CCNA 1 v3.11 Module 11 TCP/IP Transport and Application Layers

Transcription

1 CCNA 1 v3.11 Module 11 TCP/IP Transport and Application Layers 2007, Jae-sul Lee. All rights reserved. 1

2 Agenda 11.1 TCP/IP Transport Layer 11.2 The Application Layer What does the TCP/IP transport layer do? How TCP can offer connection-oriented delivery over the connectionless IP network? What are the TCP/IP application layers? What do they do and how do they work? 2

3 Overview The TCP/IP transport layer Responsible for end-to-end data delivery Transports data between applications on source and destination devices Multiplexes multiple connections between hosts TCP provides connection-oriented delivery Provides reliability, orderly delivery, and flow control Less efficient and slower due to the overhead UDP provides connectionless delivery Efficient and fast, but unreliable The TCP/IP application layer Relies on TCP, UDP/IP for the delivery 3

4 Module objectives Students who complete this module should be able to perform the following tasks: Describe the functions of the TCP/IP transport layer Describe flow control Explain how a connection is established between peer systems Describe windowing Describe acknowledgment Identify and describe transport layer protocols Describe TCP and UDP header formats Describe TCP and UDP port numbers List the major protocols of the TCP/IP application layer Provide a brief description of the features and operation of wellknown TCP/IP applications 4

5 11.1 TCP/IP Transport Layer 11.2 The Application Layer What does the TCP/IP transport layer do? - Offers reliable end-to-end connectivity over the (unreliable )IP - Offers multiplexing of upper layer communications using the port numbers How TCP can offer connection-oriented delivery over the connectionless IP network? - Using three way handshake, sequence number, acknowledgement, flow control by adjusting the window size Characteristics of TCP and UDP How do TCP and UDP support multiple various upper layer services? 5

6 Outlines Introduction to the TCP/IP transport layer Flow control Session establishment, maintenance, and termination Three-way handshake Acknowledgment Windowing TCP UDP TCP and UDP port numbers 6

7 Introduction to the TCP/IP transport layer The functions of the transport layer End-to-end logical connectivity between host applications Transport and regulate the flow of information reliably and accurately Establish end-to-end operation Divide upper layer data into segments Send segments from one end host to another end host Ensure data reliability and accuracy» Error detection, request retransmission, & acknowledgments»use sequence numbers to ensure the order of received packet Provide end-to-end flow control» Avoid Rx data buffer overflow at the destination»use sliding window mechanism to control flow rate Matter of Quality of Service (QoS) 7

8 TCP and UDP port numbers Multiplexing of upper-layer conversations Multiple connections can be made for multiple services They are multiplexed into a stream of the segments in a channel End-to-end connections are distinguished by the port number Each connection has unique pair of source port-destination port Use of port numbers are defined by IANA The Well Known Ports: 0 ~ 1023 Used only by system (or root) processes or by programs executed by privileged users (usually, the server processes) The Registered Ports: 1024 ~ Can be used by ordinary user processes or programs executed by ordinary users (usually, the client or p2p processes) The Dynamic and/or Private Ports: ~

9 TCP and UDP port numbers Example of multiple use of ports A C data A=pearl A C data A B data A C data A B data B= ( ) web telnet C=oslab.dtcinfo.net ( ) telnet telnet web 9

10 TCP and UDP port numbers Application services and port numbers Copyrighted material is cleared 10

11 Session establishment, maintenance, and termination Establishing a connection-oriented session in TCP Establishing a connection using three way handshaking Copyrighted material is cleared Sender requests synchronization (initiates a connecion) Receiver acknowledges the synchronization request from the sender and requests synchronization Sender acknowledges the synchronization request from the receiver and informs the receiver that both sides agree that a connection has been established 11

12 Session establishment, maintenance, and termination Concept of flow control in TCP Communicating hosts may experience congestion if Too fast source hosts saturate the network link Too slow destination host fail to process the receiving packets timely In both cases, excessive traffic overflows the buffer memory of the nodes (routers or the destination hosts) The packets are lost The TCP process has the control mechanism to avoid this problem Copyrighted material is cleared 12

13 Session establishment, maintenance, and termination Overview of flow control Copyrighted material is cleared 13

14 Session establishment, maintenance, and termination Termination of a connection Thesource host sends a signal (FIN) that indicates the end of the transmission The destination host acknowledges and confirms the end of transmission The source host acknowledges The connection is terminated 14

