocol. The GGSN/FA proxy the Mobile IP tunnel with the HA on behalf of the MS. The
subscriber receives an IP address from their home network. As the subscriber roams through the network, the
IP address is maintained providing the subscriber with the opportunity to use IP applications that require
seamless mobility such as transferring files.

IPv6 Stateless Address Autoconfiguration

: The mobile station may select any value for the interface identifier

portion of the address. The only exception is the interface identifier for the link-local address used by the
mobile station. This interface identifier is assigned by the GGSN to avoid any conflict between the mobile
station link-local address and the GGSN address. The mobile station uses the interface ID assigned by the
GGSN during stateless address auto-configuration procedure (e.g., during the initial router advertisement
messages). Once this is over, the mobile can select any interface ID for further communication as long as it

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