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Network Protocol HierarchiesNetwork Protocol Hierarchies
• Network software structure– Networks are organized as a series of layers.– Layer n on a host communicates with layer n
on another host.– Layer n protocol: Rules and conventions for
this communication.– The entities on each host implementing the
layer n protocol are peers.
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Layers, protocols, and interfacesLayers, protocols, and interfaces
Layer 4
Layer 3
Physical medium
Layer 4 protocol
Layer 3 protocol
Layer 1 protocol
Layer 2 protocol
Layer 2
Layer 1
Layer 4
Layer 3
Layer 2
Layer 1
Layer 3/4 interface
Layer 2/3 interface
Layer 1/2 interface
Host 1 Host 2Physical Communication
VirtualCommunication
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Philosopher - Translator - Secretary Philosopher - Translator - Secretary ArchitectureArchitecture
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Flow of info supporting virtual Flow of info supporting virtual communication in layer 4communication in layer 4
M
MH3
M1H3H2 M2H2
M
MH3
M1H3H2 M2H2
Layer 4 Protocol
Layer 3 Protocol
Layer 2 Protocol
Source Machine Destination Machine
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Layer Design IssuesLayer Design Issues• Mechanism for identifying senders and receivers
(addressing).• Simplex, half-duplex, or full-duplex communication.• Error detection/correction.• Fragmentation• Preserving message order.• Fast sender vs. slow receiver.• Routing
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Connection-Oriented vs. Connection-Oriented vs. Connectionless ServicesConnectionless Services
• Connection-oriented service– Connection established and terminated.– Modeled after the telephone system.– Message arrive in the the order they are sent.– e.g. TCP
• Connectionless service (datagram service)
– Modeled after the postal system.– No guarantees on message ordering.– Unreliable: Messages may be lost.– e.g. UDP
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OSI Reference ModelOSI Reference Model
• ISO OSI– Importance of Open Standards
• 7 layer model– Each layer performs a well-defined function in the
context of the overall communication subsystem.• Peers exchange messages according to protocol.
• Message = user data + control information.
– Lower layers are network dependent.
– Higher layers are application oriented.
– Each layer provides an interface for the layer above.
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Transport
PhysicalPhysical
Data link
Network
PhysicalPhysical
Session
Presentation
Application
Data link
Network
Data link
Network
Physical
Data link
Network
Transport
Session
Presentation
ApplicationApplication protocol
Presentation protocol
Session protocol
Transport protocol
Communication subnet boundary
1
2
3
4
5
6
7OSI Reference Model
Router RouterHOST A HOST B
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Network Dependent Layers Network Dependent Layers
• Physical Layer (exchanged unit: bit)
– Transmits/Receives “raw” bits over comm. channel.
– Mechanical and electrical network interface definitions.
• Data Link Layer (exchanged unit: frame)
– Transforms (i.e. “cleans up”) raw transmission.
– Frames data using special bit patterns at the beginning and end of the frame.
– Serial/Parallel conversion.
– Medium Access Sublayer (broadcast networks)• controlling shared channel
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Network Dependent Layers, cont.Network Dependent Layers, cont.
• Network Layer (exchanged unit: packet)
– Operation of the subnet.
– Addressing
– Routing (point-to-point networks).
• Transport Layer– End-to-end message transfer.
– Connection management
– Error control
– Fragmentation
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Application Oriented LayersApplication Oriented Layers
• Session Layer– Dialogue control– Synchronization (i.e. “who does what when”)– “Thin” layer
• Presentation Layer– Syntax and semantics of transferred data.– Data representation transformations.
• e.g. Floating point number format.
• e.g. Encryption
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Application Oriented Layers, Application Oriented Layers, cont.cont.
• Application Layer– Variety of protocols:
• File Transfer
• Remote access and management
• Document/message interchange
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OSI layer indexOSI layer index
• Application
• Presentation
• Session
• Transport• Network (packets)
• Data Link (frames)
• Physical (raw bits)
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Finish reading Chap 1