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TCP/IP Protocol Suite

Arun Aggarwal

GM ( NW)

Tel: +91-120-2728294(O)+91-120-2728410(R)

E-Mail: arun_aggarwal@bsnl.in

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Objectives

What is Internet?

TCP/IP Layers

Data Encapsulation

TCP-IP Protocol Suite

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What is Internet?

Internet is network of networks, withdifferent hardware/software technologies

Also known by the name TCP/IP Internet

Name TCP/IP is taken from the names ofthe one of the transport layer protocols(Transport Control Protocol) and thenetwork layer protocol (Internet Protocol)

TCP/IP is backbone of the Internet

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TCP/IP and OSI

OSI is made of seven layers.

TCP/IP protocol is made of five layers.

PHYSICAL

DATA LINK

NETWORK

TRANSPORT

APPLICATION

PHYSICAL

DATA LINK

NETWORK

TRANSPORT

SESSION

PRESENTATION

APPLICATION

OSI Model TCP/IP Model

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Frame Head Trailer

Frame

Data Encapsulation

Data

Data

Data

TCP Header

TCP Segment

UDP Header

UDP Message

TCP-UDP DataIP Header

IP Datagram

IP Header TCP-UDP Data

Application

TPT Layer

NW Layer

Data Link

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D

P

N

T

A

TCP/IP Protocol Suite..

ICMP IGMPRARPARP

FTP

SMTPTELNETHTTP

TFTP

NFSSNMPDNS

TCP UDP

IP

Protocols defined by the underlying networks

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Applications using TCP

File Transfer Protocol (FTP) Provides the ability to upload and download files

between hosts on the network. Simple Mail Transport Protocol (SMTP)

Provides the ability to send mail between userson the network.

TELNET Provides the ability to login into a remote host

and administer the machine.

Hyper Text Transfer Protocol (HTTP) Provides the ability to supply web pages between

a browser and the server.

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Applications using UDP

Trivial File Transfer Protocol (TFTP) Provides simplex file transfer for network booting

of devices. Network File System (NFS)

Provides the ability for sharing directoriesbetween hosts on the network.

Simple N/w Management Protocol (SNMP) Provides the ability to supply network

management services on the network.

Domain Name Service (DNS) Provides mapping between domain name and IP

address and vice versa.

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TCP Details

Provides application programs access to thenetwork using a reliable connection-oriented

transport layer service TCP sends and receives data reliably using

sequence numbers and acknowledgements

Every byte in each packet is assigned asequence number

Data stream handed over to TCP is called anunstructured stream

TCP divides this data stream into segmentsfor transmission to remote network

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TCP Header..

76543210765432107654321076543210

ACKNOWLEDGEMENT NUMBER

DESTINATION PORTSOURCE PORT

OPTIONS AND PADDING

URGENT POINTERCHECKSUM

WINDOW SIZEFIN

SYN

RST

PSH

ACK

URG

HELEN

Octet +3Octet +2

SEQUENCE NUMBER

Octet +1Octet +0

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TCP Header

Source & Destination Port (16 Bits) Can run number of applications using same

transport by multiplexing through port numbers Port numbers (0-65535) are used to identify a

unique application in a machine

The first 1024 ports, port numbers 0-1023

known as well known port numbers, areassigned and are reserved for standardapplications and are controlled by IANA

The remaining ports, 1024-65535, are dynamic

and can be used freely by applications Source port is randomly generated by the source

machine

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Well known port numbers

Network Time Protocol123

File Transfer-Data20

File Transfer-Control21

Telnet23

SMTP25

Domain Name Server53

Trivial File Transfer69

WWW80

DESCRIPTIONPORT

Border Gateway Protocol179

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TCP Header

Sequence Number & Acknowledgement Number (32Bits each)

Helps in establishing TCP connections, along withSYN bit, called as Three Way Handshake

Helps in maintaining account of amount of databeing transferred

Sequence number is incremented, in the system,every 4 microsecond

Acknowledgement Number identifies the

sequence number expected from the other end ofdata transmission unit

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Seq/Ack numbers relation

During TCP Connection Establishment/Three way handshake

Acknowledgement Number Sent = SequenceNumber Received+1

During Data Transfer

Acknowledgement Number Sent = SequenceNumber Received + Data Received in Bytes

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Three-Way-Handshake

ReceiverSender 0 1

0) Closed; 1) Listen; 2) SYN-Sent; 3) SYN-Received; 4) Link Established

AN-00000

000B01

SN-95426

2

AN- 95427

000B11

SN-16780 3

AN-16781

000B10

SN-95427

4

Ack. FlagSyn. Flag

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TCP Header.