15 Three-way handshake Establishing a connection before data transmission Sequence numbers are needed for reliable communication For orderly delivery, error detection, and flow control Sequence numbers act as the reference of each end s starting point Each host has its own sequence number It starts with an arbitrary number at the connection establishment phase It represents the position of the starting data octet in the segment relative to the first octet of all data stream in a whole TCP session Each end must know the other s sequence number Two hosts must synchronize their initial sequence numbers to establish a connection Three-way handshake is used for this purpose 1.Originating end send its own sequence number to the other end 2.The other end responds with its own sequence number and the acknowledge (= the originating end s sequence number +1) 3.The originating end responds with the acknowledge (the other s sequence number + 1) 15

16 Three-way handshake ACK=1 SYN=1 SYN=1, ACK=1 = = Copyrighted material is cleared SYN: My sequence number is 100 ACK: I have received yours, too. Give me next (301) ACK: I have received yours. Give me next (101) SYN: My sequence number is 300 Connection is established 16

17 Three-way handshake example 17

18 Acknowledgment TCP must support reliable, orderly delivery of segments Implemented by the sequence number and the acknowledgement Positive acknowledgment with retransmission (PAR) Data stream is divided into small segments The sender assigns sequence numbers to each segment of the data stream 1. The sender transmits a segment of sequence number N 2. If the receiver received the segment, it calculates the checksum If the checksum is good, it sends back an ACK of sequence number N + data bytes received (positive acknowledgement) It means next anticipated data octet If NOT, it discards the segment and does not send the acknowledgement 3. If the receiver did not receive the segment, it does not send the acknowledgement 4. If the sender receives ACK before the preset timer expires, it transmits a segment with sequence number (received ACK number) If NOT, the sender retransmits the segment of sequence number N 5. The receiver reassembles the segments 18

19 Acknowledgment You received #10. I send #10. Now I send #11. Copyrighted material is cleared 19

20 Acknowledgment Ex) Imagine a TCP connection is transferring a file of 6000 bytes. The sequence number for the first octet of the data is numbered What are the sequence numbers for each segment if data is sent in five segments with the first four segments carrying 1,000 bytes and the last segment carrying 2,000 bytes of data? The following shows the sequence number for each segment: Segment 1 10,010 (10,010 to 11,009) Segment 2 11,010 (11,010 to 12,009) Segment 3 12,010 (12,010 to 13,009) Segment 4 13,010 (13,010 to 14,009) Segment 5 14,010 (14,010 to 16,009) 20

21 Windowing TCP must be able to control the amount of data flow Implemented by controlling the window size (sliding window) Window size defines number of data octets that can be sent without receiving the acknowledgement Data octets = window size x 2 window scale factor (defined in the option field) The receiving end sends acknowledgement with the preferred window size The sending end transmits number of data octets specified by the received window size The sending end waits another ACK The receiving end receives the data and replies ACK with window size If the buffer overflows before it receives all data octets, send reduced window size with ACK number (=received seq. number + received data octets) If it receives all data octets and the buffer is not filled up, send increased window size with ACK number The larger the window size, the faster and the more efficient the transmission is 21

22 Windowing Comparing the transmission with window size=1 and 3 Copyrighted material is cleared 22

23 Windowing Sliding window Copyrighted material is cleared Currently, Now, window size=2 size=3 23

24 TCP Features of TCP A connection-oriented transport layer protocol Supplies a virtual circuit between end-user applications Provides reliable full-duplex data transmission Breaks messages into segments Reassembles them at the destination Resends anything that is not received Upper layer application protocols supported by TCP FTP HTTP SMTP Telnet 24

25 TCP Header fields of a TCP segment Copyrighted material is cleared Source port Number of the port that sends data Destination port Number of the port that receives data 25

26 TCP Sequence number Randomly assigned at the TCP connection establishment phase Prevents spoofing of a hacker Represents the position of starting data octet in a segment relative to the first octet of all data stream in a whole TCP session Ensure the data arrives in the correct order Acknowledgement number Represents the position of next expected TCP data octet relative to the first octet of all data stream in a whole TCP session HELEN Header length in number of 4 octets (32 bits words) Reserved Set to 0 26

27 TCP Control field Copyrighted material is cleared Window size Number of data octets in a segment that the receiver can accept The receiver sets in the acknowledgement for the sender s next transmission Checksum Calculated checksum of the header and data fields 27

28 TCP Urgent pointer If the URG bit is set, this field points to the sequence number of the last byte in a sequence of urgent data. Option Includes padding End of option No operation Copyrighted material is cleared Data Upper-layer protocol data 28

29 UDP Features of UDP The connectionless transport protocol in the TCP/IP protocol stack Exchanges datagrams without guaranteed delivery Does not use windows or sequence numbers/acks Designed for applications that do not need to put sequences of segments together Relies on higher-layer protocols to handle errors and retransmit data Upper layer application protocols supported by UDP TFTP SNMP DHCP DNS 29

