Cisco ASR 5000 Series, Обзор продукта

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GGSN Support in GPRS/UMTS Wireless Data Services
How GGSN Works ▀
Cisco ASR 5000 Series Product Overview ▄
OL-22938-02
1.
The Mobile Station (MS) goes through the process of attaching itself to the GPRS/UMTS network.
2.
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.
3.
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 signaling 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).
4.
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.
If the MS required the dynamic assignment of an IP address (i.e., the PDP Address received from the mobile
was null), the GGSN will assign one. The IP address assignment methods supported by the system GGSN are
described in the
Dynamic IP Address Assignment section of this guide.
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.
5.
The SGSN returns an Activate PDP Context Accept response to the MS.
The MS can now send and receive data to or from the PDN until the session is closed or times out. The MS can
initiate multiple PDP contexts if desired and supported by the system. Each additional PDP context can share
the same IP address or use alternatives.
6.
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.
7.
The SGSN sends a Delete PDP Context Request message to the GGSN facilitating the data session. The message
includes the information elements necessary to identify the PDP context (i.e., TEID, and NSAPI).
8. The GGSN removes the PDP context from memory and returns a Delete PDP Context Response message to the
SGSN. If the PDP context was the last associated with a particular dynamically assigned PDP Address, the
GGSN will re-claim the IP address for use by subsequent PDP contexts.
9. The SGSN returns a Deactivate PDP Context Accept message to the MS.
10. The GGSN delivers the GGSN Charging Detail Records (G-CDRs) to a Charging Gateway (CG) using GTP
Prime (GTPP). Note that, though not shown in this example, the GGSN could optionally be configured to send
partial CDRs while the PDP context is active.
11.
For each accounting message received from the GGSN, the CG responds with an acknowledgement.
Non-Transparent IP Session Call Flow
The following figure and the text that follows describe the call flow for a successful non-transparent data session.