ECE 766

1
Protocol Hierarchies

• First networks hardware comes first
• Increased complexity ? network architecture
  becomes more important

2
Layered 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

3
Layered 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

4
Layered Protocols
Host 1
Host 2
5
ISOs 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

6
OSI Layers
7
OSI Layers

• 1. Physical
• Transmission of unstructured data stream over
  physical
• medium
• Data Unit Bit
• Aspects Mechanical
• Electrical
• Functional
• Procedural

8
OSI 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

9
OSI 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

10
OSI Layers

• 5. Session
• Dialog control and additional synchronization
• 6. Presentation
• Data format translation, encryption, and
  compression
• 7. Application
• Tools to access the network

11
OSI Model

• Biggest contribution Distinction of services,
  interfaces, and protocols
• OSI model is very useful to classify other
  protocol stacks
• Protocol implementations never became popular

12
TCP/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!)

13
OSI Model vs. TCP/IP Model
14
OSI 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