Header Length (4 Bits) Sometimes called Data Offset

Indicates the length of header in 32-bit words Identifies the beginning of data

Typical value is 5 unless there are options

Flags (6 Bits) Urgent (URG)

Acknowledgement (ACK)

Push (PSH)

Reset (RST)

Synchronisation (SYN)

Finish (FIN)

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TCP Header..

Window Size (16 Bits)

Indicates the size of the sliding window

Specifies the number of octets, starting with theoctet indicated by the acknowledgementnumber, that the sender of the segment willaccept from its peer at the other end of theconnection before the peer must stoptransmitting and wait for an acknowledgement

A default window size is 4096 bytes

Used for flow control by using Sliding windowmechanism

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Flow Control

Sender retains a copy of transmitted data until itreceives an acknowledgment from the remotenetwork.

If no acknowledgment is received, within aspecified time, the data is retransmitted by usingadaptive retransmission algorithm. TCP records the time of the transmission and sequence

number of the segment.

TCP again records the time of the acknowledgementreceived.

Using this delta, TCP builds a sample round-trip delay time

and uses this to build an average time for a packet to besent and to receive an acknowledgement

TCP will time out after a number of unsuccessfulretransmissions

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TCP Header..

Checksum(16 Bits) Used for error detection

Covers both header and the encapsulated data

Urgent Pointer(16 Bits) Used only when urgent flag is set

Points to the last octet of urgent data Options

One of the important options is MSS (MaximumSegment Size)

Informs the receiver of the largest segmentthe sender is willing to accept, withoutcausing fragmentation

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User Datagram Protocol

Provides unreliable connectionless service

Transfers data without establishing a

session

Used for services that have an inbuiltreliability

Does not use end to end error checking andcorrection

Does not order the packets; may loose orduplicate a packet

Runs faster than TCP due to less overheads

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UDP Header..

DESTINATION PORTSOURCE PORT

CHECKSUMMESSAGE LENGTH

76543210765432107654321076543210

Octet +3Octet +2Octet +1Octet +0

Source Port & Destination Port

Same as in TCP

Message length (16 Bits)

Indicates the size of the UDP header and its data in

bytes.

Checksum (16 Bits)

Covers the UDP header and UDP data.

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Internet Protocol.

Provides best-effort or connectionlessdelivery service.

No error checking or tracking If reliability is important, IP must be paired

with a reliable protocol like TCP

Transmits blocks of data called datagramseach of which is transported separately

Responsible for IP addressing

Datagrams may travel along different routesand may arrive out of sequence orduplicated.

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IP Header..

HEADER CHECKSUMPROTOCOLTIME TO LIVE

DESTINATION ADDRESS OF HOST

SOURCE ADDRESS OF HOST

PADDINGOPTIONS

76543210765432107654321076543210

FRAGMENT OFFSETMFDFIDENTIFICATION

TOTAL LENGTHTOSHLENVER

Octet +3Octet +2Octet +1Octet +0

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IP Header

Version (4 Bits)

Identifies the IP version of the packet Type of Service (8 Bits)

Used for specifying special handling of packet.

Has two sub-fields:Precedence & TOS Total Length (16 Bits)

Specifies total length of the packet, including

header, in octets Maximum possible size of an IP packet is 65535

octets

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IP Header.

0CRTDPPP

Reliability0-Normal1-Maximise

Precedence000-Routine001-Priority

010-Immediate011-Flash100-Flash Override101-CRITIC/ ECP110-Internetwork Control111-Network Control

Delay0-Normal1-Minimise

Throughput0-Normal1-Maximise

Cost0-Normal1-Minimise

Reserved:Always set to 0

0 = No TOS0000000

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IP Header

Identification (16 Bits)

Each datagram is identified by a identification number setby the source.

