TCP/IP Architecture:An Introduction

Julie EarpNCSU

Fall 2000

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Host A Host B

Application module Application module

Middleware

Operating system Operating system

Network

MiddlewareMiddleware

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Standards Architecture Begin With an Architecture (Framework)

General plan for dividing up the work of allowing application programs to work together across a network

Defines individual layers Defines how layers work together

Then Create Standards for Individual Layers

One Architecture: TCP/IP

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OSI OSI (Reference Model of

Open Systems Interconnection) Open systems are those that

are open to communicating with all other systems

“Reference model” is another name for “architecture”

Subnet Layers

OSIApplication (7)

Presentation (6)Session (5)

Transport (4)Network (3)Data Link (2)Physical (1)

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Internet Standards Framework for standards setting is

called TCP/IP

Originally under DARPA (Defense Advanced Research Projects Agency)

Now under an independent body, the IETF (Internet Engineering Task Force)

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TCP/IP TCP/IP is the Dominant Architecture

above the Subnet Layer Simple Standards

Simplicity leads to rapid product development

Simplicity leads to inexpensive products that are easy to implement

“Fast to market and inexpensive” because of simplicity has led to TCP/IP’s dominance

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OSI TCP/IP versus OSI

OSIApplication (7)

Presentation (6)Session (5)

Transport (4)

Network (3)

Data Link (2)Physical (1)

TCP/IP

Application

Transport

Internet

Subnet

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Hybrid TCP/IP Architecture

OSI Standards are Dominant for Subnet Transmission TCP/IP Does Not

Challenge that Dominance

Therefore we have the Hybrid TCP/IP architecture for the Internet

TCP/IP

Application

TransportInternet

Subnet

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Hybrid TCP/IP Architecture

OSI Standards are Dominant for Subnet Transmission TCP/IP Does Not

Challenge that Dominance

Therefore we have the Hybrid TCP/IP architecture for the Internet

TCP/IP

Application

TransportInternet

Data Link

Physical

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TCP/IP - Five Layers Application Transport Internet Data Link Physical

A

T

A

I

D

P

D

I

T

P

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Internet Standards Application Layer Standards

… allow two application programs to work together

What if the 2 programs come from different vendors?

Doesn’t matter

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Internet Standards Protocol

A standard to govern communication between peer processes at the same layer on different systems

Browser and webserver programs are at the same layer (application)

Browser and webserver programs are on different machines (user PC and webserver)

So HTTP is a protocol.

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Internet Standards Transport Layer Protocols

… allow any two computers to exchange messages

What if they come from different vendors?

What if they are of different platform types?

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Internet Standards Internet Layer Protocols

… allow packets to be routed across multiple routers from a source host to a destination host.

R

R

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Internet Standards Different Subnets Can Have Different

Subnet Protocols IP at the internet layer routes across

different protocols between subnets

R

RLAN SubnetProtocol 1

WAN SubnetProtocol 2

R

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Internet Standards The IETF Does Not Create Subnet

Standards Uses standards from OSI Reference Model of Open Systems

InterconnectionApplication

Transport

Internet

Subnet: Use OSI Standards

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Internet Standards Data Link Layer

organize transmissions into collections of bits and manage their transmission within a single network

10010001001

Data Link

Frame

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Internet Standards

Data Link Layer Standards Point-to-Point Protocol (PPP)

ISPPPP

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Internet Standards Physical Layer Standards

connector plugs transmission media electrical signaling other physical matters you can see

and touch, even if they come from different vendors

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Internet Standards Physical Layer Standards in Internet Access from Home

External modem RJ11 Wall jack Serial port Telephone wire

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Internet Standards Subnet Versus Internet Layer

Standards

Internet Layer

R

R

Subnet Layer (Data Link and Physical)

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Internet Standards Accessing the WWW from Home

AppApp

TransTrans

IntInt

DLDL

PhyPhy

User PC

IntInt

DLDL

PhyPhy

Router

AppApp

TransTrans

IntInt

DLDL

PhyPhy

Webserver

IP

Modem

PPP

IP

?

?

