The Routing module implements the Network Routing layer described
    by the Digital Network Architecture.  It routes messages in the
    network and manages the message packet flow. The Routing module
    components provide the following functions:

    o  Routing-determines packet paths. A path is the sequence
       of connected nodes and links between a source node and a
       destination node. The combined knowledge of all the network
       Routing layer modules of all the nodes in a network is used to
       determine the existence of a path, and route the packet to its
       destination. The routing component at a routing node has the
       following specific functions:

       -  Extracts and interprets the route header in a packet.

       -  Performs packet forwarding based on the destination
          address.

       -  Performs packet fragmentation where necessary.

       -  Manages the characteristics of the path and if a node or
          link fails on a path, finds an alternate route.

       -  Interfaces with the Network Routing Subnetwork Dependent
          sublayer to receive reports concerning a circuit or node
          that has failed or the subsequent recovery of a circuit or
          node.

       -  Performs packet reassembly at the destination.

       -  Returns error reports to the source where necessary, for
          instance when the destination is unreachable or when the
          packet would have needed to be fragmented but segmentation
          permitted was not set in the packet. Segmentation permitted
          is always set in data packets generated by DNA nodes.
          However, non-DNA nodes may do otherwise.

    o  Congestion control-manages the resources used at each packet
       switching node (each node that permits route-through).

    o  Packet lifetime control-bounds the amount of time a packet can
       exist in the network.

    o  Initialization-identifies the adjacent node and the
       adjacent node's network routing layer. It also performs node
       verification, if required.

    o  Dynamic circuit management-determines when to dial calls, when
       to hang up calls, and (on dynamically assigned circuits) which
       DTE address to dial. It exists only on dynamically established
       data links.