30 UDP Header fields of a UDP segment Copyrighted material is cleared Source port Number of the port that sends data Destination port Number of the port that receives data Length Number of bytes in header and data Checksum Calculated checksum of the header and data fields Data Upper-layer protocol data 30

31 11.1 TCP/IP Transport Layer 11.2 The Application Layer What are the TCP/IP application layers? What do they do and how do they work? 31

32 Outlines Introduction to the TCP/IP application layer DNS FTP and TFTP HTTP SMTP SNMP Telnet 32

33 Introduction to the TCP/IP application layer TCP/IP application layer Layers 5~7 of the OSI model are bundled into it Handles representation, encoding, and dialog control in a layer Provides maximum flexibility at the application layer for software developers Copyrighted material is cleared 33

34 DNS Domain naming system Helps easier use of the Internet Domain names can be used instead of unfamiliar IP addresses It has systematic naming rules It has the hierarchical naming structure A FQDN (fully qualified domain name) is assigned to a host A hostname with its registered domain name attached gtld Root domain. cctld org int com net edu gov mil biz name pro kr us tv yahoo daum naver ac ne co pe go blog cafe www dongyang danawa www doumi mail www dica 34

35 DNS IP address resolution Translating a domain name into an IP address Done by the domain name servers 35

36 DNS 36

37 FTP and TFTP FTP Used for file transfer between the systems A reliable, connection-oriented service that uses TCP Needs two TCP connections Control channel (21/TCP) Data transfer channel (20/TCP) 37

38 FTP and TFTP Multiple connections and states TCP connection established FTP session 4 38

39 FTP and TFTP TFTP Connectionless service that uses UDP Designed to be small and easy to implement Operates faster than FTP Works reliably in a stable environment Used on the router to transfer configuration files and Cisco IOS images It lacks most of the features of FTP Cannot list directories No authentication features available 39

40 HTTP Features Works with the World Wide Web Fastest growing and most used part of the Internet Easy access to information Contents are represented in the form of the hypertext Hypertext contains the multimedia contents and the hyperlinks to other resources in the Internet Hypertext markup language (HTML) is used to describe the location and the format of the contents in a hypertext The URL describes the access method and the location of the content scheme://[id:password@]server[:port number][/path[/resource_filename]] 40

41 HTTP Client-server operation of the Web #80 See next page for an example 41

42 HTTP TCP connection established HTTP session 4 HTTP header HTTP data (HTML Document) End of HTTP session TCP connection closed 42

43 HTTP How the browser displays the HTML document Browser s view HTML document 43

44 HTTP Overall transaction for a page view CLIENT (request URL) Internet SERVERS ns.dtcinfo.net htmltest.html dc5.donga.com crw_3736_rt8.jpg 44

45 SMTP Features Sends and receives the Internet mail Transports messages in ASCII format using TCP Mail flow DNS MX of naver.com? Mail to: Hi MUA 1 SMTP #25 MTA Mail queue MDA 4 SMTP #25 Mail queue MTA 6 7 MDA Mail box 9 POP3 #110 IMAP4 #143 8 MUA Hi daum.net naver.com 45

46 SMTP 1. An SMTP mail transaction TCP connection established SMTP session End of SMTP session TCP connection closed 46

47 SMTP 2. Filtering by the SPAM blocker 3. Received by mail.dongyang.ac.kr (see next page) 47

48 SMTP Retrieving a message using POP3 TCP connection established POP session End of POP session TCP connection closed 48

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50 SNMP Features Facilitates the exchange of management information between network devices Network administrators can Manage network performance Find and solve network problems Plan for network growth Uses UDP as its transport layer protocol Key components of the SNMP managed network NMS monitor and control managed devices Managed devices collect and store management information and make this information available to NMSs using SNMP Agents are network-management software modules that reside in managed devices. An agent translates management information into a form compatible with SNMP 50

51 SNMP SNMP SNMP SNMP Copyrighted material is cleared 51

52 Telnet Features Provides the ability to login to a remote Internet host (Telnet server) Local client acts as a remote text terminal of the Telnet server Local keystrokes are transmitted to the remote server Commands are executed at the remote server The results are displayed at the local client s display Works at the application layer of the TCP/IP model The application layer of the OSI model deals with commands The presentation layer of the OSI model handles formatting, usually ASCII The session layer of the OSI model transmits 52

53 Summary Students should understand the following main points: The functions of the TCP/IP transport layer Flow control The processes of establishing a connection between peer systems Windowing Acknowledgment Transport layer protocols TCPand UDP header formats TCP and UDP port numbers The processes and protocols at the TCP/IP application layer Domain Name Services File Transfer Protocols Simple Mail Transfer Protocol Simple Network Management Protocol Telnet 53