Pgm_Receive_Nak_Ttl

The Pgm_Receive_Nak_Ttl option specifies the initial time to live (TTL) for a NAK sent by an RTclient to an RTgms. This is one less than the maximum number of routers that a NAK can travel through before reaching the RTgms process.

NAKs are generated by an RTclient when data from the RTgms fails to reach the RTclient or arrives corrupted. When the RTgms receives a NAK, it generates repair data.

The time to live (TTL) for a NAK is automatically decremented every time the NAK passes through a router. The NAK is discarded by the router if, after it decrements the TTL, the TTL is 0. This allows a NAK stuck in a loop between routers to eventually be eliminated. Too small a value for Pgm_Receive_Nak_Ttl can cause the NAK to be discarded too soon, before it ever reaches an RTgms. The RTgms never gets a chance to generate repair data and the RTclient that generated the NAK can have unrecoverable losses. Too large a value for Pgm_Receive_Nak_Ttl can increase the amount of congestion caused by routing loops.

The default value of 1 only works if a NAK does not pass through any routers to reach an RTgms. Consider the number of routers a NAK must pass through to reach an RTgms, especially if the RTgms is on another network, when setting the value for Pgm_Receive_Nak_Ttl.