Larger NPDUs must be segmented as necessary. If a system wishes to avoid segmentation and reassembly, it should use transport layer mechanisms to discourage others from sending large PDUs. A router switching an OSI packet may find that the beginning of the packet falls on an inconvenient memory boundary when the hardware used to transmit the packet to its next hop requires a particular alignment. This situation can be addressed by the use of leading zero padding. These zero octets correspondingly reduce the maximum length of the NPDU that may be transmitted.
Empirical evidence suggests that the greatest time deficit for re-alignment exists at the receiver.
It is recommended that alignment be entirely through header compression combinations whenever possible. This option is negotiated separately in each direction. A receiver which does not need alignment MUST NOT request the option. It is recommended that the receiver request alignment based on the needs of the highest speed next hop link. By default, the alignment is done according to the needs of the sender, and all receivers MUST be capable of accepting packets with any alignment.