1. © 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 1 Chapter 7: Transport Layer Introduction to Networking

2. Presentation_ID 2 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Chapter 7 7.0 Introduction 7.1 Transport Layer Protocols 7.2 TCP and UDP 7.3 Summary

3. Presentation_ID 3 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Chapter 7: Objectives  The purpose of the transport layer  Characteristics of the TCP and UDP protocols  TCP session establishment and termination  TCP protocol data units transmission and acknowledgement  UDP client processes to establish communication with a server  High-reliability TCP transmissions and non-guaranteed UDP transmissions

4. © 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 4 7.1: Transport Layer Protocols

5. Presentation_ID 5 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Transportation of Data Role of the Transport Layer The transport layer is responsible for  establishing a temporary communication session between two applications  delivering data between them TCP/IP uses two protocols to achieve this:  Transmission Control Protocol (TCP)  User Datagram Protocol (UDP) Responsibilities of Transport Layer Protocols  Tracking the individual communication between applications  Segmenting data for manageability and reassembling  Identifying the proper application for each communication stream

6. Presentation_ID 6 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Transportation of Data Role of the Transport Layer (Cont.)

7. Presentation_ID 7 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential 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 send and receive data when running multiple applications.  Adds header to each segment to identify it.

8. Presentation_ID 8 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Transportation of Data Conversation Multiplexing (Cont.)

9. Presentation_ID 9 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Transportation of Data Conversation Multiplexing (Cont.)

10. Presentation_ID 10 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Transportation of Data Transport Layer Reliability Different applications have different transport reliability requirements. TCP/IP provides two transport layer protocols, TCP and UDP. 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. UDP  Provides just the basic functions for delivery – no reliability.  Less overhead. TCP or UDP  The value of reliability vs. the burden it places on the network.  Choose the TCP or UDP according to your requirements.

11. Presentation_ID 11 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Introducing TCP and UDP Introducing TCP  Connection-oriented – Creates a session between the source and destination  Reliable delivery – Retransmits lost or corrupt data  Ordered data reconstruction – Reconstructs numbering and sequencing of segments  Flow control – Regulates the amount of data transmitted  Stateful protocol – Tracks the session

12. Presentation_ID 12 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Introducing TCP and UDP Introducing UDP  Connectionless  Unreliable delivery  No ordered data reconstruction  No flow control  Stateless protocol Applications that use UDP:  Domain Name System (DNS)  Video Streaming  VoIP (telephone)

13. Presentation_ID 13 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Introducing TCP and UDP Separating Multiple Communications TCP and UDP use port numbers to differentiate between applications..

14. Presentation_ID 14 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Introducing TCP and UDP TCP and UDP Port Addressing

15. Presentation_ID 15 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Introducing TCP and UDP TCP and UDP Port Addressing (Cont.)

16. Presentation_ID 16 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Introducing TCP and UDP TCP and UDP Port Addressing (Cont.)

17. Presentation_ID 17 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Introducing TCP and UDP TCP and UDP Port Addressing (Cont.) The program Netstat is used to examine TCP connections that are open and running on a networked host. Zkuste příkaz netstat z příkazového řádku.

18. Presentation_ID 18 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Introducing TCP and UDP TCP and UDP Segmentation The transport layer divides the data into pieces and adds a header for delivery over the network

19. © 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 19 7.2 TCP and UDP

20. Presentation_ID 20 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential TCP Communication TCP Server Processes Tento chce otevřít internetovou stránku. Tento chce otevřít poštu.

21. Presentation_ID 21 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential TCP Communication TCP Server Processes (Cont.) Tento chce otevřít internetovou stránku. Tento chce otevřít poštu.

22. Presentation_ID 22 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential TCP Communication TCP Connection, Establishment and Termination Three-Way Handshake  Establishes that the destination device is present on the network  Verifies that the destination device has an active service 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

23. Presentation_ID 23 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential TCP Communication TCP Three-Way Handshake – Step 1 Step 1: The initiating client requests a client-to-server communication session with the server

24. Presentation_ID 24 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential 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. Podstatné věci, o kterých je řeč, v obrázku vůbec nejsou vidět: ACK flag Acknowledgement number SYN flag Destination port number Source port number

25. Presentation_ID 25 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential TCP Communication TCP Three-Way Handshake – Step 3 Step 3: The initiating client acknowledges the server-to-client communication session. Podstatné věci, o kterých je řeč, v obrázku vůbec nejsou vidět: ACK flag Acknowledgement number Source port number Destination port number

26. Presentation_ID 26 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential TCP Communication TCP Session Termination FIN = Finish

27. Presentation_ID 27 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Reliability and Flow Control TCP Reliability – Ordered Delivery Sequence numbers are used to reassemble segments into their original order.

28. Presentation_ID 28 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Reliability and Flow Control Acknowledgement and Window Size The sequence number and acknowledgement number are used together to confirm receipt. The window size is the amount of data that a source can transmit before an acknowledgement must be received.

29. Presentation_ID 29 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Reliability and Flow Control Window Size and Acknowledgements Pošle zpátky číslo, které očekává

30. Presentation_ID 30 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Reliability and Flow Control TCP Flow Control – Congestion Avoidance Ten se snaží poslat další a další 3001-4500 nedostal Proto znovu žádá 3001-4500

31. Presentation_ID 31 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Reliability and Flow Control TCP Reliability - Acknowledgements Žádá dvojku Nedostal, proto znovu a znovu žádá dvojku Až dvojku dostane, tak požádá o trojku.

32. Presentation_ID 32 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential UDP Communication UDP Low Overhead vs. Reliability UDP  Simple protocol that provides the basic transport layer function  Used by applications that can tolerate small loss of data  Used by applications that cannot tolerate delay Used by  DNS  Simple Network Management Protocol (SNMP)  Dynamic Host Configuration Protocol (DHCP)  Trivial File Transfer Protocol (TFTP)  IP telephony or VoIP  Online games  Video

33. Presentation_ID 33 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential UDP Communication Datagram Reassembly Části, došlé ve špatném pořadí, se nepřerovnávají. Ztracené části se neposílají znovu.

34. Presentation_ID 34 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential 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. Server používá dobře známá registrovaná čísla portů. Klient používá náhodně zvolená čísla portů.

35. Presentation_ID 35 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential TCP or UDP Applications that use TCP

36. Presentation_ID 36 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential TCP or UDP Applications That Use UDP Telefon Video

37. © 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 37 7.3 Summary

38. Presentation_ID 38 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Chapter 7: Summary  The transport layer provides these services: multiplexing segmentation reassembly error checking  The transport layer: Divides data into segments. Adds a header to each segment. Reassembles the segments back into application data. Passes the assembled data to the correct application.  Transport Layer addresses issues in QoS and security.  Ports help data to get from the transport layer to the appropriate application at the destination.