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  1. 1. Copyright 2011 1 Module 5 TCP/IP (The Transport and Internetworking Layer Protocol) By Dr. Percy Dias
  2. 2. Copyright 2011 2 History and Future of TCP/IP • The U.S. Department of Defense (DoD) created the TCP/IP reference model because it wanted a network that could survive any conditions. • Some of the layers in the TCP/IP model have the same name as layers in the OSI model.
  3. 3. Copyright 2011 3 Internet Layer The purpose of the Internet layer is to send packets from a network node and have them arrive at the destination node independent of the path taken. Internet Protocol (IP) Internet Control Message Protocol (ICMP) Address Resolution (ARP) Reverse Address Resolution Protocol (RARP) Dynamic Host Configuration Protocol (DHCP)
  4. 4. Copyright 2011 4 Internet Layer Protocols • IP performs the following operations – Defining a packet and an addressing scheme – Transferring data between the Internet Layer and the Network Access Layer – Routing packets to remote hosts • IP is sometimes referred to as an unreliable protocol – Provides connectionless, best-effort delivery routing of packets
  5. 5. Copyright 2011 Network Layer Protocols and Internet Protocol (IP)
  6. 6. Copyright 2011 Network Layer Protocols and Internet Protocol (IP)
  7. 7. Copyright 2011 Transport Layer Role and Services • Supporting Reliable Communication 7
  8. 8. Copyright 2011 8 Transport Layer Perspective
  9. 9. Copyright 2011 9 The Transport Layer Functions Five basic services: • Segmenting upper-layer application data • Establishing end-to-end operations • Sending segments from one end host to another end host • Ensuring data reliability provided by sequence numbers and acknowledgments • Ensuring flow control provided by sliding windows
  10. 10. Copyright 2011 10 Reliable Data Transport • Ensure that segments delivered will be acknowledged to the sender • Provide for retransmission of any segments that are not acknowledged • Put segments back into their correct sequence at the destination • Provide congestion avoidance and control
  11. 11. Copyright 2011 11 Connectionless and Connection- Oriented Protocols • Connection-oriented protocol – A protocol either that requires an exchange of messages before data transfer begins or that has a required pre-established correlation between two endpoints • Connectionless protocol – A protocol that does not require an exchange of messages and that does not require a pre- established correlation between two endpoints
  12. 12. Copyright 2011 Connectionless Communication
  13. 13. Copyright 2011 13 Three-way Handshake • TCP is connection-oriented, so it requires connection establishment before data transfer begins • For a connection to be established, two hosts must synchronize on each other’s initial sequence numbers (ISNs) • Initial Sequence numbers are actually large random numbers chosen by each host • Connection establishment refers to the process of initializing sequence and acknowledgement fields and agreeing to the port numbers used.
  14. 14. Copyright 2011 14 Three-Way Handshake
  15. 15. Copyright 2011 15 TCP Connection Establishment
  16. 16. Copyright 2011 16 Windowing • Flow-control mechanism requiring that source device receive an acknowledgment from the destination • TCP uses expectational acknowledgments (Forward Acknowledgment) • Window size determines the amount of data can transmit at one time before receiving an acknowledgment • Larger window sizes increase communication efficiency. • Window field implies the maximum number of unacknowledged bytes allowed outstanding at any instance in time.
  17. 17. Copyright 2011 17 Window Size Larger window sizes increase communication efficiency.
  18. 18. Copyright 2011 18 Window Size • TCP window sizes are variable during the lifetime of a connection. • The window “Slides” up and down based on network performance, so it is called sliding window.
  19. 19. Copyright 2011 19 Flow Control
  20. 20. Copyright 2011 20 TCP Dynamic Sliding Windows
  21. 21. Copyright 2011 21 TCP Dynamic Sliding Windows
  22. 22. Copyright 2011 22 Acknowledgment • Sender keeps a record of each data packet that it sends and expects an acknowledgment. • Sender starts a timer when it sends a segment, and it retransmits if the timer expires before an acknowledgment (transmission rate should be slowed) • Each Acknowledgement contains a window advertisement that indicates the number of bytes receiver can accept
  23. 23. Copyright 2011 23 Segmentation, Reassembly, and In-Order Delivery • TCP on the receiving computer reassembles data into its original form • The data is put in the correct order – If segments of a file are assembled out-of- order, the file is useless – TCP provides a guarantee of in-order delivery
  24. 24. Copyright 2011 24 Segmentation, Reassembly, and In-Order Delivery • Due to IP routing, a TCP receiver can receive data out of order • If multiple routes exist between a source and a destination, routers can load-balance over several routes • Packets can arrive out of order
  25. 25. Copyright 2011 25 TCP Providing In-Order Delivery
  26. 26. Copyright 2011 26 Port Numbers
  27. 27. Copyright 2011 27 TCP and UDP Port Numbers • Internet layer delivers data (packets) from one computer to another, but it does not think about which application sent the data or which application on the receiving computer needs the data. • For example, if you have five web-browser windows open, the internet layer delivers the data to the computer, but the transport layer works to ensure that each browser gets the data destined for it and not one of the others. • TCP and UDP use port numbers to pass information to the upper layers • Port numbers use to keep track of different conversations crossing the network at the same time (Enables the receiving computer to know which application to give the data to).
