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Transport layer

Transport layer. Chapter 7 Intro to Routing & Switching. objectives. Upon completion of this chapter, you should be able to: Explain the need for the transport layer. Identify the role of the transport layer as it provides the end-to-end transfer of data between applications.

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Transport layer

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  1. Transport layer Chapter 7 Intro to Routing & Switching

  2. objectives • Upon completion of this chapter, you should be able to: • Explain the need for the transport layer. • Identify the role of the transport layer as it provides the end-to-end transfer of data between applications. • Describe the role of two TCP/IP transport layer protocols: TCP and UDP. • Explain the key functions of the transport layer, including reliability, port addressing, and segmentation. • Explain how TCP and UDP each handle key functions. • Identify when it is appropriate to use TCP or UDP and provide examples of applications that use each protocol.

  3. Layer 4 protocols used • Each protocol does its’ own job • IP addresses & routes data • Doesn’t say how it is transported • Different applications use different protocols for transport of the data • How data is sent/exchanged • TCP or UDP

  4. 7.1.1 The transport layer

  5. transport layer introduction • What PDU? • Segments • Simply, the responsibilities: • Ensures end-to-end delivery of data • Establish a session between applications • Segmenting the data • Transport the data • Handling the flow of data • Reassembling the data • Passing the data to the proper application • Retransmit if necessary

  6. transport layer introduction • Protocols • TCP- most common • UDP

  7. Connection-oriented protocol • TCP • Establish a connection 1st, then sends data • 3-way handshake • SYN, SYN-ACK, ACK

  8. Connectionless protocol • UDP • No connection • Doesn’t ensure error-free delivery • Faster than TCP, more efficient for quicker delivery • Live audio/video over Internet or VoIP • TCP would bog it down; incomplete pics or audio; pics wouldn’t coincide with audio

  9. segmentation • Large amounts of data broken into smaller units • Segments • Also consider the MTU of the media • 6000 byte message on a 1500 byte MTU Ethernet • 4 segments • Reassembled at destination • Sequencing • Identifies the segments & helps is re-ordering

  10. Segmentation & reassembly • Words split to send • Dest. reassembles the words • Words may arrive out of order • Sequence #’s help re-order into sentence

  11. Review- q • What is the PDU of the Transport Layer? • Segment • What helps put a TCP segmented message back in order at the destination? • Sequence numbers • Which Layer 4 protocol could deliver data with errors or not be delivered at all? • UDP • How is TCP able to establish a connection? • 3-way handshake

  12. Review- q • When sending a web page, which Layer 4 protocol would be used? • TCP • In the same scenario as above, what would happen if the destination did not receive an ACK after sending data? • It would re-send just that segment • Which layer 4 protocol is able to deliver data quickly? • UDP

  13. 7.1.2 Introducing tcp & udp

  14. Tcp summary • Connection-oriented • Sends acknowledgements • Like tracking a FedEx delivery • Breaks messages into small segments • If sender doesn’t get an ACK of message received, it retransmits • Only portion lost is resent • On receiving host, TCP reassembles data • FTP & HTTP are examples of protocols using TCP

  15. Tcp segment

  16. Tcp conversation SEQUENCE #= 200 SYN SYN-ACK SEQ#= 1450 ACK= 201 ACK SEQ#= 201 ACK= 1451

  17. Tcp sliding window • How much data it can receive

  18. Tcp end the conversation

  19. Tcp summary • Connection-oriented • Guaranteed delivery • 3-way handshake • Segments & sequence # • Acknowledgements • Flow control • Retransmission • Generates more traffic because of all this

  20. Review- q • What significance does the ACK# have? • It’s the next expected byte number • Sequence # received PLUS 1 • When a conversation is ready to end, nothing more is being sent, what flag gets sent? • FIN • What are 2 protocols that use TCP? • HTTP & FTP • Explain flow control. • Adjusting the amount/flow of data being sent/received

  21. 7.2.3 udp

  22. udp • Connectionless • Used for faster transmissions • Low overhead • “Best effort delivery” • Regular mail / no guarantee of delivery • No ACK or retransmission • No error checking* • Used for streaming audio, video, VoIP • DNS, DHCP, TFTP, VoIP, Gaming, SNMP are examples of protocols that use UDP