Flags (3 Bits)

First bit is not used.

Second bit is Dont Fragment (DF) bit Third bit is More Fragment (MF) bit

Maximum Transmit Unit (MTU) is the size of thelargest packet, including IP Header, that can be

transmitted or received through a data link Default MTU is 576 bytes, which can be handled by

any network without fragmentation

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IP Header

Fragment Offset (13 Bits)

The fragmentation occurs at the routers, if the

original packet length exceeds the MTU of a datalink

Used only in the cases when a datagram isfragmented on its way

Specifies the offset, in units of eight octets, fromthe beginning of header to the beginning of thefragment

Each fragment is marked, by router, with thesame identifier number

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IP Header

Time to live-TTL (8 Bits)

Assigns a life to an IP datagram

Protocol (8 Bits) Specifies the protocol that runs on the top of IP.

TCP-6; EGP-8; UDP-17; OSPF-89

Header Checksum (16 Bits)

Error detection field for IP header

As each router decrements the TTL, the checksum iscalculated by each router

Source Address of Host (32 Bits)

IP Address of the Originating Machine

Destination Address of Host (32 Bits)

IP Address of the Destination Machine

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IP Header.

Options Security:

Specifies how secret the datagram is Strict Source Routing(SSR):

Gives the complete path to be followed Loose Source Routing(LSR):

Gives the list of routers not to be missed Record Route:

Makes each router to append its IP address. Time Stamp:

Makes each router to append its IP addressand time stamp

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Underlying Networks Protocols

Ethernet

Token Ring

FDDI Fiber Distributed Data Interface

HDLC

High-level Data Link Control Frame Relay

PPP

Point-to-Point Protocol ATM

Asynchronous Transfer Mode

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Internet Control Message Protocol

Internet Control Message Protocol is amechanism used by hosts and routers to

send notification of datagram problems backto the sender.

Sends error messages only to the source

and not to intermediate routers. Sole function is to report problems, not to

correct them.

An important use of ICMP is echo/reply totest whether a destination is reachable andresponding.

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Internet Control Message Protocol

Echo request/reply (PING; Packet INternetGropher) Destination unreachable

0-Network unreachable

1-Host unreachable

2-Protocol unreachable 3-Port unreachable

4-Fragment needed but DF bit is set

5-Source route failed

Time exceeded message format

0-TTL exceeded

1-Fragment reassembly time exceeded

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Internet Group Message Protocol

Internet Group Message Protocol providesallows for multicast to operate on an

internetwork. Multicast is one-to-many communication.

A message sent can be simultaneously received

by a group of hosts. Special type of Class-D IP addresses,

starting with 1110, are reserved as

multicast addresses.

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Address Resolution Protocol

Address Resolution Protocol is used totranslate 32 bits IP addresses to 48 bits

Ethernet addresses. A hosts physical address is determined by

broadcasting its IP address to all machines.

The machine with matching IP address, inbroadcast message, sends its hardwareaddress to the machine originating

broadcast.

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ARP Operation

RequestIgnored

RequestIgnored

ARPResponseAccepted

Give me MAC address of 129.1.1.4

ThatsMe

Here is my MAC address

129.1.1.1 129.1.1.4

129.1.1.2 129.1.1.308-00-39-00-2F-C3

08-00-10-99-AC-54

08-00-5A-21-A7-2208-00-39-00-2F-AB

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Reverse Address Resolution Protocol

Reverse Address Resolution Protocol isused to get the 32 bits Source IP

address, knowing the 48 bits Hardwareaddress.

It is reverse of ARP, hence named

Reverse Address Resolution Protocol. A diskless workstation broadcasts RARP-

Request to find its IP Address at the time

of boot up.

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RARP Operation

Give me my IP address RARP Response

Disklesswork

station RARPServer

08-00-39-00-2F-C3 08-00-10-99-AC-54

08-00-5A-21-A7-22

223.1.2.1 223.1.2.2

223.1.2.3

08-00-39-00-2F-AB

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