Overview

A PCA DSR consists of a number of PCA DA-MP server, a number of SBR servers, OAM servers, and optional IPFE servers. The PCA DA-MPs are responsible for handling Diameter signaling and implementing the Policy DRA and Online Charging DRA functionalities, as well as the overall PCA application itself.

SBR servers host the policy session and policy binding databases for the P-DRA function and session database for the OC-DRA function. These are special purpose MP blades that provide an off-board database for use by the PCA feature hosted on the DA-MPs.

Each PCA DSR hosts connections to clients and to policy/charging servers such as OCSs and PCRFs. Clients are devices that request authorization for access to network resources on behalf of user equipment (such as mobile phones) from a PCRF, or request billing/charging instructions from an OCS. Policy Clients sit in the media stream and enforce Policy rules specified by the PCRF. Policy authorization requests and rules are carried in Diameter messages that are routed through Policy DRA. Policy DRA makes sure that all Policy authorization requests for a given subscriber in an APN are routed to the same PCRF. Charging clients (CTF) generates charging events based on the observation of network resource usage and collects the information pertaining to chargeable events within the network element, assembling this information into matching charging events, and sending these charging events towards the OCS. Online Charging DRA makes sure that these charging events are routed to the correct OCS.

PCA DSRs can be deployed in mated pairs such that policy and/or online charging session state is not lost, even if an entire PCA DSR fails or becomes inaccessible. When PCA mated pairs are deployed, the clients and PCRFs/OCSs are typically cross-connected such that both PCA DSRs have connections to all clients and all PCRFs/OCSs at both mated sites.

PCA DSRs can also be deployed in mated triplets such that session states are not lost, even if two PCA DSRs fail or become inaccessible. When a PCA mated triplet is deployed, clients and PCRFs/OCSs are cross-connected such that all three PCA DSRs have connections to all policy clients and all PCRFs/OCSs associated with the mated triplet.

“PCA network” is the term used to describe a set of PCA mated pairs and NOAM server pair/triplet. All clients and PCRFs/OCSs are reachable for Diameter signaling from any PCA DSR in the PCA network.

PCA is also designed to do the following:

Reduce Diameter signaling latency where possible by doing the following:
- Limiting the need to access off-board databases
  Note: "Off-board" in this context means on a server separate from the server handling the Diameter signaling
- Limiting to a single WAN traversal to route a diameter message within the PCA network
- Optimization of the most frequent "sunny day" scenarios, possibly at the expense of less common, or rainy day, scenarios
Provide server redundancy by supporting clusters of active DA-MP servers
Provides site redundancy by supporting mated pairs of P-DRA DSRs, as well as provide 3-site redundancy by supporting mated triplets of P-DRA DSRs
Provide triple data redundancy for subscriber binding data by having geographically dispersed active, standby, and spare copies of each binding record for mated pair configuration
Provide quadruple data redundancy for subscriber binding data by having geographically dispersed active, standby, spare, and spare copies of each binding record for mated triplet configuration
Support scalability of each DSR by the addition of DA-MP blades, as well as support network scalability by the addition of PCA sites
Limit network configuration complexity by makign use of naming conventions for clients and PCRFs/OCSs
Facilitate troubleshooting of network-wide database accesses and Diameter signaling by including correlation information in logs and traces