Hi Ahmed :)

Every packet that gets sent out has a TTL field which is set to a relatively high number (ping packets get a TTL of 255). As the packet travels over the network, the TTL field gets decreased by one for each node, server, or router it passes through. When the TTL drops to 0, the packet is discarded by the router. The main purpose of this is so that a packet doesn't live forever on the network and will eventually die when it is deemed "lost." If the TTL field varies in successive pings, it could indicate that the successive reply packets are going via different routes. This could indicate that certain network routes may be experiencing problems. Packets are being sent along different paths (and not the same path each time) trying to find the quickest alternative route.

HTH, please rate if it does help,

Mohammed Mahmoud.