HTTP

TCP

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Internet Standards End-to-End Layers

AppApp

TransTrans

IntInt

DLDL

PhyPhy

User PC

IntInt

DLDL

PhyPhy

Router

AppApp

TransTrans

IntInt

DLDL

PhyPhy

Webserver

HTTP

TCP

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Hops What is a hop? Hop-by-Hop layers

internet data link physical

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Internet Standards Connection between User PC and First Router

AppApp

TransTrans

IntInt

DLDL

PhyPhy

User PC

IntInt

DLDL

PhyPhy

FirstRouter

AppApp

TransTrans

IntInt

DLDL

PhyPhy

Webserver

IP

PPP

Modem

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Internet Standards Other Connections

Router-Router Router-DestinationHost IP at internet layer Subnet standard unknown to user PC

IntInt

DLDL

PhyPhy

OtherRouter

AppApp

TransTrans

IntInt

DLDL

PhyPhy

Webserver

IP

?

?

IntInt

DLDL

PhyPhy

FirstRouter

IP

?

?

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Widely Used on the Internet

Client/Server Processing

Browser

Webserver

E-mailServer

TCP/IP: Messaging at the Higher Layers

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Communication Standards govern various parts of the

messages being exchanged Form

syntax of the message Content

what the sender can say limited because receiver is not intelligent

Timing when can each side send

Responses Responses must be limited in number Responses must also be limited in content

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TCP/IP: 5 layer summary

Application (browser-webserver application)

Transport (user PC-webserver)

Internet (transmission across routers)

Data Link (transmission within subnet)

Physical (physical/electrical within subnet)

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Layers and Messaging

How do standards work? by exchanging messages at top 4 layers

What happens at the Physical layer? it uses bit-by-bit transmission without

message structure

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Layers and Messaging

AppApp

TransTrans

IntInt

DLDL

IntInt

DLDL

AppApp

TransTrans

IntInt

DLDL

message

message

packet

frame

packet

frame

User PC Router Webserver

Physical

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Message Exchange Standards work through message

exchange

AppApp

TransTrans

IntInt

DLDL

PhyPhy

User PC

IntInt

DLDL

PhyPhy

Router

AppApp

TransTrans

IntInt

DLDL

PhyPhy

Webserver

HTTP

TCP

IP

PPP

Modem

IP

?

?

Message

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Octets

Lengths are often given in groups of eight bits - called octets

Octet vs. Byte

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Message Structure Header (trailers too)

Gives instructions to peer on other system Usually has several parts (fields)

Address, error handling information, etc. Like salutation and address in a letter

Data FieldData Field

Header

Header Fields

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Message Structure Data Field

The information to be delivered to the peer process on the other system

Usually far longer than the header and trailer

Just as body of letter is usually longer than the salutation and closingData FieldData Field

Trailer(if needed)

Header

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Message Structure

Total Length in bytes (16)

Time to Live (8)

Options (if any)

Bit 0Version

(4)Hdr Len

(4) TOS (8)

Indication (16 bits) Flags (3) Fragment Offset (13)

Source IP Address

Destination IP Address

Header Checksum (16)Protocol (8)

PAD

Data Field

IP message structure (compressed to fit on slide)

Bit 96

Bit 64

Bit 32

Bit 128

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TrailerTrailer

Message Structures Not All Fields are Always Present

Header alone may be sufficient in a supervisory message

Header plus data field for delivering data

Sometimes all threeData FieldData Field HeaderHeader

Data FieldData Field HeaderHeader

HeaderHeader

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Message Time Diagrams Standards also govern message timing

When each side may transmit For example, webserver may not send an

HTTP response message until it receives a request

Browser Webserver

Time

HTTP RequestMessage

HTTP ResponseMessage

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Telephone Webserver Access

Modem, etc.Physical

Point-to-Point Protocol (PPP) - Messages are frames

Data Link

Internet Protocol (IP) -Messages are packets

Internet

Transmission Control Protocol (TCP)

Transport

HyperText Transport Protocol (HTTP)

Application

StandardLayer

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ENCAPSULATION

Combination of data from the next-higher layer and control information

ApplicationApplication

TransportTransport

InternetInternet

Data LinkData Link

ApplicationApplication

TransportTransport

InternetInternet

Data LinkData Link

PhysicalUser PC Webserver

data

data TCP-h

data TCP-h IP-h

data TCP-h IP-h D-h

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Hops What is a hop? Hop-by-Hop layers

internet data link physical