Basic Data Transfer:

Basic Data Transfer:

    The TCP is able to transfer a continuous stream of octets in each    direction between its users by packaging some number of octets into    segments for transmission through the internet system.  In general,    the TCPs decide when to block and forward data at their own    convenience.

    Sometimes users need to be sure that all the data they have    submitted to the TCP has been transmitted.  For this purpose a push    function is defined.  To assure that data submitted to a TCP is    actually transmitted the sending user indicates that it should be    pushed through to the receiving user.  A push causes the TCPs to    promptly forward and deliver data up to that point to the receiver.    The exact push point might not be visible to the receiving user and    the push function does not supply a record boundary marker.

  Reliability:

    The TCP must recover from data that is damaged, lost, duplicated, or    delivered out of order by the internet communication system.  This    is achieved by assigning a sequence number to each octet    transmitted, and requiring a positive acknowledgment (ACK) from the    receiving TCP.  If the ACK is not received within a timeout    interval, the data is retransmitted.  At the receiver, the sequence    numbers are used to correctly order segments that may be received    out of order and to eliminate duplicates.  Damage is handled by    adding a checksum to each segment transmitted, checking it at the    receiver, and discarding damaged segments.

    As long as the TCPs continue to function properly and the internet    system does not become completely partitioned, no transmission    errors will affect the correct delivery of data.  TCP recovers from    internet communication system errors.

  Flow Control:

    TCP provides a means for the receiver to govern the amount of data    sent by the sender.  This is achieved by returning a "window" with    every ACK indicating a range of acceptable sequence numbers beyond    the last segment successfully received.  The window indicates an    allowed number of octets that the sender may transmit before    receiving further permission.

  Multiplexing:

    To allow for many processes within a single Host to use TCP    communication facilities simultaneously, the TCP provides a set of    addresses or ports within each host.  Concatenated with the network    and host addresses from the internet communication layer, this forms    a socket.  A pair of sockets uniquely identifies each connection.    That is, a socket may be simultaneously used in multiple    connections.

    The binding of ports to processes is handled independently by each    Host.  However, it proves useful to attach frequently used processes    (e.g., a "logger" or timesharing service) to fixed sockets which are    made known to the public.  These services can then be accessed    through the known addresses.  Establishing and learning the port    addresses of other processes may involve more dynamic mechanisms.