Chapter 7 Intro to Routing & Switching

 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.

 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

7.1.1

 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

 Protocols  TCP- most common  UDP

 TCP  Establish a connection 1 st, then sends data  3-way handshake  SYN, SYN-ACK, ACK

 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

 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

 Words split to send  Dest. reassembles the words  Words may arrive out of order  Sequence #’s help re-order into sentence

 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

 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

7.1.2

 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

SEQUENCE #= 200 SYN SYN-ACK SEQ#= 1450 ACK= 201 ACK SEQ#= 201 ACK= 1451

 How much data it can receive

 Connection-oriented  Guaranteed delivery  3-way handshake  Segments & sequence #  Acknowledgements  Flow control  Retransmission  Generates more traffic because of all this

 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

7.2.3

 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

 TCP  HTTP  IP  FTP  Telnet  SMTP/POP  DNS  UDP  DHCP  TFTP  SNMP  VoIP  Internet TV/Radio  DNS

UDPTCP  Faster  Best effort delivery  No acknowledgements  No retransmit  Connectionless  Slower  Segments  Acknowledgements  Retransmission  Reassembles  Connection-oriented  Flow control

 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

 Speed?  Fast  Connection or connectionless?  Connectionless  Reliability?  Unreliable  No ACK or retransmission  Flow control?  None  Protocols used:  DNS, VoIP, Video Stream, SNMP

 You have many conversations at the same time  Web   DHCP  VoIP  Video streaming  Transport Layer tracks each one

 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…………………………………

 Sends data to proper application  Your many conversations:  Web  goes to web browser   goes to 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

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

 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

 1-65,535  Well-known ports   Common applications  Registered ports  ,151  Can be source or destination ports  Used for specific applications like IM  Private ports  49,152 & above  For source ports

 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

source & destination IP source & destination port number  The combo of the source & destination IP AND the source & destination port number is known as a socket.  :80

 Check your active connections  Unexplained ones could be threats!  C:\> netstat

  Drag each description to TCP or UDP

 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

 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

  80 or TCP or UDP  01-5A-FF DC   DHCP or POP3 or HTTP

 Complete the study guide handout  Take the quiz on netacad.com  Jeopardy review

In this chapter, you learned:  The role of the Transport layer is to provide three main functions: multiplexing, segmentation and reassembly, and error checking.  These functions are necessary in order to address issues in quality of service and security on networks.  Knowing how TCP and UDP operate and which popular applications use each protocol will allow the implementation of quality of service and build more reliable networks.  Ports provide a “tunnel” for data to get from the Transport layer to the appropriate application at the destination.

Chapter 7 Intro to Routing & Switching