TCP-IP Intro-i
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TCP/IP Architecture:An Introduction
Julie EarpNCSU
Fall 2000
Copyright 2000 Earp
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Copyright 2000 Earp
Host A Host B
Application module Application module
Middleware
Operating system Operating system
Network
MiddlewareMiddleware
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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
Internet Standards
Data Link Layer Standards Point-to-Point Protocol (PPP)
ISPPPP
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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
Hops What is a hop? Hop-by-Hop layers
internet data link physical
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Copyright 2000 Earp
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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Copyright 2000 Earp
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
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TCP/IP: Messaging at the Higher Layers
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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
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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Copyright 2000 Earp
Hops What is a hop? Hop-by-Hop layers
internet data link physical