Data Communication and Networking - Transport and Application Layer of the OSI model

UNIT -5 TRANSPORT &
APPLICATION LAYER

TRANSPORT
LAYER
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Ms P Abirami Asst Prof Dept of Comp Sci

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✓ 4th layer from the top.
✓ provide the communication services directly to the application processes running on different hosts.
✓ provides a logical communication between application processes running on different hosts.
✓ protocols are implemented in the end systems but not in the network routers.
✓ A computer network provides more than one protocol to the network applications. For example, TCP and UDP are
two transport layer protocols that provide a different set of services to the network layer.
✓ protocols provide multiplexing/demultiplexing service. It also provides other services such as reliable data
transfer, bandwidth guarantees, and delay guarantees.
✓ Each of the applications in the application layer has the ability to send a message by using TCP or UDP. The
application communicates by using either of these two protocols. Both TCP and UDP will then communicate with
the internet protocol in the internet layer. The applications can read and write to the transport layer. Therefore,
we can say that communication is a two-way process.
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The services provided by the transport layer protocols can be divided into five
categories:
•End-to-end delivery
•Addressing
•Reliable delivery
•Flow control
•Multiplexing
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TCP [Transmission Control Protocol] & UDP[User Datagram Protocol]
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TCP
1. TCP SERVICES
2. TCP FEATURES
3. TCP SEGMENT
4. TCP CONNECTION
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TCP FEATURES
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TCP FEATURES
• NUMBERING SYSTEM
• FLOW CONTROL
• ERROR CONTROL
• CONGESTION CONTROL
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TCP FEATURES
• FLOW CONTROL – receiver controls the amount of data sent by
sender to avoid overflowing
• ERROR CONTROL – implements error detection & error correction
during data transfer
• CONGESTION CONTROL – data sent by sender is not only controlled
by the receiver also by the level of congestion in the network
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TCP FEATURES
• NUMBERING SYSTEM
• SEQUENCE NUMBER
• ACKNOWLEDGMENT NUMBER
BYTE NUMBER – byte of data transferred in each connection is numbered by TCP
from 0 – 1
SEQUENCE NUMBER – 1st data byte in the segment
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DEPENDS ON BYTE NUMBER NOT THE SEGMENT NUMBER

TCP FEATURES
SEQUENCE NUMBER – 1st data byte in the segment
• Segment has 1 byte of data each
• Combo of control & data
• Used in establishing the connection, data transmission, connection termination
• Valid only if it has data
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TCP FEATURES
ACKNOWLEDGMENT NUMBER – Cumulative , that is add 1 when last byte is received
e.g : x + 1 for x , 5043 for 5042
• It is used to confirm the byte has to be received
• It defines the number of next byte expects to be received
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TCP SEGMENT
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TCP SEGMENT
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TCP SEGMENT
• Data packets in the TCP are called as segments
• Segment divide into - Header & data
• Header- 20 to 60 bytes of data
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TCP SEGMENT
• Header – identify the sender / receiver of the data
• 40 bytes of Option & Padding - for future purpose (data storage)
• 16 bit of source port address & 16 bit of destination port address
[application used for sending & receiving purpose has 16 bit each]
• 32 bits Sequence number – 1st byte of the segment
• 32 bits acknowledgment number – identify the next data to be received from sender to receiver
• 16 bits window size – sender have to send only 16 bit to receiver , to avoid overflow [window size determines the
receiver size]
• 16 bits - 4bits HLEN (Header length ), 6bits Reserved (Reserved for the future),
• 6 bits controls (1bit each ) –
• URG - URGENT
• ACK - ACKNOWLEDGMENT
• PSH - PUSH
• RST - RESET
• SYN - SYNCHRONIZE
• FIN - FINAL
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THE FLAG IS SET ON WHEN THESE CONTROL BITS ARE ACTIVE
• RESET BIT IS SET DURING RESET OTHER WISE IN OFF STATE
• PUSH BIT IS SET ON WHEN THE DATA IS PUSHED
• FIN BIT IS SET ON WHEN THE DATA TRANSMISSION IS COMPLETED

