Transport Layer

Upon completion of this chapter, you will be able to:
Explain the need for the Transport layer.
Identify the role of the Transport layer as it provides the end-to-end transfer of data between applications.
Describe the role of two TCP/IP Transport layer protocols: TCP and UDP.
Explain the key functions of the Transport layer, including reliability, port addressing, and segmentation.
Explain how TCP and UDP each handle key functions.
Identify when it is appropriate to use TCP or UDP and provide examples of applications that use each protocol.
Suleyman Demirel University, 2011

Transport Layer
Suleyman Demirel University, 2011

Suleyman Demirel University, 2011
Purpose of Transport Layer

Tracking Individual Conversations
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.
Suleyman Demirel University, 2011

Tracking Individual Conversations
Suleyman Demirel University, 2011

Segmenting Data
The Transport layer protocols describe services that segment data from the Application layer.
This includes the encapsulation required on each piece of data.
Each piece of application data requires headers to be added at the Transport layer to indicate to which communication it is associated.
Suleyman Demirel University, 2011

Segmentation
Suleyman Demirel University, 2011
Web Surfing
Network
data
data
data
data
data
data
Segment Header
Segment

Segmentation
Suleyman Demirel University, 2011
Network
segment
segment
segment
segment
segment

Reassembling Segments
At the receiving host, each piece of data may be directed to the appropriate application.
Additionally, these individual pieces of data must also be reconstructed into a complete data stream that is useful to the Application layer.
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.
Suleyman Demirel University, 2011

Reassembling Segments, Application Identification
Suleyman Demirel University, 2011
Web Surfing
Network
data
data
data
data
data
data
Segment Header

Controlling the Conversations
Suleyman Demirel University, 2011

Establishing a Session
The Transport layer can provide this connection orientation by creating a sessions between the applications. These connections prepare the applications to communicate with each other before any data is transmitted. Within these sessions, the data for a communication between the two applications can be closely managed.
Suleyman Demirel University, 2011

Reliable Delivery
For many reasons, it is possible for a piece of data to become corrupted, or lost completely, as it is transmitted over the network. The Transport layer can ensure that all pieces reach their destination by having the source device to retransmit any data that is lost.
Suleyman Demirel University, 2011

Same Order Delivery
Because networks may provide multiple routes that can have different transmission times, data can arrive in the wrong order. By numbering and sequencing the segments, the Transport layer can ensure that these segments are reassembled into the proper order.
Suleyman Demirel University, 2011

Flow Control Mechanism
Network hosts have limited resources, such as memory or bandwidth. When Transport layer is aware that these resources are overtaxed, some protocols can request that the sending application reduce the rate of data flow. This is done at the Transport layer by regulating the amount of data the source transmits as a group. Flow control can prevent the loss of segments on the network and avoid the need for retransmission.
Suleyman Demirel University, 2011

Transport Layer Protocols
Computers uses different types of Transport layers protocols by some reasons.
What is the reason for it?
Suleyman Demirel University, 2011

Question
What kind of Computer Network Communications do you know?
Suleyman Demirel University, 2011

Different kinds of Computer Networks
Web Browsing
File sharing
IP Telephony
Video Streaming (conference or online lesson)
Working with mail
Suleyman Demirel University, 2011

Question
For which of them we need reliability in delivery?
Suleyman Demirel University, 2011

Question
For which of them we need Speed in delivery?
Suleyman Demirel University, 2011

Transport Layer Protocols
Suleyman Demirel University, 2011

TCP - Transmission Control Protocol and UDP – User Datagram Protocol
TCP
Web Browsers
E-mail
File Transfers
UDP
Video Streaming
Voice over IP (VoIP)
Suleyman Demirel University, 2011

Identifying Conversations
Suleyman Demirel University, 2011
Network
segment
segment
segment
segment
segment

Question
We can see visual different colors of segments, by using colors we separate segments.
How computers make separation between segments?
Suleyman Demirel University, 2011

Answer
Computers use Port Addresses
Suleyman Demirel University, 2011

Port Addressing
Ports are using to identify conversations
Suleyman Demirel University, 2011

Port Addresses
Well Known Ports (Numbers 0 to 1023)
Registered Ports (Numbers 1024 to 49151)
Dynamic or Private Ports (Numbers 49152 to 65535)
NETSTAT is an important network utility that can be used to verify current connections
Suleyman Demirel University, 2011

Well Known Ports
Are served for services and applications.
They are commonly used for applications such as HTTP (web server) POP3/SMTP (e-mail server) and Telnet.
Suleyman Demirel University, 2011

Registered Ports
Are assigned to user processes or applications.
These processes are primarily individual applications that a user has chosen to install rather than common applications that would receive a Well Known Port.
When not used for a server resource, these ports may also be used dynamically selected by a client as its source port.
Suleyman Demirel University, 2011

Dynamic or Private Ports
Also known as Ephemeral Ports, these are usually assigned dynamically to client applications when initiating a connection.
It is not very common for a client to connect to a service using a Dynamic or Private Port (although some peer-to-peer file sharing programs do).
Suleyman Demirel University, 2011

Question
How to view states of connection in your computer?
Suleyman Demirel University, 2011

Answer
Use Netstat
Suleyman Demirel University, 2011

Netstat Snapshot
Suleyman Demirel University, 2011

TCP and UDP Handle Segmentation Differently.
Suleyman Demirel University, 2011

TCP Header
Suleyman Demirel University, 2011

UDP Header
Suleyman Demirel University, 2011

TCP in process
Suleyman Demirel University, 2011

Clients Define Destination Ports
Suleyman Demirel University, 2011

Clients Define Source Ports
Suleyman Demirel University, 2011

Server Defines Destination Ports
Suleyman Demirel University, 2011

Server Defines Source Ports
Suleyman Demirel University, 2011

TCP CONNECTION ESTABLISHMENT AND TERMINATION
Suleyman Demirel University, 2011

Question
Establishment?
Suleyman Demirel University, 2011

Answer
Suleyman Demirel University, 2011

Question
How me make handshake?
Suleyman Demirel University, 2011

Answer
Suleyman Demirel University, 2011

Question
How many way do we have in handshake process?
Suleyman Demirel University, 2011

Answer
Suleyman Demirel University, 2011

TCP Have to do Establishment before it Starts Transmission
This process is called 3 way handshake
Suleyman Demirel University, 2011

3 way handshake
Suleyman Demirel University, 2011

TCP Session Termination
Suleyman Demirel University, 2011

Question
How people say goodbye?
Suleyman Demirel University, 2011

Answer
Suleyman Demirel University, 2011

REORDERING SEGMENTS AFTER RECEIVING
Suleyman Demirel University, 2011

Question
Why it is needed?
Suleyman Demirel University, 2011

Answer
Segments can be delivered in wrong order
Suleyman Demirel University, 2011

Re-ordering segments
Suleyman Demirel University, 2011

Acknowledgement
is?
Suleyman Demirel University, 2011

Computer Acknowledgment
Computers often sends acknowledgement to each other, to confirm that they have received data.
Suleyman Demirel University, 2011

Clients retransmit data if they don’t get acknowledgement
Suleyman Demirel University, 2011

Flow Control
Suleyman Demirel University, 2011

Flow Control with problems
Suleyman Demirel University, 2011

UDP – USER DATAGRAM PROTOCOL
Suleyman Demirel University, 2011

UDP
UDP protocol is the protocol of OSI model’s 4th layer (transport layer), is not reliable but very very very fast!!!
Suleyman Demirel University, 2011