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Elements of the Internetwork System

Written By nuriyati mauji on Monday, 21 October 2013 | Monday, October 21, 2013

  Elements of the Internetwork System

  The internetwork environment consists of hosts connected to networks  which are in turn interconnected via gateways.  It is assumed here  that the networks may be either local networks (e.g., the ETHERNET) or  large networks (e.g., the ARPANET), but in any case are based on  packet switching technology.  The active agents that produce and  consume messages are processes.  Various levels of protocols in the  networks, the gateways, and the hosts support an interprocess  communication system that provides two-way data flow on logical  connections between process ports.
  The term packet is used generically here to mean the data of one  transaction between a host and its network.  The format of data blocks  exchanged within the a network will generally not be of concern to us.
  Hosts are computers attached to a network, and from the communication  network’s point of view, are the sources and destinations of packets.  Processes are viewed as the active elements in host computers (in  accordance with the fairly common definition of a process as a program  in execution).  Even terminals and files or other I/O devices are  viewed as communicating with each other through the use of processes.  Thus, all communication is viewed as inter-process communication.
  Since a process may need to distinguish among several communication  streams between itself and another process (or processes), we imagine  that each process may have a number of ports through which it  communicates with the ports of other processes.


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