The network layer is also not burdened with the characteristics of the media on which packets are transported. IP operates independently of the media that carry the data at lower layers of the protocol stack. As shown in the figure, any individual IP packet can be communicated electrically over cable, as optical signals over fiber, or wirelessly as radio signals.

It is the responsibility of the OSI data link layer to take an IP packet and prepare it for transmission over the communications medium. This means that the transport of IP packets is not limited to any particular medium.

There is, however, one major characteristic of the media that the network layer considers: the maximum size of the PDU that each medium can transport. This characteristic is referred to as the maximum transmission unit (MTU). Part of the control communication between the data link layer and the network layer is the establishment of a maximum size for the packet. The data link layer passes the MTU value up to the network layer. The network layer then determines how large packets should be.

In some cases, an intermediate device, usually a router, must split up a packet when forwarding it from one medium to a medium with a smaller MTU. This process is called fragmenting the packet or fragmentation.