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▀ How Proxy Mobile IP Works in 3GPP Network
Step
Description
2
The terminal equipment (TE) aspect of the MS sends AT commands to the mobile terminal (MT) aspect of the MS to place
it into PPP mode.
The Link Control Protocol (LCP is then used to configure the Maximum-Receive Unit size and the authentication protocol
(Challenge-Handshake Authentication Protocol (CHAP), Password Authentication Protocol (PAP), or none). If CHAP or
PAP is used, the TE will authenticate itself to the MT, which, in turn, stores the authentication information.
Upon successful authentication, the TE sends an Internet Protocol Control Protocol (IPCP) Configure-Request message to
the MT. The message will either contain a static IP address to use or request that one be dynamically assigned.
3
The MS sends an Activate PDP Context Request message that is received by an SGSN. The message contains information
about the subscriber such as the Network layer Service Access Point Identifier (NSAPI), PDP Type, PDP Address, Access
Point Name (APN), quality of service (QoS) requested, and PDP configuration options.
4
The SGSN authenticates the request message and sends a Create PDP Context Request message to a GGSN using the
GPRS Tunneling Protocol (GTPC, "C" indicates the control signalling aspect of the protocol). The recipient GGSN is
selected based on either the request of the MS or is automatically selected by the SGSN. The message consists of various
information elements including: PDP Type, PDP Address, APN, charging characteristics, and tunnel endpoint identifier
(TEID, if the PDP Address was static).
5
The GGSN determines if it can facilitate the session (in terms of memory or CPU resources, configuration, etc.) and creates
a new entry in its PDP context list and provides a Charging ID for the session.
From the APN specified in the message, the GGSN determines whether or not the subscriber is to be authenticated, if Proxy
Mobile IP is to be supported for the subscriber, and if so, the IP address of the HA to contact.
Note that Proxy Mobile IP support can also be determined by attributes in the user's profile. Attributes in the user's profile
supersede APN settings.
If authentication is required, the GGSN attempts to authenticate the subscriber locally against profiles stored in memory or
send a RADIUS Access-Request message to a AAA server.
6
If the GGSN authenticated the subscriber to a AAA server, the AAA server responds with a RADIUS Access-Accept
message indicating successful authentication and any attributes for handling the subscriber PDP context.
7
If Proxy Mobile IP support was either enabled in the APN or in the subscriber's profile, the GGSN/FA forwards a Proxy
Mobile IP Registration Request message to the specified HA. The message includes such things as the MS's home address,
the IP address of the FA (the care-of-address), and the FA-HA extension (security parameter index (SPI)).
8
The HA responds with a Proxy Mobile IP Registration Response. The response includes an IP address from one of its
locally configured pools to assign to the MS (its Home Address). The HA also creates a mobile binding record (MBR) for
the subscriber session.
9
The HA sends an RADIUS Accounting Start request to the AAA server which the AAA server responds to.
10
The GGSN replies with an affirmative Create PDP Context Response using GTPC. The response will contain information
elements such as the PDP Address representing either the static address requested by the MS or the address assigned by the
GGSN, the TEID used to reference PDP Address, and PDP configuration options specified by the GGSN.
11
The SGSN returns an Activate PDP Context Accept message to the MS. The message includes response to the
configuration parameters sent in the initial request.
12
The MT, will respond to the TE's IPCP Config-request with an IPCP Config-Ack message.
The MS can now send and receive data to or from the PDN until the session is closed or times out. Note that for Mobile IP,
only one PDP context is supported for the MS.
13
The FA periodically sends Proxy Mobile IP Registration Request Renewal messages to the HA. The HA sends responses
for each request.
14
The MS can terminate the data session at any time. To terminate the session, the MS sends a Deactivate PDP Context
Request message that is received by the SGSN.
▄ Cisco ASR 5x00 Packet Data Network Gateway Administration Guide
442
Proxy-Mobile IP
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