Time-to-live (TTL) and (HOP)
Fields in the Internet Protocol packet header, are the terms we use to describe how long a packet can live in a network. During development of the Internet’s (IP) Internet Protocol, the term Time-to-live started at 30 or 60 to represent time value of 30 seconds or 60 seconds. Early implementations of Internet Protocol actually had each router in low speed networks calculate the time it took to traverse a router and decrement that time element.
As networks got much faster and time was under a second like it is today where packets can be routed in well under a thousandth of a second, the term Hop became more appropriate so that regardless the time, the router would decrement the TTL/HOP field in the IP header as it traversed a router or node acting as a router.
So now the term represents hops or each router in the network. If you have ever sent a “ping” from a network device, you will see that the response from the other side tells you the TTL remaining on the packet when its Ping responds. Time-to-live TTL=118 for instance means that there is 118 TTL/HOPs remaining in the packet before it expires and is discarded by going through 118 more routers. That means you have TTL/HOP headroom remaining in your network topology to that particular device.