Protocols. Basics Defining Interactions VERTICAL Application Presentation Session Transport Network...
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Transcript of Protocols. Basics Defining Interactions VERTICAL Application Presentation Session Transport Network...
Defining InteractionsVERTICAL
Application
Presentation
Session
Transport
Network
Data Link
Physical
Please do this for me
OK It’s Done orSorry I couldn’t
Horizontal Interactions
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
http request
http response
Route to 137.155.2.1?
Send to 137.155.38.4
Problems Solved by Link Layer Protocols
• Error CORRECTION
Sender Receiver
• Flow Control
Speed it Up!
Basic InteractionSimplest strategy
Sender ReceiverMessage 1
Sender ReceiverACK
Sender ReceiverMessage 2
etc
Sender Receiverabcdefghijklmnop Bill
Where is the error?
Sender Receiverabcdefghijklmnop Bill
data corrupted
Sender Receiverabcdefghijklmnop Bill
address corrupted
Whether Lost or Damaged
It all looks the same to the sender!
Damaged messages are discarded because you can’t be sure the message
is even intended for the receiver
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network layer passes message To Data Link for transmission
Application
Presentation
Session
Transport
Network
Data Link
Physical2 1
Application
Presentation
Session
Transport
Network
Data Link
Physical1
Data Link layer passes First part of message
To Physical layer for transmission
Application
Presentation
Session
Transport
Network
Data Link
Physical2 1
Application
Presentation
Session
Transport
Network
Data Link
Physical1 1
Physical Layer sends across the network
Application
Presentation
Session
Transport
Network
Data Link
Physical2 1
Application
Presentation
Session
Transport
Network
Data Link
Physical1 1
1
Ack
Receiver accepts, passes up to data link,data link sends ACK
ACK is lost
Application
Presentation
Session
Transport
Network
Data Link
Physical2 1
Application
Presentation
Session
Transport
Network
Data Link
Physical1 1
1
Ack
Sender resends message 1
Application
Presentation
Session
Transport
Network
Data Link
Physical2 1
Application
Presentation
Session
Transport
Network
Data Link
Physical1 1
1
Ack
Receiver gets message 1Recognizes it already has 1
Re ACKS
Ack
If ACK lost
• Message only delivered once
• ACK was retransmitted and eventually sender get ACK
• Sender moves on to part 2 of the message
Application
Presentation
Session
Transport
Network
Data Link
Physical2
Application
Presentation
Session
Transport
Network
Data Link
Physical2
Sender passes Message 2to Physical Layer to xmit
1
Application
Presentation
Session
Transport
Network
Data Link
Physical2
Application
Presentation
Session
Transport
Network
Data Link
Physical2 2
2
Receiver gets message 2ACKS and passes message 2
Up to data link at receiver
Ack
1
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
2
Upon receiving ACKSender discard at link layerAssuming xmit complete
1
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
2
Receiver passes message 2 up to network layer
1
XMIT of network PDU complete!
Please do this for me Sorry I couldn’t
Sends message “n” times but always fails.
How many times is it repeated?Horizontal and Vertical Interaction
Network Network
Data Link Data Link
Sender Receiver
Timer Tradeoff
• Set the alarm time too large– Sender sits around waiting needlessly– Increased delay
• Set the alarm time too small– Sender repeats transmission unnecessarily– Additional unnecessary network traffic is
generated– Unnecessary traffic -> Increased delay
Timer will never be perfect
• This is a queueing system• The time it should take for the receiver to
respond is defined by a probability distribution
• Unpredictable loads– Network traffic– Other receiver cpu loads– Local NIC card