Compaq 222863-001 - TaskSmart W2200 Model 10 Administration Manual page 107

Networking Basics B-3
Layer 5: Session
The Session layer controls data transfer, designating which computers transfer
data. Data recovery is another main task of this layer.
Layer 4: Transport
The Transport layer has multiple tasks. It is responsible for establishing a
connection between the devices that will be talking and the termination of that
connection when the communication is completed. The establishment of the
connection entails the matching of the rate and dependability of data flow
between the devices. The layer is also responsible for initiating and managing
the data transfer.
Layer 3: Network
The Network layer is responsible for several functions. The routing of data
between addresses is conducted on this level. Data flow and assembly is
controlled here. The data is handled in a form of blocks that are segmented
into frames. The frames are then passed to the Data Link layer.
Layer 2: Data Link
The Data Link layer breaks the levels apart by separating the upper layers
from the Physical layer. This layer is where data problems and isolation of
problems are detected and possibly corrected.
Layer 1: Physical
The Physical layer is the portion that is responsible for delivering data from
one computer to another. The breaking of bits into a passable media is
conducted here. For example, the Physical layer conducts the breaking of a
packet of data into a signal, transmitting the signal, receiving the signal and
converting the signal back to a data package.
Transmission Control Protocol/Internet Protocol (TCP/IP) layers are a separate
scheme or addendum to the conventional ISO/OSI reference model previously
described. TCP is equivocal to Layer 4 and IP is equivocal to Layer 3 in
function and responsibilities. TCP/IP originated separately from the ISO/OSI
reference model as well as being the entity that has evolved into the Internet.
TCP/IP layers are covered in more detail later in this appendix.