  28. 28. Copyright 2011 28 Using Port Numbers to Identify the Correct Application Process
  29. 29. Copyright 2011 29 Identifying Application Processes Using Port Numbers • In previous slide, the application was assigned a dynamic port number by the host computer – A host typically dynamically allocates port numbers of value 1024 (210 ) through 65,535 (216 - 1). – When a host starts a new application process, it allocates a dynamic port number that is not already in use by another process. – By each process having its own port number, a PC can have multiple conversations with other PCs (sometimes called multiplexing).
  30. 30. Copyright 2011 30 Identifying Application Processes Using Port Numbers • Connection to Servers: Well-Known Ports – Most TCP/IP applications use a client/server model for communications. – Servers cannot use dynamic port numbers because clients must know ahead of time what port numbers servers use. – Numbers below 1024 are considered well-known port numbers. – well-known port numbers are used by Servers, other port numbers used by clients. – Each client on the same host uses a different port number, but a server uses a same port number for all connections. – Well-Know Port Numbers are controlled by Internet Assigned Number Authority (IANA).
  31. 31. Copyright 2011 31 Client Connecting to Well-Known Port of a Web Server (80)
  32. 32. Copyright 2011 32 Popular Well-Known Port Numbers
  33. 33. Copyright 2011 33 TCP Sequence and Acknowledgment
  34. 34. Copyright 2011 34 TCP • Connection Establishment and Termination • Reliable (Error recovery – consume more bandwidth and use more processing cycles) • Divides outgoing messages into segments • Reassembles messages at the destination station
  35. 35. Copyright 2011 35 TCP • Flow control using sliding windows • Multiplexing using port numbers • TCP relies on IP for end-to-end delivery of data • At the receiving station, TCP reassembles the segments into a complete message using sequence numbers. TCP must recover data that is damaged, lost or delivered out of order.
  36. 36. Copyright 2011 UDP Protocol 36
  37. 37. Copyright 2011 UDP Protocol 37
  38. 38. Copyright 2011 38 UDP • Connectionless • Unreliable ( No error recovery – use less bandwidth and fewer processing cycle.) • Does not reassemble incoming messages • Uses no acknowledgments • Provides no flow control • Less overhead than TCP •
  39. 39. Copyright 2011 39 TCP Function Summary Function Description Multiplexing Function that allows receiving hosts to decide the correct application for which the data is destined, based on the port number Error recovery (reliability) Process of numbering and acknowledging data with Sequence and Acknowledgment header fields Flow control using windowing Process that uses window sizes to protect buffer space
  40. 40. Copyright 2011 40 Comparing TCP and UDP
  41. 41. Copyright 2011 41 Cisco Academy 3 References Slide 2 CCNA1 9.1.1 Slide 3-4 CCNA1 9.1.4 Slide 9-10 CCNA1 11.1.1 Slide 11 CCNA1 10.1.4 Slide 13-15 CCNA1 11.1.4 Slide 16-18 CCNA1 11.1.5-11.1.6 Slide 19 CCNA1 11.1.2-11.1.3 Slide 20-22,33 CCNA1 11.1.5-11.1.6 Slide 26-27,30,32 CCNA1 11.1.9 Slide 34-35,38-39 CCNA1 11.1.7-11.1.8
  42. 42. Copyright 2011 42 Cisco Academy 4 Exploration Reference Networking Fundamentals Slide 2-4 5.1.1-5.1.5 Slide 8-10 4.1.1 Slide 11 4.2.1 Slide 13-14 4.2.3-4.2.4 Slide 16-18 4.3.2 Slide 19 4.3.4 Slide 20-22 4.3.4 Slide 32 4.1.4 Slide 38 4.4.1-4.4.3 Slide 40 4.1.4