OSI Transport Layer : OSI Transport Layer Network Fundamentals – Chapter 4
Objectives : Objectives Why is the Transport layer needed and what is it’s role in network communication
Analyze the application and operation of TCP mechanisms that support reliability
Analyze the application and operation of TCP mechanisms that support reassembly and manage data loss.
Analyze the operation of UDP to support communicate between two processes on end devices
Key Terms : Key Terms Flow control
IANA
Well-known ports
Registered ports
Dynamic ports
Acknowledgement Window Size
ACK
PSH
RST
SYN
FIN
Transport Layer Role and Services : Transport Layer Role and Services PDU = Segment
Major Functions of Transport Layer : Major Functions of Transport Layer Enables multiple applications to communicate over the network at the same time on a single device
Ensures that, if required, all the data is received reliably and in order by the correct application
Employs error handling mechanisms
Transport Layer Protocols: TCP & UDP : Transport Layer Protocols: TCP & UDP
TCP/UDP Header Structure : TCP/UDP Header Structure Similarities: ports
Differences: acknowledgement/sequence numbers
Role of Port Numbers : Role of Port Numbers Port addressing is used at Layer 4 to identify communication between host applications
Port Numbers Example : Port Numbers Example
Port Number Ranges : Port Number Ranges IANA assigns port numbers
Well-known ports: 0 through 1023
Sometimes called privileged port numbers
Registered ports: 1024 to 49,151
Sometimes called user port numbers
Private/Dynamic Ports: 49,152 to 65,535
Sometimes called public port numbers
Sample Well-Known Ports : Sample Well-Known Ports
Segments – Putting Them Back Together : Segments – Putting Them Back Together How do the different protocols re-assemble data segments? UDP solution:
Application must re-assemble data and verify integrity
Application and Operation of TCP Mechanisms : Application and Operation of TCP Mechanisms TCP is known as a connection-oriented protocol
Header fields ensure reliable delivery
Establish End-to-End Connection : Establish End-to-End Connection TCP features synchronization (SYN) and acknowledgements (ACK) in datagram
SYN and ACK values are created artificially
Reversed as packets are exchanged
SYN --> ACK value
Values are incremented to show progression
TCP uses expectational ACK’s
First, a three-way handshake is established
Three-way Handshake Example : Three-way Handshake Example Note: ACK bit not set in first packet
Ending a TCP Session : Ending a TCP Session Once host applications are done communicating, a FINished flag is exchanged and confirmed
Windowing = Flow Control : Windowing = Flow Control Hosts accept data at different rates
What could affect data transfers?
Host may become overwhelmed and drop data
TCP assigns Window sizes to compensate
Window = total data received before ACK
Examples of Windowing : Examples of Windowing
TCP Congestion and Flow Control : TCP Congestion and Flow Control
UDP Protocol : UDP Protocol UDP is a connectionless protocol (best effort)
Segment is called a datagram
UDP Protocols Problems : UDP Protocols Problems Datagrams may arrive out of order – no sequence #
No session – no verification of data reception
UDP Protocol and Ports : UDP Protocol and Ports TCP and UDP both use ports for application layer conversations
Chapter 4 Labs : Chapter 4 Labs Lab 4.x.x: TCP/IP Transport Layer Protocols Capture
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