Registration Method Of The Failover/Fallback Mode; Fallback Server Redundancy Configuration - Yealink SIP-T2 Series Administrator's Manual

1. Sends the INVITE request to the primary server.
2. If the primary server does not respond correctly to the INVITE (that is, the primary server responds to the INVITE
with 503 message or the request for responding with 100 Trying message times out (64*T1 seconds, defined in
3261)), then tries to make the call using the secondary server.
3. If the secondary server is also unavailable, the IP phone will try the fallback server until it either succeeds in making
a call or exhausts all servers at which point the call will fail.
At the start of a call, server availability is determined by SIP signaling failure. SIP signaling failure depends on the
SIP protocol being used as described below:
If TCP is used, then the signaling fails if the connection or the send fails.
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If UDP is used, then the signaling fails if ICMP is detected or if the signal times out. If the signaling has been
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attempted through all servers in the list (this list contains all the server addresses resolved by the DNS server) and
this is the last server, then the signaling fails after the complete UDP timeout defined in
last server in the list, the maximum number of retries depends on the configured retry counts (configured by the
parameter "account.X.sip_server.Y.retry_counts").

Registration Method of the Failover/Fallback Mode

Registration method of the failover mode:
The IP phone must always register to the primary server first except in failover conditions. If this is unsuccessful, the
phone will re-register as many times as configured until the registration is successful. When the primary server regis-
tration is unavailable, the secondary server will serve as the working server. As soon as the primary server registration
succeeds, it returns to be the working server.
Registration methods of the fallback mode include (not applicable to outbound proxy servers):
Concurrent registration (default): The IP phone registers to SIP server 1 and SIP server 2 (working server and fall-
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back server) at the same time. Note that although the IP phone registers to two SIP servers, only one server works at
the same time. If it fails, a fallback server can take over the basic calling capability, but without some advanced fea-
tures (for example, shared lines and MWI) offered by the working server.
Successive registration: The IP phone only registers to one server at a time. The IP phone first registers to the work-
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ing server. In a failure situation, the IP phone registers to the fallback server, and the fallback server can take over all
calling capabilities.

Fallback Server Redundancy Configuration

The following table lists the parameters you can use to configure fallback server redundancy.
Parameter account.X.fallback.redundancy_type
It configures the registration mode in fallback mode.
Description
Note: It is not applicable to outbound proxy servers.
0-Concurrent registration
Permitted
Values
1-Successive registration
Default 0
Parameter account.X.fallback.timeout
It configures the time interval (in seconds) for the IP phone to detect whether the working server is avail-
able by sending the registration request after the fallback server takes over call control.
Description
Note: It is not applicable to outbound proxy servers.
Permitted
Integer from 10 to 2147483647
Values
[1]
<MAC>.cfg
[1]
<MAC>.cfg
Account Settings
RFC
RFC 3261. If it is not the
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