Local survivability is possible because each application server has a built-in Avaya Distributed Cache (ADCS). This rolling cache holds messages for three days, that is, 72 hours, but you can change this duration to suit your business requirements.
The system caches messages on the application server and then immediately attempts to deliver the message to the storage destination of the recipient when:
A caller leaves a message (Call Answering).
A user plays a message (Message review using a TUI).
A user sends a message (Voice messaging).
After 72 hours, the message is deleted from the cache on the application server. If the user plays a message that is older than 72 hours, the system retrieves the message from the message store. Then the system caches the message again on the application server as if the message was a new message.
Messaging uses the cache mechanism to avoid delays in message retrieval. Sometimes, the Messaging system takes longer than three seconds to retrieve a message depending on the available network bandwidth, the length of the message, and the server from which message is retrieved. To avoid an extended period of silence, Messaging plays a tone after three seconds to indicate that the message retrieval is in progress and the call is alive.
Creating an ad hoc list
Selecting a predefined personal or system distribution list from their address directory
When the caller sends a message to an ad hoc list, the application server only caches the message in the mailbox of the first person on the list. But after the message reaches the storage server, the system delivers the message to all the recipients. After a recipient who is not first on the ad hoc list plays the message, the system caches the message on the application server for that user.
When a recipient retrieves a message, the application server goes to the storage destination of the recipient to get a list of the recipient messages and their state, that is, unread, read, or saved. For the content of the message, the application server first looks locally in its own cache. If the message is not present in the local cache, the application server looks in the other application servers in the cluster. If the message is not on any of the application servers, the application server retrieves the message from the storage destination of the recipient and places the message into the local cache of the application servers.