TCP SEGMENT
• 6 bits controls (1bit each ) –
• URG – The value of the URGENT pointer field is valid
• ACK - The value of the ACKNOWLEDGMENT field is valid
• PSH – PUSH the data
• RST – RESET the connection
• SYN – SYNCHRONIZE sequence number during connection
• FIN – Terminate the connection
• 16 bits of CHECKSUM – Added into stream to check the error occurrence in
the data transfer, mandatory in TCP not in the UDP.
• 16 bits of URGENT POINTER – it is used to store data when it is true
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TCP SERVICES
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TCP SERVICES
1. PROCESS – PROCESS COMMUNICATION
2. STREAM DELIVERY SERVICE
3. SENDING & RECEIVING BUFFER
4. FULL DUPLEX COMMUNICATION
5. CONNECTION ORIENTED SERVICES
6. RELIABLE SERVICES
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1.PROCESS - PROCESS
• There are different port
• Eg:
• 1 – communication
• 7 - echo
• 9 – discard
• 11 – available users
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2.STREAM DELIVERY SERVICES
• SENDING PROCESS
• RECEIVING PROCESS
• TCP act on sending process to send the stream of data to receiver
• TCP act on receiving process to receive the stream of data from sender
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TCP PROCESS

Stream delivery services
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SENDING RECEIVING
TCP TCP
STREAM OF BYTES

1. BUFFER – STORAGE
3. CIRCULAR ARRAY
4. SENDING BUFFER
5. RECEIVER BUFFER
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3.SENDING & RECEIVING BUFFER
• BUFFER – TO STORE DATA
• Circular array is used
• Sender – white, Gray & Coloured
• Receiver – White & Coloured
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WHITE DATA HAVE TO BE STORED BY THE SENDER
GRAY STORED DATA WAITING FOR THE ACKNOWLEDGMENT
COLOURED DATA IS READY TO SEND
WHITE EMPTY PLACE WAITING FOR THE DATA FROM THE SENDER THROUGH NETWORK
COLOURED IT IS ALREADY RECEIVED AND READ BY THE RECEIVER

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4. FULL DUPLEX COMMUNICATION
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• In full-duplex mode, transmission is simultaneously bi-directional.
• The end devices can transmit and receive simultaneously.
• A prime example of full-duplex communications is the PSTN that
provides two-way communications.

5.CONNECTION ORIENTED SERVICES
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There is a sequence of operations that are needed to b followed by users.
1.Establishing Connection – (BETWEEN SENDER & RECEIVER)
It generally requires a session connection to be established just before any data is
transported or sent with a direct physical connection among sessions.
2.Transferring Data or Message – (BETWEEN SENDER & RECEIVER)
When this session connection is established, then we transfer or send message or data.
3.Releasing the Connection – (BETWEEN SENDER & RECEIVER)
After sending or transferring data, we release connection.

6. RELIABLE SERVICES
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SECURITY & INTEGRITY OF DATA TRANSMISSION

TCP CONNECTION
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TCP CONNECTION
• TCP is connection oriented
• Establish virtual path between the source and destination
• Messages are send over the virtual path
• TCP uses the IP address to deliver individual segment to the receiver
• The lost/corrupted messages are retransmitted in TCP
• Connection oriented transmission has 3 phase
1. Connection establishment
2. Data transfer
3. Connection termination
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TCP CONNECTION
1 – CONNECTION ESTABLISHMENT
1. TCP transfer data in full duplex mode
2. Two nodes can send segments simultaneously
3. The connection should be established before data transmission
4. The connection establishment in TCP is called as “Three Way Handshaking”
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Three way handshaking
✓Server is in the passive open mode
✓Client is in the active open mode
✓The server program inform TCP, that it is ready to accept the connection ->
request for a passive open
✓The client program issues a request for an active open
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Three steps:
STEP -1
• The client sends the first segment , SYN segment with SYN flag set
• SYN– cannot carry data but it consumes one sequence number
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SEQ : 8000
S
SENDER - RECEIVER
Client - Server
SEQUENCE NO : 8000
SYN FLAG IS SET

