mode, Nano CUBE provides end-to end telephony services when access to the
centralized servers is interrupted because of a WAN outage or other factors,
like the server being down.
illustration shows how a call is established between two end points when WAN
link is down during survivability by directly dialing into an extension.
Figure 3. Nano CUBE
Survivability when WAN is Down
Earlier, when WAN
was down, User A could only contact User B using either the alias or the
user-id of User B, and not using their extensions or phone numbers.
Now, in the event
the WAN link or registration server is down, when a local call is made, INVITE
is sent to Nano CUBE. Nano CUBE maps the details of the user like extension
number and phone-number stored during registration. Local phones can now be
reached on their short extensions or phone numbers by similar phones subscribed
to the server through the same Nano CUBE.
It is possible to
register multiple contacts for a single AOR; however, if multiple contacts are
registered for a single subscriber, the Nano CUBE uses only the topmost
registered contact to deliver the call to that subscriber. For this reason,
multiple contacts are not supported.