Computer Network No2 Layer Approch to Network Design From APCOMS [ UandiStar ]
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Transcript of Computer Network No2 Layer Approch to Network Design From APCOMS [ UandiStar ]
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‰ Networks are complex!‰ Composed of many “pieces”:
o hostso routerso links of various mediao applicationso protocolso hardware, software
‰ Tobetter understand the issue let us firstconsider an analogy of “Air Travel Process”
‰ Canyou break down the process of air travel into“sub-processes”
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Organization of air travel
Service Counter(ticket purchase)
Check-in Counter(baggage check)
gates (Departure)
runway (takeoff)
Service Counter(Future Travel)
Check-in Counter(baggage claim)
gates (Arrival)
runway (landing)
airplane routing
‰ a series of steps
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Organization of air travel: a different view
Service Counter(ticket purchase)
Check-in Counter(baggage check)
gates (Departure)
runway (takeoff)
Service Counter(Future Travel)
Check-in Counter(baggage claim)
gates (Arrival)
runway (landing)
airplane routing
Layers: each layer implements a serviceo via its own internal-layer actionso relying on services provided by layer below
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Layered air travel: services
Counter-to-counter Ticketing services
baggage-deposit-to-baggage-claim delivery
people transfer:Departure gate to Arrival gate
runway-to-runway delivery of plane
airplane routing from source to destination
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Dep
arti
ngai
rpor
t
arri
ving
airp
ort
Distributed implementation of layer functionality
Service Counter(purchase)
baggage (check)
gates (Departure)
runway takeoff
airplane routing
Service Counter(future booking)
baggage (claim)
gates (Arrival)
runway landing
airplane routing
We can refer to this collection as a “stack”
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Similarly……‰While developing a model for networkarchitecture, designers distilled the process oftransmitting data into its most fundamentalelements.They identified which networking functions hadrelated uses and collected those functions intodiscrete groups that became “Protocol Layers”which collectively form a “Protocol Stack”.
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Why layering?Dealing with complex systems:‰ explicit structure allows identification, relationship
of complex system’s pieceso layered reference model for discussion/design
‰ modularization eases maintenance, updating ofsystemo change of implementation of layer’s service
transparent to rest of systemo e.g., change in gate procedure doesn’t affect rest
of system
applicationtransportnetwork
linkphysical
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Layering: logical communication
Each layer:� distributed� “entities”
implementlayer functionsat each node� entities
applicationtransportnetwork
linkphysical
networklink
physical
performactions,exchangemessages withpeers
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
transport
transport
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Layering: logical communication
E.g.: transport� take data fromapp� add
addressing,reliability checkinfo to form“datagram”� send
datagram to peer
dataapplicationtransport
networklink
physical
applicationtransportnetwork
link
ack
data
networklink
physical
data
� wait forpeer to
ack receipt� analogy:
post office
physical applicationtransportnetwork
linkphysical
applicationtransport
networklink
physical
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Layering: physical communicationdata
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
networklink
physical
dataapplicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
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Protocol layering and dataMaj Faisal CPS 422
Each layer takes data from above� adds header information to create new dataunit� passes new data unit to layer below
source destinationM
Ht MHnHt M
Hl HnHt M
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
MHt M
HnHt MHl HnHt M
messagesegmentdatagramframe
Notice theseHeaders
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Protocol Revisited
How does a Protocol Work ……
A Protocol implements its Functionality throughits “HEADER”
A Header contains all the controlinformation to complete the
protocol’s tasks
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‰ Key Elements of a Protocolo Syntax - Formato Semantics - Control Info for Coord and error handlingo Timings - Sequencing and Speed matching
‰ Categories of Protocol Functionso Segmentation and Re-assemblyo Encapsulationo Connection Controlo Ordered Deliveryo Flow Controlo Error Controlo Addressingo Multiplexingo Transmission Services
application
transport
network
link
physical
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TCP / IP Protocol Suite
‰ application: supporting networkapplicationso ftp, smtp, http
‰ transport: host-host data transfero tcp, udp
‰ network: routing of datagrams fromsource to destinationo ip, routing protocols
‰ link: data transfer betweenneighboring network elementso ppp, ethernet
‰ physical: bits “on the wire”