Time to live (TTL) is the “hop limit”, or number of routing devices a message is allowed to pass through before expiring.
TTL enables RAP to operate on networks where there is a router between a publisher and a subscriber. TTL is represented as an 8-bit unsigned integer on each packet on a network. The TTL of a message is stored as part of the message, and every time the message passes through a router, its TTL value is decreased by the amount of time the message spent at that routing station, with a minimum of one second. This is equivalent to the hop limit. When the TTL on a packet reaches zero, the packet is discarded and an error datagram is returned to the sender.
TTL prevents packets from becoming immortal on the network—if a packet cannot reach its destination, its TTL eventually expires, preventing it from clogging up the network.
For networks with routers between publisher and subscriber machines, set the TTL for all publishers attempting to send data through the router.