The WLAN-GW supports N:M warm standby redundancy on an MDA level. With this feature, it is possible to configure separate MDAs in the WLAN-GW group without the restriction that all MDAs in an IOM be BB modules. Up to 14 BB modules can be configured and active at one time.
MDA-based redundancy makes hardware provisioning more flexible but does not guarantee that all ESM session states is recovered after an MDA failure. Because BB MDAs share IOM resources with another MDA in the same IOM, there is no guarantee that the same set of resources is available on the IOM of the new MDA after a failure. This restriction does not apply to DSM.
There are several ways to ensure that the system has adequate IOM resources following a failure.
Use symmetric provisioning over all IOMs with BB modules. For example, do not create a 2:3 active:standby group by putting two BB MDAs on one IOM (IOM A) and one BB MDA on another IOM (IOM B). When the active ISAs are spread over IOM A and IOM B, the WLAN-GW has the full resources of two IOMs. However, after a failure, it is possible that both active ISAs is on IOM A and limited to the resources of a single IOM.
Combine BB MDAs with MDAs and services using predictable and fixed resources. For example, combining BB functionality with AA modules provides enhanced traffic services because AA modules typically have a fixed resource usage that allows you to predict resources following a failure.
Create a safety buffer by leaving some resources unallocated. By not maximizing resource usage on a single IOM, it is more likely those resources are also available on a backup location.
For more details, contact a Nokia representative.