  23. Udp header

  24. Udp interruptions

  25. Use tcp or udp? • TCP • HTTP • IP • FTP • Telnet • SMTP/POP • DNS • UDP • DHCP • TFTP • SNMP • VoIP • Internet TV/Radio • DNS

  26. Comparing TCP & UDP • Faster • Best effort delivery • No acknowledgements • No retransmit • Connectionless • Slower • Segments • Acknowledgements • Retransmission • Reassembles • Connection-oriented • Flow control UDP TCP

  27. Activity 1

  28. Activity 2

  29. Review- q

  30. TCP-What do you remember? • Which is connection-oriented? • TCP • TCP establishes a connection or a ________ with the destination. • Session • Why is TCP reliable? • Sends acknowledgments of receiving & retransmits missing data • Explain flow control for TCP. • Regulates the flow of data • Protocols used? • HTTP, SMTP, Telnet, FTP

  31. udP-What do you remember? • Speed? • Fast • Connection or connectionless? • Connectionless • Reliability? • Unreliable • No ACK or retransmission • Flow control? • None • Protocols used: • DNS, VoIP, Video Stream, SNMP

  32. Tracking the convo • You have many conversations at the same time • Web • Email • DHCP • VoIP • Video streaming • Transport Layer tracks each one

  33. Many convos, one stream • All of those conversations come out as one stream of data • Example: your streaming video coming in does not take up the entire connection • Multiplexing (sending) • Demultiplexing (receiving) • This is what it does…………………………………

  34. Pass data to application • Sends data to proper application • Your many conversations: • Web  goes to web browser • Email  goes to email program • DHCP  goes to IP config • VoIP  goes to VoIP software • Video streaming  goes to media player • Each protocol has a port # • In the segment to direct to the correct application

  35. Port numbers • All the conversations need to be tracked • Port Number in each segment • Helps identify what service the message is for • Web request, email, DHCP, etc. • Protocols identified by port numbers

  36. Port # example

  37. Port # & communication • Each message sent, has a source & destination port number • Source Port • Randomly generated & placed into segment • Tracks incoming segment • Destination Port • Used to pass data to proper application at destination

  38. Review- q

  39. Port numbers • 1-65,535 • Well-known ports • 1- 1023 • Common applications • Registered ports • 1024- 49,151 • Can be source or destination ports • Used for specific applications like IM • Private ports • 49,152 & above • For source ports

  40. Important port #’s • Destination- tells about service requested • 20 & 21- FTP • 23- Telnet • 25- SMTP • 53- DNS (BOTH TCP & UDP) • 67 & 68- DHCP • 69- TFTP • 80- HTTP • 110- POP3 • 161- SNMP • 443- HTTPS

  41. sockets • The combo of the source & destination IP AND the source & destination port number is known as a socket. • 192.168.1.7:80

  42. Check it! • Check your active connections • Unexplained ones could be threats! • C:\> netstat

  43. activity • 7.1.2.11 • Drag each description to TCP or UDP

  44. Review-

  45. Review-

  46. Sending a message • Web Server to client (you) • Application data broken into TCP segments • Each segment has a header w/ source & dest ports • Segment encapsulates HTTP & HTML data • Encapsulates into a packet w/ IP header • IP header has source & dest IP addresses • IP Packet sent to Ethernet protocol • Encapsulates into frame header & trailer • Source & destination MAC AND error checking • Bits encoded onto the media

  47. Receiving the message • Last process in reverse • Bits received by NIC & decoded • Destination MAC recognized • Ethernet header & trailer removed • Source & dest MAC removed • IP header removed • Source & dest IP removed • TCP header removed • Source & dest ports removed • Web page data passed to HTTP & browser • TCP segment received, reassembled, & page displays

  48. activity • 192.168.5.101 • 80 or TCP or UDP • 01-5A-FF-65-80-DC • 1100101101000010 • DHCP or POP3 or HTTP

  49. Review- 4q

  50. Review- 3q

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