The figure is an animation of the trace route process.  A host forms an echo request with a TTL of one and a destination IP address and sends the packet.  The command line syntax for the example is trace r t one hundred ninety two dot one hundred sixty eight dot one dot two.  The first router receives this packet and it decrements the TTL by one since it is a hop.  The TTL is now zero so the packet is returned to the sender.  The sending host does not receive the expected echo reply so it increases the TTL to a value of two and resends the packet.  The first router receives the packet and decrements the TTL by one.  The TTL now has a value of one so the router sends the packet to the next router, and this router will decrement the TTL by one.  Now that the TTL is zero the router returns the packet to the sender.  The sender increments the TTL to three and again sends the packet through the network.  When the third router receives the packet the TTL is decremented to zero and the packet is returned to the sender.  Still not receiving an echo reply, the sender increases the TTL to four and sends it across the network.  The packet moves through three routers and now has a TTL of one.  The receiving host receives the packet and sends back the echo reply to the sender.