Transport Layer
OSI Model
The transport layer is responsible for the
segmentation and the delivery of a message
from one process to another.
Transport layer
Sender
Receiver
OSI Model
Transport Layer
Ensures that the data units are delivered
error free.
Ensures that data units are delivered in
sequence.
Ensures that there is no loss or duplication of
data units.
Provides connectionless
oriented service.
or
connection
Provides for the connection management.
Transport Layer
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Provides reliable data
delivery
It’s the TCP in TCP/IP
Receives info from
upper layers and
segments it into packets
Can provide error
detection and
correction
3
Transport Layer
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Facilitates end to end communication over
internetwork
Allows logical connections between devices via
unreliably and reliably
Identification of the specific source and destination
are noted
Transport Layer
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Segmentation - Transport layer protocols break
large data units received from Session layer into
smaller segments
Maximum transmission unit (MTU): largest data
unit a given network will carry
Reassembly: process of reconstructing segmented
data units
Sequencing: method of identifying segments that
belong to same group of subdivided data
Transport Layer
Segmentation and Reassembly
Connection Oriented / Connectionless
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Connection Oriented – when devices communicate,
they perform handshaking to set up an end-to-end
connection.
Connectionless - usually achieved by transmitting
information in one direction, from source to destination
without checking to see if the destination is still there, or
if it is prepared to receive the information
Transport Layer Protocols

UDP (User Datagram Protocol) - service provided by UDP
is unreliable that provides no guarantees for delivery and no
protection from duplication
 Connectionless protocol
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TCP (Transmission Control Protocol) -a connectionoriented reliable protocol.
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approximately 90% of current traffic uses this transport service
no loss, no duplication, FIFO, must be delivered within a
reasonable time