Specifications

Chapter 4 - MGCP Protocol Features Retransmission Parameters
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Mediatrix 4100
Retransmission Parameters
Retransmission is a method of error control in which hosts receiving messages acknowledge the receipt of
correct messages and do not acknowledge the receipt of incorrect messages. The lack of acknowledgement
indicates to the sending host that it should transmit the failed message again.
 To set Retransmission information:
1. In the mgcpMIB, locate the mgcpRetransmission group.
2. Set the Retransmission algorithm used in the mgcpRetransmissionAlgorithm variable.
The following values are available.
The default value is exponentialWithJitter.
3. Set the following variables:
Table 51: Retransmission Algorithm Parameters
Parameter Description
static(0) The retransmission period stays the same.
Ex.: Period of 500 ms. The following retransmissions will be at
500 ms, 1000 ms, 1500 ms, etc.
exponential(1) The retransmission period is doubled at each period.
Ex.: Initial period of 500 ms. The retransmissions will be at
500 ms, 1000 ms, 2000 ms, 4000 ms, etc.
exponentialWithJitter(2) The retransmission period is exponentially calculated with a
random weighting factor varying from 88% to 112% of the
calculated period.
Ex.: Initial period of 500 ms.
Period = (Period x 2) * (Random value (0 to 24) + 88) / 100
Period2 = (Initial period x 2) * (Random value (0 to 24) + 88) /
100
etc.
Table 52: MGCP Retransmission Information
Variable Description
mgcpRetransmissionInitialPeriod Retransmission initial period in ms.
Default Value: 200
mgcpRetransmissionMaxPeriod Retransmission maximum period in ms. Must be greater
than or equal to the retransmission initial period.
Default Value: 30000
mgcpRetransmissionDisconnect
Timeout
Time elapsed (in ms) at which an endpoint becomes
disconnected.
Default Value: 20000
mgcpRetransmissionSuspicion
Threshold
Number of retransmissions at which an endpoint may
actively query the name server to detect the possible
change of the Call Agent’s interfaces.
Default Value: 7