The NSP module implements one of the protocols in the Transport layer
    described by the Digital Network Architecture.

    The entities that constitute the NSP module are listed below. The indention
    indicates the hierarchical relationships between the entities.

                         NSP
                          Port
                          Local NSAP
                             Remote NSAP

   NSP performs the following functions:

   o  Enables the creation and destruction of transport connections used for
      sending messages within a network node and between network nodes.

   o  Manages the movement of expedited and normal data from transmit buffers
      to receive buffers, using flow control mechanisms.

   o  Breaks up normal data messages into segments that can be transmitted
      individually, and reassembles these segments into correct order after they
      have been received.

   o  Guarantees the delivery of data and control messages to a specified
      destination using an error correction mechanism.

   The NSP entity is the top-level entity in the hierarchy of
   entities belonging to the NSP module.