Site Redundancy

2-Site Redundancy

2-Site redundancy is the ability to lose an entire site, for example due to a natural disaster or major network failure, without losing signaling or application state data. For PCA, this means no loss of Policy Binding or Policy Session data. To achieve site redundancy, a specific configuration applies:

• PCA is deployed on at least one mated pair of PCA DSRs.
• Clients and PCRFs/OCSs are able to connect to both sites in the mated pair.
• SBR server groups are set up to use the Active/Standby/Spare or Active/Spare redundancy model.
• System OAM (SOAM) server groups are set up to use the Active/Standby/Spare redundancy model.
• Diameter Agent MP servers are recommended to be engineered at 40% capacity across the mated pair.

3-Site Redundancy

3-Site redundancy is the ability to lose two entire PCA sites simultaneously, for example due to a natural disaster or major network failure, without losing signaling or application state data. For PCA, this means no loss of Policy Binding or Session data. To achiever 3-site redundancy, a specific configuration applies:

• PCA is deployed on at least one mated triplet of PCA DSRs.
• Clients and PCRFs/OCSs connect to all sites in the mated triplet.
• SBR Server groups use the Active/Standby/Spare/Spare redundancy model.
• System OAM server groups use the Active/Standby/Spare/Spare redundancy model.
• Diameter Agent MP servers are recommended to be engineered at 26⅔% capacity across the mated triplet, for example, if two sites fail, then each remaining DA-MP operates at 80% capacity.

Comparing 2-Site and 3-Site Redundancy

To achieve the same redundant capacity of a mated pair in a mated triplet, multiple things need to be added:

• One Preferred Spare SOAM to every existing SOAM server group.
• One SOAM quadruplet server group for the third DSR.
• One Preferred Spare SBR to every existing SBR server group (total of two spares per group).
• [Optional] One new SBR quadruplet server group homed to the new site for every existing pair of SBR server groups. This increases total Session SBR capacity, but is primarily intended to balance flows.
• The same quantities of IPFEs and DA-MPs of the original DSR to the new DSR and Diameter connections to all of the Policy and Charging Clients and Policy and Charging Servers associated with the mated triplet.

Figure 3-11 Comparing 2-Site and 3-Site Redundancy