Three steps:
STEP -2
• The server sends the second segment , SYN + ACK with 2 flag bit set
• It cannot carry data but it consumes one sequence number
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SEQ : 15000
ACK : 8001
A S
SENDER - RECEIVER
server - client
SEQUENCE NO : 15000
ACK : 8001
ACK & SYN FLAG IS SET

Three steps:
STEP -3
• The client sends the third segment , just an ACK segment
• It cannot carry data & consumes no sequence number
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SEQ : 8000
ACK : 15001
A
SENDER - RECEIVER
Client - Server

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• Simultaneous open - When both the processes issues an active open
• SYN Flooding Attack & Denial Of Service Attack – SYN flooding attack
belongs to a type of security attacks.
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TCP CONNECTION
2 – DATA TRANSFER
✓The data transfer will be take place once the connection has established
between client and the server
✓Both client and server will send and acknowledge the data
✓The data travelling in the same direction as an acknowledgment are carried on
the same segment
✓TCP implementation have the option to SET/NOT SET the PUSH & URGENT flag
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Three steps:
STEP -1
• The client sends the request to server to transfer the data( push the
data)
• Data – bytes from (8001-9000) as one segment and (9001-10000) as
another segment
SEQ : 8001
ACK:15001
A P
SENDER - RECEIVER
Client - Server
SEQUENCE NO : 8001
ACKNOWLEDGMENT NO:15001
ACK & PSH FLAGS ARE SET

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Three steps:
STEP -2
• The server sends the acknowledgment to server for the request of
transferring the data( push the data)
• Data – bytes from (8001-9000) as one segment and (9001-10000) as
another segment
SEQ : 15001
ACK:10001
A P
SENDER - RECEIVER
Server - Client
SEQUENCE NO : 15001
ACK & PSH FLAGS ARE SET

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Three steps:
STEP -3
• The client sends the acknowledgment to server
SEQ : 10000
ACK:17001
A
SENDER - RECEIVER
Client- Server
SEQUENCE NO : 10000
ACK FLAGS ARE SET

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TCP CONNECTION
3 – TERMINATE THE CONNECTION
✓The connection has been terminated between client and the server after the
data transmission
✓Three way handshaking
✓ACK & FIN flag is set
✓Client side – active close & Server side – passive close
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• Half close – connection closes before the complete transmission
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APPLICATION LAYER
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• DOMAIN NAME SYSTEM
• NAME SPACE
• DOMAIN NAME SPACE
• DOMAIN
• REMOTE LOGGING
• TELNET
• E-MAIL
• FILE TRANSFER
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DOMAIN NAME SPACE
(DNS)
• Naming database
• Internet domain names are located & translated into IP address
• It is hierarchical & decentralized naming system for computers
• Services or resources connected to internet / private network
• It assign domain name & mapping those to internet
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How DNS works?...
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server
server
server
server

Name Space
• The name assigned to a machine are unique because the address are unique
• The map each other using unique name
• The way it is organised as:
• Flat Name Space
• Hierarchical Name Space - several parts such as – nature of the organisation, name,
department etc.,
• E.g (www.ethirajcollege_computerscience.edu.in)
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Domain Name Space
• It is designed to have a hierarchical name space
• Inverted tree structure
• Root at the top
• Only 128 levels that is 0 – 127
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e.g: computerscience.ethirajcollege.edu.in
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in
root
edu
ethirajcollege
computerscience
in
Edu.in
ethirajcollege.edu.in
computerscience.ethirajcollege.edu.in

