MTU and data splitting

MTU and data splitting

When a packet is sent from a source to a destination, it is delivered to the destination via various communication lines.

 MTU is specified for communication lines. MTU (Maximum Transmission Unit) is the maximum transfer unit and the maximum data length that can be transferred.

The MTU for each communication line is defined as follows.

data linkMaximum MTU
Ethernet1,500
IEEE 802.3 Ethernet1,492
IP over ATM9,180
FDDI4,352
TokenRing 4Mbps IEEE802.54,464
TokenRing 16Mbps IBM17,914

Fragmentation (division process)

 Since the MTU is determined for each communication line, when passing through a communication route with a smaller MTU than the packet length, the packet is fragmented and divided according to the smaller MTU size. If you don't do it, you won't be able to pass through the communication line.

Fragmentation thus divides a packet into multiple packets to reduce the size of a single packet.

*A minimum 20-byte IP header is attached to all the divided packets.

The split packets are combined into a single packet when it reaches its destination and passed to the upper layers.

 In this way, such processing is performed in the network layer of the OSI reference model, making it possible to communicate without being affected by various types of data link layers.