Page 128 - Handout Computer Network.

• Establishing end-to-end operations

• Sending segments from one end host to another end host

• Ensuring flow control provided by sliding windows

• Ensuring reliability provided by sequence numbers and acknowledgments

The transport layer assumes that it can use the network as a “cloud,” to send data
packets from source to destination. The cloud deals with issues of which of several paths is best
for a given route. This starts to illustrate the role that routers perform in this process. TCP/IP is
a combination of two individual protocols, TCP and IP.
IP is a Layer 3 protocol, a connectionless service that provides best-effort delivery across
a network. TCP is a Layer 4 protocol, a connection-oriented service that provides flow control as
well as reliability. Pairing the protocols enables them to provide a wider range of services.

The TCP/IP protocol suite is made up of many protocols, but TCP and IP are the key ones.
TCP/IP is the protocol suite on which the Internet is based.

6.2.1 Flow Control

As the TCP transport layer protocol sends data segments, it can ensure the integrity of
the data. One method of doing this is called flow control.
Flow control avoids the problem of a transmitting host overflowing the buffers in the
receiving host. Overflows can present serious problems because they can result in the loss of
data.

Transport layer services enable reliable data transport between hosts and destinations.
To obtain such reliable transport of data, a connection-oriented relationship is used between
the communicating end systems.

Reliable transport can accomplish the following:

• Ensure that segments delivered will be acknowledged to the sender

• Provide for retransmission of any segments that are not acknowledged

• Put segments back into their correct sequence at the destination

• Provide congestion avoidance and control.

6.2.2 TCP

Transmission Control Protocol (TCP) is a connection-oriented transport layer protocol
that provides reliable full-duplex data transmission. TCP is part of the TCP/IP protocol stack. In a
connection-oriented environment, a connection is established between both ends before
transfer of information can begin.

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