Logical Interfaces - Cisco ASR 5000 Series Administration Manual

Understanding the Service Operation
The system context in which accounting functionality is configured depends on the protocol used. Accounting for
subscriber PDP contexts can be performed using either the GPRS Tunneling Protocol Prime (GTPP) or RADIUS.
Accounting for administrative user sessions is based on RADIUS.
When using GTPP, it is recommended that accounting functionality be configured in a system source context along with
the GGSN service.
When using RADIUS for subscriber accounting, it must be configured in the same context as RADIUS authentication.
To simplify the configuration process, RADIUS-based authentication and accounting can be configured in a destination
context as long as the APN templates are configured there as well.
RADIUS-based accounting for administrative user sessions can either be configured in the local context or in the same
context used for subscriber accounting.
Important:
local context.
Local context: This is the default context on the system used to provide out-of-band management functionality.
The local context is described in the Command Line Reference.

Logical Interfaces

Prior to allowing the flow of user data, the port must be associated with a virtual circuit or tunnel called a logical
interface. A logical interface within the system is defined as the logical assignment of a virtual router instance that
provides higher-layer protocol transport, such as Layer 3 IP addressing. Interfaces are configured as part of the VPN
context and are independent from the physical port that will be used to bridge the virtual interfaces to the network.
Logical interfaces are assigned to IP addresses and are bound to a specific port during the configuration process. Logical
interfaces are also associated with services through bindings. Services are bound to an IP address that is configured for a
particular logical interface. When associated, the interface takes on the characteristics of the functions enabled by the
service. For example, if an interface is bound to a GGSN service, it will function as a Gn interface between the GGSN
service and the SGSN. Services are defined later in this section.
There are several types of logical interfaces that must be configured to support the service as described below:
Gn: This is the interface used by the GGSN to communicate with SGSNs on the same GPRS/UMTS Public
Land Mobile Network (PLMN). This interface serves as both the signalling and data path for establishing and
maintaining subscriber PDP contexts.
The GGSN communicates with SGSNs on the PLMN using the GPRS Tunnelling Protocol (GTP). The
signalling or control aspect of this protocol is referred to as the GTP Control Plane (GTPC) while the
encapsulated user data traffic is referred to as the GTP User Plane (GTPU).
One or more Gn interfaces can be configured per system context. Gn interfaces are bound to ports on either the
Ethernet 10/100 or Ethernet 1000 Line Cards or on the four-port Quad Gig-E Line Card (QGLC) (ASR 5000
only).
Ga: This is the interface used by the GGSN to communicate with the charging gateway (CG). The charging
gateway is responsible for sending GGSN charging detail records (G-CDRs) received from the GGSN for each
PDP context to the billing system.
The GGSN communicates with the CGs on the PLMN using GTP Prime (GTPP).
OL-22944-02
To ensure scalability, accounting functionality for subscriber sessions should not be configured in the
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