Balancing is the distribution of new endpoints, identified by the combination of unique source and destination address pairs, among the members of the Subscriber-Aware Load Balancer cluster, and sending SIP traffic to the most appropriate member, based on your configuration. You define this balancing by configuring policies to apply to address pair and global balancing configuration. Distribution policies (lb-policy) define and direct traffic specifying target realms by address pairs. After identifying a target realm, or for packets that do no match a distribution policy, the Subscriber-Aware Load Balancer calculates the best cluster member for this traffic from the pool of candidates (lbp-config). The simplest configuration can skip realm participation, instead distributing traffic in a round-robin fashion across the entire pool of cluster members. SBCs can also report themselves as overloaded, which excludes them as candidate targets until they report themselves as available for service again.

The section Distribution Policy Configuration expands upon address pair and target realm and, ultimately, candidate pool identification. The load balance config (lbp-config) specifies how to identify the best SBC in the candidate pool. Regardless of the distribution method, policy-based or round-robin, the Subscriber-Aware Load Balancer, by default, weighs each candidate SBC, and identifies the one with the lowest current utilization. In addition, the lbp-config allows you to specify traffic constraints that controls state timing and the amount of traffic managed by each config.

Within the lbp-config, you can select from two strategies for weighing target SBC utilization:

Least Occupied—This strategy distributes to the SBC with the least current endpoint count.

Capacity Proportional—This strategy causes the Subscriber-Aware Load Balancer to maintain a calculation using the maximum occupancy and the current endpoint count on each applicable SBC. A higher maximum capacity indicates the ability to support a higher number of endpoints.

The Subscriber-Aware Load Balancer balances traffic distribution by checking status detail on each SBC in the cluster, and forwarding to the best target, as follows:

1. If the SBC reports itself as overloaded, the Subscriber-Aware Load Balancer skips that SBC from consideration.
2. If the traffic matches a policy, the Subscriber-Aware Load Balancer iterates through the SBCs that match the policy using either round robin or capacity proportional (referring to the strategy configuration).
3. If there is no policy configured, the Subscriber-Aware Load Balancer uses round-robin or capacity-proportional to identify SBCs.
   • For least-occupied (default) the Subscriber-Aware Load Balancer selects the SBC with the fewest endpoints.
   • For capacity-proportional, the Subscriber-Aware Load Balancer selects the SBC with the lowest endpoint to maximum capacity ratio.
4. The Subscriber-Aware Load Balancer skips over any SBC that has exceeded its maximum Subscriber-Aware Load Balancer-assigned endpoints.
5. The Subscriber-Aware Load Balancer identifies and forward to the target SBC.

 slb-1# show balancer metrics
              local remote               max        max Over
 SBC   Name   epts  epts   max reg  CPU  CPU   Mem% Mem Load
 -------------------------------------------- -------- -------------
 1021  SBC-1b 501   501    1000     0.2  90.0  21.0 95.0 no
 1022  SBC-1c 501   501    1000     0.1  90.0  21.0 95.0 no 
 1023  SBC-1a 501   501    1200     0.0  90.0  21.0 95.0 no

 slb-1# show balancer metrics
              local remote               max        max Over
 SBC   Name   epts  epts   max reg  CPU  CPU   Mem% Mem Load
 -------------------------------------------- -------- -------------
 1021  SBC-1b 470   470    1000     0.2  90.0  21.0 95.0 no
 1022  SBC-1c 470   470    1000     0.1  90.0  21.0 95.0 no 
 1023  SBC-1a 563   563    1200     0.0  90.0  21.0 95.0 no