Why is fragmentation needed on Internet not on a typical WAN?
TCP/IP protocol utilizes the name IP datagram to demote to an Internet packet. The amount of data carried into a datagram is not fixed. The sender selects an amount of data which is suitable for a particular purpose. Fragmentation is performed, if size of a datagram is larger than network MTU.
If a datagram is larger than the MTU of a network over that it is sent, the router separates the datagram into smaller pieces termed as fragments.
Fragmentation is required on Internet as this in connection of different networks using various LAN technologies (as Ethernet and Token ring). Each technology has a several frame size that is smaller to fit an entire IP datagram.
When a typical Wan is have electronic devices termed as packet switches interconnected through communication lines. The packet switches contains special purpose hardware. A packet switch is implemented along with special purpose computer which is dedicated to the task of providing communication.