TTL (Time To Live) is the number of devices a packet can traverse before being discarded. When a device reads and re-transmits a packet it subtracts one from the current TTL. If the TTL reaches zero, the packet is discarded. TTL is specifically designed to end infinite loops, while hop count is simply the number of devices between the transmission and destination.
Time to live (TTL) or hop limit is a mechanism which limits the lifespan or lifetime of data in a computer or network. TTL may be implemented as a counter or timestamp attached to or embedded in the data. Once the prescribed event count or timespan has elapsed, data is discarded or revalidated. In computer networking, TTL prevents a data packet from circulating indefinitely. In computing applications, TTL is commonly used to improve the performance and manage the caching of data.