Concept Exercise Chapter 12 Name:
Date: Class:


Cisco Exercises - Semester 1 - Networking Fundamentals
Chapter 12 Layer 4: The Transport Layer


Introduction

Services located in the transport layer, which is Layer 4 of the OSI reference
model, allow users to segment several upper-layer applications onto the same
Layer 4 data stream. These services also allow for the reassembly of the same
upper-layer application segments at the receiving end.

The Layer 4 data stream provides transport services from the host to the
destination. Services such as these are sometimes referred to as end-to-end
services. The Layer 4 data stream is a logical connection between the endpoints
of a network.

As the transport layer sends its data segments, it can also ensure the
integrity of the data. One method of doing this is called flow control. Flow
control avoids the problem of a host at one side of the connection overflowing
the buffers in the host at the other side. Overflows can present serious
problems because they can result in data loss.

Transport-layer services also allow users to request 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:

It can ensure that segments delivered will be acknowledged back to the sender.
It can provide for retransmission of any segments that are not acknowledged.
It can put segments back into their correct sequence at the destination.
It can provide congestion avoidance and control.

Concept Questions

Demonstrate your knowledge of these concepts by answering the following
questions in the space provided.

One user of the transport layer must establish a connection-oriented session
with its peer system.

For data transfer to begin, both the sending and receiving application programs
inform their respective operating systems that a connection will be initiated.
How is this accomplished?

In concept, one machine places a call that must be accepted by the other. If
the receiving machine does not accept the call, what happens?








Protocol software modules in the two operating systems communicate by sending
messages. Messages are sent across the network to verify that the transfer is
authorized and that both sides are ready. How is this accomplished?








After all synchronization has occurred, a connection is established, and data
transfer begins. How do both machines know that the data is flowing correctly?