The Server creates special Local Nodes called Call Legs. Each Call Leg terminates signaling for one phone call. Each PBX Task is a Call Leg, and each XIMSS session can create one or more Call Legs to handle phone calls initiated or accepted by the XIMSS session user.
The settings in the Call Legs panel are applied to all types of Call Legs:
Session-Expiration: Use this setting to specify how often the parties should exchange the INVITE (or OPTION) requests to verify that the call has not been broken.
Hop Limit: Use this setting to specify the Max-Forwards field value for the requests sent with Call Legs.