reference model. goal: 2 message exchange between application processes
TRANSCRIPT
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Reference model
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Goal:
2
message exchange between application processes
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What we should do?
message
Electrical signal
message
Where is the destination station?How to reach the station?What if error happens?What if congestion happens?How to make electrical signal?………..
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Reference model
message
Electrical signal
message
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Reference model
• Divide and conquer; divide the whole work into separate small tasks – layers
• Each layer is independent of other layers.
• Each layer in a station is communicating with the same layer in the corresponding station.
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Introduction 1-6
analogy: overseas air travel
• Each task is working independently.
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing
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Introduction 1-7
ticket (purchase)
baggage (check)
gates (load)
runway (takeoff)
airplane routing
departureairport
arrivalairport
intermediate air-trafficcontrol centers
airplane routing airplane routing
ticket (complain)
baggage (claim
gates (unload)
runway (land)
airplane routing
ticket
baggage
gate
takeoff/landing
airplane routing
Reference model for the travel
layers: each layer has its own mission.– Each layer works independently.– Lower layers provide services to the very
higher layer.
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Reference model
application
transport
network
link
physical
application
presentation
session
transport
network
data link
physical
OSI 7 layersInternet layers
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Application layer
• Application process has its own task to provide some services.– Web client/server, email, ftp, DNS etc.
• Then how can processes exchange messages to provide some services.
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Transport Layer• Transport layer delivers all messages from
several application processes to the corresponding transport layer. – Then, how they can differentiate all messages?
networkaccess 1
IP
Transport
networkAccess 2
IP
transport
network networkaccess1 access2
IP
subnet 1
end-to-end
subnet 2
AP1 AP2 AP3 AP1 AP2 AP3
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Network layernode-to-node delivery
• How to find the path to reach the destination.
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Link layer
• Link layer takes the responsibility of delivering data between two nodes which are connected by the same physical link.
4.12
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Link layer
• The data unit to be delivered at the link layer is called a frame.
• goal– How to know where the frame begins and
ends?• In addition,
– Is there any error during transmission?– Is there any frame loss because of the
processing speed difference between a sender and a receiver?
– And others.
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Physical layer
• How to make a data frame into an electrical signal? (coding)
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Physical layer and link layer
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• How is the data unit (PDU) at each layer delivered to its lower or higher layer at the boundary?– encapsulation
• PDU consists of data part and header part.
• The header has the information with which each layer can do its own functions.
encapsulation
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Introduction 1-17
source
application
transportnetwork
linkphysical
HtHn M
segment Ht
datagram
destination
application
transportnetwork
linkphysical
HtHnHl M
HtHn M
Ht M
M
networklink
physical
linkphysical
HtHnHl M
HtHn M
HtHn M
HtHnHl M
router
switch
message M
Ht M
Hn
frame
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encapsulation
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Communication protocol
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Common protocol
TCP connection req
TCP connectionresponse
<file>
Hi
Hi
Got thetime?
2:00
time
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How to specify in protocol
• Procedure to exchange messages• What kind of information should be
exchanged to do jobs.• How these information is contained
in the header.