WAN links

Actually, network packets may traverse several routers and WAN links to reach the destination network, and each router traversed is called a hop. In the context of packet analysis, you should be aware that WAN links can introduce packet delivery delays or latency due to the following four major factors:

• Physical speed-of-light propagation delay: This is the amount of time required for electrical or light signals to travel across copper/fiber cables over long distances.
• Network routing/geographical distance: The WAN link routes are never in a straight line between points. They have to traverse major telephony switching centers and route along railways, roads, and other opportunistic paths.
• Serialization delay into and across WAN links: The WAN links are often slower speed links, and it takes a finite amount of time to send packet data across these links one bit at a time.
• Queuing delays: In network device buffers, including additional delays that may be induced by Quality of Service policies, some packets receive priority and others have to wait longer for their turn to be transmitted.

The effects of network delay incurred across LAN and WAN links can be seen and measured in Wireshark packet traces by inspecting the elapsed times between session setup packets.