Retransmission Logic

The retransmission of DNS queries is controlled by three timers. These timers are derived from the configured DNS timeout value and from underlying logic that the minimum allowed retransmission interval should be 250 milliseconds; and that the Oracle® Enterprise Session Border Controller should retransmit 3 times before timing out to give the server a chance to respond.

• Init-timer is the initial retransmission interval. If a response to a query is not received within this interval, the query is retransmitted. To safeguard from performance degradation, the minimum value allowed for this timer is 250 milliseconds.
• Max-timer is the maximum retransmission interval. The interval is doubled after every retransmission. If the resulting retransmission interval is greater than the value of max-timer, it is set to the max-timer value.
• Expire-timer: is the query expiration timer. If a response is not received for a query and its retransmissions within this interval, the server will be considered non-responsive and the next server in the list will be tried.

The following examples show different timeout values and the corresponding timers derived from them.

timeout >= 3 seconds
Init-timer = Timeout/11
Max-Timer = 4 * Init-timer
Expire-Timer = Timeout
timeout = 1 second
Init-Timer = 250 ms
Max-Timer = 250 ms
Expire-Timer = 1 sec
timeout = 2 seconds 
Init-Timer = 250 ms
Max-Timer = 650 ms
Expire-Timer = 2sec