CCNA 1 v3.11 Module 11 - dongyang.ac.krocw.dongyang.ac.kr/cms_ocw/network/435/note/5_14.pdf · 2008-02-19 · CCNA1 / 1st semester, 2007 4 Network Information & Communication Program,

1© 2007, Jae-sul Lee. All rights reserved.

TCP/IP Transport and Application Layers

CCNA 1 v3.11 Module 11

22CCNA1 / 1st semester, 2007Network Information & Communication Program,

Dongyang Technical College

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?



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



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 well-known TCP/IP applications




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?



Outlines11.1.1 Introduction to the TCP/IP transport layer

11.1.2 Flow control

11.1.3 Session establishment, maintenance, and termination

11.1.4 Three-way handshake

11.1.6 Acknowledgment

11.1.5 Windowing

11.1.7 TCP

11.1.8 UDP

11.1.9 TCP and UDP port numbers



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)



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 ~ 49151– 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: 49152 ~ 65535



TCP and UDP port numbers • Example of multiple use of ports

B=www.dtcinfo.net(203.237.160.8)

web

telnet

web

telnet

80 data1587AB

C=oslab.dtcinfo.net(203.237.160.90)

telnet

23 data1511AB

23 data1509AC

23 data1510AC

80 data1559AC

A=pearl



TCP and UDP port numbers • Application services and port numbers

Copyrighted material is cleared



Session establishment, maintenance, and termination

• Establishing a connection-oriented session in TCP–Establishing a connection using three way handshaking

Sender requests synchronization (initiates a connecion)

Receiver acknowledges the synchronization request from the sender and requests synchronizationSender acknowledges the synchronization request from the receiver and informs the receiver that both sides agree that a connection has been established





• 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





• Overview of flow control





• Termination of a connection– The source 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



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 purpose1.Originating end send its own sequence number to the other end2.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)



Three-way handshake

= 100

SYN=1

= 101

= 300

SYN=1, ACK=1ACK=1

= 301

ACK: I have received yours.Give me next (101)

SYN: My sequence number is300ACK: I have received

yours, too. Give me next (301) Connection is established

= 101


SYN: My sequence numberis 100



Three-way handshake – example



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

stream1. The sender transmits a segment of sequence number N2. 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 N5. The receiver reassembles the segments



Acknowledgment

You received #10.Now I send #11.I send #10.




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 10010. 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)



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



Windowing • Comparing the transmission with window size=1 and 3




Windowing • Sliding window

Currently, window size=3Now, window size=2




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



TCP• Header fields of a TCP segment

– Source port• Number of the port that sends data

– Destination port• Number of the port that receives data




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



TCP– Control field

– 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




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

– Data• Upper-layer protocol data



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



UDP • Header fields of a UDP segment

– 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





11.2 The Application Layer

• What are the TCP/IP application layers?• What do they do and how do they work?



Outlines11.2.1 Introduction to the TCP/IP application layer 11.2.2 DNS 11.2.3 FTP and TFTP 11.2.4 HTTP 11.2.5 SMTP 11.2.6 SNMP 11.2.7 Telnet



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




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 attachedRoot domain.

org int com …pronamebizmilgovedunet tv…uskr

ac pe

dongyang

…ne

www doumi mail

co

danawa

www dica

yahoo daum naver

blog cafe www

go

gTLD ccTLD



DNS • IP address resolution

– Translating a domain name into an IP address

– Done by the domain name servers



DNS



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)



FTP and TFTP– Multiple connections and states

4

TCP connection establishedFTP session



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



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]]



HTTP • Client-server operation of the Web

– See next page for an example

#80



HTTP

12

34

HTTP header

HTTP data(HTML Document)

TCP connection establishedHTTP session

End of HTTP sessionTCP connection closed



HTTP • How the browser displays the HTML document

HTML document

Browser’s view



HTTP• Overall transaction for a page view

http://www.dtcinfo.net/htmltest.html (request URL)ns.dtcinfo.net

dc5.donga.com

htmltest.html

http://dc5.donga.com/zero2/data/cool/IMG_8928.jpg

Internet

CLIENT

SERVERS

crw_3736_rt8.jpg

www.dtcinfo.net



SMTP • Features

– Sends and receives the Internet mail– Transports email messages in ASCII format using TCP

• Mail flow

MUA MUA②

MTA MTA

⑤ ⑥

Mail to: [email protected]

Hi…

Hi…

SMTP#25

SMTP#25

POP3 #110IMAP4 #143

③

Mail queue

Mail box

⑦

DNS

①

④

Mail queue

⑧

⑨

daum.net naver.com

MX of naver.com?

MDA

MDA



SMTP 1. An SMTP mail transaction

TCP connection established

SMTP session

End of SMTP sessionTCP connection closed



SMTP 2. Filtering by the SPAM blocker

3. Received by mail.dongyang.ac.kr (see next page)



SMTP – Retrieving a

message usingPOP3 TCP connection established

POP session

End of POP sessionTCP connection closed



1

2

3



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



SNMP

SNMP SNMP SNMP




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



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– TCP and 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

CCNA 1 v3.11 Module 11 - dongyang.ac.krocw.dongyang.ac.kr/cms_ocw/network/435/note/5_14.pdf · 2008-02-19 · CCNA1 / 1st semester, 2007 4 Network Information & Communication Program,

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