Manual

Cisco Packet Data Serving Node (PDSN) Release 2.0
System Overview
4
12.3(11)T
How PDSN Works
When a mobile station makes a data service call, it establishes a Point-to-Point Protocol (PPP) link with
the Cisco PDSN. The Cisco PDSN authenticates the mobile station by communicating with the AAA
server. The AAA server verifies that the user is a valid subscriber, determines available services, and
tracks usage for billing.
The method used to assign an IP address and the nature of the connection depends on service type and network
configuration. Simple IP operation and Mobile IP operation are referred to as service types. The service
type available to a user is determined by the mobile station, and by the type of service that the service
provider offers. In the context of PDSN, a mobile station is the end user in both Simple IP and Mobile
IP operation.
Once the mobile station is authenticated, it requests an IP address. Simple IP stations communicate the
request using the Internet Protocol Control Protocol (IPCP). Mobile IP stations communicate the request
using Mobile IP registrations.
The following sections describe the IP addressing and communication levels for each respective topic:
• Cisco PDSN Simple IP
• Cisco PDSN Mobile IP
• PMTU Discovery by Mobile IP Client
Cisco PDSN Simple IP
With Simple IP, a service provider’s Cisco PDSN assigns a dynamic or static IP address to the mobile
station during the PPP link setup. The mobile station retains this IP address as long as it is served by a
radio network that has connectivity to the address-assigning PDSN.
Therefore, as long as the mobile station remains within an area of RANs that is served by the same
PDSN, the MS can move or roam inside the coverage area and maintain the same PPP links. If the mobile
station moves outside the coverage area of the given PDSN, the mobile station is assigned a new IP
address, and any application-level connections are terminated.
Note A static IP address can be requested by the mobile station, and will be assigned if the address is within
the pool of addresses and is available. Also an IP address can be statically specified in the AAA profile
of the user using the “Framed-IP-Address” attribute.
Figure 3 illustrates the placement of the Cisco PDSN in a Simple IP scenario.