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Data Communication

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

 Data Communication

  The data that flows on a connection may be thought of as a stream of  octets.  The sending user indicates in each SEND call whether the data  in that call (and any preceeding calls) should be immediately pushed  through to the receiving user by the setting of the PUSH flag.
  A sending TCP is allowed to collect data from the sending user and to  send that data in segments at its own convenience, until the push  function is signaled, then it must send all unsent data.  When a  receiving TCP sees the PUSH flag, it must not wait for more data from  the sending TCP before passing the data to the receiving process.
  There is no necessary relationship between push functions and segment  boundaries.  The data in any particular segment may be the result of a  single SEND call, in whole or part, or of multiple SEND calls.
  The purpose of push function and the PUSH flag is to push data through  from the sending user to the receiving user.  It does not provide a  record service.
  There is a coupling between the push function and the use of buffers  of data that cross the TCP/user interface.  Each time a PUSH flag is  associated with data placed into the receiving user’s buffer, the  buffer is returned to the user for processing even if the buffer is  not filled.  If data arrives that fills the user’s buffer before a  PUSH is seen, the data is passed to the user in buffer size units.
  TCP also provides a means to communicate to the receiver of data that  at some point further along in the data stream than the receiver is
  currently reading there is urgent data.  TCP does not attempt to  define what the user specifically does upon being notified of pending  urgent data, but the general notion is that the receiving process will  take action to process the urgent data quickly.

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