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Module 4

OSI Transport Layer

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• Roles of the Transport Layer• The TCP Protocol – Communicating with Reliability• Managing TCP Sessions• The UDP Protocol – Communicating with Low Overhead

Objectives

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Roles of the Transport Layer

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Purpose of the Transport Layer• Functions of the

Transport layer are:– Tracking the

individual communication between applications on the source and destination hosts

– Segmenting data and managing each piece

– Reassembling the segments into streams of application data

– Identifying the different applications

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Tracking the Conversations

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Segmentation

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Controlling the Conversations

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Supporting Reliable Communication

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Transport Layer Protocols• Transmission Control

Protocol (TCP)– Connection-oriented– Reliable– Divide outgoing messages

into segments– Reassembles messages at

the destination station by order

– Re-send anything not received

– Reassembles messages from incoming segments

• User Datagram Protocol (UDP)– Connectionless– Unreliable– Transmit messages– Provides no software

checking for message delivery

– Does not reassemble incoming messages by order

– Uses no acknowledgements

– Provides no flow control

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TCP and UDP

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Port Addressing

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Port Addressing• Well Known Ports

(Numbers 0 to 1023): These numbers are reserved for services and applications

• Registered Ports (Numbers 1024 to 49151): These port numbers are assigned to user processes or applications

• Dynamic or Private Ports (Numbers 49152 to 65535): Also known as Ephemeral Ports, these are usually assigned dynamically to client applications when initiating a connection

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Port Addressing

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Port Addressing

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Segmentation and Reassembly – Divide and Conquer

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The TCP ProtocolCommunicating with Reliability

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TCP – Make Conversations Reliable

TCP Segment Header Fields

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TCP Server Processes

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TCP Connection Establishment and Termination

TCP Connection Establishment

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TCP Connection Establishment and Termination

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Managing TCP Sessions

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TCP Segment Reassembly

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TCP Acknowledgement with Windowing

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TCP Retransmission

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TCP Congestion Control – Minimizing Segment Loss

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TCP Congestion Control – Minimizing Segment Loss

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The UDP ProtocolCommunicating with Low Overhead

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UDP Low Overhead vs. Reliability

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UDP Datagram Reassembly

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UDP Server Processes and Requests

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UDP Client Processes

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Good luck with this module!