Server Redundancy - Yealink SIP-T4X Administration Manual

Administrator's Guide for SIP-T4X IP Phones
2. Enter the IP address or any in the Action URI allow IP List field.
Multiple IP addresses are separated by commas. If you enter "any" in this field, the
IP phone can receive and handle GET requests from any IP address. If you leave
the field blank, the IP phone cannot receive or handle any HTTP GET request.
3. Click Confirm to accept the change.
Server redundancy is often required in VoIP deployments to ensure continuity of phone
service, for events where the server needs to be taken offline for maintenance, the
server fails, or the connection between the IP phone and the server fails.
Two types of redundancy are possible. In some cases, a combination of the two may be
deployed:
Failover: In this mode, the full phone system functionality is preserved by having a

second equivalent capability call server take over from the one that has gone
down/off-line. This mode of operation should be done using the DNS mechanisms
from the primary to the secondary server.
Fallback: In this mode, a second less featured call server (fallback server) with SIP

capability takes over call control to provide basic calling capability, but without
some of the advanced features offered by the working server (for example, shared
lines, call recording and MWI). IP phones support configuration of two SIP servers
per SIP registration for fallback purpose.
Phone Configuration for Redundancy Implementation
To assist in explaining the redundancy behavior, an illustrative example of how an IP
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