Cisco ASR 5000 series Product Overview page 459

Packet Data Interworking Function Overview
Figure 123. Active-Standby Online Upgrade Model
The active and standby chassis are connected by an SRP redundancy link to monitor and control the chassis state. Both
active and standby chassis have SRP-activated resources defined. Resources could mean loopback interfaces, broadcast
interfaces, or IP pools, depending on the installation. For this example, use loopback interfaces.
These resources are the same between the active and standby PDIF. Loopback IP addresses in ingress and egress
contexts, and IP pools in egress contexts, are usually SRP-activated resources. The result is that only the currently active
chassis enables the SRP-activated resources. The activate command is
Important:
In the network diagram below, each ingress context has loopback interface A defined, which is SRP-activated. PDIF
service A is bound to this interface. The standby chassis has the same interface and PDIF service defined. Both interface
and service can only be enabled on the active chassis. Similarly, interface B is defined in the egress context, which can
be activated only in the active chassis.
When the active chassis switches over, the standby chassis becomes active and enables all SRP-activated IP interfaces
and IP pools so that it can function as a mirror image of the former primary PDIF.
OL-22938-02
Ingress and egress contexts could be the same context. The SRP context must be a separate context.
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