Cisco ASR 5000 Series Administration Manual page 90

▀ Terminology
Figure 19. Service, Interface, and Context Relationship Within the System for GPRS/UMTS Networks
Source
Ctx.
To
G
CGF(s)
a
Net. Req.
PDP Ctx.
Cfg.
To
G
GGSN-
SGSN(s) n
Service
Context (Ctx.)
Interface
Service or
Configuration (Cfg.)
The source context used to service a subscriber session is the same as the context in which the GGSN service is
configured. Each GGSN service is bound to an IP address in a source context. The SGSNs select which IP address to
use, typically by using DNS. Once a subscriber has established a PDP context with a GGSN, the SGSNs continue to use
that same PDP context and GGSN as the subscriber moves about the network.
Destination contexts are selected based on APN configuration. When the system receives a Create PDP Context
Request message from the SGSN, it examines the APN that was provided. If the APN is not found on the system, the
system rejects the request.
After the APN has been found, the system may choose a different APN based on the system's virtual APN
configuration. In any event, a final APN is selected by the system
The system determines the destination context to use based on a parameter contained within the final APN
configuration. If a valid destination context name is configured for this parameter, it is used. If the name is not valid, or
if it is not configured, the system uses the context in which the APN is configured.
Once the system locates the context in which the APN is configured, it uses that context for subscriber authentication
and RADIUS-based accounting (if enabled). Any parameters returned by the RADIUS server during the subscriber
authentication/authorization override APN configuration parameters.
If GTPP-based accounting is enabled, the system uses the source context for accounting. That context may be
overridden by configuring a different accounting context to use in the GGSN service configuration.
▄ Cisco ASR 5000 Series Gateway GPRS Support Node Administration Guide
AAA Ctx.
AAA
AAA
Cfg.
GTPP
APN IP Addr.
Cfg.
Cfg. Pool Cfg.
DHCP
DHCP
Cfg.
Gi
FA-Service
MIP Dest. Ctx.
Optional
Gi
Dest. Ctx.
Data Network
GGSN
Configuration
To
AAA
Servers
To
AAA
Servers
AAA
AAA Cfg.
To
Source
DHCP
Ctx.
Servers
Gi
Service
To Packet
Configuration
Understanding the Service Operation
P
D
N
Destination
Ctx.
HA-
Local Ctx.
HA
To Packet
Data Network
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