Domain
• Subtree of Domain Name Space
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REMOTE LOGGING
• E.G STUDENT USE TO ACCESS COLLEGE LAB LOG IN ID FROM THEIR HOME
• USE REMOTE SITE FROM THEIR LOCAL SITE
• CLIENT/SERVER IS USED FOR THAT SERVICE
• FTP,EMAIL ARE USED
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TELNET
• General purpose of client/server application program
• Terminal Network
• Standard TCP/IP protocol
• Local terminal is appears ate the remote system
• Time sharing environment – large computer supports multiple users
• Interaction between user and computer done through terminals
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TELNET - logging
• TELNET
----------→ NVT(Network Virtual Terminal)
-----→TCP/IP
-----→NVT
………..
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EMAIL
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E-MAIL
• Beginning – only short message consist of text
• Later – text, audio, image, video
• Message can be sent to more than one recipients
• General architecture : I , II ,III, IV - SCENARIOS
• User agent
• Message transfer agent
• Message access agent
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• USER AGENT
1. COMPOSING MESSAGES
2. READING MESSAGES
3. REPLYING TO MESSAGES
4. FORWARDING MESSAGES
5. HANDLING MAILBOX
• MESSAGE TRANSFER AGENT
1. SMTP – PROTOCOL TO TRANSFER MESSAGE
2. MTA – MAIL TRANSFER AGENT – CLIENT & SERVER
• MESSAGE ACCESS AGENT
1. POP – POST OFFFICE PROTOCOL – POP3 (VERSION 3)
2. IMAP – INTERNET MAIL ACCESS – IMAP4 (VERSION 4)
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ARCHITECTURE
• FIRST SCENARIO
• SECOND SCENARIO
• THIRD SCENARIO
• FOURTH SCENARIO
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ARCHITECTURE
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SCENARIO SENDER RECEIVER USER AGENT MTA
FIRST SHARED SYSTEM TWO -
SECOND SYSETM1 SYSTEM2 TWO TWO
THIRD MAIL SERVER SYSTEM2 TWO TWO
FOURTH MAIL SERVER MAIL SERVER TWO TWO

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User
agent
FIRST
User
agent

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User
agent
SECOND
User
agent
INTERNET
MTA
CLIENT
MTA
SERVER

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User
agent
THIRD
User
agent
INTERNET
MTA
CLIENT
MTA
SERVER
MTA
SERVER
INTERNET

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User
agent
FOURTH
User
agent
INTERNET
MTA
CLIENT
MAA
SERVER
MTA
SERVER
INTERNET
MTA
SERVER
INTERNET

FILE TRANSFER
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FILE TRANSFER
• Transfer files from one computer to another
• Protocol – FTP provided by TCP/IP
• It provides two connections between hosts
1. Data transfer
2. Control information (command & responses)
• FTP uses TCP ports 20 –data connection & 21 – control information
• Different FTP for client & server
• Client – 3 components
• Server – 2 components
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USER INTERFACE
CONTROL PROCESS
DATA TRANSFER PROCESS DATA TRANSFER PROCESS
CONTROL PROCESS
TCP/IP
CONTROL
CONNECTION
CLIENT
SERVER

• Control connection and data connection is done between the client &
server
• Control connection – remains connected
• Data connection – open & close for each file transfer
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Communication over control connection
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CONTROL PROCESS CONTROL PROCESS
NVT ASCIIT
CLIENT SERVER

Communication over data connection
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DATA TRANSFER
PROCESS
DATA TRANSFER
PROCESS
DATA CONNECTIONT
CLIENT SERVER
FILE TYPE
DATA STRUCTURE
TRANSMISSION MODE

ANONYMOUS FTP
• To use FTP , user need account & password
• To use anonymous , FTP user can use
user name : anonymous
password : guest
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MORE WAY TO GO……………
ALL THE BEST
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