程序代写代做代考 Review COMP90007 Internet Technologies – cscodehelp代写

Review COMP90007 Internet Technologies
Lecturer: Semester 2, 2021
© University of Melbourne 2021
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Medium Access Control (1)
 MAC sub-layer is used to assist in resolving transmission conflicts
 Static channel allocation
 Time division multiplexing
 Frequency division multiplexing
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Medium Access Control (2)
 Contention
 ALOHA, Slotted ALOHA
 Carrier Sense Multiple Access: 1-persistent, non- persistent, p-persistent, with collision detection
 Collision Free: bit map, binary countdown
 Limited Contention: adaptive tree walk
 Wireless LANs: MACA
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Data Link Layer
 Reliable, efficient communication of “frames” between two adjacent machines.
 Functions of the data link layer:
 Provide a well-defined service interface to network
layer
 Handling transmission errors  Data flow regulation
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Framing
 Methods:
 Character (Byte) count
 Flag bytes with byte stuffing
 Start and end flags with bit stuffing
 Most data link protocols use a combination of character count and one other method
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Error Control
 Error Control
 Detecting errors
 Parity
 Checksum
 Cyclical Redundancy Check (CRC)
 Correcting errors  Hamming Code
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Flow Control
 The fast senders vs slow receivers problem requires a solution
 Feedback based flow control: ack
 Stop and wait
 Sliding window: go-back-N, selective repeat
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Go-Back-N vs. Selective Repeat
 Trade-off between efficient use of bandwidth and data link layer buffer space
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Physical Layer
 The physical layer is concerned with the electrical, timing and mechanical interfaces of the network
 Timing: data rate, latency
 Mechanical: different media …
 Electrical: modulations, voltage levels, signal strength …
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Network Protocol Hierarchies (1)
 Layers, protocols and interfaces
Consider the network as a stack of layers
Each layer offers services to layers above it through interface
Protocol is an agreement between the communicating parties on how communication is to proceed
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Network Protocol Hierarchies (2)
 Information flow supporting virtual communication in layer 5
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