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Transport layer


Khoula Al Sadi

on 30 March 2016

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Transcript of Transport layer

Empower my Willayat
OSI Transport Layer

2. System Analysis

1. Proposed System
3. System Requirements

1. Hardware Requirements
2. Software Requirements

4. System Design

1. Context Level Diagram
2. Level 0 Diagram
5. System Testing

6. List of Figures and Screenshots

7. Conclusion and Future Work

2. Segmenting Datas
Controlling the conversation
3. Reassembling Segments
1.Tracking Individual Conversations

1. Flow Control

2. Error control

3. Access Control
Node-to-node delivery
The transport layer is responsible for process-to-process delivery of the entire message

The transport layer ensures that the whole message arrives intact and in order, overseeing both error control and flow control at the process-to-process level.

Connection Oriented & Connection less Protocol
Transport Layer
Two Sets of Layers
OSI Protocol Suite
Source-to-destination delivery

1. Congestion Control

2. Flow Control
Functions of the transport layer
The application layer is the OSI layer closest to the end user

It provides User Interface and support for services.
Application Layer
The data link layer is responsible for transmitting frames from one node to the next.
The data link layer is responsible for node-to-node delivery.

It makes the physical layer appear error free to the upper layer (network layer).

Data Link Layer
The network layer is responsible for the delivery of packets from the original source to the final destination.
Network Layer
The session layer is the network dialog controller.

It is designed to establish, maintain, and synchronize the interaction between communicating devices.
Session Layer
The presentation layer is designed to handle the syntax and semantics of the information exchanged between the two systems.

It is designed for data translation, encryption, decryption and compression.
Presentation Layer
The physical layer is responsible for transmitting individual bits from one node to the next.
Physical Layer
To Session Layer
From Session Layer
The transport layer is responsible for delivery of a message from one process to another.
Transport layer
From Presentation Layer
To Presentation Layer
Application Layer
The application layer is responsible for providing services to the user.
Functionalities of Data Link Layer

4. Identifying the Applications

5.Data Requirements Vary
1.Tracking Individual Conversation
3. Reassembling Segments
Other Transport layer protocols describe processes that provide additional features, such as ensuring reliable delivery between the applications.
2.Conversation Multiplexing.
1.Segmentation and Reassembly.
3.Establishing a Session
6.Same Order Delivery
5.Flow Control
Primary Function of transport layer by all transport layer Protocols
4.1.5 Port addressing
6.Separating Multiple Communications
Any host may have multiple applications that are communicating across the network. Each of these applications will be communicating with one or more applications on remote hosts.

It is the responsibility of the Transport layer to maintain the multiple communication streams between these applications.
As each application creates
a stream data
to be sent to a remote application, this data must be prepared to be sent across the media in manageable pieces.
The Transport layer protocols describe
services that segment this data from the Application layer.
This includes the encapsulation required on each piece of data.
Each piece of application data requires
to be added at the Transport layer
to indicate to which communication it is associated
The protocols at the Transport layer describe the
how the Transport layer header information is used to reassemble the data pieces into streams to be passed to the Application layer.
At the receiving host, each piece of data may be directed to the appropriate application
4.Relaible Delivery
4.4.1 UDP-Low Overhead vs.Reliability
This does not mean that applications that use UDP are always unreliable. UDP

means does not provide the sophisticated

retransmission, sequencing, and flow control mechanisms.
Applications with very different transport needs may be communicating on the same network.
For instance, For some applications, segments must arrive in a very specific sequence in order to be processed successfully.
6.Separating Multiple Communications
5.Data Requirements Vary
The TCP/IP protocols call the identifier of target application a port number.

Each software process that needs to access the network is assigned a port number unique in that host.

This port number is used in the Transport layer header to indicate to which application that piece of data is associated.
4.Identifying the Applications
Web browser: port number 80

Email: port number 110,25
2.Segmenting Data
Purpose of Transport Layer
For example, an HTTP web page request being sent to a web server
(port 80)
running on a host with a Layer 3 IPv4 address of would be destined to

If the web browser requesting the web page is running on host and the
Dynamic port number
assigned to the web browser is
, the
for the web page would be
In the header of each segment or datagram, there is a
destination port.

The source port number:
is the number for this communication associated with the originating application on the local host.

The destination port number:
is the number for this communication associated with the destination application on the remote host.

The combination of the Transport layer
port number
and the Network layer
IP address
assigned to the host uniquely identifies a particular process running on a specific host device.
TCP , UDP Header:

Identify and Differentiate the
for each application by using
Port numbers
as identifiers .
Identifying the conversation

The Internet Assigned Numbers Authority
assigns port numbers.
There are different types of port numbers:
TCP Ports
Well Known ports

These numbers are reserved for services and applications.

Registered Ports:
Are assigned to user processes or applications. User has chosen to install rather than common applications that would receive a Well Known Port.
Dynamic or Private Ports :
Also known as Ephemeral Ports, these are usually assigned dynamically to client applications when initiating a connection

Using both TCP and UDP:
Some applications use both TCP and UDP.
For example, the low overhead of UDP enables DNS to serve many client requests very quickly. Sometimes, however, sending the requested information may require the reliability of TCP. In this case, the well known port number of 53 is used by both protocols with this service.
UDP Ports
Using both TCP and UDP
Is an important network utility that can be used to verify those connections.
IT list the following:
The protocol in use,
The local address and port number
The foreign address and port number
The state of the connection.
Netstat Command
Refer to Exploration
4.1.5 Netstat output
Although the total amount of UDP traffic found on a typical network is often relatively low, key Application layer protocols that use UDP include:

Domain Name System (DNS)
Simple Network Management Protocol (SNMP)
Dynamic Host Configuration Protocol (DHCP)
Routing Information Protocol (RIP)
Trivial File Transfer Protocol (TFTP)
Some applications, such as DNS, will simply retry the request if they do not receive a response, and therefore they do not need TCP to guarantee the message delivery.
4.1.6 Segmentation and Reassembly – Divide and Conquer

TCP and UDP Handle Segmentation Differently

Dividing application data into pieces both ensures that data is transmitted within the limits of the media and that data from different applications can be multiplexed on to the media.
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