Overview of Networking
2-16
Interoperability and Standards Bodies
Layer Four: Transport
The Transport layer deals with the optimization of data transfer from source to
destination by managing network data flow and implementing the quality of
service requested by the Session layer. The Transport layer determines the packet
size requirements for transmission based on the amount of data to be sent and the
maximum packet size allowed by the network architecture. If the data to be sent is
larger than the maximum packet size allowed on the network, the Transport layer
is responsible for dividing the data into acceptable sizes and sequencing each
packet for transmission.
When receiving data from the Network layer, the Transport layer ensures that the
data is received in order and checks for duplicate and lost packets. If data is
received out of order, the Transport layer correctly orders the data and passes the
data up to the Session layer for additional processing.
Layer Three: Network
The Network layer accepts data from the Transport layer and adds the
appropriate information to the packet to provide proper network routing and
some level of error control. Data is formatted by this layer for the appropriate
communications method, such as IP, IPX, or X.25.
Layer Two: Data Link
The Data Link layer is involved with transmission, error detection, and flow
control of the data. The major function of the Data Link layer is to act as a shield
for the higher layers of the OSI model, controlling the actual processes of
transmission and reception. Error detection and control of the Physical layer are
the primary functions of this layer, ensuring that data received by the upper
layers is error-free. For purposes of understanding networking, it is useful to
divide the Data Link layer into two sub-layers; the Logical Link Control layer and
the Media Access Control layer (see Figure 2-7).
Figure 2-7. Data Link Layer
Logical Link Control
Media Access Control
Application
Presentation
Session
Transport
Network
Data Link
Physical
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1706n07
Summary of Contents for MMAC-5FNB
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