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Winter 2006 ECE 766Computer Interfacing and Protocols
103 -
Protocol HierarchiesProtocol Hierarchies
• First networks: hardware comes first
• Increased complexity network architecture becomes more important
file
NetworkService
Network
file
NetworkService
Winter 2006 ECE 766Computer Interfacing and Protocols
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Layered ProtocolsLayered Protocols
• From structured programming concepts• Modular implementation• Distribute responsibilities to different layers• Problems to be addressed:
– Addressing– Transmission mode and data transfer (channels)– Error detection and recovery– Message fragmentation– Order of delivery– Buffering
Winter 2006 ECE 766Computer Interfacing and Protocols
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Layered ProtocolsLayered Protocols
• Each layer has a predefined set of functions• Layers provide services to their immediate upper layers,
hiding the details of the service• Peer layers communicate using a Peer Protocol• Layers are separated from each others with interfaces• Service provided at Service Access Points (SAP)
passing control information and data
Layer N Layer NLayer N Peer Protocol
Winter 2006 ECE 766Computer Interfacing and Protocols
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Layered ProtocolsLayered Protocols
Layer 5 Layer 5Layer 5 Protocol
Layer 4 Layer 4Layer 4 Protocol
Layer 3 Layer 3Layer 3 Protocol
Layer 2 Layer 2Layer 2 Protocol
Layer 1 Layer 1Layer 1 Protocol
Physical Medium
Host 1 Host 2
Interface
Interface
Interface
Interface
M
MH4
H3 M1H4 M2H3
H3 M1H4 M2H3H2 H2T2 T2
M
MH4
H3 M1H4 M2H3
H3 M1H4 M2H3H2 H2T2 T2
Host 1 Host 2
Winter 2006 ECE 766Computer Interfacing and Protocols
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ISO’s OSI ModelISO’s OSI Model
• OSI: Open System Interconnection• Model is not a protocol itself; it is a set of
functional specifications• “Open” accessible, not proprietary• First conceptual design, then
implementation• Consists of 7 layers• ISO has also produced standards that are
not part of the model
Winter 2006 ECE 766Computer Interfacing and Protocols
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OSI LayersOSI Layers
Application ApplicationApplication Protocol
Presentation PresentationPresentation Protocol
Session SessionSession Protocol
Transport TransportTransport Protocol
Network NetworkNetwork LayerHost-Router
Protocol
Host 1 Host 2
Interface
Interface
Interface
Interface
Data Link Data Link
Interface
Physical Physical
Interface
Data Link LayerHost-Router
Protocol
Physical LayerHost-Router
Protocol
Network LayerHost-Router
Protocol
Data Link LayerHost-Router
Protocol
Physical LayerHost-Router
Protocol
Network
Data Link
Physical
Network
Data Link
Physical
Internal Subnet Protocols
Communication Network
Winter 2006 ECE 766Computer Interfacing and Protocols
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OSI LayersOSI Layers
1. Physical: Transmission of unstructured data stream over physical
medium
Data Unit: Bit
Aspects: Mechanical
Electrical
Functional
Procedural
Winter 2006 ECE 766Computer Interfacing and Protocols
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OSI LayersOSI Layers
2. Data Link: Transforms the physical layer to a reliable link to achieve
node-to-node delivery
Data Unit: Frame• Framing: Creation, detection, acknowledgment• Physical addressing• Flow control• Error control• Access control MAC
Winter 2006 ECE 766Computer Interfacing and Protocols
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OSI LayersOSI Layers
3. Network: End-to-end delivery of packets across the network
Data Unit: Packet• Logical addressing• Routing
4. Transport: End-to-end delivery of the entire message• Service point addressing (port)• Connection and flow control• Error control
Winter 2006 ECE 766Computer Interfacing and Protocols
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OSI LayersOSI Layers
5. Session: Dialog control and additional synchronization
6. Presentation: Data format translation, encryption, and compression
7. Application: Tools to access the network
Winter 2006 ECE 766Computer Interfacing and Protocols
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OSI ModelOSI Model
• Biggest contribution: Distinction of services, interfaces, and protocols
• OSI model is very useful to classify other protocol stacks
• Protocol implementations never became popular
Winter 2006 ECE 766Computer Interfacing and Protocols
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TCP/IP ModelTCP/IP Model
• Developed by DARPA
• Main goal: Resilience to loss of network hardware
• Model developed after protocol implementation, merely a description of the protocols The model never became popular
• 4 Layer structure (not 7!)
Winter 2006 ECE 766Computer Interfacing and Protocols
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OSI Model vs. TCP/IP ModelOSI Model vs. TCP/IP Model
Application
Presentation
Session
Transport
Network
Data Link
Physical
OSI Model
Application
Transport
Internet
Host-to-network
TCP/IP Model
Not present in the model
Merged
Winter 2006 ECE 766Computer Interfacing and Protocols
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OSI Model vs. TCP/IP ModelOSI Model vs. TCP/IP Model
OSI TCP/IP
Developer ISO DARPA
Planning Model first (Proactive) Protocol first (Reactive)
Layers 7 4
Strength Widely used to classify protocol stacks
Interoperable, widely used protocol implementation
Weakness No widely accepted protocol implementation
Model fits no other protocol stack
