When the SIP signaling path for a call between user agents is disconnected due to SIP element failure or the network unavailability, the user agents cannot exchange the signaling messages. The SIP signaling path can also be disconnected when one or more SIP elements such as proxy or location server are not working, if the user switches the network from WiFi to 4G and from 4G to Wifi, or the failure of Session Manager.

Using SIP Resiliency feature, Session Manager reconstructs the call between endpoints when the SIP signaling path for a call or a conference call is disconnected. Avaya recommends using same domain names for signaling groups to support call reconstruction.

Session Manager reconstructs the impacted SIP dialog by initiating a new dialog towards SIP user agents to replace the dialog of broken end to end call. In case of Session Manager failure, alternate Session Manager reconstructs the call.

Communication Manager supports SIP Resiliency feature by replacing SIP dialogs for each dialog of a SIP session. When Communication Manager receives INVITE request containing a Replaces header message, Communication Manager attempts to replace the SIP dialog specified in the Replaces header. The Communication Manager also maintains the integrity of a call so that the features such as hold or transfer during the call are available for the parties of the call.

For the best performance of call reconstruction, ensure that the administration settings on the signaling groups, trunk groups, network regions, and codec settings are uniform between primary Session Manager, alternate Session Manager, and Communication Manager that are configured for call reconstruction. Also, ensure that all the incoming SIP trunks must connected to Communication Manager through Session Manager.

The call reconstruction might fail if the call topology consists of old as well as new instances of Session Manager and Communication Manager.

SIP device must also support the new call reconstruction method for SIP Resiliency feature to work.

You can enable SIP Resiliency only if all the Session Managers in the configuration are 8.0 or later.

For more information on Communication Manager settings for SIP Resiliency, see Avaya Aura® Communication Manager Screen Reference.