State about the communications network

1) The communications network may only accept blocks of data up to a specific size.  

(2) Error control might be more effective with a smaller PDU size. With smaller PDUs, fewer bits need to be retransmitted when a PDU suffers an error.

(3) More equitable access to shared transmission facilities, with shorter delay, can be given.

(4) A smaller PDU size might be mean that receiving entities can assign smaller buffers.

(5) An entity may be need that data transfer comes to some sort of "closure" from time to time, for checkpoint and restart/recovery operations