1. Lecture 7 Transport Layer
Objectives:
Describe characteristics of the TCP and UDP protocols, including port numbers and their uses.
Explain how TCP session establishment and termination processes facilitate reliable communication.
Explain how TCP protocol data units are transmitted and acknowledged to guarantee delivery.
Explain the UDP client processes to establish communication with a server.

2. Transportation of Data Role of the Transport Layer
Chapter 7
7.1.1

3. Transportation of Data Role of the Transport Layer
The Transport Layer is responsible for establishing a temporary communication session between two applications and delivering data between them. TCP/IP uses two protocols to achieve this:
Transmission Control Protocol (TCP)
User Datagram Protocol (UDP)
Primary Responsibilities of Transport layer Protocols
Tracking the individual communication between applications on the source and destination hosts
Segmenting data for manageability and reassembling segmented data into streams of application data at the destination
Identifying the proper application for each communication stream
and Role of the Transport Layer

4. Transportation of Data Conversation Multiplexing
Segmenting the data
Enables many different communications, from many different users, to be interleaved (multiplexed) on the same network, at the same time.
Provides the means to both send and receive data when running multiple applications.
Header added to each segment to identify it.
Conversation Multiplexing

5. Transportation of Data Transport Layer Protocols
Transmission Control Protocol (TCP)
Provides reliable delivery ensuring that all of the data arrives at the destination. 
Uses acknowledged delivery and other processes to ensure delivery
Makes larger demands on the network – more overhead
User Datagram Protocol (UDP)
Provides just the basic functions for delivery – no reliability
Less overhead
Transport Layer Reliability
TCP
UDP
The Right Transport Layer Protocol for the Right Application

6. Transportation of Data TCP or UDP
There is a trade-off between the value of reliability and the burden it places on the network.
Application developers choose the transport protocol based on the requirements of their applications.
Applications that use TCP: HTTP, FTP, SMTP, Telnet
Applications that use UDP: DHCP, DNS, SNMP, TFTP, VoIP, IPTV
7.2.4 TCP or UDP, that is the Question
Applications that use TCP

7. Introducing TCP and UDP Introducing TCP
Transmission Control Protocol (TCP)
RFC 793
Connection-oriented – creating a session between source and destination
Reliable delivery – retransmitting lost or corrupt data
Ordered data reconstruction – numbering and sequencing of segments
Flow control - regulating the amount of data transmitted
Stateful protocol – keeping track of the session
Introducing TCP and UDP
Introducing TCP
Role of TCP

8. Introducing TCP and UDP Introducing UDP
Applications that use UDP:
Domain Name System (DNS)
Video Streaming
Voice over IP (VoIP)
Introducing UDP
Role of UDP

9. Introducing TCP and UDP Separating Multiple Communications
TCP and UDP Port addressing

10. Introducing TCP and UDP TCP and UDP Port Addressing

11. Introducing TCP and UDP TCP and UDP Port Addressing
TCP and UDP Port Addressing (cont)

12. Introducing TCP and UDP netstat
Used to examine TCP connections that are open and running on a networked host
TCP and UDP Port Addressing (cont)
6 sessions
1 client
Browsing different web sites

13. TCP Communication TCP Server Processes

14. TCP Communication TCP Connection Establishment
Three-Way Handshake
Establishes that the destination device is present on the network.
Verifies that the destination device has an active service and is accepting requests on the destination port number that the initiating client intends to use for the session.
Informs the destination device that the source client intends to establish a communication session on that port number.
TCP Connection, Establishment and Termination

15. TCP Communication TCP Connection Establishment
Within the TCP segment header, there are six 1-bit fields that contain control information used to manage the TCP processes. Each of these fields is only 1 bit and, therefore, has only two values: 1 or 0. When a bit value is set to 1, it indicates what control information is contained in the segment.

16. TCP Communication TCP Session Termination
Four steps
when the client has no more data to send, it sends a segment with the FIN flag set
the server responds with an ACK to acknowledge receipt of the FIN to terminate the session
the server sends a FIN to the client to terminate the session
the client responds with an ACK to acknowledge the FIN request from the server
TCP Connection, Establishment and Termination

17. TCP Communication TCP Session Termination

18. Reliability and Flow Control Ordered Delivery
Sequence numbers are used to reassemble segments into original order
TCP Reliability – Ordered Delivery

19. Reliability and Flow Control Acknowledgement and Window Size
The sequence number and acknowledgement number are used together to confirm receipt.
TCP Reliability –Acknowledgement and Window size
Window Size - The amount of data that a source can transmit before an acknowledgement must be received.

20. Reliability and Flow Control Window Size and Acknowledgements
TCP Flow Control- Window Size and Acknowledgements

21. Reliability and Flow Control Congestion Avoidance
TCP Flow Control –Congestion Avoidance

22. UDP Communication UDP Low Overhead vs. Reliability
Simple protocol that provides the basic transport layer functions
Used by applications that can tolerate small loss of data
Used by applications that cannot tolerate delay
Used by
Domain Name System (DNS)
Simple Network Management Protocol (SNMP)
Dynamic Host Configuration Protocol (DHCP)
Trivial File Transfer Protocol (TFTP)
IP telephony or Voice over IP (VoIP)
Online games
7.2.3 UDP Communication
UDP Low Overhead vs. Reliability

23. UDP Communication Datagram Reassembly

24. UDP Communication UDP Server and Client Processes
UDP-based server applications are assigned well-known or registered port numbers.
UDP client process randomly selects port number from range of dynamic port numbers as the source port.
UDP Server Processes and Requests
UDP Client Processes

25. Animation Activity 7212 TCP server processes
7213 TCP connection establishment
7217 TCP session termination
7234 UDP client processes
Activity
TCP/UDP characteristics
7118 TCP or UDP?
7219 TCP connection establishment/termination

26. Further Exploration … Introduction to Networks
Chapter 7: Transport Layer
Further Exploration …

27. TCP Communication TCP Three-Way Handshake – Step 1
Step 1: The initiating client requests a client-to-server communication session with the server.
TCP Three Way Handshake – Step 1

28. TCP Communication TCP Three-Way Handshake – Step 2
Step 2: The server acknowledges the client-to-server communication session and requests a server-to-client communication session.
TCP Three Way Handshake – Step 2

29. TCP Communication TCP Three-Way Handshake – Step 3
Step 3: The initiating client acknowledges the server-to-client communication session.
TCP Three Way Handshake – Step 3