CTI 2572 Technical Overview Manual
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TCP will notify both application programs. Typically one host computer (server) issues a
passive open to a port, making the services available. Another host computer (client)
issues an active open to initiate the connection. When the application session is
complete, the connection is terminated by issuing a close to the port.
TCP supports multiple connections to a single port and full duplex connections (two
concurrent data streams flowing in the opposite direction). Using full duplex, TCP can
send control information for one stream back to the source in datagrams containing data
in the opposite direction.
3) Reliable Data Transfer
TCP software provides a reliable data transfer service by a using a technique known as
positive acknowledgement with retransmission. When a group of packets has been
successfully received, the recipient TCP software sends an acknowledgement message
back to the sender TCP software. TCP keeps a record of each packet sent and waits for
acknowledgement before sending the next group of packets. If no acknowledgement is
returned after a designated time, then TCP re-sends the packets.
To improve throughput and to reduce network loading, TCP allows multiple packets to be
sent before an acknowledgement is required. The number of packets which can be sent
before an acknowledgement is required is called the window size. TCP dynamically
manages the window size to optimize network utilization and to exercise flow control.
TCP maintains a Sequence Number
field in the header which identifies
the sequence in which the packets
were sent. Using this sequence
number, TCP ensures that data is
delivered to the destination
application program in the same
sequence that is was sent by the
source application program. The
Acknowledgement Number field
allows TCP to acknowledge receipt
of packets while sending new data.
Figure 14 shows the format of the
TCP segment. You may note that
both the TCP segment header and the
segment data are contained in the
data area of the IP datagram.
HEADER DATA
DATA
OFF
SET
RES WINDOW (16)
OPTIONS (Variable)
CHECKSUM (16)
IP DATAGRAM
TCP SEGMENT
DATA (Variable)
ACKNOWLEDGEMENT NUMBER (32)
SEQUENCE NUMBER (32)
SOURCE PORT (16) DESTINATION PORT (16)
A
C
K
P
S
H
R
S
T
S
Y
N
F
I
N
U
R
G
URGENT POINTER (16)
PADDING
Figure 14 TCP Segment
