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Chapter 7 Intro to Routing & Switching
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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.
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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
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7.1.1
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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
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Protocols TCP- most common UDP
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TCP Establish a connection 1 st, then sends data 3-way handshake SYN, SYN-ACK, ACK
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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
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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
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Words split to send Dest. reassembles the words Words may arrive out of order Sequence #’s help re-order into sentence
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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
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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
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7.1.2
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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
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SEQUENCE #= 200 SYN SYN-ACK SEQ#= 1450 ACK= 201 ACK SEQ#= 201 ACK= 1451
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How much data it can receive
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Connection-oriented Guaranteed delivery 3-way handshake Segments & sequence # Acknowledgements Flow control Retransmission Generates more traffic because of all this
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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
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7.2.3
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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
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TCP HTTP IP FTP Telnet SMTP/POP DNS UDP DHCP TFTP SNMP VoIP Internet TV/Radio DNS
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UDPTCP Faster Best effort delivery No acknowledgements No retransmit Connectionless Slower Segments Acknowledgements Retransmission Reassembles Connection-oriented Flow control
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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
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Speed? Fast Connection or connectionless? Connectionless Reliability? Unreliable No ACK or retransmission Flow control? None Protocols used: DNS, VoIP, Video Stream, SNMP
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You have many conversations at the same time Web Email DHCP VoIP Video streaming Transport Layer tracks each one
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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…………………………………
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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
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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
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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
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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
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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
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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. 192.168.1.7:80
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Check your active connections Unexplained ones could be threats! C:\> netstat
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7.1.2.11 Drag each description to TCP or UDP
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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
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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
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192.168.5.101 80 or TCP or UDP 01-5A-FF-65-80-DC 1100101101000010 DHCP or POP3 or HTTP
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Complete the study guide handout Take the quiz on netacad.com Jeopardy review
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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.
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Chapter 7 Intro to Routing & Switching
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